https://earthwise.bgs.ac.uk/api.php?action=feedcontributions&user=EmilyCrane&feedformat=atomMediaWiki - User contributions [en-gb]2024-03-28T11:59:50ZUser contributionsMediaWiki 1.41.0https://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Kenya&diff=12647Hydrogeology of Kenya2015-06-11T15:08:04Z<p>EmilyCrane: /* Transboundary aquifers */</p>
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<div> [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya<br />
<br />
==Authors==<br />
<br />
Maxwell Barasa, Rural Focus Ltd, Kenya<br />
<br />
==Geographical & Political Setting==<br />
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<br />
<br />
[[File:Kenya_Political.png | right | frame | Political Map of Kenya (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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===General===<br />
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{| class = "wikitable"<br />
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|-<br />
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|Estimated Population in 2013* || 44353691<br />
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|-<br />
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|Rural Population (% of total)* || 75.2%<br />
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|-<br />
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|Total Surface Area* || 569140 sq km<br />
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|-<br />
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|Agricultural Land (% of total area)* || 48.2%<br />
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|-<br />
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|Capital City || Nairobi<br />
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|-<br />
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|Region || Eastern Africa<br />
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|-<br />
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|Border Countries || Somalia, Ethiopia, South Sudan, Uganda, Tanzania<br />
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|-<br />
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|Annual Freshwater Withdrawal (2013)* || 2735 Million cubic metres<br />
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|-<br />
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|Annual Freshwater Withdrawal for Agriculture* || 79.16%<br />
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|-<br />
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|Annual Freshwater Withdrawal for Domestic Use* || 17.18%<br />
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|-<br />
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|Annual Freshwater Withdrawal for Industry* || 3.66%<br />
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|-<br />
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|Rural Population with Access to Improved Water Source* || 55.1%<br />
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|-<br />
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|Urban Population with Access to Improved Water Source* || 82.3%<br />
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|}<br />
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<nowiki>*</nowiki> Source: World Bank<br />
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===Climate===<br />
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<br />
Broad description of Kenya – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
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Climate classification of Kenya. Spatial variations in annual average rainfall and temperature.<br />
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<gallery widths="375px" heights=365px mode=nolines><br />
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File:Kenya_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Kenya_ClimatePrecip.png |Average Annual Precipitation<br />
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File:Kenya_ClimateTemp.png |Average Temperature<br />
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</gallery><br />
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Temporal variations in temperature and rainfall.<br />
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Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Kenya | Kenya Climate Page]].<br />
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[[File:Kenya_pre_Monthly.png| 255x124px| Average monthly precipitation for Kenya showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Kenya_tmp_Monthly.png| 255x124px| Average monthly temperature for Kenya showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Kenya_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Kenya_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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===Surface water===<br />
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{|<br />
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|-<br />
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|”The country’s hydrographic network is dominated by the Rift Valley which bisects the plateaus region from north to south. The floor of the Rift Valley is occupied by lakes in the centres of endorheic basins. West of the Rift Valley, the surface water flows towards Lake Victoria and into the Nile Basin: to the east it flows south-east to the Indian Ocean.<br />
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The country has five large systems of drainage basins, with many small lakes in the intervening areas.<br />
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The Athi drains most of the south-east of the country from the slopes of the Aberdare mountains and the eastern side of the Rift Valley and flows into the Indian Ocean. Some other watercourses reach the coast and others peter out before the coast.<br />
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The Tana drains the western slopes of the Aberdare, the southern slopes of Mt. Kenya and the Nyambeni mountains, flowing towards the Indian Ocean.<br />
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The waters of the Ewaso Ng'iro region come from the northern slopes of the Aberdare and Mt. Kenya and from the high plateaus and lower mountains in the north and north-east. With the exception of the Ewaso Ng'iro itself the flows, which are of the torrential type, occur immediately after rain.<br />
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These large basins are in turn subdivided into 52 main basins and sub-basins.”<br />
<br />
(United Nations 1989)<br />
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| [[File:Kenya_Hydrology.png | frame | Surface Water Map of Kenya (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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===Soil===<br />
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{|<br />
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|-<br />
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| [[File:Kenya_soil.png | frame | Soil Map of Kenya (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
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|General information about Kenya soils.<br />
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|}<br />
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===Land cover===<br />
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{|<br />
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|-<br />
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|General information about Kenya land cover.<br />
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| [[File:Kenya_LandCover.png | frame | Land Cover Map of Kenya (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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==Geology==<br />
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The following section provides a summary of the geology of Kenya. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Kenya at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
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[[File:Kenya_Geology.png | right]]<br />
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{| class = "wikitable"<br />
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|+ Geological Environments<br />
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|Key Formations||Period||Lithology||Structure<br />
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!colspan="4"|Unconsolidated sedimentary<br />
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|-<br />
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|<br />
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||Quaternary<br />
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||Soils, alluvial beach sands, evaporates, fossil coral reefs and sandstones at the coast: alluvial and lacustrine sediments of the Rift Valley.<br />
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||<br />
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|Name of formation2<br />
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||Time period<br />
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||Structure<br />
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!colspan="4"| Igneous – largely volcanic<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
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|-<br />
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|Name of formation1<br />
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|| Cretaceous-Tertiary<br />
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||Limestones and argillaceous limestones<br />
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||<br />
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|-<br />
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!colspan="4"| Sedimentary – Mesozoic-Palaeozoic, sometimes with unconsolidated cover<br />
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|-<br />
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|Karoo?<br />
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|| Mesozoic-Palaeozoic<br />
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||Description<br />
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||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Sedimentary – Coastal basin, sometimes with unconsolidated cover<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Precambrian Craton<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Precambrian Metasedimentary<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Precambrian Mobile/Orogenic Belt<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|Name of formation2<br />
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||Description<br />
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||Structure<br />
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|}<br />
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==Hydrogeology==<br />
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This section will contain a broad overview of the hydrogeology.<br />
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===Aquifer properties===<br />
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[[File:Kenya_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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<br />
====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
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|-<br />
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|Lotikipi and Lodwar aquifers<br />
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||Alluvial sands and sediments.<br />
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||<br />
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||<br />
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|}<br />
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<br />
====Igneous – mainly volcanic ====<br />
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{| class = "wikitable"<br />
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|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
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|-<br />
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|Volcanic<br />
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||”Volcanic rocks cover about 26 percent of the country. The petrology/lithology of these rocks includes phonolites, trachytes, tuffs and basalts. The thickness of these rocks varies from a few meters to several hundred metres and thereby implies that groundwater may occur at great depths. The successive lava flows are reflective of the old land surfaces. This means that in a borehole, more than five aquifer layers may be struck. Aquifers in these formations are often confined. The yields, depth to aquifers and static water level are also expected to vary significantly. Water in these rocks is of low total dissolved solids and high bicarbonate.” (Pavelic et al. 2012)<br />
<br />
Boreholes in the volcanic rocks of Kenya can be drilled at depths up to 125 m (United Nations 1989). United Nations (1989) estimated that 9% of boreholes in volcanic rocks were abandoned on completion, due to poor yield or unsuitable water chemistry. They state an average yield of 7.6 m3/h for volcanic rocks (United Nations 1989).<br />
<br />
||<br />
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||The volcanic deposits of the East African Rift System are rich in fluoride which leads to high groundwater fluoride concentrations. For example, concentrations over 10 mg/L were found in the Nairobi area (Coetsiers et al. 2008)<br />
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||<br />
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|-<br />
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|Nairobi Aquifer<br />
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||The Nairobi Aquifer is in the Nairobi area. It comprises layered volcanics interbedded with old land surface and intervolcanic sediments. Boreholes are typically drilled to 250 - 400 m depth.<br />
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||Overabstraction causing lowered water levels.<br />
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||Generally good quality.<br />
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||Recharge from Ngong Hills.<br />
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|-<br />
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|Kabatini aquifer<br />
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||The Kabatini aquifer occurs within the volcanic rocks of the Nakuru area. Boreholes are typically drilled to about 150 m depth.<br />
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||<br />
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||Elevated fluoride concentrations.<br />
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||<br />
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|-<br />
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|Gongoni and Baricho aquifers<br />
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||<br />
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||<br />
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|}<br />
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References:<br />
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Coetsiers, M., Kilonzo, F. & Walraevens, K. 2008. Hydrochemistry and source of high fluoride in groundwater of the Nairobi area, Kenya, Hydrological Sciences Journal, 53:6, 1230-1240, DOI: 10.1623/ hysj.53.6.1230<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
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|-<br />
<br />
|Name of aquifer<br />
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||General Description of aquifer<br />
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||Water quantity issues<br />
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||Water quality issues<br />
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||Recharge<br />
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|-<br />
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|Tiwi Aquifer<br />
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||The Tiwi Aquifer occurs in the Kwale area. High yields can be obtained from the Mazeras sandstone and Pleistocene sands. Boreholes are typically 40 – 80 m deep.<br />
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||<br />
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||Typically good quality.<br />
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||<br />
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|-<br />
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|Gongoni/Msambweni Aquifer<br />
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||The Gongoni/Msambweni Aquifer occurs in the Kwale area. High yields can be obtained from the Mazeras sandstone and Pleistocene sands. Boreholes are typically 40 – 100 m deep.<br />
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||<br />
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||Generally good quality, apart from high iron concentrations.<br />
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||<br />
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|-<br />
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|Baricho Aquifer<br />
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||The Baricho Aquifer occurs in the Malindi area. The best yields are obtained from sand deposits. Boreholes are typically drilled to 25 – 60 m depth.<br />
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||<br />
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||Generally good quality, sometimes elevated total dissolved solids (TDS)<br />
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||<br />
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|-<br />
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|Merti Aquifer<br />
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||The Merti Aquifer occurs in Wajir County and comprises sandstone. “The Merti aquifer is defined by permeable water-bearing layers in the Merti Formation… The Merti Formation within the Anza Rift consists of rotated and faulted sediments and/or (near-)horizontal post-rift formations. The Anza Rift is bound by major faults.” (Oord et al. 2014)<br />
<br />
“Generally, groundwater in the Merti aquifer is confined and is found at rather uniform depths between 110 and 180 m below ground level (m bgl). Successful boreholes tap the more permeable zone of the Merti Formation commonly between 105 m to 150 m bgl (GIBB, 2004). The actual thickness of the Merti Aquifer is unknown, because generally boreholes do not fully penetrate the aquifer.” (Oord et al. 2014).<br />
<br />
||<br />
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|| “Occurrence of saline water has been observed in the outer fringes of the Merti aquifer and is also believed to underlie the fresh water layer. … Water quality in the Dadaab refugee camps has deteriorated over time, mainly due to increasing salinity, and also in Habaswein evidence exists of some salinization as a result of long term abstraction (Mumma et al., 2011)” (Oord et al. 2014).<br />
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||<br />
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|}<br />
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References:<br />
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Oord, A., Collenteur, R. and Tolk, L. 2014. Hydrogeological Assessment of the Merti Aquifer, Kenya. Technical report no 1 of ARIGA. Assessing Risks of Investment in Groundwater Development in Sub-Saharan Africa. https://www.worldagroforestry.org/sites/default/files/TR1%20ARIGA-%20Hydrological%20Assessment%20of%20the%20Merti%20Aquifer%20Kenya.pdf<br />
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GIBB Africa Ltd., 2004. UNICEF Kenya Country Office - Study of the Merti Aquifer - Technical Report ISsue 2.0.<br />
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Mumma, A., Lane, M., Kairu, E., Tuinhof, A. and Hirji, R., 2011. Kenya: Groundwater Governance Case Study.<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
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{| class = "wikitable"<br />
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|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
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|-<br />
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|Name of aquifer<br />
<br />
||General Description of aquifer<br />
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||Water quantity issues<br />
<br />
||Water quality issues<br />
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||Recharge<br />
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|}<br />
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====Basement====<br />
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{| class = "wikitable"<br />
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|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Name of aquifer<br />
<br />
||General Description of aquifer<br />
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||Water quantity issues<br />
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||Water quality issues<br />
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||Recharge<br />
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|}<br />
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===Groundwater Status===<br />
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Groundwater quantity<br />
<br />
The groundwater potential of Kenya is estimated to be 619 million m3 (Pavelic et al. 2012). The total present [as of 2012] groundwater abstraction rate in Kenya is estimated at 7.21 million m3/y. Total safe abstraction rate in Kenya is estimated to be 193 million m3/y (Ministry of Water Development. 1992) (Pavelic et al. 2012).<br />
<br />
Groundwater quality<br />
<br />
Most aquifers have groundwater quality issues. Some aquifers, mostly with recharge from fresh water rivers, are excellent groundwater sources e.g.: the Lodwar Aquifer recharged by the River Turkwel, the Merti Aquifer recharged by the River Ewaso, the Gongoni Aquifer recharged by the Mkurumudzi River and the Baricho Aquifer recharged by the River Galena.<br />
<br />
The Nairobi aquifer has high fluoride concentrations which mostly exceed WHO standards, especially towards the Embakasi area.<br />
<br />
The Lotikipi Aquifer is very saline with EC25 values exceeding 8000 µS/cm.<br />
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Surface water-groundwater interaction<br />
<br />
Various contamination problems are arising due to the hydraulic continuity between surface water and shallow groundwater systems in Kenya, e.g.:<br />
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*Poor sewerage and drainage systems are major contributors to groundwater contamination, this is an increasing problem in Nairobi and its environs.<br />
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*Open cast mining of building blocks and stones pose a threat to groundwater as a result of contaminated water infiltrating into the ground.<br />
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*The Kiserian dam has suffered contamination problems due to inadequate sewage systems in nearby towns; this contaminated water may find its way into groundwater. Equally, groundwater may be becoming directly contaminated as a result of reliance on pit latrines and soakaway pits.<br />
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*River pollution by industrial wastes and sewage pose a great risk for groundwater protection.<br />
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==Groundwater use and management==<br />
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=== Groundwater use===<br />
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Summary of groundwater use<br />
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<br />
<br />
Water supply systems in several towns are reliant on groundwater sources, e.g.: Mombasa and Malindi depends on Baricho well field, Kwale depends on Tiwi well field, Wajir town depends on Merti aquifer.<br />
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Mining activity, e.g. the Gongoni well field for Base Titanium mining company.<br />
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The Daadab refugee camp depends on groundwater abstracted from the Merti Aquifer.<br />
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=== Groundwater management===<br />
<br />
Summary of groundwater management<br />
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=== Transboundary aquifers===<br />
<br />
Kenya shares several transboundary aquifers with neighbouring countries, defined by IWMI (2014) as:<br />
<br />
*AFS31 Coastal sedimentary basin 1 (Kenya/Tanzania) - Quaternary and consolidated sedimentary rocks<br />
<br />
*AFS32 Kilimanjero aquifer (Kenya/Tanzania) - Volcanic alluvium<br />
<br />
*AFNE1 Rift aquifer (Kenya/Tanzania/Uganda) - Volcanic<br />
<br />
*AFNE2 Merti aquifer (Kenya/Somalia) - Semi-consolidated sedimentary<br />
<br />
*AFNE3 Mount Elgon (Kenya/Uganda) - Volcanic<br />
<br />
*AFNE4 Dawa (Ethiopia/Kenya/Somalia) - Volcanic rocks, alluvials and Precambrian basement<br />
<br />
*AFNE5 Juba aquifer (Ethiopia/Kenya/Somalia) - Aquifers in Precambrian and intrusive rocks<br />
<br />
*AFNE7 Sudd basin (Ethiopia/Kenya/South Sudan/Sudan) - Precambrian and volcanic rocks with patches of alluvials/sedimentary <br />
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Source:<br />
IWMI. 2014. Transboundary Aquifer Mapping and Management in Africa. https://www.iwmi.cgiar.org/Publications/Other/PDF/transboundary_aquifer_mapping_and_management_in_africa.pdf<br />
<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
Summary of groundwater monitoring<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
Ministry of Water Development. 1992. The Study on the National Water Master Plan. Prepared with the assistance of Japan International Cooperation Agency (JICA)<br />
<br />
Pavelic, P.; Giordano, M.; Keraita, B.; Ramesh, V.; Rao, T.. 2012 Groundwater availability and use in Sub-Saharan Africa: a review of 15 countries.. International Water Management Institute. <br />
<br />
United Nations. 1989. Groundwater in Eastern, Central and Southern Africa: Kenya. United Nations Department of Technical Cooperation for Development.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Kenya please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=KE African Groundwater Literature Archive's Kenya page].<br />
<br />
===Other sources of data and information===<br />
<br />
*The Ministry of Mining – sells geological maps and geological reports carried out by the Geological Survey of Kenya: https://www.mining.go.ke/<br />
<br />
*The Water Resources Management Authority licences their hydrogeological data (borehole logs, aquifer units and yields): https://www.wrma.or.ke/<br />
<br />
*The National Oil Corporation of Kenya (NOCK) licences their seismic data, seismic lines and oil well logs: https://nationaloil.co.ke/site/3.php?id=1<br />
<br />
*Samsam Water Foundation has a website with hydrogeological information: https://www.samsamwater.com/about.php<br />
<br />
*University of Nairobi offers a platform on its website on student research topics which provides useful geological information: https://geology.uonbi.ac.ke/uon_student_projects<br />
<br />
*International Livestock research institute (ILRI) has digitized and shapefiles of Kenya Geology, soils and landcover: https://data.ilri.org/geoportal/catalog/main/home.page<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya<br />
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[[Category:Hydrogeology by country|k]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Kenya&diff=12646Hydrogeology of Kenya2015-06-11T14:59:28Z<p>EmilyCrane: </p>
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<div> [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya<br />
<br />
==Authors==<br />
<br />
Maxwell Barasa, Rural Focus Ltd, Kenya<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Kenya_Political.png | right | frame | Political Map of Kenya (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 44353691<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 75.2%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 569140 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 48.2%<br />
<br />
|-<br />
<br />
|Capital City || Nairobi<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Somalia, Ethiopia, South Sudan, Uganda, Tanzania<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 2735 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 79.16%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 17.18%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 3.66%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 55.1%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 82.3%<br />
