Difference between revisions of "Hydrogeology of Uganda"

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Directorate of Water Resources Management. 2012. [http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCEQFjAAahUKEwjP8v_QpqbHAhUImBoKHX26DFU&url=http%3A%2F%2Fwww.mwe.go.ug%2Findex.php%3Foption%3Dcom_docman%26task%3Ddoc_download%26gid%3D406%26Itemid%3D223&ei=Aa7MVY_uJIiwav30sqgF&usg=AFQjCNFijhSpYVQm97AsnI29ueL5t2o0hA&sig2=z3WeTv2MuA1smDYm2uSe1g&bvm=bv.99804247,d.d2s Kole District Groundwater Report: Mapping Groundwater Resources in Uganda. Ministry of Water and Environment, Uganda].
 
Directorate of Water Resources Management. 2012. [http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCEQFjAAahUKEwjP8v_QpqbHAhUImBoKHX26DFU&url=http%3A%2F%2Fwww.mwe.go.ug%2Findex.php%3Foption%3Dcom_docman%26task%3Ddoc_download%26gid%3D406%26Itemid%3D223&ei=Aa7MVY_uJIiwav30sqgF&usg=AFQjCNFijhSpYVQm97AsnI29ueL5t2o0hA&sig2=z3WeTv2MuA1smDYm2uSe1g&bvm=bv.99804247,d.d2s Kole District Groundwater Report: Mapping Groundwater Resources in Uganda. Ministry of Water and Environment, Uganda].
  
Ministry of Water and Environment. 2010. Uganda Water Supply Atlas. Available at http://www.mwe.go.ug/index.php?option=com_docman&task=cat_view&gid=12&Itemid=223 .  
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Ministry of Water and Environment. 2010. [http://www.mwe.go.ug/index.php?option=com_docman&task=cat_view&gid=12&Itemid=223 Uganda Water Supply Atlas].  
  
 
Tindimugaya C. 2004. [http://wedc.lboro.ac.uk/resources/conference/30/Tindimugaya.pdf Groundwater mapping and its implications for rural water supply coverage in Uganda]. Presentation at 30th WEDC International Conference, Vientane, Lao PDR.  
 
Tindimugaya C. 2004. [http://wedc.lboro.ac.uk/resources/conference/30/Tindimugaya.pdf Groundwater mapping and its implications for rural water supply coverage in Uganda]. Presentation at 30th WEDC International Conference, Vientane, Lao PDR.  

Revision as of 15:25, 2 September 2015

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

Authors

Michael Owor, Makerere University, Uganda

Callist Tindimugaya, Ministry of Water and Environment, Uganda

Lawrence Brown, Hafren Water, UK

Kirsty Upton, Brighid Ó Dochartaigh, British Geological Survey, UK


Geographical Setting

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

General

Much of Uganda is located on the East African plateau, which has an elevation of 800-2000 m above sea level. Mountainous regions along the western (Ruwenzori Mountains) and eastern borders reach an elevation of over 4000 m.

Estimated Population in 2013* 37,578,876
Rural Population (% of total)* 85%
Total Surface Area* 199,810 sq km
Agricultural Land (% of total area)* 71%
Capital City Kampala
Region Eastern Africa
Border Countries South Sudan, Democratic Republic of the Congo, Rwanda, Tanzania, Kenya
Annual Freshwater Withdrawal (2013)* 317 Million cubic metres
Annual Freshwater Withdrawal for Agriculture* 38%
Annual Freshwater Withdrawal for Domestic Use* 48%
Annual Freshwater Withdrawal for Industry* 14%
Rural Population with Access to Improved Water Source* 71%
Urban Population with Access to Improved Water Source* 95%

* Source: World Bank


Climate

The climate of Uganda is classified as tropical, but varies from rainforest or monsoon in the southeast to drier and hotter savannah in the north. Average annual precipitation in the north is around 600 mm, while in the south it is more than 1600 mm.


Rainfall generally occurs throughout the year, particularly in the south of Uganda. There are two wetter seasons between March and May, and September and November. Temperatures are slightly higher during the wet seasons.

