Difference between revisions of "Hydrogeology of Kenya"

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[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya
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[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya
  
 
==Authors==
 
==Authors==
  
==[[Geographical Setting]]==
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Maxwell Barasa, Rural Focus Ltd, Kenya
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==Geographical & Political Setting==
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[[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]])]]
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 +
  
 
===General===
 
===General===
  
===[[Climate]]===
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Type here . .
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{| class = "wikitable"
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|-
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|Estimated Population in 2013* || 44353691
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|-
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 +
|Rural Population (% of total)* || 75.2%
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 +
|-
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 +
|Total Surface Area* || 569140 sq km
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|-
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|Agricultural Land (% of total area)* || 48.2%
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|-
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|Capital City || Nairobi
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|-
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|Region || Eastern Africa
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|-
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|Border Countries || Somalia, Ethiopia, South Sudan, Uganda, Tanzania
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|-
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|Annual Freshwater Withdrawal (2013)* || 2735 Million cubic metres
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|-
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|Annual Freshwater Withdrawal for Agriculture* || 79.16%
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|-
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|Annual Freshwater Withdrawal for Domestic Use* || 17.18%
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|-
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|Annual Freshwater Withdrawal for Industry* || 3.66%
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|-
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|Rural Population with Access to Improved Water Source* || 55.1%
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|-
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|Urban Population with Access to Improved Water Source* || 82.3%
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|}
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<nowiki>*</nowiki> Source: World Bank
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===Climate===
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Broad description of Kenya – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...
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Climate classification of Kenya. Spatial variations in annual average rainfall and temperature.
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 +
<gallery widths="375px" heights=365px mode=nolines>
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 +
File:Kenya_ClimateZones.png |Koppen Geiger Climate Zones
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 +
File:Kenya_ClimatePrecip.png |Average Annual Precipitation
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File:Kenya_ClimateTemp.png |Average Temperature
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 +
</gallery>
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Temporal variations in temperature and rainfall.
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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]].
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 +
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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)]]
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For further detail on the climate datasets used see the [[Climate | climate resources section]].
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===Surface water===
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{|
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|-
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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.
 +
 
 +
The country has five large systems of drainage basins, with many small lakes in the intervening areas.
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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.
 +
 
 +
The Tana drains the western slopes of the Aberdare, the southern slopes of Mt. Kenya and the Nyambeni mountains, flowing towards the Indian Ocean.
 +
 
 +
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.
 +
 
 +
These large basins are in turn subdivided into 52 main basins and sub-basins.”
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 +
(United Nations 1989)
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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]])]]
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|}
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===Soil===
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 +
{|
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|-
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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]])]]
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|General information about Kenya soils.
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 +
|}
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===Land cover===
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{|
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|-
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|General information about Kenya land cover.
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 +
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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]])]]
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 +
|}
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 +
 +
 
 +
==Geology==
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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 [http://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
 +
 
 +
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.''
 +
 
 +
[[File:Kenya_Geology.png | right]]
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{| class = "wikitable"
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|+ Geological Environments
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|Key Formations||Period||Lithology||Structure
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|-
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!colspan="4"|Unconsolidated sedimentary
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|-
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|
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||Quaternary
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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.
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||
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|-
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|Name of formation2
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||Time period
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||Description
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||Structure
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|-
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!colspan="4"| Igneous – largely volcanic
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|-
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|Name of formation1
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||Time period
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||Description
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||Structure
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|-
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!colspan="4"| Sedimentary – Cretaceous-Tertiary
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|-
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|Name of formation1
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|| Cretaceous-Tertiary
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||Limestones and argillaceous limestones
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||
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|-
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!colspan="4"| Sedimentary – Mesozoic-Palaeozoic, sometimes with unconsolidated cover
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|-
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|Karoo?
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|| Mesozoic-Palaeozoic
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||Description
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||Structure
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|-
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|Name of formation2
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||Time period
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||Description
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||Structure
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|-
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!colspan="4"| Sedimentary – Coastal basin, sometimes with unconsolidated cover
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|-
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|Name of formation1
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||Time period
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||Description
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||Structure
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|-
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|Name of formation2
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||Time period
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||Description
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||Structure
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|-
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!colspan="4"| Precambrian Craton
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|-
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|Name of formation1
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||Time period
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||Description
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||Structure
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|-
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|Name of formation2
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||Time period
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||Description
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||Structure
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|-
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!colspan="4"| Precambrian Metasedimentary
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|-
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|Name of formation1
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||Time period
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||Description
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||Structure
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|-
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|Name of formation2
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||Time period
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 +
||Description
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||Structure
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 +
|-
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 +
!colspan="4"| Precambrian Mobile/Orogenic Belt
 +
 