<br />
|}<br />
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<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
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<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Kenya – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Kenya. Spatial variations in annual average rainfall and temperature.<br />
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<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Kenya_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Kenya_ClimatePrecip.png |Average Annual Precipitation<br />
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File:Kenya_ClimateTemp.png |Average Temperature<br />
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</gallery><br />
<br />
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<br />
Temporal variations in temperature and rainfall.<br />
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Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Kenya | Kenya Climate Page]].<br />
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<br />
<br />
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[[File:Kenya_pre_Monthly.png| 255x124px| Average monthly precipitation for Kenya showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Kenya_tmp_Monthly.png| 255x124px| Average monthly temperature for Kenya showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Kenya_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Kenya_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|”The country’s hydrographic network is dominated by the Rift Valley which bisects the plateaus region from north to south. The floor of the Rift Valley is occupied by lakes in the centres of endorheic basins. West of the Rift Valley, the surface water flows towards Lake Victoria and into the Nile Basin: to the east it flows south-east to the Indian Ocean.<br />
<br />
The country has five large systems of drainage basins, with many small lakes in the intervening areas.<br />
<br />
The Athi drains most of the south-east of the country from the slopes of the Aberdare mountains and the eastern side of the Rift Valley and flows into the Indian Ocean. Some other watercourses reach the coast and others peter out before the coast.<br />
<br />
The Tana drains the western slopes of the Aberdare, the southern slopes of Mt. Kenya and the Nyambeni mountains, flowing towards the Indian Ocean.<br />
<br />
The waters of the Ewaso Ng'iro region come from the northern slopes of the Aberdare and Mt. Kenya and from the high plateaus and lower mountains in the north and north-east. With the exception of the Ewaso Ng'iro itself the flows, which are of the torrential type, occur immediately after rain.<br />
<br />
These large basins are in turn subdivided into 52 main basins and sub-basins.”<br />
<br />
(United Nations 1989)<br />
<br />
| [[File:Kenya_Hydrology.png | frame | Surface Water Map of Kenya (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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<br />
===Soil===<br />
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{|<br />
<br />
|-<br />
<br />
| [[File:Kenya_soil.png | frame | Soil Map of Kenya (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Kenya soils.<br />
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|}<br />
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<br />
===Land cover===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Kenya land cover.<br />
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<br />
<br />
| [[File:Kenya_LandCover.png | frame | Land Cover Map of Kenya (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Kenya. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Kenya at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Kenya_Geology.png | right]]<br />
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{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
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|Key Formations||Period||Lithology||Structure<br />
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|-<br />
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!colspan="4"|Unconsolidated sedimentary<br />
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|-<br />
<br />
|<br />
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||Quaternary<br />
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||Soils, alluvial beach sands, evaporates, fossil coral reefs and sandstones at the coast: alluvial and lacustrine sediments of the Rift Valley.<br />
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||<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Igneous – largely volcanic<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
<br />
||Description<br />
<br />
||Structure<br />
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|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
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|-<br />
<br />
|Name of formation1<br />
<br />
|| Cretaceous-Tertiary<br />
<br />
||Limestones and argillaceous limestones<br />
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||<br />
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|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic, sometimes with unconsolidated cover<br />
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|-<br />
<br />
|Karoo?<br />
<br />
|| Mesozoic-Palaeozoic<br />
<br />
||Description<br />
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||Structure<br />
<br />
|-<br />
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|Name of formation2<br />
<br />
||Time period<br />
<br />
||Description<br />
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||Structure<br />
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|-<br />
<br />
!colspan="4"| Sedimentary – Coastal basin, sometimes with unconsolidated cover<br />
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|-<br />
<br />
|Name of formation1<br />
<br />
||Time period<br />
<br />
||Description<br />
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||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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!colspan="4"| Precambrian Craton<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
<br />
||Description<br />
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||Structure<br />
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|-<br />
<br />
!colspan="4"| Precambrian Metasedimentary<br />
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|-<br />
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|Name of formation1<br />
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||Time period<br />
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||Description<br />
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||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
<br />
||Description<br />
<br />
||Structure<br />
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|-<br />
<br />
!colspan="4"| Precambrian Mobile/Orogenic Belt<br />
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|-<br />
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|Name of formation1<br />
<br />
||Time period<br />
<br />
||Description<br />
<br />
||Structure<br />
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|-<br />
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|Name of formation2<br />
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||Time period<br />
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||Description<br />
<br />
||Structure<br />
<br />
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<br />
<br />
<br />
<br />
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|}<br />
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==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
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<br />
===Aquifer properties===<br />
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[[File:Kenya_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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<br />
<br />
<br />
====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lotikipi and Lodwar aquifers<br />
<br />
||Alluvial sands and sediments.<br />
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||<br />
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||<br />
<br />
||<br />
<br />
|}<br />
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<br />
====Igneous – mainly volcanic ====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Volcanic<br />
<br />
||”Volcanic rocks cover about 26 percent of the country. The petrology/lithology of these rocks includes phonolites, trachytes, tuffs and basalts. The thickness of these rocks varies from a few meters to several hundred metres and thereby implies that groundwater may occur at great depths. The successive lava flows are reflective of the old land surfaces. This means that in a borehole, more than five aquifer layers may be struck. Aquifers in these formations are often confined. The yields, depth to aquifers and static water level are also expected to vary significantly. Water in these rocks is of low total dissolved solids and high bicarbonate.” (Pavelic et al. 2012)<br />
<br />
Boreholes in the volcanic rocks of Kenya can be drilled at depths up to 125 m (United Nations 1989). United Nations (1989) estimated that 9% of boreholes in volcanic rocks were abandoned on completion, due to poor yield or unsuitable water chemistry. They state an average yield of 7.6 m3/h for volcanic rocks (United Nations 1989).<br />
<br />
||<br />
<br />
||The volcanic deposits of the East African Rift System are rich in fluoride which leads to high groundwater fluoride concentrations. For example, concentrations over 10 mg/L were found in the Nairobi area (Coetsiers et al. 2008)<br />
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||<br />
<br />
|-<br />
<br />
|Nairobi Aquifer<br />
<br />
||The Nairobi Aquifer is in the Nairobi area. It comprises layered volcanics interbedded with old land surface and intervolcanic sediments. Boreholes are typically drilled to 250 - 400 m depth.<br />
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||Overabstraction causing lowered water levels.<br />
<br />
||Generally good quality.<br />
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||Recharge from Ngong Hills.<br />
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|-<br />
<br />
|Kabatini aquifer<br />
<br />
||The Kabatini aquifer occurs within the volcanic rocks of the Nakuru area. Boreholes are typically drilled to about 150 m depth.<br />
<br />
||<br />
<br />
||Elevated fluoride concentrations.<br />
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||<br />
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|-<br />
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|Gongoni and Baricho aquifers<br />
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||<br />
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||<br />
<br />
||<br />
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||<br />
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|}<br />
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References:<br />
<br />
Coetsiers, M., Kilonzo, F. & Walraevens, K. 2008. Hydrochemistry and source of high fluoride in groundwater of the Nairobi area, Kenya, Hydrological Sciences Journal, 53:6, 1230-1240, DOI: 10.1623/ hysj.53.6.1230<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Name of aquifer<br />
<br />
||General Description of aquifer<br />
<br />
||Water quantity issues<br />
<br />
||Water quality issues<br />
<br />
||Recharge<br />
<br />
|-<br />
<br />
|Tiwi Aquifer<br />
<br />
||The Tiwi Aquifer occurs in the Kwale area. High yields can be obtained from the Mazeras sandstone and Pleistocene sands. Boreholes are typically 40 – 80 m deep.<br />
<br />
||<br />
<br />
||Typically good quality.<br />
<br />
||<br />
<br />
|-<br />
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|Gongoni/Msambweni Aquifer<br />
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||The Gongoni/Msambweni Aquifer occurs in the Kwale area. High yields can be obtained from the Mazeras sandstone and Pleistocene sands. Boreholes are typically 40 – 100 m deep.<br />
<br />
||<br />
<br />
||Generally good quality, apart from high iron concentrations.<br />
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||<br />
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|-<br />
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|Baricho Aquifer<br />
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||The Baricho Aquifer occurs in the Malindi area. The best yields are obtained from sand deposits. Boreholes are typically drilled to 25 – 60 m depth.<br />
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||<br />
<br />
||Generally good quality, sometimes elevated total dissolved solids (TDS)<br />
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||<br />
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|-<br />
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|Merti Aquifer<br />
<br />
||The Merti Aquifer occurs in Wajir County and comprises sandstone. “The Merti aquifer is defined by permeable water-bearing layers in the Merti Formation… The Merti Formation within the Anza Rift consists of rotated and faulted sediments and/or (near-)horizontal post-rift formations. The Anza Rift is bound by major faults.” (Oord et al. 2014)<br />
<br />
“Generally, groundwater in the Merti aquifer is confined and is found at rather uniform depths between 110 and 180 m below ground level (m bgl). Successful boreholes tap the more permeable zone of the Merti Formation commonly between 105 m to 150 m bgl (GIBB, 2004). The actual thickness of the Merti Aquifer is unknown, because generally boreholes do not fully penetrate the aquifer.” (Oord et al. 2014).<br />
<br />
||<br />
<br />
|| “Occurrence of saline water has been observed in the outer fringes of the Merti aquifer and is also believed to underlie the fresh water layer. … Water quality in the Dadaab refugee camps has deteriorated over time, mainly due to increasing salinity, and also in Habaswein evidence exists of some salinization as a result of long term abstraction (Mumma et al., 2011)” (Oord et al. 2014).<br />
<br />
||<br />
<br />
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|}<br />
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References:<br />
<br />
Oord, A., Collenteur, R. and Tolk, L. 2014. Hydrogeological Assessment of the Merti Aquifer, Kenya. Technical report no 1 of ARIGA. Assessing Risks of Investment in Groundwater Development in Sub-Saharan Africa. https://www.worldagroforestry.org/sites/default/files/TR1%20ARIGA-%20Hydrological%20Assessment%20of%20the%20Merti%20Aquifer%20Kenya.pdf<br />
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GIBB Africa Ltd., 2004. UNICEF Kenya Country Office - Study of the Merti Aquifer - Technical Report ISsue 2.0.<br />
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Mumma, A., Lane, M., Kairu, E., Tuinhof, A. and Hirji, R., 2011. Kenya: Groundwater Governance Case Study.<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Name of aquifer<br />
<br />
||General Description of aquifer<br />
<br />
||Water quantity issues<br />
<br />
||Water quality issues<br />
<br />
||Recharge<br />
<br />
|}<br />
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<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Name of aquifer<br />
<br />
||General Description of aquifer<br />
<br />
<br />
<br />
||Water quantity issues<br />
<br />
||Water quality issues<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
Groundwater quantity<br />
<br />
The groundwater potential of Kenya is estimated to be 619 million m3 (Pavelic et al. 2012). The total present [as of 2012] groundwater abstraction rate in Kenya is estimated at 7.21 million m3/y. Total safe abstraction rate in Kenya is estimated to be 193 million m3/y (Ministry of Water Development. 1992) (Pavelic et al. 2012).<br />
<br />
Groundwater quality<br />
<br />
Most aquifers have groundwater quality issues. Some aquifers, mostly with recharge from fresh water rivers, are excellent groundwater sources e.g.: the Lodwar Aquifer recharged by the River Turkwel, the Merti Aquifer recharged by the River Ewaso, the Gongoni Aquifer recharged by the Mkurumudzi River and the Baricho Aquifer recharged by the River Galena.<br />
<br />
The Nairobi aquifer has high fluoride concentrations which mostly exceed WHO standards, especially towards the Embakasi area.<br />
<br />
The Lotikipi Aquifer is very saline with EC25 values exceeding 8000 µS/cm.<br />
<br />
Surface water-groundwater interaction<br />
<br />
Various contamination problems are arising due to the hydraulic continuity between surface water and shallow groundwater systems in Kenya, e.g.:<br />
<br />
*Poor sewerage and drainage systems are major contributors to groundwater contamination, this is an increasing problem in Nairobi and its environs.<br />
<br />
*Open cast mining of building blocks and stones pose a threat to groundwater as a result of contaminated water infiltrating into the ground.<br />
<br />
*The Kiserian dam has suffered contamination problems due to inadequate sewage systems in nearby towns; this contaminated water may find its way into groundwater. Equally, groundwater may be becoming directly contaminated as a result of reliance on pit latrines and soakaway pits.<br />
<br />
*River pollution by industrial wastes and sewage pose a great risk for groundwater protection.<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
Summary of groundwater use<br />
<br />
<br />
<br />
Water supply systems in several towns are reliant on groundwater sources, e.g.: Mombasa and Malindi depends on Baricho well field, Kwale depends on Tiwi well field, Wajir town depends on Merti aquifer.<br />
<br />
Mining activity, e.g. the Gongoni well field for Base Titanium mining company.<br />
<br />
The Daadab refugee camp depends on groundwater abstracted from the Merti Aquifer.<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater management===<br />
<br />
Summary of groundwater management<br />
<br />
<br />
<br />
<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
Summary of groundwater monitoring<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
Ministry of Water Development. 1992. The Study on the National Water Master Plan. Prepared with the assistance of Japan International Cooperation Agency (JICA)<br />
<br />
Pavelic, P.; Giordano, M.; Keraita, B.; Ramesh, V.; Rao, T.. 2012 Groundwater availability and use in Sub-Saharan Africa: a review of 15 countries.. International Water Management Institute. <br />
<br />
United Nations. 1989. Groundwater in Eastern, Central and Southern Africa: Kenya. United Nations Department of Technical Cooperation for Development.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Kenya please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=KE African Groundwater Literature Archive's Kenya page].<br />
<br />
===Other sources of data and information===<br />
<br />
*The Ministry of Mining – sells geological maps and geological reports carried out by the Geological Survey of Kenya: https://www.mining.go.ke/<br />
<br />
*The Water Resources Management Authority licences their hydrogeological data (borehole logs, aquifer units and yields): https://www.wrma.or.ke/<br />
<br />
*The National Oil Corporation of Kenya (NOCK) licences their seismic data, seismic lines and oil well logs: https://nationaloil.co.ke/site/3.php?id=1<br />
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*Samsam Water Foundation has a website with hydrogeological information: https://www.samsamwater.com/about.php<br />
<br />
*University of Nairobi offers a platform on its website on student research topics which provides useful geological information: https://geology.uonbi.ac.ke/uon_student_projects<br />
<br />
*International Livestock research institute (ILRI) has digitized and shapefiles of Kenya Geology, soils and landcover: https://data.ilri.org/geoportal/catalog/main/home.page<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
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[[Category:Hydrogeology by country|k]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12529Hydrogeology of Zimbabwe2015-06-10T09:09:05Z<p>EmilyCrane: /* Groundwater use and management */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
||<br />
<br />
|-<br />
|Bulawayan Supergroup of the Greenstone Belts<br />
||The rocks of the Greenstone Belts generally have very low permeability, but groundwater occurs where fracturing and weathering have created adequate porosity and permeability. The Bulawayan Supergroup can support yields of 1.2 - 2.9 l/s (Interconsult 1986). The average borehole depth is in the range 30 - 50 m, and the water level is typically from 5 to greater than 20 m below ground level.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al. 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al. 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC (2012):<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
*Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
*Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]].<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12528Hydrogeology of Zimbabwe2015-06-10T09:07:55Z<p>EmilyCrane: /* Basement */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
||<br />
<br />
|-<br />
|Bulawayan Supergroup of the Greenstone Belts<br />
||The rocks of the Greenstone Belts generally have very low permeability, but groundwater occurs where fracturing and weathering have created adequate porosity and permeability. The Bulawayan Supergroup can support yields of 1.2 - 2.9 l/s (Interconsult 1986). The average borehole depth is in the range 30 - 50 m, and the water level is typically from 5 to greater than 20 m below ground level.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12527Hydrogeology of Zimbabwe2015-06-10T09:06:43Z<p>EmilyCrane: /* Basement */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
||<br />
<br />
|-<br />
|Bulawayan Supergroup of the Greenstone Belts<br />
||The Greenstone Belt is generally a very low permeability rock mass, but groundwater occurs in areas where fracturing and weathering has created porosity and permeability. The Bulawayan Supergroup can support yields of 1.2 - 2.9 l/s (Interconsult 1986). The average borehole depth is in the range 30 - 50 m, and the water elvel is typically from 5 to greater than 20 m below ground level.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12520Hydrogeology of Zimbabwe2015-06-10T08:59:04Z<p>EmilyCrane: </p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12519Hydrogeology of Zimbabwe2015-06-10T08:58:26Z<p>EmilyCrane: /* Groundwater monitoring */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
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<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
===General===<br />
<br />
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<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
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|-<br />
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|Total Surface Area* || 386850 sq km<br />
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|-<br />
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|Agricultural Land (% of total area)* || 41.9%<br />
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|-<br />
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|Capital City || Harare<br />
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|-<br />
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|Region || Eastern Africa<br />
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|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
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|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
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|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
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|-<br />
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|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
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|Urban Population with Access to Improved Water Source* || 97.3%<br />
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|}<br />
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<nowiki>*</nowiki> Source: World Bank<br />
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===Climate===<br />
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<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
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Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
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<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
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File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
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<br />
<br />
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[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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===Surface water===<br />
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{|<br />
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|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
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| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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===Soil===<br />
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{|<br />
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|-<br />
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| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
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<br />
<br />
|General information about Zimbabwe soils.<br />
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|}<br />
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===Land cover===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
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<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
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|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
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|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
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|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
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|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
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|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
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|-<br />
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|}<br />
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==Hydrogeology==<br />
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This section will contain a broad overview of the hydrogeology.<br />
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===Aquifer properties===<br />
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[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
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||<br />
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||<br />
|}<br />
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====Consolidated Sedimentary - Intergranular Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
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||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
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|}<br />
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====Igneous - Fracture Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
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||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
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||<br />
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|}<br />
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====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
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{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
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|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
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|}<br />
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====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
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||<br />
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|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