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

Average monthly precipitation for Uganda showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Uganda 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 southeast of Uganda is dominated by Lake Victoria, which also extends into neighbouring Kenya and Tanzania.. Several lakes are also located within the Western Rift Valley, which runs approximately north-south along the western border of the country.

The majority of Uganda sits within the drainage basin of the River Nile. Lake Victoria is the source of the White Nile, which runs north through Uganda as the Victoria Nile, through Lake Kyoga in central Uganda and into Lake Albert in the west. From Lake Albert, the Albert Nile runs northwards towards the border with South Sudan.

Lake Albert, Lake George and Lake Edward are situated in the Western Rift Valley along the border with the Democratic Republic of the Congo.

River flow gauging has been carried out at various locations in Uganda since the early-mid 1950s. Most stations provide daily measurements, which are held by the Directorate of Water Resources Management, Ministry of Water and Environment (Entebbe).


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

Soil

Soil Map of Uganda (For more information on the datasets used in the map see the soil resources section)
Fluvisols are present along the main river systems, particularly the Victoria Nile as it flows towards the Western Rift Valley.

The south and centre of Uganda is dominated by Ferrasols, Acrisols, and Nitisols. Ferrasols are widespread in central and eastern Africa and are generally associated with high rainfall and relatively old (Tertiary) land surfaces. As a result, they are highly leached. Acrisols, which are acidic and clay-rich, also form in areas with high rainfall and are generally nutrient-deficient.

Nitisols are commonly found on iron-rich basic rocks with gently sloping ground. They have a high clay content and are very fertile. Clay-rich Vertisols have also developed over weathered basic rocks, but are more commonly found on valley floors in the north-east of Uganda.

Leptosols, which are generally shallow and form over hard rock or gravelly material, are common in the northwest of Uganda.


Land cover

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

Geology

This section provides a summary of the geology of Uganda. The geology map on this page shows a simplified version of the geology at a national scale (see the Geology resources page for more details). A higher resolution national geological map, at 1: 1 million scale, was published in 2014 by the Geological Survey of Finland (Lehto et al. 2014), with detailed supporting information in an accompanying report ([ http://tupa.gtk.fi/julkaisu/specialpaper/sp_055.pdf Westerhof et al. 2014).

Further information can be found in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive.

Uganda Geology.png
Geological Environments
Key Formations Period Lithology Structure
Unconsolidated Sedimentary
Lake Victoria strandline deposits, Lake Kyoga raised beach deposits, and Albertine Nile deposits Pleistocene-Holocene Discontinuous deposits, predominantly beach sands and gravels, with finer silts and clays.
Igneous
Elgon Complex Neogene Pyroclastic and lahar-type alkaline/sodic volcanic rocks and associated carbonatite plugs and fenites Deposited in the linear Elgon depression in eastern Uganda
Albertine Group Pleistocene-Holocene Ultrapotassic and carbonatitic volcanic rocks Deposited in the Albertine Rift in the northern segment of the Western Rift
Sedimentary – Cretaceous-Tertiary
Albertine Graben Late Eocene-Neogene This is a hydrocarbon-bearing sequence of terrigenous sediments, alkaline/sodic volcanics and ultra-potassic and carbonatitic volcanics. This thick (4 km) sequence was laid down in the Albertine Rift, which forms part of the Western Rift of the East African Rift System.
Sedimentary – Mesozoic-Palaeozoic
Karoo Basins Mesozoic-Palaeozoic Karoo deposits are restricted to a few small occurrences in southern Uganda and comprise clays, minor arenaceous and carbonaceous beds, siltstone, diamictites and dropstones.
Precambrian Metasedimentary
Rwenzori Fold Belt Palaeoproterozoic Gneissose-granitoid basement in southern Uganda formed during the Eburnian Orogenic Cycle. The fold belt wraps around the Tanzania Craton with a predominantly ENE-WSW structural trend in the east, curving into a N-S trend in the south-west.
Buganda Group Palaeoproterozoic Metasediments and mafic, partly pillow-textured volcanics overlying the Rwenzori fold belt. The Buganda group is intruded by syn- and post-tectonic granitoids of the Sembabule and Mubende-Singo suites.
Kagera-Buhweju Supergroup Palaeoproterozoic Deposited following the Eburnian Orogenic Cycle, these platform deposits comprise post-tectonic molasse-type sediments, including quartzite, pelite, conglomerate, shale and phyllite. These rocks have been subjected to complex tectonic processes and are mildly deformed.
North Kibaran Belt Palaeoproterozoic This belt in southwest Uganda, which is younger than the Kagera-Buhweju Supergroup, includes metasediments of the Akanyaru-Ankole Supergroup and the North Kibaran Igneous Province. The North Kibaran Igneous Province consists of an alignment of mafic and ultramafic layered complexes and mafic dykes and sills, including the Lake Victoria Arcuate Dyke Swarm. The estimated thickness of the North Kibaran Belt ranges from 9-14.5 km in central Rwanda (this represents the centre of the North Kibaran trough), to a few kilometres thick in NW Tanzania.
Mityana Group & Bunyoro Group Palaeoproterozoic The Mityana Group overlies the Buganda Group and consists of platform sediments including conglomerate, sandstone, siltstone and gritstone. It is not intruded by dykes of the Lake Victoria Arcuate Dyke Swarm and is therefore younger than the metasediments of the North Kibaran Belt.