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|-
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|Name of formation1
 +
 
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||Time period
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||Description
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 +
||Structure
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 +
|-
 +
 
 +
|Name of formation2
 +
 
 +
||Time period
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 +
||Description
 +
 
 +
||Structure
  
====Climate zones====
+
Type here . .
 
  
===[[Surface water]]===
+
Type here . .
 
  
===[[Soil]]===
+
Type here . .
 
  
===[[Land cover]]===
+
|}
Type here . .
 
  
==[[Geology]]==
+
Type here . .
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 +
  
 
==Hydrogeology==
 
==Hydrogeology==
Type here . .
 
  
===[[Aquifer properties]]===
+
This section will contain a broad overview of the hydrogeology.
Type here . .
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 +
 +
 
 +
===Aquifer properties===
 +
 
 +
[[File:Kenya_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]
 +
 
 +
 +
 
 +
 +
 
 +
====Unconsolidated====
 +
 
 +
{| class = "wikitable"
 +
 
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 +
 
 +
|-
 +
 
 +
|Lotikipi and Lodwar aquifers
 +
 
 +
||Alluvial sands and sediments.
 +
 
 +
||
 +
 
 +
||
 +
 
 +
||
 +
 
 +
|}
 +
 
 +
 +
 
 +
====Igneous – mainly volcanic ====
 +
 
 +
{| class = "wikitable"
 +
 
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 +
 
 +
|-
 +
 
 +
|Volcanic
 +
 
 +
||”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)
 +
 
 +
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).
 +
 
 +
||
 +
 
 +
||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)
 +
 
 +
||
 +
 
 +
|-
 +
 
 +
|Nairobi Aquifer
 +
 
 +
||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.
 +
 
 +
||Overabstraction causing lowered water levels.
 +
 
 +
||Generally good quality.
 +
 
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||Recharge from Ngong Hills.
 +
 
 +
|-
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 +
|Kabatini aquifer
 +
 
 +
||The Kabatini aquifer occurs within the volcanic rocks of the Nakuru area.  Boreholes are typically drilled to about 150 m depth.
 +
 
 +
||
 +
 
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||Elevated fluoride concentrations.
 +
 
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||
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|-
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 +
|Gongoni and Baricho aquifers
 +
 
 +
||
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 +
||
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||
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||
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 +
|}
  
===[[Groundwater quality issues | Groundwater quality]]===
+
References:
Type here . .
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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
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 +
 +
 
 +
====Consolidated Sedimentary - Intergranular Flow====
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 +
{| class = "wikitable"
 +
 
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
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|-
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 +
|Name of aquifer
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||General Description of aquifer
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||Water quantity issues
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||Water quality issues
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||Recharge
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|-
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|Tiwi Aquifer
 +
 
 +
||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.
 +
 
 +
||
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 +
||Typically good quality.
 +
 
 +
||
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 +
|-
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 +
|Gongoni/Msambweni Aquifer
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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.
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 +
||
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||Generally good quality, apart from high iron concentrations.
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 +
||
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|-
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|Baricho Aquifer
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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.
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 +
||
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 +
||Generally good quality, sometimes elevated total dissolved solids (TDS)
 +
 
 +
||
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 +
|-
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 +
|Merti Aquifer
 +
 
 +
||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)
 +
 
 +
“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).
 +
 
 +
||
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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).
 +
 
 +
||
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 +
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 +
|}
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 +
References:
 +
 
 +
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.  http://www.worldagroforestry.org/sites/default/files/TR1%20ARIGA-%20Hydrological%20Assessment%20of%20the%20Merti%20Aquifer%20Kenya.pdf
 +
 