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|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12518Hydrogeology of Zimbabwe2015-06-10T08:57:51Z<p>EmilyCrane: /* Groundwater use and management */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12517Hydrogeology of Zimbabwe2015-06-10T08:57:31Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the Precambrian calcareous metasediments and quartzites. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12516Hydrogeology of Zimbabwe2015-06-10T08:56:06Z<p>EmilyCrane: /* Unconsolidated */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary) <br />
<br />
||Alluvial deposits are only locally developed within Zimbabwe, with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley. They form unconfined aquifers. <br />
<br />
The aquifer properties of the alluvial deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table ranges from about 5 - 40 m deep, and is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
||These aquifers have high groundwater development potential.<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
||<br />
|-<br />
|Kalahari Sand Aquifer<br />
||The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone. It is an unconfined aquifer. Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d. The aquifer properties of the Kalahari Sands are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
||<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12514Hydrogeology of Zimbabwe2015-06-10T08:48:16Z<p>EmilyCrane: /* Basement */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: <br />
*the granite and gneiss below the African erosion surface; and <br />
*the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12513Hydrogeology of Zimbabwe2015-06-10T08:47:46Z<p>EmilyCrane: /* Basement */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
||These aquifers have low groundwater development potential. The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12512Hydrogeology of Zimbabwe2015-06-10T08:47:17Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer has high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer has moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
|| The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12511Hydrogeology of Zimbabwe2015-06-10T08:46:52Z<p>EmilyCrane: /* Basement */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer is classed as having moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
|| The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12510Hydrogeology of Zimbabwe2015-06-10T08:45:25Z<p>EmilyCrane: /* Basement */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
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<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
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|Total Surface Area* || 386850 sq km<br />
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|-<br />
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|Agricultural Land (% of total area)* || 41.9%<br />
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|-<br />
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|Capital City || Harare<br />
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|-<br />
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|Region || Eastern Africa<br />
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|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
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|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
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|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
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<nowiki>*</nowiki> Source: World Bank<br />
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===Climate===<br />
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<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
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<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
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<br />
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[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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===Surface water===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
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| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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===Soil===<br />
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{|<br />
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|-<br />
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| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
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|}<br />
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<br />
===Land cover===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
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|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
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|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
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|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
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|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
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|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
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|-<br />
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|}<br />
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==Hydrogeology==<br />
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This section will contain a broad overview of the hydrogeology.<br />
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===Aquifer properties===<br />
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[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
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||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
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||<br />
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|}<br />
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====Consolidated Sedimentary - Intergranular Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
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||<br />
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|}<br />
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====Igneous - Fracture Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
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||This aquifer has moderate groundwater development potential.<br />
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|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
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||<br />
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|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
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|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
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||<br />
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||<br />
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||<br />
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|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer is classed as having moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
''''''<br />
<br />
<br />
<br />
''''''<br />
<br />
<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the African erosion surface<br />
||Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
||<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
||<br />
<br />
|-<br />
|Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces<br />
||The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
||<br />
||In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
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|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12509Hydrogeology of Zimbabwe2015-06-10T08:43:31Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (about 10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
||This aquifer is classed as having moderate groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12508Hydrogeology of Zimbabwe2015-06-10T08:42:37Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Dolomite formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having moderate groundwater development potential.<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12507Hydrogeology of Zimbabwe2015-06-10T08:40:09Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
Yields of 500 - >2000 m<sup>3</sup>/d are possible.<br />
<br />
||<br />
<br />
||<br />
<br />
||<br />
<br />
|-<br />
|Lomagundi Dolomite <br />
||Typical borehole depths are 60 – 80 m in the Lomagundi Formations. The water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
The specific capacity of boreholes in the Lomagundi Dolomite is 505 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having high groundwater development potential.<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|-<br />
|Tengwe River Formation<br />
||Typical borehole depths are 50 – 70 m in the Tengwe River Formation. Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone.<br />
<br />
The specific capacity of boreholes in the Tengwe River Formation is 4 -120 m<sup>3</sup>/d/m.<br />
<br />
||This aquifer is classed as having moderate groundwater development potential.<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12506Hydrogeology of Zimbabwe2015-06-10T08:34:42Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence) */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
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|Total Surface Area* || 386850 sq km<br />
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|-<br />
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|Agricultural Land (% of total area)* || 41.9%<br />
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|-<br />
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|Capital City || Harare<br />
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|-<br />
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|Region || Eastern Africa<br />
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|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
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<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
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===Climate===<br />
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<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
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Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
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<br />
<br />
<br />
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[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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===Surface water===<br />
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<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
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<br />
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| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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===Soil===<br />
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{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
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<br />
<br />
|General information about Zimbabwe soils.<br />
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|}<br />
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<br />
===Land cover===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
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|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
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|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
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|-<br />
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|}<br />
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==Hydrogeology==<br />
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This section will contain a broad overview of the hydrogeology.<br />
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===Aquifer properties===<br />
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[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
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||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
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||<br />
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|}<br />
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====Consolidated Sedimentary - Intergranular Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
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|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange (Wankie) Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. It was previously known as the Wankie Sandstone. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
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|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
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||<br />
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|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12505Hydrogeology of Zimbabwe2015-06-10T08:34:11Z<p>EmilyCrane: /* Geology */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Hwange) Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12504Hydrogeology of Zimbabwe2015-06-10T08:33:27Z<p>EmilyCrane: /* Groundwater Status */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie (Hwange) Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12503Hydrogeology of Zimbabwe2015-06-10T08:32:38Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity ranges from 0.1 to 2.09 m/d and specific yield from 0.02 to 0.11.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12502Hydrogeology of Zimbabwe2015-06-10T08:31:07Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite and Tengwe River Formation<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12501Hydrogeology of Zimbabwe2015-06-10T08:28:15Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. It is mainly confined, being unconfined only close to outcrop. Boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth. Yields range from 0.1 to 5.9 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||Water quality is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
||Recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu 2005).<br />
|-<br />
|Escarpment Grit<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields range from 1.2 to 3.5 l/s.<br />
||This aquifer has high groundwater development potential.<br />
||<br />
|| <br />
|-<br />
|Madumabisa Mudstone<br />
||The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. Yields are relatively low in the Madumabisa Mudstone (0.1 - 0.6 l/s); successful boreholes are usually sited in the vicinity of rivers.<br />
||This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones. Yields range from 1.2 to 5.8 l/s.<br />
||This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12500Hydrogeology of Zimbabwe2015-06-10T08:12:35Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow (Karoo sequence)====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|<br />
||<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
||In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|-<br />
<br />
|Escarpment Grit<br />
<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Madumabisa Mudstone<br />
||In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers.<br />
|| This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
|| The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
|| This aquifer has high groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12499Hydrogeology of Zimbabwe2015-06-10T08:11:27Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Karoo sequence<br />
||<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
|| <br />
||<br />
|| <br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
||In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|-<br />
<br />
|Escarpment Grit<br />
<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Madumabisa Mudstone<br />
||In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers.<br />
|| This aquifer has low groundwater development potential.<br />
|| <br />
|| <br />
|-<br />
|Upper and Lower Hwange Sandstone<br />
|| The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined. Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
|| <br />
|| <br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12496Hydrogeology of Zimbabwe2015-06-10T08:08:26Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Karoo sequence<br />
||The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| <br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
||In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|-<br />
<br />
|Escarpment Grit<br />
<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Madumabisa Mudstone<br />
||In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers.<br />
|| This aquifer has low groundwater development potential.<br />
<br />
|| <br />
<br />
|| <br />
<br />
|-<br />
<br />
|<br />
<br />
|| <br />
|| <br />
<br />
|| <br />
<br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12493Hydrogeology of Zimbabwe2015-06-10T08:04:21Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Karoo sequence<br />
<br />
||<br />
<br />
The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| <br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
||In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|-<br />
<br />
|Escarpment Grit<br />
<br />
||The Escarpment Grit forms a confined aquifer in the Hwange and Save-Limpopo basin.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
||This aquifer has high groundwater development potential.<br />
<br />
||<br />
<br />
|| <br />
<br />
|-<br />
<br />
|Madumabisa Mudstone<br />
<br />
|| In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
|| This aquifer has low groundwater development potential.<br />
<br />
|| <br />
<br />
|| <br />
<br />
|-<br />
<br />
|<br />
<br />
|| <br />
|| <br />
<br />
|| <br />
<br />
|| <br />
|-<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12478Hydrogeology of Zimbabwe2015-06-10T07:58:24Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||These aquifers have low groundwater development potential.<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12477Hydrogeology of Zimbabwe2015-06-10T07:57:13Z<p>EmilyCrane: /* Aquifer properties */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12476Hydrogeology of Zimbabwe2015-06-10T07:55:15Z<p>EmilyCrane: /* Hydrogeology */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
'''Groundwater development potential'''<br />
In the National Master Plan for Rural Supply, Interconsult (1986) classed aquifers by their Groundwater development potential, as follows:<br />
*High: Suitable for primary supply, piped supplies, and small and large-scale irrigation schemes<br />
*Moderate: Suitable for primary supplies, small piped schemes and small-scale irrigation schemes<br />
*Low: Suitable for primary supplied from boreholes.<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Senegal&diff=12445Hydrogeology of Senegal2015-06-09T16:54:52Z<p>EmilyCrane: /* References */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Senegal<br />
<br />
==Authors==<br />
'''Dr Diakher Hélène Madioune''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Ibrahima Mall''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Moctar Diaw''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Professor Serigne Faye''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Emily Crane''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK<br />
<br />
==Geographical Setting==<br />
<br />
[[File:Senegal_Political.png | right | frame | Political Map of Senegal (For more information on the datasets used in the map see the [[Geography | geography resources section]])]] <br />
<br />
<br />
===General===<br />
{| class = "wikitable"<br />
|-<br />
|Estimated Population in 2013* || 14133280<br />
|-<br />
|Rural Population (% of total)* || 56.92%<br />
|-<br />
|Total Surface Area* || 192530 sq km<br />
|-<br />
|Agricultural Land (% of total area)* || 46.82%<br />
|-<br />
|Capital City || Dakar<br />
|-<br />
|Region || Western Africa<br />
|-<br />
|Border Countries || Gambia, Guinea-Bissau, Guinea, Mali, Mauritania<br />
|-<br />
|Annual Freshwater Withdrawal (2013)* || 2.611 Million cubic metres<br />
|-<br />
|Annual Freshwater Withdrawal for Agriculture* || 92.98%<br />
|-<br />
|Annual Freshwater Withdrawal for Domestic Use* || 4.412%<br />
|-<br />
|Annual Freshwater Withdrawal for Industry* || 2.611%<br />
|-<br />
|Rural Population with Access to Improved Water Source* || 60.3%<br />
|-<br />
|Urban Population with Access to Improved Water Source* || 92.5%<br />
|}<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
===Climate===<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
File:Senegal_ClimateZones.png |Koppen Geiger Climate Zones<br />
File:Senegal_ClimatePrecip.png |Average Annual Precipitation<br />
File:Senegal_ClimateTemp.png |Average Temperature<br />
</gallery><br />
<br />
Temporal variations in temperature and rainfall.<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Senegal | Senegal Climate Page]]. <br />
<br />
[[File:Senegal_pre_Monthly.png| 255x124px| Average monthly precipitation for Senegal showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Senegal_tmp_Monthly.png| 255x124px| Average monthly temperature for Senegal showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Senegal_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Senegal_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]] <br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
===Surface water===<br />
<br />
{|<br />
|-<br />
|The following institutions have responsibilities for surface water in Senegal:<br />
<br />
*Organisation pour la Mise en Valeur du Fleuve Sénégal (OMVS)<br />
*Organisation pour la Mise en Valeur du Fleuve Gambie (OMVG)<br />
*Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE) <br />
<br />
| [[File:Senegal_Hydrology.png | frame | Surface Water Map of Senegal (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
|}<br />
<br />
===Soil===<br />
{|<br />
|-<br />
| [[File:Senegal_soil.png | frame | Soil Map of Senegal (For the map key and more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
|<br />
|}<br />
<br />
===Land cover===<br />
{|<br />
|-<br />
|<br />
<br />
| [[File:Senegal_LandCover.png | frame | Land Cover Map of Senegal (For the map key and more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
|}<br />
<br />
==Geology==<br />
The following section provides a summary of the geology of Senegal. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Senegal at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
[[File:Senegal_Geology.png | right]]<br />
<br />
{| class = "wikitable"<br />
|+ Geological Environments<br />
|Key Formations||Period||Lithology||Structure<br />
|-<br />
!colspan="4"| Quaternary unconsolidated sediments<br />
|-<br />
|<br />
||Quaternary<br />
||Variable deposits including alluvium in river valleys and coastal deposits. Including sand and clay.<br />
||Up to 42 m thick.<br />
|-<br />
!colspan="4"|Tertiary - Cretaceous sedimentary rocks<br />
|-<br />
|Continental Terminal<br />
||Neogene<br />
||Variable deposits, often carbonates<br />
||Up to 92 m thick<br />
|-<br />
|Ypresian<br />
||Eocene<br />
||Marly calcareous and limestone deposits, clayey or sandy in places.<br />
||Up to 260 m thick<br />
|-<br />
|Thanetian<br />
||Palaeocene<br />
||Limestone<br />
||Up to 220 m thick<br />
|-<br />
|Montian<br />
||Palaeocene<br />
||Limestone<br />
||<br />
|-<br />
|Danian<br />
||Palaeocene<br />
||Marly calcareous<br />
||<br />
|-<br />
|Maastrichtian<br />
||Mesozoic<br />
||Sand, sandy clay, calcareous sandstone<br />
||Up to 488 m thick<br />
|-<br />
|Campanian<br />
||Mesozoic<br />
||Predominantly clayey<br />
||Up to 102 m thick<br />
|-<br />
|Lower Senonian<br />
||Mesozoic<br />
||Laterally variable; clayey in the western part of the basin<br />
||Up to 92.5 m thick<br />
|-<br />
|Turonian<br />
||Mesozoic<br />
||Black clay; a stratigraphic marker bed<br />
||<br />
|-<br />
!colspan="4"| Tertiary-Quaternary volcanic rocks<br />
|-<br />
|Mamelles volcanics<br />
||Tertiary-Quaternary<br />
||Basalt, basanite, tuffs<br />
||Up to 25 m thick<br />
|-<br />
|Diack formations<br />
||Tertiary<br />
||Gabbro and basalt<br />
||<br />
|-<br />
!colspan="4"| Hercynian-Panafrican Mobile/Orogenic belt<br />
|-<br />
|Mauritanides formations<br />
||Hercynian-Panafrican<br />
||Schists and quartzites<br />
||<br />
|-<br />
!colspan="4"| Precambrian: Birimian<br />
|-<br />
|Birimian formations<br />
||Mesoproterozoic<br />
||Saraya Granite, complex granodiorite-granite of Sandikounda-Soukouta, Boboti Granite<br />
||<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
<br />
===Aquifer properties===<br />
[[File:Senegal_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
====Superficial: Unconsolidated====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Superficial aquifer system<br />
||The Superficial aquifer system covers the whole Senegal sedimentary basin. It is dominantly made of sand and sandy clay, which vary in proportion across its extent. The aquifers are intergranular, and the best groundwater potential occurs in sand layers. It comprises the following aquifers: infrabasaltic (occurs below basalts), Thiaroye, Littoral Nord, alluvial, Continental Terminal and Oligo-Miocene aquifers. This aquifer system overlies the more consolidated deposits of the Eocene, Palaeocene, and the Maastrichtian.<br />
<br />
The Superficial aquifer system ranges between 0 to 150 m thick, with a water table depth between a few metres to 72.5 metres depth. Typical borehole depth varies between 7.6 to 540 m. <br />
<br />
Typical values for aquifer parameters for the Superficial aquifer system are: <br />
<br />
*Permeability = 1 x 10-5 to 8.9 x 10-4 m/s<br />
*Transmissivity = 8.64 to 1728 m²/day<br />
*Storage coeffiecient = 0.01-0.15<br />
*Borehole yield = 50-183 m³/h<br />
||<br />
||Nitrate contamination is known to occur in places. <br />
||<br />
|}<br />
<br />
====Cretaceous - Tertiary Sedimentary - Intergranular and Fracture Flow====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Intermediate aquifer system<br />
||The Intermediate aquifer system includes Eocene and Palaeocene formations, and mainly comprises limestone, often karstic or affected by faults. <br />
<br />
The Eocene aquifer is exploited in the central western part of Senegal and along the Senegal river. <br />
The Palaeocene aquifer occurs mainly in western Senegal, around Pout. These aquifers constitute one of the main sources of drinking water for Dakar. The Intermediate aquifer system ranges between 40 to 120 m thick, with a water table depth between a few metres to 102.5 metres depth. Typical borehole depth varies between 7.6 to 540 m. <br />
<br />
Typical values for aquifer parameters for the Intermediate aquifer system:<br />
*Permeability = 1 x 10-5 to 2.5x10-8 m/s<br />
*Transmissivity = 1.728 – 9504 m²/day<br />
*Storage coeffiecient = 0.05 - 0.10<br />
*Borehole yield = 54 – 300 m³/h<br />
||<br />
||High iron, fluoride and salinity seen in the central western part of Senegal. Saline intrusion in the coastal areas. <br />
||Groundwater recharge depends only on rainwater and rivers.<br />
<br />
|-<br />
|Deeper aquifer system<br />
||The deeper aquifer system, of Maastrichtian age, extends across the whole of the Senegalo-Mauritanian basin and generally consists of sand, sandy-clay and calcareous sandstone. Groundwater storage and flow are largely intergranular. This aquifer constitutes the main source of groundwater supply in Senegal. It is a transboundary system.<br />
<br />
The deeper aquifer system is about 250 m thick, with a water table depth between a few metres to 140 metres depth. Typical borehole depth varies between 25 to 680 m. It is typically highly productive, although aquifer properties vary according to local characteristics (lithology, thickness, etc.). Where there are thick clay sequences, the aquifers can be semi-confined or confined. Typical values for aquifer parameters for the deeper aquifer system are:<br />
<br />
*Permeability = 1 x 10-5 m/s<br />
*Transmissivity = 0.95 – 652578 m²/day<br />
*Storage coeffiecient = 1 x 10-4 – 6 x 10-4 in the western central part<br />
*Borehole yield = 80 – 362 m³/h<br />
||Groundwater depletion occurs locally due to overabstraction<br />
||High iron, fluoride and salinity seen in the central western part of Senegal. Saline intrusion in the coastal areas.<br />
||Recharge occurs from direct rainfall and indirectly from rivers, and is estimated at about 103 x 10^6 m³/a to the Maastrichtian deeper aquifer system. This is mainly recharged in the western central part in Diass horst where formations outcrop, and at the contact with the basement formations and the unconsolidated formations in southeastern part of Senegal.<br />