The younger Bunyoro Group comprises rocks of glacial and periglacial origin related to the Sturtian glaciation.

Precambrian Mobile/Orogenic Belt
West Nile Block Archean This forms the Ugandan section of the Bomu-Kibalian Shield of northeastern Congo. It is predominantly composed of Mesoarchean granulite, gneiss, granitoid and charnokite, and is intruded by younger (Neoarchean) mafic volcanics.
North Uganda Terrane Archean This unit is mainly composed of Neoarchean gneissose-migmatic rocks and is separated from the western Nile Block by the Madi-Igisi Belt.
Madi Igisi Belt Archean-Proterozoic This is a narrow thrust and shear belt trending north-south between the West Nile Block (WNB) and North Uganda Terrane (NUT). It is composed of reworked rocks of the WNB and NUT and younger Proterozoic meta-volcanics, metasediments and ultramafics.
Karamoja Belt Proterozoic The Karamoja Belt is found along the border with Kenya and is a representation of the East African Orogen. It comprises a west to north-west trending thrust belt of amphibolite-grade supracrustals, granitoids and ophiolites. This belt contains the Aswa Shear Zone, which is a brittle-ductile, north-west trending, mega strike-slip shear zone, with complex, anastomosing fault planes.
Midigo-Adjumani Suite Proterozoic This suite of granitoids is found in the West Nile Block and North Uganda Terrane in northern Uganda.
Precambrian Craton
Lake Victoria Terrane Neoarchean Forms part of the Tanzania Craton and is a predominantly a granite-greenstone terrane with nepheline syenite and gabbro intrusions.
West Tanzania Terrane Neoarchean Also forms part of the Tanzania Craton comprising granitoid-gneissic-migmatic rocks.

Hydrogeology

This section provides a summary of the hydrogeology of the main aquifers in Uganda. More information is available in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive.

The hydrogeology map on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see the Aquifer properties resource page for more details). Other hydrogeological maps at different scales have been produced in different formats, including:

- A 1989 national hydrogeological map of Uganda, which can be viewed on the WHYMAP website.
- A series of national and district groundwater maps, produced through the EU-funded Mapping of Groundwater Resources Programme, including maps of water supply coverage, hydrogeological characteristics, water quality, groundwater development technology options and groundwater potential. An introduction to this programme can be found in Tindimugaya (2004). Some outputs from the programme, including maps and reports, can be found on the Ministry of Water and Environment website.