 +
GIBB Africa Ltd., 2004. UNICEF Kenya Country Office - Study of the Merti Aquifer - Technical Report ISsue 2.0.
 +
 
 +
Mumma, A., Lane, M., Kairu, E., Tuinhof, A. and Hirji, R., 2011. Kenya: Groundwater Governance Case Study.
 +
 
 +
====Consolidated Sedimentary - Intergranular & Fracture Flow====
 +
 
 +
{| class = "wikitable"
 +
 
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
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 +
|-
 +
 
 +
|Name of aquifer
 +
 
 +
||General Description of aquifer
 +
 
 +
||Water quantity issues
 +
 
 +
||Water quality issues
 +
 
 +
||Recharge
 +
 
 +
|}
 +
 
 +
 +
 
 +
====Basement====
 +
 
 +
{| class = "wikitable"
 +
 
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 +
 
 +
|-
 +
 
 +
|Name of aquifer
 +
 
 +
||General Description of aquifer
 +
 
 +
 +
 
 +
||Water quantity issues
 +
 
 +
||Water quality issues
 +
 
 +
||Recharge
 +
 
 +
|}
 +
 
 +
 +
 
 +
===Groundwater Status===
 +
 
 +
Groundwater quantity
 +
 
 +
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).
 +
 
 +
Groundwater quality
 +
 
 +
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.
 +
 
 +
The Nairobi aquifer has high fluoride concentrations which mostly exceed WHO standards, especially towards the Embakasi area.
 +
 
 +
The Lotikipi Aquifer is very saline with EC25 values exceeding 8000 µS/cm.
 +
 
 +
Surface water-groundwater interaction
 +
 
 +
Various contamination problems are arising due to the hydraulic continuity between surface water and shallow groundwater systems in Kenya, e.g.:
 +
 
 +
*Poor sewerage and drainage systems are major contributors to groundwater contamination, this is an increasing problem in Nairobi and its environs.
 +
 
 +
*Open cast mining of building blocks and stones pose a threat to groundwater as a result of contaminated water infiltrating into the ground.
 +
 
 +
*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.
 +
 
 +
*River pollution by industrial wastes and sewage pose a great risk for groundwater protection.
  
 
==Groundwater use and  management==
 
==Groundwater use and  management==
Type here . .
 
  
===[[Groundwater use]]===
+
=== Groundwater use===
Type here . .
+
 
 +
Summary of groundwater use
 +
 
 +
 +
 
 +
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.
 +
 
 +
Mining activity, e.g. the Gongoni well field for Base Titanium mining company.
 +
 
 +
The Daadab refugee camp depends on groundwater abstracted from the Merti Aquifer.
 +
 
 +
 +
 
 +
 +
 
 +
=== Groundwater management===
 +
 
 +
Summary of groundwater management
 +
 
 +
 +
 
 +
 +
 
 +
=== Transboundary aquifers===
 +
 
 +
Summary of transboundary aquifers
 +
 
 +
 +
 
 +
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]
 +
 
 +
 +
 
 +
 +
 
 +
=== Groundwater monitoring===
  
===[[Groundwater management]] and [[Transboundary aquifers]]===
+
Summary of groundwater monitoring
Type here . .
 