|}<br />
<br />
'''Key references for information on these aquifers''':<br />
<br />
Faye S, Faye SC, Ndoye S and Faye A. 2003. Hydrogeochemistry of the Saloum (Senegal) superficial coastal aquifer. Env Geo 44 (2):127–136<br />
<br />
Diaw M, Faye S, Stichler W and Maloszewski P. 2012. Isotopic and geochemical characteristics of groundwater in the Senegal River delta aquifer: implication of recharge and flow regime. Environ Earth Sci DOI: 10.1007/s12665-010-0710-4.<br />
<br />
Diaw M. 2008. Approches hydrochimique et isotopique de la relation eau de surface/nappe et du mode de recharge de la nappe alluviale dans l’estuaire et la basse vallée du fleuve Sénégal: Identification des zones inondées par Télédétection et par traçage isotopique; Thèse, Univ. C. A. Diop de Dakar. Dakar, Sénégal, pp. 210.<br />
<br />
Re V Cissé, Faye S, Faye A, Faye S, Gaye CB, Sacchi E and Zuppi GM. 2010. Water quality decline in coastal aquifers under anthropic pressure: the case of a suburban area of Dakar (Senegal). Environmental Monitoring Assessment. DOI 10.1007/s10661-010-1359-s.<br />
<br />
Sall M and Vanclooster M. 2009. Assessing the well water pollution problem by nitrates in the small scale farming systems of the Niayes region (Senegal). Agricultural Water Management, 96: 1360–1368.<br />
<br />
Gueye-Girardet A. 2010. Evaluation des pratiques d’irrigation, de fertilisation et d’application de pesticides dans l’agriculture périurbaine de Dakar, Sénégal. Thèse de Doctorat, Université de Lausanne, 276p.<br />
<br />
Tandia AA, Diop ES and Gaye CB. 1999. Nitrate groundwater pollution in suburban areas: example of groundwater from Yeumbeul, Senegal. Journal of African Earth Sciences, 29(4): 809-822.<br />
<br />
<br />
====Basement: Hercynian-Panafrican and Birimian====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Metamorphic basement (of Hercynian-Panafrican Mobile/Orogenic belt)<br />
||The lithologies within this group are extremely heterogeneous and have been subjected to significant metamorphism, so they also vary greatly in their aquifer properties. It is possible to define major aquifer groups comprising quartzite in the north, and schist and greywacke in the south.<br />
<br />
These aquifers are less productive than the Birimian volcaniclastics (see below). Aquifer layers are typically between 18 and 94 m thick, with water table typically between 4 and 62 m depth. Boreholes are between 25 and 131 m deep. The mean borehole yield is 6.95 m³/hour, and the mean transmissivity is 1.42 m²/day.<br />
||Abstracted yields are usually low, from handpumps (India Mark II)<br />
||Some anomalously highly mineralised water, with an electrical conductivity of over 2000 μS/cm, has been sampled in the north. Nitrate pollution is frequently identified in these aquifers, particularly in the north.<br />
||<br />
|-<br />
|Volcaniclastic strata of the Birimian<br />
||Groundwater can be obtained from various strata within the Birimian volcaniclastics found in the south east of the country. These rocks are highly heterogeneous, predominantly volcano-sedimentary rocks including sandstone and quartzite, rhyolitic to dacitic sediments, mudstones, siltstones, and greywacke. These formations are affected by a regional shear zone (the main transcurrent zone, MTZ), which is oriented NNE-SSW; boreholes are sometimes highly productive in affected formations.<br />
<br />
These strata form aquifers where they are adequately weathered or fractured. The weathered zone varies in thickness from less than 6 m up to about 20 m, being typically thicker in the south due to climatic factors. The fractured zone is typically between 10 and 20 m thick.<br />
<br />
The volcaniclastic aquifers are unconfined. The water table is usually between 3 and 21 m depth; seasonal fluctuations in water level lead to some wells drying up periodically. Boreholes are typically between 20 and 70 m deep. The mean yield is 10.2 m³/hour, with a median of 6.5 m³/hour. Mean transmissivity is 17.3 m²/d.<br />
||Mainly low yields from handpumps. Water resource is impacted in some areas by mine dewatering and abstraction for ore processing.<br />
||Generally good quality. Some contamination results from artisanal gold mining (ASGM). Mercury and nitrate contamination has also been identified in places.<br />
||<br />
|-<br />
|Saraya granite and Sandikounda-Soukouta granite (Precambrian)<br />
||These formations comprise leucogranite, monzogranite, granodiorite and tonalite granite lithologies. The upper weathered zone is predominantly sandy, providing a relatively permeable zone with storage capacity, forming an unconfined aquifer. The weathered profile ranges from about 5 to 15 m deep. The weathered aquifer is mainly tapped by hand dug wells that dry up at the end of the dry season (end of April).<br />
<br />
Beneath the weathered zone, secondary (fracture) permeability supports productive wells with average flows of about 6 m³/h.<br />
<br />
Boreholes are typically 20 – 70 m deep. Median yields are of the order of 3.8 m³/h. The transmissivity is about 12 m²/d.<br />
<br />
Numerous dykes intersect the Saraya granite and are probably a significant control on groundwater flow in this aquifer; they are oriented N030°.<br />
<br />
||Borehole yields vary considerably, and are often very low. It is difficult to site boreholes successfully in these aquifers. <br />
||Generally good, but nitrate contamination has been detected in some boreholes.<br />
|| Mainly recharged during rainy season and along the major rivers.<br />
|}<br />
<br />
'''Key references for information on these aquifers''':<br />
<br />
COWI. 2000. Etude Hydrogéologique de la Nappe Profonde du Maastrichtien. Service de Gestion et de Planification des Ressources en Eau (SGPRE)<br />
<br />
Diouf S. 1999. Hydrogéologie en zone de socle cristallin et cristallophyllien du Sénégal Oriental. Application de la méthode électrique 1D et 2D à la localisation et à la caractérisation des aquifères du batholite de Saraya et ses environs. Thèse de doctorat de 3e cycle. Université Cheikh Anta Diop de Dakar, 86 p. + annexes.<br />
<br />
Mall I. 2009. Contribution à l’étude hydrogéochimique en zone de socle: cas du Sénégal Oriental. Mémoire de DEA de l’Université Cheikh Anta Diop, 81p.<br />
<br />
Wuilleumier A, Théveniaut H, Mall I et Ndiaye PM. 2010. Notice explicative de la carte hydrogéologique à 1/500 000 du Sénégal oriental, Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar.<br />
<br />
<br />
==Groundwater Status==<br />
===Groundwater Quantity===<br />
Senegal has significant groundwater resources but the distribution of availability and demand do not match. This means that some groundwater systems are over exploited, leading to groundwater depletion: this has been observed in the Palaeocene and Maastrichtian in the Diass aquifer system.<br />
<br />
===Groundwater Quality===<br />
<br />
'''Saline intrusion'''<br />
<br />
The shallow river delta aquifer and the Saloum superficial aquifer in Senegal have been affected by seawater intrusion as far as, respectively, 200 km and 100 km inland, with wells adjacent to the rivers reporting salt concentrations as high as 10 g/L in the Senegal delta (Diaw et al. 2012) and 3 g/L in Saloum (Faye et al. 2003). The whole coastline (1,700 km) of Senegal and the deep Maastrichtian aquifer have been also highly affected by seawater intrusion. In the western part, the deep Maastrichtian aquifer is characterized by the presence of salt water depth or true "brine" with concentrations above 100 g/l. The interface limit of fresh and salt waters is very variable, which makes it difficult to estimate the volume and water flow direction.<br />
<br />
'''Soil and shallow groundwater salinity'''<br />
Large-scale irrigation in alluvial valleys (Senegal, Saloum and Casamance) may also act to gradually increase the salinity levels in soil water, surface water systems and/or aquifers. This is because the crops transpire almost pure water, which means that applied irrigation leaves a residue of dissolved substances. The effects are most pronounced under arid conditions but also with the use various anthropogenic pollutants (fertilizers, domestic, industrial and agricultural effluents etc). In addition, the using brackish water or treated waste waters for irrigation in Niayes area (north coastline) may promote salinization of the underlying groundwater system in particularly around of large cities like Dakar. It is assumed that the groundwater salinization because of irrigation is restricted to the first meters to tens of meters below the groundwater table in sands dunes (Niayes area). Groundwater salinization effects of these processes will be rather localised. <br />
<br />
'''Agricultural and industrial contaminants'''<br />
In Senegal, agricultural and industrial activities affect the quality of surface water and groundwater that undergo also strong alteration due to chemical pollution from industrials effluents and used products in agriculture including pesticides and fertilizers. This depends on several factors: soil characteristics, irrigation, crops performed, regulation deficiencies, illiteracy of farm operators and funding facility of chemical inputs. These are sensitive problems in areas such as Senegal River Delta, Dakar, Mbour and Fatick etc. The studies carried out in the Senegal delta showed that the river and distributaries channels are affected by mineral pollution from private irrigation discharges in the alluvial plain of Djeuss, pumping stations discharges of Ndong and Gaela on the Gorom channel and high mineralized drainage water discharge of sugar company in Guiers Lake (Diaw 2008). <br />
<br />
The presence of dangerous herbicides or insecticide residues were detected in the analysis carried at several locations in Guiers Lake and in the alluvial aquifer. <br />
<br />
'''Other anthropogenic contaminants'''<br />
In addition to these phenomena mentioned above, other factors may cause water quality degradation, especially in alluvial and coastal unconfined aquifers that are most vulnerable. These shallow groundwaters have been contaminated by anthropogenic pollution in Dakar city and suburbs, most likely a consequence of high population growth, uncontrolled land use and poor hygiene and lack sanitation of the people. Pollution is shown by the presence of nitrates and organic micro-pollutants and bacteriological contamination. Groundwater pollution by nitrates in Dakar region, is important particularly at Mbeubeuss discharge in the Pikine-Thiaroye area, but also occurs in outcropping groundwaters in the Dakar slums (Dalifor, Medina-Gounass). The nitrogen concentrations are increasing in shallow groundwater (sometime to over 400 mg/L) and several studies have been carried out to characterize the problem of nitrate pollution in groundwater in the Dakar Region (Cisse Faye 2013, Diédhiou et al. 2011; Re et al. 2010; Sall & Vanclooster 2009; Gueye-Girardet 2010; Tandia et al. 1999).<br />
<br />
===Groundwater Dependent Ecosystems===<br />
Senegal has areas known as 'niayes' ,which are depressions between dunes which have a very shallow groundwater level. These are common in the Niayes region of northwest Senegal. These areas are prone to groundwater depletion.<br />
<br />
Mangrove forests occur in the Saloum and Casamance estuaries.<br />
<br />
==Groundwater use and management==<br />
=== Groundwater use===<br />
About 60% of Dakar's drinking water is supplied from groundwater, obtained from the Cretaceous-Tertiary Intermediate and Deeper aquifers.<br />
<br />
Groundwater is also used elsewhere for drinking water, industry and agriculture, abstracted largely from basement aquifers.<br />
<br />
Abstraction from the Intermediate and Deeper aquifer systems is from boreholes with electric pumps, while hand pumps are more common in the basement areas.<br />
<br />
=== Groundwater management===<br />
Groundwater and surface water management in Senegal, including water policy, are the responsibility of the Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE). Permits are required for drilling and water abstraction.<br />
<br />
Currently, there is no legislative protection for groundwater in vulnerable areas, and water disposal is not controlled.<br />
<br />
=== Transboundary aquifers===<br />
The Deeper aquifer system of the Maastrichtian is a transboundary aquifer, which is shared by Senegal, Gambia, Mauritania and Guinea-Bissau but there is no specific management issue.<br />
<br />
For links to further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
'''Groundwater levels'''<br />
<br />
Groundwater levels are monitored twice a year: before and after the rainy season. This work is funded through the Ministry of Hydraulics and Sanitation.<br />
<br />
'''Groundwater quality'''<br />
Groundwater quality is measured twice per year, before and after the rainy season, funded by the Ministry of Hydraulics and Sanitation. This work is sometimes extended by NGOs, researchers or others who want to better understand water quality.<br />
<br />
These data are collected and stored by the Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE) and the Société Nationale des Eaux du Sénégal (SONES).<br />
<br />
==References==<br />
===Geology: key references===<br />
Roger J, Noël BJ, Barusseau JP, Serrano O, Nehlig P and Duvail C. 2009. Notice explicative de la carte géologique du Sénégal à 1/500 000, feuilles nord-ouest, nord-est et sud-ouest. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 61 pages.<br />
<br />
Roger J, Duvail C, Barusseau JP, Noël BJ, Nehlig P and Serrano O. 2009. Carte géologique du Sénégal à 1/500 000, feuilles nord-ouest, nord-est et sud-ouest. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 3 coupures.<br />
<br />
Théveniaut H, Ndiaye PM, Buscail F, Couëffé R, Delor C, Fullgraf T and Goujou J-C. 2010. Notice explicative de la carte géologique du Sénégal oriental à 1/500 000. Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar<br />
<br />
===Hydrogeology: key references===<br />
Cowi-Polyconsult. 1998-2002. Etude hydrogéologique de la nappe profonde du Maastrichtien,Sénégal. Rapps. Cowi-Polyconsult, Rép. Sénég., Min. Hydrau.<br />
<br />
Roger J, Banton O, Barusseau JP, Castaigne P, Comte J-C, Duvail C, Nehlig P, Noël BJ, Serrano O and Travi Y. 2009. Notice explicative de la cartographie multi-couches à 1/50 000 et 1/20 000 de la zone d’activité du Cap-Vert. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 245 pages.<br />
<br />
Wuilleumier A, Théveniaut H, Mall I et Ndiaye PM. 2010. Notice explicative de la carte hydrogéologique à 1/500 000 du Sénégal oriental, Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
For more references for the hydrogeology of Senegal please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=SN African Groundwater Literature Archive's Senegal page].<br />
<br />
==Return to the index pages==<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Senegal<br />
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[[Category:Hydrogeology by country|s]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Senegal&diff=12444Hydrogeology of Senegal2015-06-09T16:54:01Z<p>EmilyCrane: /* Jump up to the index pages */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Senegal<br />
<br />
==Authors==<br />
'''Dr Diakher Hélène Madioune''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Ibrahima Mall''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Moctar Diaw''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Professor Serigne Faye''', Cheikh Anta Diop University, Senegal<br />
<br />
'''Emily Crane''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK<br />
<br />
==Geographical Setting==<br />
<br />
[[File:Senegal_Political.png | right | frame | Political Map of Senegal (For more information on the datasets used in the map see the [[Geography | geography resources section]])]] <br />
<br />
<br />
===General===<br />
{| class = "wikitable"<br />
|-<br />
|Estimated Population in 2013* || 14133280<br />
|-<br />
|Rural Population (% of total)* || 56.92%<br />
|-<br />
|Total Surface Area* || 192530 sq km<br />
|-<br />
|Agricultural Land (% of total area)* || 46.82%<br />
|-<br />
|Capital City || Dakar<br />
|-<br />
|Region || Western Africa<br />
|-<br />
|Border Countries || Gambia, Guinea-Bissau, Guinea, Mali, Mauritania<br />
|-<br />
|Annual Freshwater Withdrawal (2013)* || 2.611 Million cubic metres<br />
|-<br />
|Annual Freshwater Withdrawal for Agriculture* || 92.98%<br />
|-<br />
|Annual Freshwater Withdrawal for Domestic Use* || 4.412%<br />
|-<br />
|Annual Freshwater Withdrawal for Industry* || 2.611%<br />
|-<br />
|Rural Population with Access to Improved Water Source* || 60.3%<br />
|-<br />
|Urban Population with Access to Improved Water Source* || 92.5%<br />
|}<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
===Climate===<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
File:Senegal_ClimateZones.png |Koppen Geiger Climate Zones<br />
File:Senegal_ClimatePrecip.png |Average Annual Precipitation<br />
File:Senegal_ClimateTemp.png |Average Temperature<br />
</gallery><br />
<br />
Temporal variations in temperature and rainfall.<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Senegal | Senegal Climate Page]]. <br />
<br />
[[File:Senegal_pre_Monthly.png| 255x124px| Average monthly precipitation for Senegal showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Senegal_tmp_Monthly.png| 255x124px| Average monthly temperature for Senegal showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Senegal_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Senegal_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]] <br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
===Surface water===<br />
<br />
{|<br />
|-<br />
|The following institutions have responsibilities for surface water in Senegal:<br />
<br />
*Organisation pour la Mise en Valeur du Fleuve Sénégal (OMVS)<br />
*Organisation pour la Mise en Valeur du Fleuve Gambie (OMVG)<br />
*Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE) <br />
<br />
| [[File:Senegal_Hydrology.png | frame | Surface Water Map of Senegal (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
|}<br />
<br />
===Soil===<br />
{|<br />
|-<br />
| [[File:Senegal_soil.png | frame | Soil Map of Senegal (For the map key and more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
|<br />
|}<br />
<br />
===Land cover===<br />
{|<br />
|-<br />
|<br />
<br />
| [[File:Senegal_LandCover.png | frame | Land Cover Map of Senegal (For the map key and more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
|}<br />
<br />
==Geology==<br />
The following section provides a summary of the geology of Senegal. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Senegal at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
[[File:Senegal_Geology.png | right]]<br />
<br />
{| class = "wikitable"<br />
|+ Geological Environments<br />
|Key Formations||Period||Lithology||Structure<br />
|-<br />
!colspan="4"| Quaternary unconsolidated sediments<br />
|-<br />
|<br />
||Quaternary<br />
||Variable deposits including alluvium in river valleys and coastal deposits. Including sand and clay.<br />
||Up to 42 m thick.<br />
|-<br />
!colspan="4"|Tertiary - Cretaceous sedimentary rocks<br />
|-<br />
|Continental Terminal<br />
||Neogene<br />
||Variable deposits, often carbonates<br />
||Up to 92 m thick<br />
|-<br />
|Ypresian<br />
||Eocene<br />
||Marly calcareous and limestone deposits, clayey or sandy in places.<br />
||Up to 260 m thick<br />
|-<br />
|Thanetian<br />
||Palaeocene<br />
||Limestone<br />
||Up to 220 m thick<br />
|-<br />
|Montian<br />
||Palaeocene<br />
||Limestone<br />
||<br />
|-<br />
|Danian<br />
||Palaeocene<br />
||Marly calcareous<br />
||<br />
|-<br />
|Maastrichtian<br />
||Mesozoic<br />
||Sand, sandy clay, calcareous sandstone<br />
||Up to 488 m thick<br />
|-<br />
|Campanian<br />
||Mesozoic<br />
||Predominantly clayey<br />
||Up to 102 m thick<br />
|-<br />
|Lower Senonian<br />
||Mesozoic<br />
||Laterally variable; clayey in the western part of the basin<br />
||Up to 92.5 m thick<br />
|-<br />
|Turonian<br />
||Mesozoic<br />
||Black clay; a stratigraphic marker bed<br />
||<br />
|-<br />
!colspan="4"| Tertiary-Quaternary volcanic rocks<br />
|-<br />
|Mamelles volcanics<br />
||Tertiary-Quaternary<br />
||Basalt, basanite, tuffs<br />
||Up to 25 m thick<br />
|-<br />
|Diack formations<br />
||Tertiary<br />
||Gabbro and basalt<br />
||<br />
|-<br />
!colspan="4"| Hercynian-Panafrican Mobile/Orogenic belt<br />
|-<br />
|Mauritanides formations<br />
||Hercynian-Panafrican<br />
||Schists and quartzites<br />
||<br />
|-<br />
!colspan="4"| Precambrian: Birimian<br />
|-<br />
|Birimian formations<br />
||Mesoproterozoic<br />
||Saraya Granite, complex granodiorite-granite of Sandikounda-Soukouta, Boboti Granite<br />
||<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
<br />
===Aquifer properties===<br />
[[File:Senegal_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
====Superficial: Unconsolidated====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Superficial aquifer system<br />
||The Superficial aquifer system covers the whole Senegal sedimentary basin. It is dominantly made of sand and sandy clay, which vary in proportion across its extent. The aquifers are intergranular, and the best groundwater potential occurs in sand layers. It comprises the following aquifers: infrabasaltic (occurs below basalts), Thiaroye, Littoral Nord, alluvial, Continental Terminal and Oligo-Miocene aquifers. This aquifer system overlies the more consolidated deposits of the Eocene, Palaeocene, and the Maastrichtian.<br />
<br />
The Superficial aquifer system ranges between 0 to 150 m thick, with a water table depth between a few metres to 72.5 metres depth. Typical borehole depth varies between 7.6 to 540 m. <br />
<br />
Typical values for aquifer parameters for the Superficial aquifer system are: <br />
<br />
*Permeability = 1 x 10-5 to 8.9 x 10-4 m/s<br />
*Transmissivity = 8.64 to 1728 m²/day<br />
*Storage coeffiecient = 0.01-0.15<br />
*Borehole yield = 50-183 m³/h<br />
||<br />
||Nitrate contamination is known to occur in places. <br />
||<br />
|}<br />
<br />
====Cretaceous - Tertiary Sedimentary - Intergranular and Fracture Flow====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Intermediate aquifer system<br />
||The Intermediate aquifer system includes Eocene and Palaeocene formations, and mainly comprises limestone, often karstic or affected by faults. <br />
<br />
The Eocene aquifer is exploited in the central western part of Senegal and along the Senegal river. <br />
The Palaeocene aquifer occurs mainly in western Senegal, around Pout. These aquifers constitute one of the main sources of drinking water for Dakar. The Intermediate aquifer system ranges between 40 to 120 m thick, with a water table depth between a few metres to 102.5 metres depth. Typical borehole depth varies between 7.6 to 540 m. <br />
<br />
Typical values for aquifer parameters for the Intermediate aquifer system:<br />
*Permeability = 1 x 10-5 to 2.5x10-8 m/s<br />
*Transmissivity = 1.728 – 9504 m²/day<br />
*Storage coeffiecient = 0.05 - 0.10<br />
*Borehole yield = 54 – 300 m³/h<br />
||<br />
||High iron, fluoride and salinity seen in the central western part of Senegal. Saline intrusion in the coastal areas. <br />
||Groundwater recharge depends only on rainwater and rivers.<br />
<br />
|-<br />
|Deeper aquifer system<br />
||The deeper aquifer system, of Maastrichtian age, extends across the whole of the Senegalo-Mauritanian basin and generally consists of sand, sandy-clay and calcareous sandstone. Groundwater storage and flow are largely intergranular. This aquifer constitutes the main source of groundwater supply in Senegal. It is a transboundary system.<br />
<br />
The deeper aquifer system is about 250 m thick, with a water table depth between a few metres to 140 metres depth. Typical borehole depth varies between 25 to 680 m. It is typically highly productive, although aquifer properties vary according to local characteristics (lithology, thickness, etc.). Where there are thick clay sequences, the aquifers can be semi-confined or confined. Typical values for aquifer parameters for the deeper aquifer system are:<br />
<br />
*Permeability = 1 x 10-5 m/s<br />
*Transmissivity = 0.95 – 652578 m²/day<br />
*Storage coeffiecient = 1 x 10-4 – 6 x 10-4 in the western central part<br />
*Borehole yield = 80 – 362 m³/h<br />
||Groundwater depletion occurs locally due to overabstraction<br />
||High iron, fluoride and salinity seen in the central western part of Senegal. Saline intrusion in the coastal areas.<br />
||Recharge occurs from direct rainfall and indirectly from rivers, and is estimated at about 103 x 10^6 m³/a to the Maastrichtian deeper aquifer system. This is mainly recharged in the western central part in Diass horst where formations outcrop, and at the contact with the basement formations and the unconsolidated formations in southeastern part of Senegal.<br />
|}<br />
<br />
'''Key references for information on these aquifers''':<br />
<br />
Faye S, Faye SC, Ndoye S and Faye A. 2003. Hydrogeochemistry of the Saloum (Senegal) superficial coastal aquifer. Env Geo 44 (2):127–136<br />
<br />
Diaw M, Faye S, Stichler W and Maloszewski P. 2012. Isotopic and geochemical characteristics of groundwater in the Senegal River delta aquifer: implication of recharge and flow regime. Environ Earth Sci DOI: 10.1007/s12665-010-0710-4.<br />
<br />
Diaw M. 2008. Approches hydrochimique et isotopique de la relation eau de surface/nappe et du mode de recharge de la nappe alluviale dans l’estuaire et la basse vallée du fleuve Sénégal: Identification des zones inondées par Télédétection et par traçage isotopique; Thèse, Univ. C. A. Diop de Dakar. Dakar, Sénégal, pp. 210.<br />
<br />
Re V Cissé, Faye S, Faye A, Faye S, Gaye CB, Sacchi E and Zuppi GM. 2010. Water quality decline in coastal aquifers under anthropic pressure: the case of a suburban area of Dakar (Senegal). Environmental Monitoring Assessment. DOI 10.1007/s10661-010-1359-s.<br />
<br />
Sall M and Vanclooster M. 2009. Assessing the well water pollution problem by nitrates in the small scale farming systems of the Niayes region (Senegal). Agricultural Water Management, 96: 1360–1368.<br />
<br />
Gueye-Girardet A. 2010. Evaluation des pratiques d’irrigation, de fertilisation et d’application de pesticides dans l’agriculture périurbaine de Dakar, Sénégal. Thèse de Doctorat, Université de Lausanne, 276p.<br />
<br />
Tandia AA, Diop ES and Gaye CB. 1999. Nitrate groundwater pollution in suburban areas: example of groundwater from Yeumbeul, Senegal. Journal of African Earth Sciences, 29(4): 809-822.<br />
<br />
<br />
====Basement: Hercynian-Panafrican and Birimian====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Metamorphic basement (of Hercynian-Panafrican Mobile/Orogenic belt)<br />
||The lithologies within this group are extremely heterogeneous and have been subjected to significant metamorphism, so they also vary greatly in their aquifer properties. It is possible to define major aquifer groups comprising quartzite in the north, and schist and greywacke in the south.<br />
<br />
These aquifers are less productive than the Birimian volcaniclastics (see below). Aquifer layers are typically between 18 and 94 m thick, with water table typically between 4 and 62 m depth. Boreholes are between 25 and 131 m deep. The mean borehole yield is 6.95 m³/hour, and the mean transmissivity is 1.42 m²/day.<br />
||Abstracted yields are usually low, from handpumps (India Mark II)<br />
||Some anomalously highly mineralised water, with an electrical conductivity of over 2000 μS/cm, has been sampled in the north. Nitrate pollution is frequently identified in these aquifers, particularly in the north.<br />
||<br />
|-<br />
|Volcaniclastic strata of the Birimian<br />
||Groundwater can be obtained from various strata within the Birimian volcaniclastics found in the south east of the country. These rocks are highly heterogeneous, predominantly volcano-sedimentary rocks including sandstone and quartzite, rhyolitic to dacitic sediments, mudstones, siltstones, and greywacke. These formations are affected by a regional shear zone (the main transcurrent zone, MTZ), which is oriented NNE-SSW; boreholes are sometimes highly productive in affected formations.<br />
<br />
These strata form aquifers where they are adequately weathered or fractured. The weathered zone varies in thickness from less than 6 m up to about 20 m, being typically thicker in the south due to climatic factors. The fractured zone is typically between 10 and 20 m thick.<br />
<br />
The volcaniclastic aquifers are unconfined. The water table is usually between 3 and 21 m depth; seasonal fluctuations in water level lead to some wells drying up periodically. Boreholes are typically between 20 and 70 m deep. The mean yield is 10.2 m³/hour, with a median of 6.5 m³/hour. Mean transmissivity is 17.3 m²/d.<br />