Summary

The main aquifers in Uganda are found in weathered crystalline basement rocks. These are generally low-permeability and low-storage aquifers, and the physical properties are largely a function of tectonic history and long-term cycles of weathering and erosion. Unconsolidated deposits also form aquifers of local importance.

Igneous, sedimentary and metasedimentary rocks are not widely used as aquifers and little is therefore known about their aquifer properties.


Uganda Hydrogeology.png Hydrogeology Key.png

Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Fluvial aquifers Unconsolidated aquifers are generally found along current river channels or palaeochannels in which fluvial/alluvial gravel, sand and silt have been deposited.

Yields of more than 50 m³/hour are possible in the unconsolidated fluvial aquifers. Hydraulic conductivity typically varies between 0.02 and 15 m/day, while average transmissivity is 34 m²/day. Average storage is 0.1.

Unconsolidated aquifers in Uganda are generally unconfined or semi-confined. They can be greater than 50 m thick where there are significant palaeochannel deposits. Water table depths are highly variable and may be up to 20 m below the ground surface. Borehole depths are also variable, but may be up to 60 m when drilled into palaeochannels.

Groundwater from the unconsolidated fluvial aquifers typically has low total dissolved solids (<1000 mg/l). The shallow aquifers are highly vulnerable to pollution; microbial contamination has been observed in many urban areas as a result of inadequately contained faecal waste. The unconsolidated fluvial aquifers are actively recharged by rainfall.

Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Basement Complex The basement complex generally forms discrete aquifers of limited spatial extent. They occur within the unconsolidated weathered regolith (saprolite), or underlying fissured bedrock (saprock). The bedrock permeability is greatest close to the saprock-saprolite interface and decreases with depth. It is largely controlled by the number, distribution, and connectivity of fissures/fractures. The permeability of the saprolite is highly variable, but is an important source of groundwater storage.

Yields in the basement complex vary between 0.5 and 12 m³/hour, with higher yields generally found in the fissured granites and gneiss.

The bedrock aquifer have an average transmissivity of 14 m²/day and an average storage coefficient of 0.014 (although it can be as low as 10-4). The transmissivity of the weathered zone typically ranges from 0.1 to 20 m²/day, with an average of 16 m²/day. Average storage in the weathered zone is 0.21.

The basement aquifers are generally semi-confined or leaky. The depth of the piezometric surface or water table can range from 1 to 45 m, but is typically 5-20 m below the ground surface. The aquifers are typically between 20 and 45 m thick and boreholes are generally drilled to depths of 45-70 m.

Abstraction from the basement aquifers is usually by hand pump and rates are therefore low. Some towns with motorised pumps, which are able to abstract at higher rates, are experiencing declining water levels, for example Rukungiri in southwestern Uganda. Groundwater quality is highly variable. There are no widespread inorganic water chemistry problems. However, elevated iron and manganese are common in groundwaters from alumina-enriched laterite deposits. Total dissolved solids are typically around 500 mg/l, and pH is usually neutral to slightly acidic; where acidic, it can have the capability to corrode ferrous borehole casings and pumps. High salinity is occasionally reported. Where the weathered aquifer and groundwater levels are shallow, groundwater is vulnerable to microbiological and nitrate contamination from latrines. Groundwater in the basement aquifers is actively replenished through recharge from rainfall, particularly during the wetter monsoon periods, at an estimated rate of 12-200 mm/year.

Groundwater Status

Groundwater monitoring and the collation and archiving of groundwater data in the National Groundwater Database have led to a better understanding of groundwater resources in Uganda.

There are currently no widespread issues with groundwater quantity, although localised groundwater depletion may be an issue where the low permeability basement aquifers are exploited by high yielding electric pumps.

Groundwater quality is generally good, although high concentrations of iron and manganese are common in the crystalline basement aquifers, and microbial contamination related to faecal waste has been observed in shallow urban aquifers. High fluoride concentrations are often observed in igneous groundwaters, for example at Kisoro and Mbale.