  
 +
==References==
  
 +
===Geology: key references===
  
 +
 +
 +
===Hydrogeology: key references===
 +
 +
Ministry of Water Development. 1992. The Study on the National Water Master Plan. Prepared with the assistance of Japan International Cooperation Agency (JICA)
 +
 +
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.
 +
 +
United Nations. 1989.  Groundwater in Eastern, Central and Southern Africa: Kenya. United Nations Department of Technical Cooperation for Development.
 +
 +
===African Groundwater Literature Archive (AGLA) references===
 +
 +
For more references for the hydrogeology of Kenya please visit the [http://bgs.ac.uk/africagroundwateratlas/searchResults.cfm?country_search=KE African Groundwater Literature Archive's Kenya page].
 +
 +
===Other sources of data and information===
 +
 +
*The Ministry of Mining – sells geological maps and geological reports carried out by the Geological Survey of Kenya: http://www.mining.go.ke/
 +
 +
*The Water Resources Management Authority licences their hydrogeological data (borehole logs, aquifer units and yields): http://www.wrma.or.ke/
 +
 +
*The National Oil Corporation of Kenya (NOCK) licences their seismic data, seismic lines and oil well logs: http://nationaloil.co.ke/site/3.php?id=1
 +
 +
*Samsam Water Foundation has a website with hydrogeological information: http://www.samsamwater.com/about.php
 +
 +
*University of Nairobi offers a platform on its website on student research topics which provides useful geological information: http://geology.uonbi.ac.ke/uon_student_projects
 +
 +
*International Livestock research institute (ILRI) has digitized and shapefiles of Kenya Geology, soils and landcover:  http://data.ilri.org/geoportal/catalog/main/home.page
 +
 +
==Return to the index pages==
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[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Kenya
  
 
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[[Category:Hydrogeology by country|k]]
 
[[Category:Hydrogeology by country|k]]

Revision as of 14:59, 11 June 2015

 Africa Groundwater Atlas >>  Hydrogeology by country >> Hydrogeology of Kenya

Authors

Maxwell Barasa, Rural Focus Ltd, Kenya

Geographical & Political Setting

Political Map of Kenya (For more information on the datasets used in the map see the geography resources section)


General

Estimated Population in 2013* 44353691
Rural Population (% of total)* 75.2%
Total Surface Area* 569140 sq km
Agricultural Land (% of total area)* 48.2%
Capital City Nairobi
Region Eastern Africa
Border Countries Somalia, Ethiopia, South Sudan, Uganda, Tanzania
Annual Freshwater Withdrawal (2013)* 2735 Million cubic metres
Annual Freshwater Withdrawal for Agriculture* 79.16%
Annual Freshwater Withdrawal for Domestic Use* 17.18%
Annual Freshwater Withdrawal for Industry* 3.66%
Rural Population with Access to Improved Water Source* 55.1%
Urban Population with Access to Improved Water Source* 82.3%


* Source: World Bank



Climate

Broad description of Kenya – major topographical/geographical features e.g. mountain ranges, deserts, coastal areas etc...

Climate classification of Kenya. Spatial variations in annual average rainfall and temperature.



Temporal variations in temperature and rainfall.

Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the Kenya Climate Page.



Average monthly precipitation for Kenya showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Kenya showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature Quarterly precipitation over the period 1950-2012 Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)


For further detail on the climate datasets used see the climate resources section.


Surface water

”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.

The country has five large systems of drainage basins, with many small lakes in the intervening areas.

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.

The Tana drains the western slopes of the Aberdare, the southern slopes of Mt. Kenya and the Nyambeni mountains, flowing towards the Indian Ocean.

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.

These large basins are in turn subdivided into 52 main basins and sub-basins.”

(United Nations 1989)

Surface Water Map of Kenya (For more information on the datasets used in the map see the surface water resources section)


Soil

Soil Map of Kenya (For more information on the datasets used in the map see the soil resources section)


General information about Kenya soils.


Land cover

General information about Kenya land cover.


Land Cover Map of Kenya (For more information on the datasets used in the map see the land cover resources section)




Geology

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 Africa Groundwater Literature Archive.

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.

Kenya Geology.png


Geological Environments
Key Formations Period Lithology Structure
Unconsolidated sedimentary
Quaternary Soils, alluvial beach sands, evaporates, fossil coral reefs and sandstones at the coast: alluvial and lacustrine sediments of the Rift Valley.
Name of formation2 Time period Description Structure
Igneous – largely volcanic
Name of formation1 Time period Description Structure
Sedimentary – Cretaceous-Tertiary
Name of formation1 Cretaceous-Tertiary Limestones and argillaceous limestones
Sedimentary – Mesozoic-Palaeozoic, sometimes with unconsolidated cover
Karoo? Mesozoic-Palaeozoic Description Structure
Name of formation2 Time period Description Structure
Sedimentary – Coastal basin, sometimes with unconsolidated cover
Name of formation1 Time period Description Structure
Name of formation2 Time period Description Structure
Precambrian Craton
Name of formation1 Time period Description Structure
Name of formation2 Time period Description Structure
Precambrian Metasedimentary
Name of formation1 Time period Description Structure
Name of formation2 Time period Description Structure
Precambrian Mobile/Orogenic Belt
Name of formation1 Time period Description Structure
Name of formation2 Time period Description Structure






Hydrogeology

This section will contain a broad overview of the hydrogeology.