||Mainly low yields from handpumps. Water resource is impacted in some areas by mine dewatering and abstraction for ore processing.<br />
||Generally good quality. Some contamination results from artisanal gold mining (ASGM). Mercury and nitrate contamination has also been identified in places.<br />
||<br />
|-<br />
|Saraya granite and Sandikounda-Soukouta granite (Precambrian)<br />
||These formations comprise leucogranite, monzogranite, granodiorite and tonalite granite lithologies. The upper weathered zone is predominantly sandy, providing a relatively permeable zone with storage capacity, forming an unconfined aquifer. The weathered profile ranges from about 5 to 15 m deep. The weathered aquifer is mainly tapped by hand dug wells that dry up at the end of the dry season (end of April).<br />
<br />
Beneath the weathered zone, secondary (fracture) permeability supports productive wells with average flows of about 6 m³/h.<br />
<br />
Boreholes are typically 20 – 70 m deep. Median yields are of the order of 3.8 m³/h. The transmissivity is about 12 m²/d.<br />
<br />
Numerous dykes intersect the Saraya granite and are probably a significant control on groundwater flow in this aquifer; they are oriented N030°.<br />
<br />
||Borehole yields vary considerably, and are often very low. It is difficult to site boreholes successfully in these aquifers. <br />
||Generally good, but nitrate contamination has been detected in some boreholes.<br />
|| Mainly recharged during rainy season and along the major rivers.<br />
|}<br />
<br />
'''Key references for information on these aquifers''':<br />
<br />
COWI. 2000. Etude Hydrogéologique de la Nappe Profonde du Maastrichtien. Service de Gestion et de Planification des Ressources en Eau (SGPRE)<br />
<br />
Diouf S. 1999. Hydrogéologie en zone de socle cristallin et cristallophyllien du Sénégal Oriental. Application de la méthode électrique 1D et 2D à la localisation et à la caractérisation des aquifères du batholite de Saraya et ses environs. Thèse de doctorat de 3e cycle. Université Cheikh Anta Diop de Dakar, 86 p. + annexes.<br />
<br />
Mall I. 2009. Contribution à l’étude hydrogéochimique en zone de socle: cas du Sénégal Oriental. Mémoire de DEA de l’Université Cheikh Anta Diop, 81p.<br />
<br />
Wuilleumier A, Théveniaut H, Mall I et Ndiaye PM. 2010. Notice explicative de la carte hydrogéologique à 1/500 000 du Sénégal oriental, Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar.<br />
<br />
<br />
==Groundwater Status==<br />
===Groundwater Quantity===<br />
Senegal has significant groundwater resources but the distribution of availability and demand do not match. This means that some groundwater systems are over exploited, leading to groundwater depletion: this has been observed in the Palaeocene and Maastrichtian in the Diass aquifer system.<br />
<br />
===Groundwater Quality===<br />
<br />
'''Saline intrusion'''<br />
<br />
The shallow river delta aquifer and the Saloum superficial aquifer in Senegal have been affected by seawater intrusion as far as, respectively, 200 km and 100 km inland, with wells adjacent to the rivers reporting salt concentrations as high as 10 g/L in the Senegal delta (Diaw et al. 2012) and 3 g/L in Saloum (Faye et al. 2003). The whole coastline (1,700 km) of Senegal and the deep Maastrichtian aquifer have been also highly affected by seawater intrusion. In the western part, the deep Maastrichtian aquifer is characterized by the presence of salt water depth or true "brine" with concentrations above 100 g/l. The interface limit of fresh and salt waters is very variable, which makes it difficult to estimate the volume and water flow direction.<br />
<br />
'''Soil and shallow groundwater salinity'''<br />
Large-scale irrigation in alluvial valleys (Senegal, Saloum and Casamance) may also act to gradually increase the salinity levels in soil water, surface water systems and/or aquifers. This is because the crops transpire almost pure water, which means that applied irrigation leaves a residue of dissolved substances. The effects are most pronounced under arid conditions but also with the use various anthropogenic pollutants (fertilizers, domestic, industrial and agricultural effluents etc). In addition, the using brackish water or treated waste waters for irrigation in Niayes area (north coastline) may promote salinization of the underlying groundwater system in particularly around of large cities like Dakar. It is assumed that the groundwater salinization because of irrigation is restricted to the first meters to tens of meters below the groundwater table in sands dunes (Niayes area). Groundwater salinization effects of these processes will be rather localised. <br />
<br />
'''Agricultural and industrial contaminants'''<br />
In Senegal, agricultural and industrial activities affect the quality of surface water and groundwater that undergo also strong alteration due to chemical pollution from industrials effluents and used products in agriculture including pesticides and fertilizers. This depends on several factors: soil characteristics, irrigation, crops performed, regulation deficiencies, illiteracy of farm operators and funding facility of chemical inputs. These are sensitive problems in areas such as Senegal River Delta, Dakar, Mbour and Fatick etc. The studies carried out in the Senegal delta showed that the river and distributaries channels are affected by mineral pollution from private irrigation discharges in the alluvial plain of Djeuss, pumping stations discharges of Ndong and Gaela on the Gorom channel and high mineralized drainage water discharge of sugar company in Guiers Lake (Diaw 2008). <br />
<br />
The presence of dangerous herbicides or insecticide residues were detected in the analysis carried at several locations in Guiers Lake and in the alluvial aquifer. <br />
<br />
'''Other anthropogenic contaminants'''<br />
In addition to these phenomena mentioned above, other factors may cause water quality degradation, especially in alluvial and coastal unconfined aquifers that are most vulnerable. These shallow groundwaters have been contaminated by anthropogenic pollution in Dakar city and suburbs, most likely a consequence of high population growth, uncontrolled land use and poor hygiene and lack sanitation of the people. Pollution is shown by the presence of nitrates and organic micro-pollutants and bacteriological contamination. Groundwater pollution by nitrates in Dakar region, is important particularly at Mbeubeuss discharge in the Pikine-Thiaroye area, but also occurs in outcropping groundwaters in the Dakar slums (Dalifor, Medina-Gounass). The nitrogen concentrations are increasing in shallow groundwater (sometime to over 400 mg/L) and several studies have been carried out to characterize the problem of nitrate pollution in groundwater in the Dakar Region (Cisse Faye 2013, Diédhiou et al. 2011; Re et al. 2010; Sall & Vanclooster 2009; Gueye-Girardet 2010; Tandia et al. 1999).<br />
<br />
===Groundwater Dependent Ecosystems===<br />
Senegal has areas known as 'niayes' ,which are depressions between dunes which have a very shallow groundwater level. These are common in the Niayes region of northwest Senegal. These areas are prone to groundwater depletion.<br />
<br />
Mangrove forests occur in the Saloum and Casamance estuaries.<br />
<br />
==Groundwater use and management==<br />
=== Groundwater use===<br />
About 60% of Dakar's drinking water is supplied from groundwater, obtained from the Cretaceous-Tertiary Intermediate and Deeper aquifers.<br />
<br />
Groundwater is also used elsewhere for drinking water, industry and agriculture, abstracted largely from basement aquifers.<br />
<br />
Abstraction from the Intermediate and Deeper aquifer systems is from boreholes with electric pumps, while hand pumps are more common in the basement areas.<br />
<br />
=== Groundwater management===<br />
Groundwater and surface water management in Senegal, including water policy, are the responsibility of the Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE). Permits are required for drilling and water abstraction.<br />
<br />
Currently, there is no legislative protection for groundwater in vulnerable areas, and water disposal is not controlled.<br />
<br />
=== Transboundary aquifers===<br />
The Deeper aquifer system of the Maastrichtian is a transboundary aquifer, which is shared by Senegal, Gambia, Mauritania and Guinea-Bissau but there is no specific management issue.<br />
<br />
For links to further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
'''Groundwater levels'''<br />
<br />
Groundwater levels are monitored twice a year: before and after the rainy season. This work is funded through the Ministry of Hydraulics and Sanitation.<br />
<br />
'''Groundwater quality'''<br />
Groundwater quality is measured twice per year, before and after the rainy season, funded by the Ministry of Hydraulics and Sanitation. This work is sometimes extended by NGOs, researchers or others who want to better understand water quality.<br />
<br />
These data are collected and stored by the Direction de la Gestion et de la Planification des Ressources en Eau (DGPRE) and the Société Nationale des Eaux du Sénégal (SONES).<br />
<br />
==References==<br />
===Geology: key references===<br />
Roger J, Noël BJ, Barusseau JP, Serrano O, Nehlig P and Duvail C. 2009. Notice explicative de la carte géologique du Sénégal à 1/500 000, feuilles nord-ouest, nord-est et sud-ouest. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 61 pages.<br />
<br />
Roger J, Duvail C, Barusseau JP, Noël BJ, Nehlig P and Serrano O. 2009. Carte géologique du Sénégal à 1/500 000, feuilles nord-ouest, nord-est et sud-ouest. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 3 coupures.<br />
<br />
Théveniaut H, Ndiaye PM, Buscail F, Couëffé R, Delor C, Fullgraf T and Goujou J-C. 2010. Notice explicative de la carte géologique du Sénégal oriental à 1/500 000. Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar<br />
<br />
===Hydrogeology: key references===<br />
Cowi-Polyconsult. 1998-2002. Etude hydrogéologique de la nappe profonde du Maastrichtien,Sénégal. Rapps. Cowi-Polyconsult, Rép. Sénég., Min. Hydrau.<br />
<br />
Roger J, Banton O, Barusseau JP, Castaigne P, Comte J-C, Duvail C, Nehlig P, Noël BJ, Serrano O and Travi Y. 2009. Notice explicative de la cartographie multi-couches à 1/50 000 et 1/20 000 de la zone d’activité du Cap-Vert. Ministère des Mines, de l’Industrie et des PME, Direction des Mines et de la Géologie, Dakar, 245 pages.<br />
<br />
Wuilleumier A, Théveniaut H, Mall I et Ndiaye PM. 2010. Notice explicative de la carte hydrogéologique à 1/500 000 du Sénégal oriental, Ministère des Mines, de l’Industrie, de l’Agro-Industrie et des PME, Direction des Mines et de la Géologie, Dakar.<br />
<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
For more references for the hydrogeology of Senegal please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=SN African Groundwater Literature Archive's Senegal page].<br />
==Return to the index pages==<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Senegal<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
[[Category:Hydrogeology by country|s]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Nigeria&diff=12443Hydrogeology of Nigeria2015-06-09T16:53:45Z<p>EmilyCrane: /* Jump up to the index pages */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Nigeria<br />
<br />
==Authors==<br />
'''Professor Moshood N. Tijani''', Department of Geology, University of Ibadan, Nigeria<br />
<br />
'''Emily Crane''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK<br />
<br />
==Geographical Setting==<br />
<br />
<br />
[[File:Nigeria_Political.png | right | frame | Political Map of Nigeria (For more information on the datasets used in the map see the [[Geography | geography resources section]])]] <br />
<br />
===General===<br />
<br />
<br />
{| class = "wikitable"<br />
|-<br />
|Estimated Population in 2013* || 173615345<br />
|-<br />
|Rural Population (% of total)* || 53.91%<br />
|-<br />
|Total Surface Area* || 910770 sq km<br />
|-<br />
|Agricultural Land (% of total area)* || 79.1%<br />
|-<br />
|Capital City || Abuja<br />
|-<br />
|Region || Western Africa<br />
|-<br />
|Border Countries || Benin, Chad, Cameroon, Niger<br />
|-<br />
|Annual Freshwater Withdrawal (2013)* || 13110 Million cubic metres<br />
|-<br />
|Annual Freshwater Withdrawal for Agriculture* || 53.75%<br />
|-<br />
|Annual Freshwater Withdrawal for Domestic Use* || 31.27%<br />
|-<br />
|Annual Freshwater Withdrawal for Industry* || 14.99%<br />
|-<br />
|Rural Population with Access to Improved Water Source* || 49.1%<br />
|-<br />
|Urban Population with Access to Improved Water Source* || 78.8%<br />
|}<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
===Climate===<br />
<br />
<br />
Nigeria's climate is highly variable, from tropical in the south to semi-arid in the north.<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
File:Nigeria_ClimateZones.png |Koppen Geiger Climate Zones<br />
File:Nigeria_ClimatePrecip.png |Average Annual Precipitation<br />
File:Nigeria_ClimateTemp.png |Average Temperature<br />
</gallery><br />
<br />
Temporal variations in temperature and rainfall.<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Nigeria | Nigeria Climate Page]]. <br />
<br />
<br />
[[File:Nigeria_pre_Monthly.png| 255x124px| Average monthly precipitation for Nigeria showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Nigeria_tmp_Monthly.png| 255x124px| Average monthly temperature for Nigeria showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Nigeria_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Nigeria_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]] <br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
===Surface water===<br />
<br />
{|<br />
|-<br />
|The main rivers in Nigeria are the Niger and the Benue, which converge and flow together into the Niger Delta, one of the world's largest river deltas.<br />
<br />
There are both national and regional bodies responsible for river flow gauging and data storage. The Nigeria Hydrological Services Agency (NIHSA) is responsible for assessment of surface water resources through collection of data such as river stage, discharge, water quality and sediment transport. NIHSA maintain a nation-wide network of hydrological stations.<br />
<br />
The Niger Basin Authority (NBA) is also involved in river flow gauging of the River Niger at 18 stations in Niger, and store the data at their headquarters in Niamey, Niger Republic. The Lake Chad Basin Commission gauges river flow at 2 stations on the Komadugu–Yobe River in the Chad Basin Catchment. The Power Holding Company of Nigeria (PHCN) also maintains river flow gauging stations along the River Niger at Kainji and Jebba; they hold these data for use in operating their hydropower systems.<br />
<br />
| [[File:Nigeria_Hydrology.png | frame | Surface Water Map of Nigeria (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
|}<br />
<br />
===Soil===<br />
{|<br />
|-<br />
| [[File:Nigeria_soil.png | frame | Soil Map of Nigeria (For the key to the map and more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
|<br />
|}<br />
<br />
===Land cover===<br />
{|<br />
|-<br />
|Nigeria has highly variable land cover, including tropical rainforest, Sahel savanna, mountain plateaus and coastal plains. <br />
<br />
| [[File:Nigeria_LandCover.png | frame | Land Cover Map of Nigeria (For the key to the map and more information on the datasets used see the [[Land cover | land cover resources section]])]]<br />
|}<br />
<br />
<br />
<br />
==Geology==<br />
The following section provides a summary of the geology of Nigeria. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Nigeria at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
<br />
[[File:Nigeria_Geology2.png | center | border | 500px]]<br />
<br />
{| class = "wikitable"<br />
|+ Geological Environments<br />
|Key Formations||Period||Lithology||Structure<br />
|-<br />
!colspan="4"| Unconsolidated <br />
|-<br />
|Alluvium<br />
||Quaternary<br />
||Deposits vary in thickness and lithology, with sands, gravels, silt and clay all present in varying proportions. These occur along the main river valleys and are thickest (15 - 30 m thick) in valleys associated with the rivers Niger and Benue (Adelana et al. 2008).<br />
||<br />
|-<br />
!colspan="4"| Igneous – volcanic<br />
|-<br />
|Basalts, pyroclasts<br />
||Tertiary - Quaternary<br />
||Basalts, pyroclasts<br />
|| <br />
|-<br />
!colspan="4"| Chad Basin - Sedimentary<br />
|-<br />
|Chad, Kerri-Kerri and Gombe formations<br />
||Cretaceous - Quaternary<br />
||The dominant lithologies in the Chad Basin, in the northeast of Nigeria, are sandstone, siltstone and shale. <br />
<br />
The Quaternary age Chad Formation is up to 840 m thick and consists of poorly sorted fine to coarse-grained sand, with sandy clay, clay and diatomite (Adelana et al. 2008).<br />
<br />
The Tertiary age Kerri-Kerri Formation consists of lacustrine or fluvio-lacustrine loosely cemented cross-bedded coarse- to fine-grained sandstones, with locally occurring claystones, siltstones, ironstones, lignites and conglomerates. It rests unconformably on the Gombe Sandstone Formation, and thickens towards the centre of the Chad Basin, where it is overlain by the Chad Formation (Adelana et al. 2008).<br />
<br />
The Cretaceous age Gombe Sandstone Formation consists of estuarine and deltaic sediments, deposited on marine shales with sandstone/shale intercalations. The lower deposits of siltstone, mudstone and ironstone are overlain by well-bedded sandstones and siltstones. The upper part of the formation contains coals and cross-bedded sandstones (Adelana et al. 2008).<br />
||<br />
|-<br />
!colspan="4"| Niger Delta Basin - Sedimentary<br />
|-<br />
|Unconsolidated: Deltaic Formation<br />
||Tertiary - Quaternary<br />
||Tertiary to Quaternary unconsolidated sediments at the top of the Niger Delta Basin sequence comprise coarse to medium grained unconsolidated sands and gravels with thin peats, silts, clays and shales (Adelana et al. 2008).<br />
||<br />
|-<br />
|Benin, Agbada and Akata formations<br />
||Tertiary<br />
||There are three main deeper sedimentary formations in the Niger Delta Basin. The oldest is the Akata Formation, and is predominantly shaly, with sandstone lenses in the upper parts. The Agbada Formation is predominantly sandy in its upper part, with shale and sandstone beds in roughly equal proportion in its lower part. It may be over 3000 m thick in places, and contains petroleum. The youngest is the Benin Formation, which comprises predominantly (over 90%) sand and gravelly sandstone with shale and clay intercalations.<br />
||The Niger Delta sedimentary rocks are over 10 km thick in total.<br />
|-<br />
!colspan="4"| Sokoto Basin - Sedimentary (Iullemeden)<br />
|-<br />
| Sokoto Group (Gwandu, Kalambaina and Dange formations)<br />
||Tertiary<br />
|| Nigeria's Sokoto Basin represents the southeastern part of the Iullemmeden basin, which stretches across parts of Mali, Niger, Benin and into northwest Nigeria. The Tertiary rocks of the Sokoto Basin are mostly interbedded sandstones, clay and some limestone (Pavelic et al. 2012).<br />
<br />
The Gwandu Formation (of Eocene-Miocene age) crops out in the west of the Sokoto Basin and comprises interbedded semi-consolidated sand and clay. It unconformably overlies the Kalambaina Formation in the north and centre of the basin (Adelana et al. 2008). The Kalambaina Formation consists of clayey limestone with modular crystalline limestone, and is underlain by the Dange Formation, a marine clay shale. The Kalambaina and Dange Formations are collectively known as the Sokoto Group and are of Paleocene age (Adelana et al. 2008).<br />
||The total thickness of the Sokoto Basin is over 1250 m<br />
|-<br />
|Rima Group (Wurno, Dukamaje and Taloka formations), Illo/Gundumi Formation<br />
||Late Jurassic - Cretaceous<br />
||The uppermost Rima Group comprises a series of marine fine-grained sand and friable sandstone, mudstones, and some marly limestone and shale (Adelana et al. 2008). The group is divided into three formations north of the River Sokoto, which from younger to older are Wurno, Dukamaje and Taloka formations. The lower formations are similarly marine sandstones, clays and limestones (Adelana et al. 2008). <br />
||The total thickness of the Sokoto Basin is over 1250 m<br />
<br />
|-<br />
!colspan="4"| Nupe Basin - Sedimentary<br />
|-<br />
|Nupe, Patti and Lokoja sandstones<br />
||Cretaceous<br />
||The Nupe Basin is alternatively known as the Bida or Niger Basin. The basin contains largely continental sandstones, siltstones, claystones and conglomerates (Adelana et al. 2008).<br />
||<br />
|-<br />
<br />
!colspan="4"| Upper Benue Basin - Sedimentary<br />
|-<br />
|Bima Sandstone<br />
||Tertiary<br />
||The Upper Benue Basin consists of a thick succession of continental sandstones overlain by marine and estuarine shales and limestones. The basal formation is the Bima Sandstone (Adelana et al. 2008).<br />
||<br />
|-<br />
|Bima, Yolde, Pindija and Kerri-Kerri formations<br />
||Cretaceous<br />
||Marine arkosic, gravelly, poorly sorted cross-bedded sandstones and sandy limestones (Adelana et al. 2008).<br />
||The sedimentary rocks lie unconformably on the Precambrian Basement Complex<br />
|-<br />
!colspan="4"| Lower Benue Basin - Sedimentary <br />
|-<br />
|Ezeaku, Makurdi, Keana, Awe and Asu River formations<br />
||Cretaceous<br />
||The Lower Benue Basin consists of shales, silts and silty shales with subordinate sandstones and limestones, intruded by dolerite dykes (Adelana et al. 2008). <br />
||The sedimentary rocks lie unconformably on the Precambrian Basement Complex<br />
|-<br />
!colspan="4"| Igneous – younger granites<br />
|-<br />
|Younger granites<br />
||Jurassic<br />
||An-orogenic volcanic and hypabyssal rocks emplaced within the Precambrian Basement Complex.<br />
||Arcuate to circular intrusions forming ring-like complexes.<br />
|-<br />
!colspan="4"| Precambrian Basement Complex<br />
|-<br />
|Migmatite-Gneiss Complex (quartzites, amphibolites, marble)<br />
||Liberian (ca 2800 Ma) to Pan African (ca 600 Ma)<br />
||These rocks are found in the north-central area of Nigeria, including the Jos Plateau, and in the southwest of Nigeria. They comprise gneisses, migmatites, granites, schists, phyllites and quartzites (Adelana et al. 2008). Metamorphism is in the amphibolites facies range.<br />
|| <br />
|-<br />
|Schist belt<br />
||Precambrian<br />
||Schist belts, comprising phyllites, schists, quartzites and banded iron formations, found in northwestern Nigeria.<br />
||Folds<br />
|-<br />
| Older Granites<br />
||Upper Proterozoic<br />
||Intruded into the migmatite-gneiss complex and the schist belts.<br />
|| <br />
|-<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
[[File:Nigeria_Hydrogeology2.png| center | border | 500px]]<br />
<br />
====Dominantly Unconsolidated====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Alluvium<br />
||Alluvial aquifers occur along major river valleys, and are thickest (15 - 30 m thick) along the rivers Niger and Benue. Largely unconfined, with shallow water tables.<br />
||None<br />
||<br />
||Recharge from direct rainfall and infiltration from rivers <br />
|-<br />
|Niger Delta Basin: Deltaic Formation, Benin Formation<br />
||The unconsolidated aquifers of the Niger Delta Basin are extensive and high yielding. The upper Deltaic Formation is unconsolidated and largely unconfined with shallow water table (0-10 m below ground level) (Offodile 2002). <br />
<br />
The older Benin Formation is partly consolidated. It is largely unconfined, but locally confined by lower permeability beds. Water table is typically between 3 and 15 m below ground level (Offodile 2002), but can be as much as 55 m deep. <br />
<br />
The aquifers can provide yields from 3 to 60 l/s. Borehole depths range from 10 to 800 m.<br />
||None<br />
||Salinity problems arising from sea water intrusion; iron problems; pollution problems.<br />
||Recharge is mostly from direct rainfall.<br />
|}<br />
<br />
====Igneous - Volcanic====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Volcanic rocks, including basalts<br />
||Igneous volcanic aquifers provide low to moderate yields, usually below 3 l/s. These aquifers are typically unconfined, with typical variations in water table depth of less than 5 m. Aquifer thickness varies substantially, and borehole depths of 15 to 50 m are common. <br />
||None<br />
||Water quality is generally good.<br />
||Direct rainfall recharge.<br />
|}<br />
<br />
====Chad Basin - Sedimentary - Intergranular====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Chad, Kerri-Kerri and Gombe formations<br />
||The Chad Formation can be unconfined or confined depending on local conditions. Deeper sandstone layers are often confined and can be artesian. Yields of between 2.5 and 30 l/s are quoted. The water table depth is often between 10 and 15 m (Offodile 2002). <br />
<br />
The Gombe Sandstone has relatively low permeability, usually providing yields of about 1 to 5 l/s. <br />
<br />
Relatively little is known about the Kerri-Kerri Formation at depth.<br />
||None<br />
||Water quality is generally good.<br />
||Recharge is mainly by infiltration from rainfall.<br />
|}<br />
<br />
====Sokoto Basin - Sedimentary - Intergranular====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Sokoto Group (Gwandu and Kalambaina formations); Rima Group (Wurno, Dukamage and Taloka formations); Ilo/Gundimi Formation<br />
||The lower sands of the Gwandu Formation are often confined; upper layers are unconfined. Water table can vary from 20 to 100 m depth. Storage is typically high. The Kalambaina Formation is locally permeable with perched aquifers in sandier layers (Offodile 2002). <br />
<br />
The sand layers of the Wurno Formation are moderately yielding, with a restricted recharge area. The Taloka Formation provides variable yields. It is sometimes confined by clay layers (Offodile 2002).<br />
<br />
The gritty, conglomeratic and gravel layers of the Ilo/Gundumi Formation act as aquifers, often confined by clayey layers at depth, when artesian conditions can occur. Shallower aquifer layers are usually unconfined. Typical yields are 2 to 8 l/s. Variable transmissivity values have been quoted, from less than 10 to nearly 1000 m²/day (Offodile 2002).<br />
||<br />
||<br />
||<br />
|}<br />
<br />
====Nupe Basin - Sedimentary - Intergranular====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Nupe Sandstone, Patti & Lokoja Sandstone <br />
||The Nupe Sandstone is slightly cemented, but the dominantly fine grained sandstones and interbedded clays, mudstones nad siltstones through much of the sequence reduce groundwater potential. Overall, borehole yields are poor and highly variable, but where sandstones dominate, borehole yields of ~2 to 4 l/s are seen, and coarser conglomerate beds at the base of the sequence may support higher yields (Offodile 2002). The Patti and Lokoja sandstones are thought to have similar hydrogeological characteristics to the Nupe Sandstone.<br />
||<br />
||<br />
||Recharge is directly from rainfall and, where there are overlying alluvial deposits, through these<br />
|}<br />
<br />
<br />
<br />
====Upper Benue Basin - Sedimentary - Intergranular====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Bima Sandstone, Yolde Sandstone <br />
||These formations have relatively low permeability and usually provide poor to moderate yields of about 1 to 5 l/s. They vary substantially in thickness. The water table depth is usually between 60 and 165 m. Boreholes range in depth from 30 to 300 m.<br />
||None<br />
||Water quality is generally good.<br />
||Recharge is mainly by infiltration from rainfall.<br />
|}<br />
<br />
<br />
====Lower Benue Basin - Sedimentary - Intergranular & Fracture ====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Makurdi, Keana, Ezeaku, Awe and Asu River Group formations<br />
||These formations tend to be indurated and dominated by fracture flow (although the Makurdi Sandstone is less so). Typical yields are around 2 to 8 l/s, but wide variations are seen, depending on the degree of fracturing and deep weathering. The aquifers therefore tend to be localised, and vary greatly in thickness. They are usually unconfined with the water table at about 10 - 40 m depth. Boreholes are typically 40 - 150 m deep. <br />
||None<br />
||Water can be highly mineralised.<br />
||Direct rainfall recharge.<br />
|}<br />
<br />
====Basement====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Basement aquifers<br />
||Basement rocks can form local aquifers if the degree of weathering and/or fracturing is sufficient. Crystalline and coarse-grain rocks, such as gneiss and migmatite, become sandy on weathering, thus preferentially forming aquifers. Argillaceous meta-sedimentary rocks tend to be become clayey with low permeability when weathered, forming aquitards. Overall, basement aquifers tend not to be high yielding. They typically vary in thickness from 10 to 25 m, with water table depth varying from about 5 to 15 m. Boreholes tend to be drilled to depths between 10 and 70 m, depending on local conditions.<br />
||None<br />
||Water quality is generally good.<br />
||Direct rainfall recharge.<br />
|}<br />
<br />
===Groundwater Status===<br />
====Groundwater recharge====<br />
The total renewable groundwater resources potential in Nigeria is estimated at 155.8 billion cubic metres per year (BCM/year), derived from estimated total annual groundwater recharge (JICA 2014). This estimated groundwater recharge at a regional level:<br />
<br />
{| class="wikitable"<br />
|-<br />
!Region <br />
! Estimated Groundwater Recharge (BCM/year)<br />
|-<br />
|Niger North (Northwest Nigeria) <br />
| 5.0<br />
|-<br />
|Niger Central (West-central Nigeria) <br />
| 20.5<br />
|-<br />
|Upper Benue (East-central Nigeria) <br />
| 19.3<br />
|-<br />
|Lower Benue (East Nigeria) <br />
| 18.6<br />
|-<br />
|Niger South (South-central Nigeria) <br />
| 31.9<br />
|-<br />
|Western Littoral (Southwest Nigeria) <br />
| 23.4<br />
|-<br />
|Eastern Littoral (Southeast Nigeria) <br />
| 32.8<br />
|-<br />
|Chad Basin (North-east Nigeria) <br />
| 4.3<br />
|-<br />
|'''Total''' <br />
| '''155.8'''<br />
|}<br />
<br />
====Groundwater-surface water interaction====<br />
There is interaction between the River Niger and sedimentary aquifers in the Sokoto Basin.<br />
<br />
==Groundwater use and management==<br />
=== Groundwater use===<br />
<br />
Groundwater is used in Nigeria for domestic, agricultural and industrial purposes. The cities of Calabar (coastal southeastern Nigeria) and Port Harcourt (capital of Rivers State, south Nigeria) are totally dependent on groundwater.<br />
<br />
JICA (2014) recorded a total of 64,494 boreholes in Nigeria, extracting an estimated total of 6,340,000 m³/day. The groundwater access points identified were:<br />
<br />
*Boreholes with motorised pump :19,758<br />
*Boreholes with hand pump :44,736<br />
*Shallow hand-dug wells :13,108<br />
<br />
A 1996 survey by the Federal Ministry of Water Resources (FMWR) found only 63% of Nigerian boreholes were actually in working order, with many out of action due to pump failure (JICA 2014). <br />
<br />
=== Groundwater management===<br />
====Groundwater management institutions====<br />
There are many bodies with responsibility for groundwater management in Nigeria. They include the government agencies:<br />
<br />
#Nigeria Hydrological Services Agency (NIHSA) whose mandate is water resources (groundwater and surface water) assessment of the country; its quantity, quality, availability and distribution in time and space<br />
#Nigeria Integrated Water Resources Management Commission (NIWRMC) that is responsible for regulation of water use and allocation<br />
#The state Ministries of Water Resources and their Rural Water Supply and Sanitation Agencies (RUWATSSAN), responsible for provision of water to their various States<br />
#All the River Basin Development Authorities, which are also parastatals of the Federal Ministry of Water Resources involved in the provision of water supply to rural environments within their catchments.<br />
<br />
====Legal framework for groundwater management====<br />
Legislation has been developed but is awaiting enactment.<br />
<br />
====Groundwater for the future====<br />
Groundwater could contribute to increasing future water demand by upgrading existing borehole infrastructure, switching from hand pumps to motorised pumps (JICA 2014).<br />
<br />
During their project to update Nigeria's Water Resources Masterplan, JICA (2014) identified issues that were affecting both yield and quality of groundwater in Nigeria:<br />
<br />
*overabstraction leading to water level decline and boreholes drying up<br />
*contamination of groundwater resulting from sea water intrusion and infiltration of domestic and industrial contaminants.<br />
<br />
Modelling by JICA (2014) suggested that climate change would lead to an overall decline in groundwater recharge in Nigeria, with the impact most likely greatest in the North Niger and Chad basins. This modelling suggested declining groundwater levels would occur, leading to previously productive boreholes becoming dry. The study suggested the following measures to increase resilience to climate change in Nigeria's groundwater supply:<br />
<br />
*drill future boreholes 20 m deeper<br />
*position pumps at greater depth (20 m deeper than present)<br />
<br />
=== Transboundary aquifers===<br />
Nigeria has a number of transboundary aquifers:<br />
<br />
#The Iullemeden, Taoudeni/Tanezrout Aquifer Systems (ITAS) shared by Algeria, Benin, Burkina Faso, Mali, Mauritania, Niger and Nigeria.<br />
#The Chad Basin Aquifer shared by Cameroon, Central African Republic, Chad, Niger and Nigeria.<br />
#The Keta Basin Aquifers shared by Ghana, Togo, Benin and Nigeria.<br />
#The Benue Trough shared by Cameroon and Nigeria<br />
#The Rio Del Rey Basin shared by Cameroon and Nigeria along the coast.<br />
<br />
A mechanism for the management of the Iullemeden aquifer is in development, as Nigeria has just ratified an Agreement. The Lake Chad Basin Commission manages issues on the Chad Basin. Groundwater management activities on other Basins are yet to commence. <br />
<br />
For links to further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
There is a national groundwater level monitoring programme with 43 monitoring points, 32 of which are equipped with data loggers. The frequency of monitoring at sites with data loggers is daily, and sometimes twice daily.<br />
<br />
The Nigeria Hydrological Services Agency (NIHSA), an agency of the Federal Ministry of Water Resources (FMWR), carries out the monitoring of groundwater level, and the data are stored at their headquarters in Abuja.<br />
<br />
The NIHSA is also responsible for water quality monitoring, but as yet a full programme is not in place due to lack of equipment.<br />
<br />
==References==<br />
===Geology: key references===<br />
<br />
Adelana SMA, Olasehinde PI, Bale RB, Vrbka P, Edet AE and Goni IB. 2008. An overview of the geology and hydrogeology of Nigeria. In: Adelana, S.M.A. and MacDonald, A.M. Applied Groundwater Studies in Africa. IAH Selected Papers in Hydrogeology Volume 13. Taylor & Francis, London, UK.<br />
<br />
Mpamba NH. 2006. Comparative Analytical Model for Groundwater Monitoring in the Urban and Rural areas of Zambia – Groundwater Resources Data and Information . The University of Zambia, Lusaka, Zambia.<br />
<br />
Nwajide CS. 2013. Geology of Nigeria’s sedimentary basins. CSS Bookshops Ltd<br />
<br />
Rahaman MA and Malomo S. 1983. Sedimentary and crystalline rocks of Nigeria In: Ola, S. A. Ed. Tropical soils of Nigeria in Engineering Practice. Rotterdam. Balkema.<br />
<br />
Kogbe CA. 1976. Microbiostratigraphy of lower Tertiary sediments from the southeastern flank of the Iullemeden basin, N.W. Nigeria. In: Kogbe C. A. (Ed.). 1976. Geology of Nigeria. Elizabethan Publishing Company, Lagos, Nigeria.<br />
<br />
Obaje NG. 2009. Geology and mineral resources of Nigeria. Springer.<br />
<br />
===Hydrogeology: key references===<br />
<br />
JICA. 2014. The project for review and update of Nigeria national water resources master plan; Vol.2. Japan International Cooperation Agency : Yachiyo Engineering Co., Ltd. : CTI Engineering International Co., Ltd. : Sanyu Consultants Inc. [[https://libopac.jica.go.jp/images/report/12146544.pdf JICA report PDF]]<br />
<br />
Kogbe C. A. (Ed.). 1976. Geology of Nigeria. Elizabethan Publishing Company, Lagos, Nigeria.<br />
<br />
Offodile ME. 2002. Groundwater study and development in Nigeria. Mecon Services Ltd, Jos, Nigeria.<br />
<br />
Pavelic P, Giordano M, Keraita B, Ramesh V and Rao T. (Eds.). 2012. Groundwater availability and use in Sub-Saharan Africa: A review of 15 countries. Colombo, Sri Lanka: International Water Management Institute (IWMI). 274 p. doi: 10.5337/2012.213 [[https://www.iwmi.cgiar.org/Publications/Books/PDF/groundwater_availability_and_use_in_sub-saharan_africa_a_review_of_15_countries.pdf Pavelic et al., 2012, PDF]]<br />
<br />
Wardrop Engineering Consultants. 1985. Bauchi State hydrogeology, Hydrogeology Map 1:500000. In : Bauchi State Agricultural Development Programme. Borehole project final report. Wardrop Engineering Consultants, 1985.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
For more references for the hydrogeology of Nigeria please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=NG African Groundwater Literature Archive's Nigeria page].<br />
<br />
==Return to the index pages==<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Nigeria<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
[[Category:Hydrogeology by country|n]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12442Hydrogeology of Zimbabwe2015-06-09T16:52:17Z<p>EmilyCrane: /* Jump up to the index pages */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Return to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12441Hydrogeology of Zimbabwe2015-06-09T16:51:39Z<p>EmilyCrane: /* Geology: key references */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12440Hydrogeology of Zimbabwe2015-06-09T16:51:28Z<p>EmilyCrane: /* Hydrogeology: key references */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12439Hydrogeology of Zimbabwe2015-06-09T16:50:43Z<p>EmilyCrane: /* Igneous - Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing, and contact zones with underlying Forest Sandstone and interbedded sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90 m<sup>2</sup>/d and specific capacity of the order of 1-10 m<sup>3</sup>/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m<sup>3</sup>/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12438Hydrogeology of Zimbabwe2015-06-09T16:49:27Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
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<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
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|-<br />
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|Agricultural Land (% of total area)* || 41.9%<br />
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|-<br />
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|Capital City || Harare<br />
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|-<br />
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|Region || Eastern Africa<br />
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|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
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<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
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===Climate===<br />
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<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
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<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
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File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
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File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
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Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
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<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
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For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
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===Surface water===<br />
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<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
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<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
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|}<br />
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<br />
===Soil===<br />
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{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
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<br />
<br />
|General information about Zimbabwe soils.<br />
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|}<br />
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<br />
<br />
===Land cover===<br />
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{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
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|}<br />
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<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
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|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
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|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
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|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
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|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
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|-<br />
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|}<br />
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==Hydrogeology==<br />
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This section will contain a broad overview of the hydrogeology.<br />
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===Aquifer properties===<br />
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[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
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====Unconsolidated====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
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||<br />
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|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
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||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
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Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
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||<br />
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||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
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|}<br />
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====Igneous - Fracture Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
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These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
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The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
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||This aquifer has moderate groundwater development potential.<br />
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|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
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||<br />
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|}<br />
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====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
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The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
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In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
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Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
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Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m<sup>3</sup>/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m<sup>3</sup>/d.<br />
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|| This aquifer has high groundwater development potential.<br />
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||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
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|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
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|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
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{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
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The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
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Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
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Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
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||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
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||<br />
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|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12437Hydrogeology of Zimbabwe2015-06-09T16:48:51Z<p>EmilyCrane: /* Consolidated Sedimentary – Fracture flow (including karst development) */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m<sup>3</sup>/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m<sup>3</sup>/d/m.<br />
<br />
Water levels tend to be generally shallow (±10 m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12436Hydrogeology of Zimbabwe2015-06-09T16:48:19Z<p>EmilyCrane: /* Other references */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12435Hydrogeology of Zimbabwe2015-06-09T16:47:51Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular & Fracture Flow */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages (Rusinga and Taigbenu, 2005).<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12434Hydrogeology of Zimbabwe2015-06-09T16:47:04Z<p>EmilyCrane: /* Basement */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m<sup>3</sup>/d. Here, transmissivity is low to moderate (<10 m<sup>2</sup>/d) and specific capacity is moderate (30-50 m<sup>3</sup>/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m<sup>2</sup>/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m<sup>3</sup>/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000 mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000 mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
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==Jump up to the index pages==<br />
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[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12433Hydrogeology of Zimbabwe2015-06-09T16:42:09Z<p>EmilyCrane: /* Consolidated Sedimentary - Intergranular Flow */</p>
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<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
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<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
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<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m<sup>2</sup>/d, and specific capacity below 10 m<sup>3</sup>/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000 mg/l. The water poses a potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12432Hydrogeology of Zimbabwe2015-06-09T16:40:07Z<p>EmilyCrane: /* Unconsolidated */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m<sup>3</sup>/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m<sup>3</sup>/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m2/d, and specific capacity below 10 m3/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000mg/l. Water poses potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12431Hydrogeology of Zimbabwe2015-06-09T16:38:18Z<p>EmilyCrane: /* Geology */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000 km² of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100 m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m3/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m3/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m2/d, and specific capacity below 10 m3/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000mg/l. Water poses potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12430Hydrogeology of Zimbabwe2015-06-09T16:37:28Z<p>EmilyCrane: /* Authors */</p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
'''Daina Mudimbu''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
'''Dr Richard Owen''', Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, Aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000km2 of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m3/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m3/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m2/d, and specific capacity below 10 m3/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000mg/l. Water poses potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12429Hydrogeology of Zimbabwe2015-06-09T16:35:06Z<p>EmilyCrane: </p>
<hr />
<div>[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
Daina Mudimbu, Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
Dr Richard Owen, Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, Aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000km2 of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m3/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m3/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m2/d, and specific capacity below 10 m3/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000mg/l. Water poses potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
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[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Zimbabwe&diff=12428Hydrogeology of Zimbabwe2015-06-09T16:33:39Z<p>EmilyCrane: </p>
<hr />
<div> [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
==Authors==<br />
<br />
Daina Mudimbu, Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
Dr Richard Owen, Geology Department, University of Zimbabwe, P.O Box MP167, Mt Pleasant, Harare, Zimbabwe<br />
<br />
==Geographical & Political Setting==<br />
<br />
<br />
<br />
[[File:Zimbabwe_Political.png | right | frame | Political Map of Zimbabwe (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]<br />
<br />
<br />
<br />
===General===<br />
<br />
<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|-<br />
<br />
|Estimated Population in 2013* || 14149648<br />
<br />
|-<br />
<br />
|Rural Population (% of total)* || 67.4%<br />
<br />
|-<br />
<br />
|Total Surface Area* || 386850 sq km<br />
<br />
|-<br />
<br />
|Agricultural Land (% of total area)* || 41.9%<br />
<br />
|-<br />
<br />
|Capital City || Harare<br />
<br />
|-<br />
<br />
|Region || Eastern Africa<br />
<br />
|-<br />
<br />
|Border Countries || Mozambique, South Africa, Botswana, Namibia, Zambia<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal (2013)* || 4205 Million cubic metres<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Agriculture* || 78.9%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Domestic Use* || 14.0%<br />
<br />
|-<br />
<br />
|Annual Freshwater Withdrawal for Industry* || 7.1%<br />
<br />
|-<br />
<br />
|Rural Population with Access to Improved Water Source* || 68.7%<br />
<br />
|-<br />
<br />
|Urban Population with Access to Improved Water Source* || 97.3%<br />
<br />
|}<br />
<br />
<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
<br />
<br />
<br />
===Climate===<br />
<br />
<br />
<br />
Broad description of Zimbabwe – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...<br />
<br />
Climate classification of Zimbabwe. Spatial variations in annual average rainfall and temperature.<br />
<br />
<br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
<br />
File:Zimbabwe_ClimateZones.png |Koppen Geiger Climate Zones<br />
<br />
File:Zimbabwe_ClimatePrecip.png |Average Annual Precipitation<br />
<br />
File:Zimbabwe_ClimateTemp.png |Average Temperature<br />
<br />
</gallery><br />
<br />
<br />
<br />
Temporal variations in temperature and rainfall.<br />
<br />
Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Zimbabwe | Zimbabwe Climate Page]].<br />
<br />
<br />
<br />
<br />
<br />
[[File:Zimbabwe_pre_Monthly.png| 255x124px| Average monthly precipitation for Zimbabwe showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Zimbabwe_tmp_Monthly.png| 255x124px| Average monthly temperature for Zimbabwe showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Zimbabwe_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Zimbabwe_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]<br />
<br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
<br />
<br />
===Surface water===<br />
<br />
<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe surface water – perennial/ephemeral – major rivers – discharge points.<br />
<br />
<br />
<br />
Additional information from country authors...<br />
<br />
<br />
<br />
| [[File:Zimbabwe_Hydrology.png | frame | Surface Water Map of Zimbabwe (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
===Soil===<br />
<br />
{|<br />
<br />
|-<br />
<br />
| [[File:Zimbabwe_soil.png | frame | Soil Map of Zimbabwe (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
<br />
<br />
|General information about Zimbabwe soils.<br />
<br />
|}<br />
<br />
<br />
<br />
===Land cover===<br />
<br />
{|<br />
<br />
|-<br />
<br />
|General information about Zimbabwe land cover.<br />
<br />
<br />
<br />
| [[File:Zimbabwe_LandCover.png | frame | Land Cover Map of Zimbabwe (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
==Geology==<br />
<br />
The following section provides a summary of the geology of Zimbabwe. More detailed information can be found in the key references listed below: many of these are available through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].<br />
<br />
<br />
<br />
The geology map below was created for this Atlas. It shows a simplified version of the geology of Zimbabwe at a national scale. ''The map is available to download as a shapefile (.shp) for use in GIS packages.''<br />
<br />
[[File:Zimbabwe_Geology.png | right]]<br />
<br />
<br />
<br />
{| class = "wikitable"<br />
<br />
|+ Geological Environments<br />
<br />
|Key Formations||Period||Lithology||Structure<br />
<br />
|-<br />
<br />
!colspan="4"| Unconsolidated Sedimentary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Pleistocene<br />
<br />
||Unconsolidated sequence of clay, sand and gravel of varying thickness in the river valleys.<br />
<br />
||In Sabi Valley reported thicknesses of up to 70-80 m of alluvium are present and 45 m in the Zambezi Valley. Elsewhere the unconsolidated deposits are generally less than 25 m thick.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary Kalahari Basin<br />
<br />
|-<br />
<br />
|Lower Pipe Sandstone and the Kalahari Sand.<br />
<br />
||Tertiary and Quaternary<br />
<br />
||The Pipe Sandstone is in places unconsolidated or weakly cemented by silica and traversed by numerous hollow pipes. It is composed of buff or pink sands. In places it is cemented into a hard secondary quartzite or silcrete. The Kalahari Sand comprises pink or buff coloured, structureless, Aeolian sand with a high proportion of fine silt.<br />
<br />
||Approximately 44000km2 of western Zimbabwe is covered by unconsolidated Kalahari Sands. In places, the thickness of the sand is in excess of 100m.<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Cretaceous-Tertiary<br />
<br />
|-<br />
<br />
|<br />
<br />
||Cretaceous-Tertiary<br />
<br />
||Mudstone, arkose, grit conglomerate and sandstone bands<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous Largely Volcanic<br />
<br />
|-<br />
<br />
|Upper Karoo Batoka Basalts<br />
<br />
||Triassic<br />
<br />
||The Batoka basalts comprise amygdaloidal lava flows with interbedded tufa horizons.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Sedimentary – Mesozoic-Palaeozoic (Upper and Lower Karoo)<br />
<br />
|-<br />
<br />
|Upper and Lower Karoo<br />
<br />
|| Carboniferous - Permian<br />
<br />
||These arenaceous and argillaceous sequences are conventionally sub-divided into the Upper and Lower Karoo. The Upper Karoo comprises the Forest Sandstone and the Escarpment Grit, while the Lower Karoo consists of the Madumabisa Mudstone, and the Upper and Lower Wankie Sandstone.<br />
<br />
This thick series of alternating sandstones, siltstones and mudstone is overlain by the Karoo basalt.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Igneous intrusive (Great Dyke)<br />
<br />
|-<br />
<br />
| Great Dyke<br />
<br />
||Late Precambrian<br />
<br />
||The Great Dyke is a large linear mafic-ultramafic intrusive feature composed of norite, gabbro and anorthosite.<br />
<br />
|| Up to 1000 m thick<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian calcareous metasediments and quartzite<br />
<br />
|-<br />
<br />
|In the south-east of Kariba, sedimentary, calcareous and metamorphic rocks of the Deweras, Lomagundi and Piriwiri (all part of the Magondi orogenic belt), Sijarira and Tengwe River Groups. The Umkondo Group<br />
<br />
||Mid to Late Precambrian (Proterozoic)<br />