Aquifer properties

Kenya Hydrogeology.png Hydrogeology Key.png



Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Lotikipi and Lodwar aquifers Alluvial sands and sediments.


Igneous – mainly volcanic

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Volcanic ”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)

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).

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)
Nairobi Aquifer 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. Overabstraction causing lowered water levels. Generally good quality. Recharge from Ngong Hills.
Kabatini aquifer The Kabatini aquifer occurs within the volcanic rocks of the Nakuru area. Boreholes are typically drilled to about 150 m depth. Elevated fluoride concentrations.
Gongoni and Baricho aquifers

References:

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


Consolidated Sedimentary - Intergranular Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Name of aquifer General Description of aquifer Water quantity issues Water quality issues Recharge
Tiwi Aquifer 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. Typically good quality.
Gongoni/Msambweni Aquifer 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. Generally good quality, apart from high iron concentrations.
Baricho Aquifer 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. Generally good quality, sometimes elevated total dissolved solids (TDS)
Merti Aquifer 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)

“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).

“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).


References:

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. http://www.worldagroforestry.org/sites/default/files/TR1%20ARIGA-%20Hydrological%20Assessment%20of%20the%20Merti%20Aquifer%20Kenya.pdf

GIBB Africa Ltd., 2004. UNICEF Kenya Country Office - Study of the Merti Aquifer - Technical Report ISsue 2.0.

Mumma, A., Lane, M., Kairu, E., Tuinhof, A. and Hirji, R., 2011. Kenya: Groundwater Governance Case Study.

Consolidated Sedimentary - Intergranular & Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Name of aquifer General Description of aquifer Water quantity issues Water quality issues Recharge


Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Name of aquifer General Description of aquifer


Water quantity issues Water quality issues Recharge


Groundwater Status

Groundwater quantity

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).

Groundwater quality

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.

The Nairobi aquifer has high fluoride concentrations which mostly exceed WHO standards, especially towards the Embakasi area.

The Lotikipi Aquifer is very saline with EC25 values exceeding 8000 µS/cm.

Surface water-groundwater interaction

Various contamination problems are arising due to the hydraulic continuity between surface water and shallow groundwater systems in Kenya, e.g.:

  • Poor sewerage and drainage systems are major contributors to groundwater contamination, this is an increasing problem in Nairobi and its environs.
  • Open cast mining of building blocks and stones pose a threat to groundwater as a result of contaminated water infiltrating into the ground.
  • 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.
  • River pollution by industrial wastes and sewage pose a great risk for groundwater protection.

Groundwater use and management

Groundwater use

Summary of groundwater use


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.

Mining activity, e.g. the Gongoni well field for Base Titanium mining company.

The Daadab refugee camp depends on groundwater abstracted from the Merti Aquifer.



Groundwater management

Summary of groundwater management



Transboundary aquifers

Summary of transboundary aquifers


For further information about transboundary aquifers, please see the Transboundary aquifers resources page



Groundwater monitoring

Summary of groundwater monitoring

References

Geology: key references

Hydrogeology: key references

Ministry of Water Development. 1992. The Study on the National Water Master Plan. Prepared with the assistance of Japan International Cooperation Agency (JICA)

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.

United Nations. 1989. Groundwater in Eastern, Central and Southern Africa: Kenya. United Nations Department of Technical Cooperation for Development.

African Groundwater Literature Archive (AGLA) references

For more references for the hydrogeology of Kenya please visit the African Groundwater Literature Archive's Kenya page.

Other sources of data and information

  • The Ministry of Mining – sells geological maps and geological reports carried out by the Geological Survey of Kenya: http://www.mining.go.ke/
  • The Water Resources Management Authority licences their hydrogeological data (borehole logs, aquifer units and yields): http://www.wrma.or.ke/

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Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Kenya