<br />
||Phyllites with subordinate quartzite of the Piriwiri Formation. slates and shales with minor quartzite of the Lomagundi Formation, shales of the Tengwe River Group and shales, siltstone and fine grained sandstone of the Sijarira Group.<br />
<br />
These rocks include shales, phyllites, quartzites, siltstones, sandstones, conglomerates, limestones and dolomites as well as basic metavolcanics.<br />
<br />
||<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton - Metavolcanics and Metasediments (Greenstone Belts)<br />
<br />
|-<br />
<br />
|Greenstones made up of the supergroups of the Sebakwean, Belingwean, Bulawayan and Shamvaian<br />
<br />
||Early Precambrian / Archaean<br />
<br />
||Irregularly shaped bodies of greenstone material (also known as gold-belts). The Greenstone Belts comprise metavolcanics and metasediments.<br />
<br />
||Moderate to deep weathering occurs within the Greenstone Belts.<br />
<br />
|-<br />
<br />
!colspan="4"| Precambrian Craton (Granites, gneisses and mobile belt gneisses)<br />
<br />
|-<br />
<br />
|The Basement Complex Granitoids, and Mobile/orogenic Belts (Limpopo and Zambezi).<br />
<br />
||Archaean<br />
<br />
||The Basement Complex occupies a large portion of central Zimbabwe and is characterised by vast areas of gneissose rocks, into which younger granite bodies of various sizes were intruded. These intrusive rocks include younger Proterozoic granites and granodiorite, adamellite and tonalite of the Younger Intrusive Granites.<br />
<br />
The Limpopo and Zambezi Mobile Belts are zones of deformed and metamorphosed rocks which run SSW-NNE in the south of the country and NW-SE across the north of Zimbabwe and into Zambia respectively. They comprise paragneisses and anorthosite gneisses.<br />
<br />
There are additional lineaments formed by dolerites and sheets of dolerite composition.<br />
<br />
||Erosional surfaces distinguish the general thickness of the weathering in this unit which ranges from greater than 30 to 35 m on the African erosional surface to shallow and less than 30 m on the Post African and Pliocene/Quaternary surfaces.<br />
<br />
|-<br />
<br />
|}<br />
<br />
<br />
<br />
<br />
<br />
==Hydrogeology==<br />
<br />
This section will contain a broad overview of the hydrogeology.<br />
<br />
<br />
<br />
===Aquifer properties===<br />
<br />
[[File:Zimbabwe_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]<br />
<br />
<br />
<br />
====Unconsolidated====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
| Save Alluvial Aquifer, Umzingwane Alluvial aquifer, Grootvlei/Limpopo (transboundary), Kalahari Sand Aquifer<br />
<br />
||The Kalahari Sands and various alluvial deposits across the country form unconfined aquifers.<br />
<br />
Alluvial deposits are only locally developed within Zimbabwe with the largest occurrences found in the Save (Sabi)- Limpopo river system and major tributaries, along the Zambezi and along the Munyati and Sessami rivers in the north-west. The alluvial deposits vary in thickness, being generally less than 25 m in most areas, but as much as 45 m in the Zambezi Valley and up to 70 m in the Sabi Valley.<br />
<br />
The Kalahari Sands are mainly unconsolidated but also contain the consolidated Pipe Sandstone.<br />
<br />
The aquifer properties of the Kalahari Sands and Alluvial Deposits are extremely variable and may range from locally low to locally high average hydraulic conditions. The water table is generally over 20 m deep.<br />
<br />
Boreholes in the alluvial deposits are typically 20 – 70 m deep, and provide yields of 100-5000 m3/d.<br />
<br />
Boreholes in the Kalahari Sands are commonly 70 – 100 m deep, and provide yields of 100-1000 m3/d.<br />
<br />
||These aquifers have high groundwater development potential.<br />
<br />
||Water quality is generally good. Lenses of brackish water occur in the alluvium of the Sabi river, which may be fossil water and/or water recharging via the adjacent Karoo strata.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Cretaceous-Tertiary sedimentary strata<br />
<br />
||The aquifer properties of these sedimentary rocks are controlled by primary porosity and permeability. The more favourable horizons are the conglomerates and cleaner sandstones, and in the vicinity of rivers.<br />
<br />
Water tables are typically less than 15 m deep, and boreholes are usually drilled to 70 – 100 m depth. Transmissivity is usually less than 1.5 m2/d, and specific capacity below 10 m3/d/m.<br />
<br />
||<br />
<br />
||Water quality is moderate to good with total dissolved solids (TDS) concentrations ranging from less than 1000 mg/l to 2000mg/l. Water poses potential encrustation hazard.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Igneous - Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Igneous – largely volcanic<br />
<br />
||Aquifers in the volcanic igneous rocks are limited to discrete zones of weathering, fracturing and jointing and contact zones with underlying Forest Sandstone and Interbedded Sandstone. Wide sheets of basalt occur in the Victoria Falls and Nyamamdhlovu, and Beitbridge and Chiredzi areas with numerous smaller remnants forming high lying cappings in the Gokwe area.<br />
<br />
These aquifers are unconfined, have variable transmissivity from about 9 – 90m2/d and specific capacity of the order of 1-10 m3/d/m.<br />
<br />
The water table is usually less than 15 m depth, and borehole depths average 50 m, varying from about 40 to 60 m. Borehole yields vary from 10 to 250 m3/d.<br />
<br />
||This aquifer has moderate groundwater development potential.<br />
<br />
|| The quality of the groundwater in this unit is good, with total dissolved solids (TDS) concentrations normally below 1000 mg/l. There is no identified fluoride hazard, although it may pose a mild encrustation hazard in places.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary - Intergranular & Fracture Flow====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Nyamandhlovu Forest Sandstone aquifers (Karoo)<br />
<br />
||The Forest Sandstone is widely developed in the Hwange – Zambezi Basin and constitutes an important regional aquifer. These aquifers are mainly confined, being unconfined only close to outcrop.<br />
<br />
The Escarpment Grit also comprises a confined aquifer in the Hwange and Save -Limpopo basin. The Madumabisa Mudstone is associated with shallow weathering, but has low groundwater development potential. The Upper and Lower Hwange Sandstone is widespread in the Karoo basin; it is found at depth and the aquifer is always confined.<br />
<br />
The hydraulic conductivity and specific yield range from 0.1 to 2.09 m/d and 0.02 to 0.11, respectively.<br />
<br />
In the Forest Sandstone, boreholes are typically 30 – 100 m deep, with water levels sometimes less than 10 m depth but more commonly greater than 20 m depth.<br />
<br />
In the Escarpment Grit and Madumabisa Mudstone, boreholes are typically 30 – 100 m deep, with water levels about 10 – 15 m and greater than 20 m depth respectively.<br />
<br />
Boreholes are usually 100 – 150 m deep in the Upper and Lower Hwange Sandstones.<br />
<br />
Borehole yields are lowest in the Madumabisa Mudstone (10 - 25 m3/d) and groundwater occurrence is rare, only occurring in the vicinity of rivers. In the other units, borehole yields range between 50 – 500 m3/d.<br />
<br />
|| This aquifer has high groundwater development potential.<br />
<br />
||Water quality in the Forest Sandstone is generally good with total dissolved solids (TDS) concentration below 1000 mg/ l. There is no recognised fluoride threat, although it may pose a mild encrustation hazard.<br />
<br />
|| In the Nyamandlovu Forest Sandstone recharge estimates indicate an annual recharge of 105.5 mm with 38.4%, 52.1% and 9.5% accounting respectively for direct recharge, water mains and sewer leakages. (1Rusinga F. and Taigbenu A. E. Groundwater resource evaluation of urban Bulawayo aquifer. Water SA Vol. 31 No. 1 January 2005. ISSN 0378-4738)<br />
<br />
|}<br />
<br />
<br />
<br />
====Consolidated Sedimentary – Fracture flow (including karst development)====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|Lomagundi Dolomite<br />
<br />
||Some water-bearing horizons exist within the rocks mapped as Precambrian calcareous metasediments and quartzite. Aquifers exist primarily due to karst features in the calcareous rocks of the Tengwe River and Lomagundi Formations (massive dolomites and limestones). Karst features are thought to be developed to an average depth of approximately 60 -70 m. Weathering of shaley horizons in the limestones also increases the potential for groundwater storage and flow.<br />
<br />
The groundwater development potential of the Lomagundi Dolomite is classified as high, and that of the Tengwe River Limestone as moderate.<br />
<br />
Measurements of the specific capacity of boreholes in these formations have given the following values:<br />
<br />
*Lomagundi Dolomite: 505 m3/d/m<br />
<br />
*Tengwe River Formation: 4 -120 m3/d/m.<br />
<br />
Water levels tend to be generally shallow (±10m) in the area of Tengwe limestone/shaley limestone, while in the Lomagundi Dolomite the water level varies from ground level at spring occurrences to 50 m depth, depending on land use (commercial or subsistence farming).<br />
<br />
Typical borehole depths are 50 – 70 m in the Tengwe River Formation and 60 – 80 m in the Lomagundi Formations. Yields of 500 - >2000 m3/d are possible.<br />
<br />
||<br />
<br />
||The water quality is generally very good with a slightly hard calcium/magnesium character.<br />
<br />
||<br />
<br />
|}<br />
<br />
<br />
<br />
====Basement====<br />
<br />
{| class = "wikitable"<br />
<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
<br />
|-<br />
<br />
|<br />
<br />
||The gneissose rocks and intrusive granites are devoid of any primary porosity, so the aquifer properties of these basement rocks are controlled by the degree of secondary porosity and permeability, often associated with fracturing, jointing, schistosity planes and weathering. Two hydrogeological sub-units are recognized, each with characteristic groundwater occurrence: the granite and gneiss below the African erosion surface; and the granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces.<br />
<br />
'''Granite and gneiss below the African erosion surface'''<br />
<br />
Rocks beneath the African erosion surface have relatively well developed hydraulic properties resulting from extensive weathering, which generally exceeds 30 - 35 m in depth. Aquifer thickness is about 30 to 50 metres; boreholes are usually drilled to 40 – 50 m depth. Sustainable borehole yields are in the region of 50 - 100 m3/d. Here, transmissivity is low to moderate (<10m2/d) and specific capacity is moderate (30-50 m3/d/m).<br />
<br />
'''Granite and gneiss below the Post-African and Pliocene Quaternary erosion surfaces'''<br />
<br />
The hydraulic properties of the rocks beneath the Post-African and Pliocene-Quaternary erosion surfaces are considerably less well developed. Areas of weathering tend to be patchy and shallow (10 - 30 m). Aquifer thickness is about 10 to 30 m, often less than 15 m. Boreholes are typically 30 – 40 m depth. The transmissivity of these rocks is low (1 – 10 m2/d), while boreholes have low to moderately low specific capacity of the order 2 – 20 m3/d/m.<br />
<br />
|| Areas of granite and gneiss pavement, very shallow bedrock and inselbergs and other features producing positive relief common in the Post-African and Pliocene/Quaternary surfaces are associated with marginal to nil groundwater resources.<br />
<br />
The highest groundwater development potential is found in those areas possessing the deepest and most aerially extensive weathering as in the larger African surface. Chemical weathering along faults, shear zones and dyke contacts may produce equally important water bearing structures.<br />
<br />
Incorrectly sited boreholes may fail during the dry season.<br />
<br />
||Groundwater in the aquifers beneath the African erosion surface is generally of good quality with a total dissolved solids (TDS) concentration below 1000mg/l and no recorded fluoride hazard.<br />
<br />
In aquifers associated with the Post-African and Pliocene/Quaternary surface the groundwater quality is generally good. TDS is usually below 1000mg/l, however it is higher in the Beitbridge and Nuanesti area (TDS of 1000 to 2000 mg/l) where there is also a fluoride hazard.<br />
<br />
||Recharge<br />
<br />
|}<br />
<br />
<br />
<br />
===Groundwater Status===<br />
<br />
'''Groundwater quality'''<br />
<br />
As a general comment to the groundwater development of Zimbabwe all the hydrogeological units are equally suitable for the development of single point primary water supplies either by means of dug wells or by boreholes. Furthermore units classified as possessing moderate or high groundwater development potential are capable of supporting extensive exploitation for piped water supplies and irrigation schemes (Interconsult, 1985).<br />
<br />
'''Groundwater quantity'''<br />
<br />
The groundwater quality throughout Zimbabwe is usually good and does not pose any constraint to use for human consumption. Of the constituents that are a threat to health, the few cases of high nitrate are ascribed to poor borehole construction.<br />
<br />
High fluoride is found in isolated pockets in the Gokwe area and appear to be associated with the outcrop area of the Wankie Sandstone. At the regional scale, fluoride concentrations are not a constraint to exploitation (Interconsult, 1985).<br />
<br />
==Groundwater use and management==<br />
<br />
=== Groundwater use===<br />
<br />
According to the 2012 census, about 38% of a total of 3,059,016 Zimbabwean households fetched their water from boreholes and protected wells (Zimbabwe National Statistics Agency, 2012).<br />
<br />
“Groundwater in Zimbabwe forms the main source of drinking water in rural areas where about 70% of the population lives” (Sunguro et al, 2000).<br />
<br />
In addition to domestic use in rural and urban areas, groundwater supplies agriculture and industry in Zimbabwe.<br />
<br />
The total annual abstraction of groundwater in the rural areas, from some 40,000 boreholes, is estimated at 35 x 10 6 m3 and the total groundwater abstraction for the agricultural sector is estimated at 350 x 10 6 m3. Groundwater is also abstracted for emerging towns known as Growth Points (e.g. Gokwe), Urban Centres (e.g. Bulawayo) and Rural Institutions (e.g. schools, health and business centres). Overall, groundwater presently contributes not more than 10% to the total water use in Zimbabwe (Sunguro et al, 2000).<br />
<br />
Water is mainly abstracted by boreholes with a hand pump fitted in rural areas, due to limited electrification, while electric pumps are more common in urban areas.<br />
<br />
=== Groundwater management===<br />
<br />
The Ministry of Environment, Water and Climate Resources is responsible for the formulation and implementation of sustainable policies regarding the development, utilisation and management of water resources in cooperation with user communities and institutions.<br />
<br />
The Water Act (1998) established the Zimbabwe National Water Authority (ZINWA), a parastatal tasked with providing a framework for the development, management, utilisation and conservation of the country’s water resources through a coordinated approach. ZINWA has a groundwater branch tasked with specifically looking into the management of the national groundwater resources.<br />
<br />
The Water Act also specifies the establishment of Catchment Councils. Seven Catchment Councils were established in the major hydrological zones of the country with functions that included preparing an outline plan for their river systems, determining applications and granting water permits, regulating and supervising the use of water, supervising the performance of functions by Sub-catchment Councils, and dealing with conflicts over water. Water resources include groundwater resources, though due to the limited capacity and lack of adequate information regarding the quantity of groundwater, the management of this resource poses a challenge to the councils.<br />
<br />
Recent developments in the major cities of a collapse of the municipal water treatment and distribution systems has seen a shift towards the use of groundwater at household and even industrial levels, with a rise in bulk water suppliers abstracting huge volumes of water from the groundwater resource. This has raised new challenges of conflict over lowering groundwater levels in residential areas which the catchment councils have inadequately capacity to deal with.<br />
<br />
In addition to the Water Act (1998), groundwater regulations and guidelines were developed for Zimbabwe in 1999 to control groundwater development and management. The regulations and guidelines compliment the Water Act (1998) and have been formulated within a framework of integrated water resources management (IWRM).<br />
<br />
=== Transboundary aquifers===<br />
<br />
Summary of transboundary aquifers<br />
<br />
Zimbabwe has five transboundary aquifers as detailed by UN-IGRAC, 2012:<br />
<br />
*Limpopo Basin (Mozambique, South Africa, Zimbabwe)<br />
<br />
* Tuli Karoo Sub-basin (Botswana, South Africa, Zimbabwe)<br />
<br />
* Eastern Kalihari Karoo Basin (Botswana, Zimbabwe)<br />
<br />
*Nata Karoo Sub-basin (Angola, Botswana, Namibia, Zambia, Zimbabwe)<br />
<br />
*Medium Zambezi Aquifer (Zambia, Zimbabwe).<br />
<br />
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
<br />
<br />
<br />
<br />
=== Groundwater monitoring===<br />
<br />
The following summary is taken verbatim from the IGRAC report, “Groundwater Monitoring in the SADC Region” which was prepared for the Stockholm World Water Week in 2013 (IGRAC, 2013).<br />
<br />
'''National groundwater monitoring network'''<br />
<br />
“Groundwater resources management is carried out by the Groundwater Department of the Zimbabwe National Water Authority (ZINWA). ZINWA is a parastatal under the Ministry of Water Resources Development and Management. Monitoring of groundwater level fluctuation is currently confined to only three major aquifers. These are the Lomagundi Dolomite Aquifer situated in the north western part of the country, the Nyamadlovu Sandstone Aquifer situated in the south western part of the country and the Save Alluvial Aquifer located in the south eastern part of the country.<br />
<br />
Water levels are measured using data loggers and readings are collected monthly. Chloride deposition has been monitored in six monitoring stations throughout the country but has been discontinued due to lack of funds. The information was used in the assessment of groundwater recharge rates. The Department also used to carry out chemical surveillance on groundwater and surface water but again the programme was suspended due to lack of resources.<br />
<br />
'''Data management and assessment'''<br />
<br />
Groundwater fluctuation levels are recorded on template sheets during the last week of the month by field observers who send the records to the main office in Harare. The data is recorded in Excel and an initial quality control exercise is performed. The data is then reformatted and importated into a national groundwater database called Hydro GeoAnalyst. The software has proven to be quite versatile and meeting the needs of ZINWA. Hydrographs and groundwater maps are produced which assist in overall groundwater development and management.<br />
<br />
'''Challenges'''<br />
<br />
The main challenges encountered relate to lack of financial resources, logistical support and limited staff. Another challenge is related to vandalism of facilities by local communities. In certain instances, monitoring boreholes are clogged with debris making water level recording impossible. Specialised entrances for data loggers and locking mechanisms are currently being manufactured for monitoring boreholes in the Save Alluvial Aquifer. It is desired to revive both the chloride deposition and chemical surveillance programmes and to have telemetric (real time) data collection for the water level fluctuations.” (IGRAC, 2013).<br />
<br />
<br />
<br />
==References==<br />
<br />
===Geology: key references===<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
Zimbabwe Surveyor General. 1994. Zimbabwe Geological and Mineral Resources Map, scale 1:1,000,000. Surveyor General, Zimbabwe.<br />
<br />
<br />
<br />
Zimbabwe Geological Survey Bulletins<br />
<br />
<br />
<br />
===Hydrogeology: key references===<br />
<br />
IGRAC. 2013. Groundwater Monitoring in the SADC Region. Accessed at https://www.un-igrac.org/dynamics/modules/SFIL0100/view.php?fil_Id=242 on 09/06/2015.<br />
<br />
Interconsult. 1985. National Master Plan for Rural Water Supply and Sanitation. Volume 22 Hydrogeology. Ministry of Energy and Water Resources Development, Zimbabwe. https://www.bgs.ac.uk/sadc/fulldetails.cfm?id=ZW2024&country=Zimbabwe<br />
<br />
<br />
<br />
UN-IGRAC. 2012. Transboundary aquifers of the world, update 2012. 1:50 000 000. Sepcial Edition for the 6th World Water Forum, Marseille.<br />
<br />
===Other references===<br />
<br />
Zimbabwe National Statistics Agency. 2012. Zimbabwe Population Census, 2012.<br />
<br />
Sunguro, S., Beekman, H. E., Erbel, K., 2000. Groundwater regulations and guidelines: crucial components of integrated catchment management in Zimbabwe. “1st WARFSA/WaterNet Symposium: Sustainable Use of Water Resources; Maputo 1-2 November 2000”.<br />
<br />
===African Groundwater Literature Archive (AGLA) references===<br />
<br />
For more references for the hydrogeology of Zimbabwe please visit the [https://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=ZW African Groundwater Literature Archive's Zimbabwe page].<br />
<br />
<br />
<br />
<br />
<br />
==Jump up to the index pages==<br />
<br />
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Zimbabwe<br />
<br />
<!-- PLEASE DO NOT DELETE BELOW THIS LINE --><br />
<br />
[[Category:Hydrogeology by country|z]]</div>EmilyCranehttps://earthwise.bgs.ac.uk/index.php?title=Hydrogeology_of_Benin&diff=12318Hydrogeology of Benin2015-06-09T12:48:20Z<p>EmilyCrane: /* Geology */</p>
<hr />
<div>==Authors==<br />
'''Moussa Boukari''', Faculté des sciences et techniques, Université d’Abomey-Calavi, Benin<br />
<br />
'''Henri Totin''', Université de Parakou, Benin<br />
<br />
'''Kirsty Upton''' & '''Brighid Ó Dochartaigh''', British Geological Survey, UK<br />
<br />
==Geographical and Political Setting==<br />
<br />
[[File:Benin_Political.png | right | frame | Political Map of Benin (For more information on the datasets used in the map see the [[Geography | geography resources section]])]] <br />
<br />
===General===<br />
<br />
Benin extends from the Atlantic Ocean (Gulf of Guinea) in the south to the Niger River in the north, a distance of around 700 km. The country is relatively flat, with a granitic plateau in the centre of the country which rises to the Atakora mountain range in the northwest. The highest point is at an elevation of 658 m above sea level.<br />
<br />
{| class = "wikitable"<br />
|-<br />
|Estimated Population in 2013* || 10,323,474<br />
|-<br />
|Rural Population (% of total)* || 57%<br />
|-<br />
|Total Surface Area* || 112,760 sq km<br />
|-<br />
|Agricultural Land (% of total area)* || 33%<br />
|-<br />
|Capital City || Porto Novo<br />
|-<br />
|Region || West Africa<br />
|-<br />
|Border Countries || Nigeria, Niger, Burkina Faso, Togo<br />
|-<br />
|Annual Freshwater Withdrawal (2013)* || 130 Million cubic metres<br />
|-<br />
|Annual Freshwater Withdrawal for Agriculture* || 45%<br />
|-<br />
|Annual Freshwater Withdrawal for Domestic Use* || 32%<br />
|-<br />
|Annual Freshwater Withdrawal for Industry* || 23%<br />
|-<br />
|Rural Population with Access to Improved Water Source* || 69%<br />
|-<br />
|Urban Population with Access to Improved Water Source* || 85%<br />
|}<br />
<br />
<nowiki>*</nowiki> Source: World Bank<br />
<br />
<br />
===Climate===<br />
<br />
The majority of the country is classified as a tropical savannah climate, apart from the far north, which transitions into a hot and arid climate towards the Sahel region. Average annual rainfall across the majority of the country is between 1000 and 1100 mm. This decreases in the northern zone to almost 700 mm per year. Average temperatures also show a north-south transition, increasing by a relatively small amount towards the north. <br />
<br />
<gallery widths="375px" heights=365px mode=nolines><br />
File:Benin_ClimateZones.png |Koppen Geiger Climate Zones<br />
File:Benin_ClimatePrecip.png |Average Annual Precipitation<br />
File:Benin_ClimateTemp.png |Average Temperature<br />
</gallery><br />
<br />
There are temporal changes in precipitation and temperature throughout the year. The principal rainy season occurs between April and August, and a second, shorter and less intense rainy season occurs during September and October. Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the [[Climate of Benin | Benin Climate Page]]. <br />
<br />
[[File:Benin_pre_Monthly.png| 255x124px| Average monthly precipitation for Benin showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Benin_tmp_Monthly.png| 255x124px| Average monthly temperature for Benin showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Benin_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Benin_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]] <br />
<br />
<br />
For further detail on the climate datasets used see the [[Climate | climate resources section]].<br />
<br />
===Surface water===<br />
<br />
{|<br />
|-<br />
|The main rivers in the north of Benin are tributaries of the Niger River, and flow northwards, out of the country. The main perennial river in the south of Benin is the Oueme River, which, along with some other smaller rivers, drains into the network of lagoons which has developed along the coast - there is no natural river discharge directly into the Atlantic Ocean. <br />
<br />
The General Directorate of Water (DG-Eau) maintains 48 river flow gauging stations across Benin. Records cover the period 1950 - 2014, with daily observations. River flow data are stored in the Department of Water Information within the DG-Eau. <br />
<br />
The Early Warning System (SAP) project also collects river flow data.<br />
<br />
| [[File:Benin_Hydrology.png | frame | Surface Water Map of Benin (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]<br />
|}<br />
<br />
===Soil===<br />
{|<br />
|-<br />
| [[File:Benin_soil.png | frame | Soil Map of Benin (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]<br />
<br />
|Lixosols are the dominant soil type in Benin, reflecting stable geological conditions, a savannah climate and grassland vegetation. <br />
<br />
Leptosols are found in the mountainous region in the north west of the country while Arenosols (large sand deposits) occur in the Sahel region along the northeastern border. <br />
<br />
Productive Nitisols have developed on the alluvium in the coastal region. On the sandbars and lagoons of the coastal region are Gleysols and Arenosols. <br />
|}<br />
<br />
===Land cover===<br />
{|<br />
|-<br />
|<br />
<br />
| [[File:Benin_LandCover.png | frame | Land Cover Map of Benin (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]<br />
|}<br />
<br />
==Geology==<br />
This section provides a summary of the geology of Benin. More detail can be found in the references listed at the bottom of this page.<br />
<br />
The geology map on this page shows a simplified version of the geology of Benin. A more detailed geological map at 1:200,000 scale was produced by BRGM (1978)<br />
<br />
[[File:Benin_Geology2.png|500px]]<br />
<br />
{| class = "wikitable"<br />
|+ Geological Environments<br />
|Key Formations||Period||Lithology||Structure<br />
|-<br />
!colspan="4"|Unconsolidated Sedimentary<br />
|-<br />
|Alluvium<br />
||Quaternary<br />
||Sand, clay, silt and sometimes gravel deposits, forming outwash fan, channel and floodplain deposits along river channels.<br />
||Variable thickness but generally less than 100 m.<br />
|-<br />
!colspan="4"|Sedimentary - Coastal Basin<br />
|-<br />
|Benin Sedimentary Coastal Basin<br />
||Lower Cretaceous - Quaternary<br />
||Marine deposits (sandstone, limestone, clay, marl and conglomerate) belonging to the Keta Basin, deposited along the Atlantic coast of Ghana, Togo, Benin and Nigeria. <br />
Fine grained unconsolidated lacustrine sediments are also deposited along the coast.<br />
||Marine deposits have highly variable thickness (10 - 2000 m). <br />
Unconsolidated coastal deposits are on average 50 m thick.<br />
|-<br />
!colspan="4"|Sedimentary - Iullumeden Basin<br />
|-<br />
|Were, Goungoun, Kandi, Sende & Continental Terminal Formations<br />
||Lower Palaeozoic - Cretaceous<br />
||Conglomerate, sandstone, siltstone & clay. These Continental deposits, belonging to the southern part of the Iullemeden Basin, also occur in Nigeria, Niger and Mali.<br />
||Variable thickness (20 - 400 m). The Continental Terminal Formation contains small extensional features.<br />
|-<br />
!colspan="4"|Precambrian Metasedimentary<br />
|-<br />
|Voltaian (or Pendjari) Basin<br />
||Late Precambrian - Lower Palaeozoic<br />
||Sandstones, shales and siltstones.<br />
||Highly variable thickness.<br />
|-<br />
|Buem (Volcanic-Sedimentary) Series<br />
||Late Precambrian<br />
||Sandstone, quartzite, rhyolite and andesite<br />
||Highly variable thickness (estimated 250 - 2000 m).<br />
|-<br />
!colspan="4"|Precambrian Mobile/Orogenic Belt<br />
|-<br />
|Basement Complex<br />
||Precambrian<br />
||Crystalline gneiss and granulite with granite and syenite intrusions. Highly metamorphosed and deformed during several orogenic phases which gave rise to various episodes of igneous activity.<br />
|| Often intensely folded. Folds are generally isoclinal. Not generally steeply dipping.<br />
|-<br />
|Atacora, Kande and Kouande Series<br />
||Precambrian<br />
||Quartzite and schist. Highly metamorphosed during the Panafrican Orogeny.<br />
||<br />
|}<br />
<br />
==Hydrogeology==<br />
''This section provides a summary of the hydrogeology of the main aquifers in Benin. More information is available in the references listed at the bottom of this page, many of which are available through the Africa Groundwater Literature Archive.''<br />
<br />
===Aquifer properties===<br />
<br />
The hydrogeology map on this page shows a simplified description of the type and productivity of aquifers in Benin, at 1:5,000,000 scale. More detailed hydrogeological maps, at 1:500,000 scale and 1:200,000 scale, are produced by GIZ Germany/DGEau Benin (Achidi et al 2012). <br />
<br />
[[File:Benin_Hydrogeology2.png]] | 500x195px]]<br />
<br />
====Unconsolidated====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Alluvial and barrier beach deposits<br />
<br />
||The alluvial and barrier beach deposits of Benin are highly variable both laterally and vertically. The alluvial deposits are found along the major river valleys, the most significant of which is the River Niger valley in the north. The barrier beach deposits are found along the coast and are dominated by relatively impermeable clays. However, interbedded, generally poorly sorted, coarser grained sands and gravels can form aquifers of local importance along the coast. <br />
<br />
Yields are highly variable but are often reported around 5 l/s, and sometimes higher from sand and gravel layers. Transmissivity is generally 10 to 400 m²/d. Storage coefficient is typically 10-2 - 10-1.<br />
<br />
The thickness of the unconsolidated aquifers typically varies between 10 and 20 m. The water table is generally shallow, less than 7 m below ground level. Boreholes are typically drilled to depths of 5 to 20 m. <br />
<br />
||There are no known issues with water quantity and availability.<br />
<br />
||The unconsolidated deposits are particularly vulnerable to contamination from latrines and agriculture. Saline intrusion is an issue in the littoral area and high salinity is also reported in parts of the alluvial aquifer along the Oueme River valley.<br />
<br />
||Recharge is not well quantified. <br />
|}<br />
<br />
====Coastal Sedimentary Basin aquifers (Consolidated Sedimentary - Intergranular Flow)====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Coastal sedimentary basin aquifers<br />
||There are 4 main aquifers in the Coastal Basin, and they are the main source of drinking water for southern Benin. They are, in order of decreasing age, the Upper Cretaceous, Paleocene, Continental Terminal and Quaternary aquifers. They are separated by low permeability clays and marls, and may be confined or unconfined depending on the local geology.<br />
<br />
Yields are generally 2 to 50 l/s. Transmissivity is generally 80 - 900 m²/d. Storage coefficient is typically 10-6 - 10-5.<br />
<br />
The coastal sedimentary aquifers typically range from 20 to 150 m thick, with boreholes extending to depths of 10 to 100 m. Where the aquifers are unconfined, the water table depth may vary from 5 to 50 m below ground level. <br />
||Storage decreases where aquifer thickness is low (typically towards the upstream limits), which can lead to issues with groundwater availability.<br />
||Total dissolved solids (TDS) is generally less than 500 mg/l and usually around 200 mg/l. pH is typically neutral to acidic. Saline intrusion is an issue in the littoral zone.<br />
<br />
Unconfined aquifers are particularly vulnerable to contamination from latrines and agriculture, especially where the water table is very shallow.<br />
||Recharge is not well quantified.<br />
|}<br />
<br />
====Sedimentary - Kandi (Iullemeden) Basin and Precambrian - Voltaian (or Pendjari) Basin aquifers (Consolidated Sedimentary - Intergranular & Fracture Flow)====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Kandi Basin (Iullemeden) aquifer and Voltaian (or Pendjari) basin aquifer<br />
||The Kandi Basin can be divided into two principal aquifers: a younger Cretaceous sandstone aquifer, and an underlying Cambro-Ordivician sandstone aquifer. The two aquifers are separated by low permeability fine sandstones and argillites of Silurian age. The Cretaceous aquifer comprises coarse sandstone; groundwater is unconfined and in hydraulic continuity with overlying unconsolidated alluvial deposits along the Niger River. <br />
<br />
The underlying Cambro-Ordovician aquifer is also composed of coarse sandstone and is largely confined. It becomes unconfined in the south and west of the basin where the sandstone outcrops adjacent to Precambrian basement. <br />
<br />
The Voltaian Basin aquifer has similar regional characteristics to the aquifers in the Kandi Basin.<br />
<br />
Yields are rarely higher than 1.5 l/s. Transmissivity varies from <1 to >600 m²/d.<br />
<br />
The total thickness of these aquifers is unknown. Boreholes typically vary in depth from 30 to 100 m. <br />
Where unconfined, the depth of the water table varies between 5 and 45 m below ground level. <br />
||There are no known issues with water quantity and availability.<br />
||Conductivity, and thus total dissolved solids, is generally lower for the unconfined Cretaceous aquifer with values of 25 - 60 micro siemens per cm reported for the upper aquifer and 130 - 425 micro siemens per cm reported for the lower aquifer.<br />
||Recharge is not well quantified. <br />
|}<br />
<br />
====Basement====<br />
{| class = "wikitable"<br />
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge<br />
|-<br />
|Basement Complex Sandstone (central Benin) and Atacora Series (northwest Benin)<br />
<br />
||Basement aquifers have very low intergranular permeability in their unweathered state. Aquifer productivity depends on the development of a weathered zone. Coarser grained granites and gneiss generally weather to a more permeable sandy material which typically forms a low-moderate productivity aquifer. Weathered areas typically form shallow basins separated by largely unweathered rock. The presence and thickness of the weathered zone is highly variable, but is best developed on plateaus (often 10 to 30 m thick). Weathered basins typically thin towards outcropping inselbergs.<br />
<br />
Yields are generally 0.25-0.5 l/s but can reach 2.0 l/s.<br />
<br />
Hydraulic conductivity is generally 0.5 to 15 m/d. Tranmissivity is generally 5 to 35 m²/d. Storage coefficient is typically 10-3 - 10-2.<br />
<br />
The basement aquifers are typically unconfined. Water table depths are generally 5 to 15 m below ground level, but can be deeper (up to 30 m below ground level). Seasonal water table fluctuations are thought to be between 1 and 5 m. <br />
<br />
Boreholes are typically drilled to depths of 45 to 60 m.<br />
||Boreholes are usually fitted with handpumps, and therefore abstraction rates are typically low.<br />
||Total dissolved solids (TDS) is generally less than 1000 mg/l and usually around 500 mg/l. pH is usually neutral to slightly basic. High salinity is occasionally reported.<br />
<br />
The weathered basement is vulnerable to nitrate contamination from agricultural sources and latrines. <br />
||Recharge is not well quantified.<br />
|}<br />
<br />
===Groundwater Status===<br />
Low yields from basement aquifers, which cover most of Benin, lead to difficulties with fresh water availability in medium to large cities. <br />
<br />
Potable water supply is also an issue in parts of the coastal basin, where the saturated thickness of the shallow aquifers is not sufficient for large supplies. Where the shallow deposits are unable to sustain sufficient yields, boreholes are drilled deeper into the weathered basement below.<br />
<br />
Groundwater in shallow aquifers is often of poor quality due to contamination. Saline intrusion is a particular problem in the coastal aquifers. <br />
<br />
The Oueme River loses water to the permeable coastal sedimentary aquifer, and river flow depletion is therefore an issue in this river downstream of the contact between the Precambrian basement aquifer and the coastal sedimentary aquifer. <br />
<br />
The surface water coastal lagoons around Godomey in central-south Benin often dry up due to intensive pumping from the adjacent Godomey well field. <br />
<br />
==Groundwater use and management==<br />
=== Groundwater use===<br />
The main uses of groundwater in Benin are domestic supply (both urban and rural), agriculture, livestock and fish farming, tourism, industry and transport. <br />
<br />
Groundwater sources vary from boreholes with electric pumps, hand pumps and foot pumps, modern and traditional wells, and traditional and improved springs. <br />
<br />
=== Groundwater management===<br />
The key groundwater institutions in Benin are:<br />
<br />
* National Company of Urban Water Supply (SONEB) - responsible for groundwater supply in urban areas.<br />
* General Directorate of Water (DG-Eau) - - responsible for groundwater supply in rural areas.<br />
<br />
The "Code of Water in Benin" is the key piece of legislation related to groundwater management. Permits are required for drilling and groundwater abstraction. These are issued by the government through the Ministry of Justice and the Ministry of Water. Groundwater protection is very difficult particularly in more densely populated areas because the disposal of waste is largely uncontrolled. <br />
<br />
=== Transboundary aquifers===<br />
In the coastal region the Quaternary and Continental Terminal aquifers are shared with Nigeria, Benin, Togo and Ghana.<br />
<br />
The aquifers of the Iullemeden Basin are shared with Niger, Mali and Nigeria.<br />
<br />
For further general information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]<br />
<br />
=== Groundwater monitoring===<br />
Groundwater monitoring is carried out by the National Company of Urban Water Supply (SONEB), the General Directorate of Water (DG-Eau) and the National Institute of Water. <br />
<br />
The Laboratory of Climatology carries out work to look at climate change impacts on groundwater.<br />
<br />
=== References ===<br />
The following references provide more information on the geology and hydrogeology of Benin. <br />
<br />
====Geology References====<br />
<br />
Affaton P. 1975. Etude géologique et structurale du Nord-Ouest du Dahomey, du Nord Togo et du Sud-Est de la Haute Volta. Travaux Laboratoire Sciences de la Terre, St-Jérôme, Marseille, France, (B) 201 p.<br />
<br />
Alidou S. 1983. Etude géologique du bassin paléo-mésozoique de Kandi, Nord-Est du Bénin (Afrique de l’Ouest). Thèse de doctorat ès-Sciences, 328 p. Université de Dijon, France.<br />
<br />
Alidou S et Oyédé LM. 1984. Quaternaire du Bénin. ASEQUA, Dakar. Bulletin de Liaison, 72-73, 42-43.<br />
<br />
Boussari WT. 1975. Contribution à l’étude géologique du socle cristallin de la zone mobile Pan-africaine (région central du Dahomey). Thèse de 3ème cycle, 105 p. Université de Besançon, 236.<br />
<br />
BRGM. 1978. Carte géologique au 1/200 000 du Bénin et du Togo entre les 9ème et 10ème degré de latitude Nord. Rapport, OBEMINES. Cotonou, Bénin. 78 RDM 055 AF. 2 feuilles, 1 notice explicative.<br />
<br />
Guiraud R et Alidou S. 1981. La faille de Kandi (Bénin), témoin du rejeu fini-Crétacé d’un accident majeur à l’échelle de la plaque africaine. Comptes Rendus Académie des Sciences. Paris, France. 293 (II) 779-782.<br />
<br />
Houessou A et Lang J. 1979. La "Terre de Barre" dans le Bénin méridional (Afrique de l’Ouest). Bulletin ASEQUA 56-57, 49-58.<br />
<br />
IRB ou Istituto recerche Breda. 1982. Etude de cartographie géologique et prospection minière de reconnaissance au Nord du 11ème parallèle. Rapport final OBEMINES, Cotonou, Bénin. <br />
<br />
IRB ou Istituto recerche Breda. 1987. Etude de cartographie géologique et prospection minière de reconnaissance au Sud du 9ème parallèle. Rapport, 80 p. OBEMINES, Cotonou, Bénin. <br />
<br />
Konaté M. 1996. Evolution tectono-sédimentaire du bassin paléozoïque de Kandi (Nord-Bénin et Sud-Niger): un témoin de l’extension post-orogénique de la chaîne panafricaine. Thèse doctorat, 281 p. Université de Bourgogne et Université de Nancy I. France. <br />
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Konaté M, Guiraud M, Alidou S, Clermonté J, Drouet J-J et Lang J. 1994. Structuration et dynamique sédimentaire du bassin paléozoïque en demi-graben de Kandi (Bénin, Niger). Comptes Rendus Académie des Sciences. Paris, France. 318 (II) 535-542.<br />
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Lang J, Kogbe C, Alidou S, Alzouma K, Bellion G, Dubois D, Houessou A et Trichet J. 1986. Le sidérolithique du Tertiaire oust-africain et le concept du Continental Termial. Bulletin de la Société. Géologique de France. 8, (II) 605-622. <br />
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Oyédé LM, de Klasz I, de Klasz S, Lang J, Carbonnel G, Grosdidier E, Legoux O et Martini E. 1992. Datation de la discordance dite «oligocène» sur la partie terrestre du bassin sédimentaire côtier béninois (Afrique de l’Ouest). Comptes Rendus Académie des Sciences. Paris, France. 315(II), 971-977.<br />
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Oyédé LM. 1991. Dynamique sédimentaire actuelle et messages enregistrés dans les séquences quaternaires et néogènes du domaine margino-littoral du Bénin (Afrique de l'Ouest). Thèse de doctorat, 302 p. Université de Bourgogne, Dijon, France. <br />
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Pougnet R. 1955. Le Précambrien du Dahomey. 186 p. Bulletin de la Direction Fédérale des Mines de l’Afrique Occidentale française. Dakar, Sénégal. 22. <br />
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SERHAU ou Service d’Etude et de Recherche pour l’Habitat et l’Urbanisme. 1992. Atlas cartographique de la région nord du Bénin. Rapport, 54 p. MEHU. Cotonou, Bénin. <br />
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Slansky M. 1962. Contribution à l'étude géologique du Bassin sédimentaire côtier du Dahomey et du Togo. Thèse de doctorat, 241 p. Université de Nancy, Nancy, France. <br />
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TECHNOEXPORT. 1980. La constitution et les substances utiles de la République Populaire du Bénin entre les 10ème et 11ème parallèles de latitude nord. Rapport Office Béninois des Mines. Cotonou, Moscou, Bénin, URSS. <br />
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TECHNOEXPORT. 1984. La constitution et les substances utiles de la partie Est de la République Populaire du Bénin, entre les 10ème et 11ème parallèles de latitude nord (rapport du levé et de prospection géologiques à l’échelle de 1/200 000 effectués en 1981-1984). Rapport, 331 p. Office Béninois des Mines. Cotonou, Bénin. <br />
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Wakuti KE et Gall KG. 1968. Reconnaissance géophysique et sondages mécaniques dans le Centre, Nord-Est et Nord-Ouest du Dahomey. Rapport Direction Hydraulique, Mines et Travaux Publics. Cotonou, Bénin. <br />
<br />
<br />
====Hydrogeology References====<br />
Key references are highlighted in '''bold'''.<br />
<br />
'''Achidi, J-B, Bourguet L, Elsaesser R, Legier A, Paulvé E et Triboullard N.''' 2012. Cartes hydrogéologiques du Bénin au 1/500 000 and 1/200000. GIZ Germany or DGEau Benin.<br />
<br />
Alassane A. 2004. Etude hydrogéologique du Continental Terminal et des formations de la plaine littorale dans la région de Porto-Novo (sud du Bénin): identification des aquifères et vulnérabilité de la nappe superficielle. Thèse 3ème cycle, 145 p. Université Cheik Anta Diop, Dakar, Sénégal.<br />
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Alidou S et Oyédé LM. 1984. Quaternaire du Bénin. ASEQUA, Dakar. Bulletin de Liaison, 72-73, 42-43.<br />
<br />
'''Boukari M. 1980'''. Contribution à l’étude hydrogéologique des régions de socle de l’Afrique occidentale : mise au point des connaissances relatives à la République Populaire du Bénin. Rapport Département de Géologie. No 4. Nouvelle série. Mémoire de DEA, 141 p. Université de Dakar, Sénégal. <br />
<br />
'''Boukari M. 1982'''. Contribution à l’étude hydrogéologique des régions de socle de l’Afrique intertropicale : l’hydrogéologie de la région de Dassa-Zoumé (Bénin). Thèse 3ème cycle, 140 p. Université Cheik Anta Diop, Dakar, Sénégal. <br />
<br />
'''Boukari M. 1989'''. Etude de synthèse et de cartographie relative au cadre physique et aux ressources naturelles de la région nord du Bénin. Rapport SERHAU, 68 p. Cotonou, Bénin. <br />
<br />
Boukari M, Alidou S, Oyédé LM, Gaye CB et Maliki R. 1995. Identification des aquifères de la area littorale du Bénin (Afrique de l'Ouest) : hydrodynamique, hydrochimie et problèmes d'alimentation en eau de la ville de Cotonou. African Geoscience Review 2 (1), 139-157. <br />
<br />
Boukari M, Gaye CB, Faye A et Faye S. 1996. The impact of urban development on coastal aquifers near Cotonou (Bénin). Journal of African Earth Sciences 22 (4), 403-408.<br />
<br />
Boukari M. 1998. Fonctionnement du système aquifère exploité pour l’approvisionnement en eau de la ville de Cotonou sur le littoral béninois. Impact du développement urbain sur la qualité des ressources. Thèse de doctorat ès Sciences, 278 p. Université Cheik Anta Diop, Dakar Sénégal. <br />
<br />
Boukari M. 2002. Réactualisation des connaissances hydrogéologiques relatives au bassin sédimentaire côtier du Bénin. Rapport du programme d’Appui à la Gestion des Ressources en Eau (AGRE), 134 p. Direction Hydraulique. Cotonou, Bénin. <br />
<br />
'''Boukari, M. 2007'''. Hydrogéologie de la République du Bénin (Afrique de l’ouest). Africa Geoscience Review (2007), Vol. 14, N° 3, pp. 303-328. France.<br />
<br />
'''Boukari M et Alassane A. 2007'''. Les ressources en eaux souterraines du bassin sédimentaire côtier de la République du Bénin. Africa Geoscience Review (2007), Vol. 14, N° 3, pp. 283-301. France.<br />
<br />
'''Bouzid M. 1971'''. Développement de l’utilisation des eaux souterraines, Dahomey : hydrogéologie. Rapport technique 1, 88 p. PNUD-FAO. SF/DAH3. Rome, Italie. <br />
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'''BURGEAP-BRGM. 1986'''. Programme d’hydraulique villageoise du Nord-Borgou (Bénin). Etudes d’implantation et contrôle des travaux de points d’eau. Rapport final, 74 p. Direction de l’Hydraulique. Cotonou, Bénin. <br />
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BURGEAP-BRGM. 1994. Projet d’alimentation en eau potable des areas lacustres des Départements de l’Atlantique et de l’Ouémé. Rapport final, 64 p. Direction de l’Hydraulique, Cotonou, Bénin. <br />
CEFIGRE ou Centre de Formation Internationale à la Gestion des Ressources en Eau. 1984. Synthèse des connaissances sur l’hydrogéologie du socle cristallin et cristallophyllien, et du sédimentaire ancien de l’Afrique de l’Ouest. Rapport Ministère des Relations Extérieures. 121 p. Valbonne. France.<br />
<br />
CEFIGRE. 1984. Synthèse des connaissances sur l’hydrogéologie du socle cristallin et cristallophyllien, et du sédimentaire ancien de l’Afrique de l’Ouest. Rapport Ministère des Relations Extérieures. Valbonne. France.121 p.<br />
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Collin JJ et Mangin, A. 1985. Evolution récente de l'hydrogéologie: de la prospection à la gestion des ressources en eau. Bulletin de la Société. Géologique de France. 7, 999-1008. <br />
Descloitres, M., Séguis, L., and Wubda, M. (2006). Caractérisation des aquifères sur les sites AMMA CATCH au Bénin, apport de la résonnance magnétique des protons. Rapport de mission.<br />
Direction de l’Hydraulique. 2000. Vision Eau 2025 Bénin. Rapport 28 p. Direction de l’Hydraulique, Cotonou, Bénin. <br />
<br />
Descloitres M, Séguis L and Wubda, M. 2006. Caractérisation des aquifères sur les sites AMMA CATCH au Bénin, apport de la résonnance magnétique des protons. Rapport de mission.<br />
<br />
Dray M, Giachello L, Lazzarotto V, Mancini M, Roman E et Zuppi GM. 1988. Etude isotopique de l’aquifère crétacé du bassin côtier béninois. Actes du Séminaire sur le développement des techniques isotopiques et nucléaires en hydrologie dans les pays du Sahel. Niamey, Niger. 21-35.<br />
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'''El Fahem T. 2008'''. Hydrogeological conceptualisation of a tropical river catchment in a crystalline basement area and transfer into a numerical groundwater model, Case study for the Upper Oueme catchment in Benin. PhD thesis, Université of Bonn, Germany.<br />
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'''Engalenc M. 1978a'''. Les modalités de la recherche d’eau dan les roches cristallines fracturées de l’Afrique de l’Ouest. Bull. CIEH, nº 33-34, 22-30.<br />
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'''Engalenc M. 1978b'''. Méthode d’étude et de recherche de l’eau souterraine des roches cristallines de l’Afrique de l’Ouest. Rapport CIEH, 318 p. Ouagadougou. Haute-Volta. <br />
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'''Falola E et Sotognon FC. 2002'''. Impact de l’utilisation des intrants agricoles sur la qualité Chimique des nappes d’eaux souterraines dans les Départements du Borgou et de l’Alibori. Mémoire de Maîtrise, 59 p. Université d’Abomey-Calavi, Bénin. <br />
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GEOHYDRAULIQUE-BURGEAP. 1988. Projet d’hydraulique villageoise de l’Atlantique et du Sud du Zou. Rapport final, 185 p. Direction de l’Hydraulique, Cotonou, Bénin. <br />
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GEOHYDRAULIQUE. 1985. Note explicative de la carte hydrogéologique à 1/200 000 du bassin sédimentaire côtier du Bénin. Rapport, 23 p. Direction de l’Hydraulique, Cotonou, Bénin. <br />
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GEOHYDRAULIQUE. 1985b. Hydraulique villageoise dans les provinces de l’Atacora, du Mono et de l’Ouémé. Rapport final, 236 p. 1. Direction de l’Hydraulique, Cotonou, Bénin. <br />
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GIGG ou Groupement IGIP-GKW-GRAS. 1983. Plan Directeur Alimentation en eau potable ville de Cotonou : les ressources en eau. 2 volumes. Rapport, Société Béninoise d’Electricité et d’Eau, Cotonou, Bénin. <br />
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Gnaha EFC et Adjadji ChA. 2001. Evolution quantitative et qualitative des ressources en eaux souterraines captées dans le périmètre de pompage intensif de Godomey: impact sur l’approvisionnement en eau potable de l’agglomération de Cotonou. Mémoire Maîtrise, 53 p. Géologie Appliquée. Université.Abomey-Calavi, Cotonou, Bénin. <br />
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'''Guiraud R. 1975'''. Eléments pour une orientation nouvelle de la recherche des eaux souterraines dans les régions à substratum métamorphique ou éruptif de l’Afrique Occidentale. Réunion de Porto-Alegre. Mémoire AIH, XI, 15-19.<br />
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'''Guiraud R. 1976'''. Sur la présence des nappes aquifères de fissures dans le socle précambrien de l’Afrique intertropicale. 4ème Réunion Annuelle des Sciences de la Terre. Société Géologique de France. Paris. <br />
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'''Guiraud R. 1988'''. L’hydrogéologie de l’Afrique. Journal of African Earth Sciences 7, 519-543.<br />
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Guiraud R et Lenck P. 1975. Sur l’intérêt hydrogéologique majeur des areas de faille dans le socle métamorphique et éruptif de l’Afrique Occidentale. Actes 8ème Réunion du Centre International Etude Hydraulique. Ouagadougou. Haute-Volta. <br />
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Guiraud R et Alidou S. 1981. La faille de Kandi (Bénin), témoin du rejeu fini-Crétacé d’un accident majeur à l’échelle de la plaque africaine. Comptes Rendus Académie des Sciences. Paris, France. 293 (II) 779-782.<br />
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'''Hector B, Séguis L, Hinderer J, Descloitres M, Vouillamoz J-M, Wubda M, Boy J-P, Luck B et Moigne NL. 2013'''. Gravity effect of water storage changes in aweathered in West Africa: results from joint absolute gravity, hydrological monitoring and geophysical prospection. Geophys. J. Int. 194, 737–750. https://dx.doi.org/10.1093/gji/ggt146. <br />
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Houessou A et Lang J. 1978. Contribution à l’étude du "Continental Terminal" dans le Bénin méridional. Bulletin des Sciences Géologiques. 31 (4), 137-149.<br />
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Houessou A et Lang J. 1979. La "Terre de Barre" dans le Bénin méridional (Afrique de l’Ouest). Bulletin ASEQUA 56-57, 49-58.<br />
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IGIP-GKW-GRAS. 1989. Plans directeurs et études d'ingénierie pour l'alimentation en eau potable et l'évacuation des eaux pluviales, des eaux usées et déchets solides: ville de Cotonou. Rapport Société Béninoise d’Électricité et d’Eau, Cotonou, Bénin., 90 p. <br />
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INSAE ou Institut National de la Statistique te de l’Analyse Economique. 2003. Troisième recensement général de la population et de l'habitation, février 2002: synthèse des résultats. Rapport, 27 p. Direction des Etudes Démographiques MECCAG. Cotonou, Bénin.<br />
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'''Kamagaté B, Séguis L, Favreau G, Seidel J-L, Descloitres M et Affaton P, 2007'''. Processus et bilan des flux hydriques d’un bassin versant de milieu tropical de socle au Bénin (Donga, haut Ouémé). C.R. Geosci. 339, 418–429. https://dx.doi.org/10.1016/j.crte.2007.04.003.<br />
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Lang J, Kogbe C, Alidou S, Alzouma K, Bellion G, Dubois D., Houessou A et Trichet J. 1986. Le sidérolithique du Tertiaire oust-africain et le concept du Continental Termial. Bulletin de la Société. Géologique de France. 8, (II) 605-622. <br />
<br />
Lang J, Kogbe C, Alidou S, Alzouma K, Bellion G, Dubois D, Durand A, Guiraud R, Houessou A, de Klasz I, Romann E, Salard-Cheboldaeff M et Trichet J. 1990. The Continental Terminal in Africa. Journal of African Earth Sciences 10 (1/2) 79-99.<br />
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'''Le Barbé L, Alé G, Millet B., Borel Y et Gualde R. 1993'''. Les ressources en eaux superficielles de la République du Bénin. 457 p. Collection Monographies hydrologiques ORSTOM. Paris, France. 11. <br />
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'''Lelong F. 1963'''. Nouvelles données sur les “nappes d’arène” à la suite d’une reconnaissance hydrogéologique du Centre-Nord Dahomey (région de Parakou et de Nikki). 37 p. Publ. Centre International d’Etude Hydraulique. Ouagadougou, Haute-Volta. <br />
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Lelong F. 1966. Régime des nappes phréatiques contenues dans les formations d’altération tropicale : conséquences pour la pédogenèse. Sciences de la Terre XI (2) 201-244<br />
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Maliki R. 1993. Etude hydrogéologique du littoral béninois dans la région de Cotonou (A.O.). Thèse 3ème cycle, 162 p. Université Cheikh Anta Diop, Dakar, Sénégal. <br />
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MMEH. 2005. Document de politique Nationale de l’Eau : la gouvernance de l’eau au service du développement du Bénin. Rapport, 19 p. MMEH, Cotonou, Bénin.<br />
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Ninard B. et Besançon M. 1962. Etudes sur les eaux minérales du Dahomey. Rapport, 16 p. Laboratoire National du Ministère de la Santé Publique et de l’Académie de Médecine, Service de Contrôle des Eaux Minérales, Paris, France. <br />
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NISSAKU. 1994. Projet pour l'exploitation des eaux souterraines du Bénin, phase III. Rapport final, 204 p. Direction de l’Hydraulique, Cotonou, Bénin. <br />
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[[Category:Hydrogeology by country|b]]</div>EmilyCrane