Groundwater is known to maintain baseflow to rivers, lakes and wetlands in several areas, although the magnitude of these contributions is poorly constrained. The contribution of groundwater is particularly important in the low-relief wetlands along the Katonga River and in the semi-arid Karamoja Region. Groundwater-fed springs are also important in the eastern and western highlands of Uganda.

Groundwater use and management

Groundwater use

73 of the 98 operational water supply systems in Uganda are based on groundwater. This accounts for around 75% of all towns and cities. In Kampala City several industries are also reliant on groundwater, including mineral water and chemical industries.

Groundwater abstraction permits are provided to users of motorised pumps by the Directorate of Water Resources Management.

Information on water sources and the water supply situation in Uganda as of June 2010 is provided in the Uganda Water Atlas (2010), which is based on a nationwide baseline survey of all water sources.

Groundwater management

Legislation

The key legislation governing groundwater management in Uganda is The Water Act, Cap 152, and The Environment Act.

The main regulations under The Water Act are:

  • Water Resources Regulations (1998)
  • Waste Discharge Regulations (1998)

The main regulations under The Environment Act are:

  • Environmental Impact Assessment Regulations (1998)
  • The National Environment (Standards for Discharge of Effluent into Water or on Land) Regulations (1999)
  • The National Environment (Waste Management) Regulation (1999).

These regulations were put in place to ensure the sustainable use of the environment and natural resources across Uganda. They are implemented by two main institutions: the Directorate of Water Development (DWD) and the Directorate of Water Resources Management (DWRM). These directorates sit within the Ministry of Water and Environment.

The DWD is responsible for groundwater regulation, and for the coordination, planning and development of groundwater sources.

The DWRM is responsible for:

  • Developing and maintaining national water laws, policies and regulations
  • Managing and monitoring groundwater resources through issuing permits for water use, water abstraction (by motorised pump and canals), drilling and waste water discharge
  • Collecting information on newly drilled boreholes
  • Integrated Water Resources Management
  • Management of transboundary water resources

Borehole Information

Collecting information on newly drilled boreholes is done through drilling contractors, who are obliged to return borehole completion forms to the DWRM for each borehole drilled, with a summary of key borehole information. In most cases, the returned forms are accompanied by additional supporting information in the form of a completion report, which can include siting information, drillers log, construction data, pumping test data, water quality data and pump installation data. If the summary forms are not fully completed or the information needs to be checked, this accompanying information can be vital.

Drillers must request from DWRM 'national borehole numbers' to be allocated to boreholes drilled deeper than 30 m. These numbers are allocated to drillers in lots of 20-100 boreholes. National numbers are only allocated to boreholes deeper than 30 m, although some shallow boreholes may be given a number. In general, dug wells, hand augered wells and most boreholes shallower than 30 m are not given a national number, but instead usually receive a local District-based number. These shallow wells do not, therefore, appear in the NGWDB.

Drillers are required to submit completion forms (and any reports) to DWRM at the end of each quarter for boreholes drilled in that quarter. This information is then entered in the national groundwater database (NGWDB). A hard copy of the drilling completion reports is stored at the DWRM offices in Entebbe.

Transboundary aquifers

The Transboundary Water Resources Management Division promotes regional transboundary cooperation for the equitable and reasonable utilisation of the shared water resources of the Nile and Lake Victoria Basins. It does this through active participation in the Nile Basin Initiative (NBI) and the Lake Victoria Basin Commission (LVBC), as well as other international water resources management programmes, such as the Global Water Partnership (GWP).

The main activities of the NBI, LVBC and GWP are:

  • Policy formulation, review, implementation and advice related to transboundary water resource management
  • Regional coordination and evaluation of transboundary projects and programmes
  • Monitoring
  • Raising awareness and capacity-building on transboundary water resources management issues

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


Groundwater monitoring

The national groundwater level monitoring programme is managed by the Directorate of Water Resources Management in Entebbe. Monitoring started in 1998 and daily observations are available for 30 stations across a range of hydrogeological environments. Data are collected using chart recorders and pressure transducers, which are corrected against dip meter readings.

Groundwater quality is monitored nationally by the 8 major hydrological catchments of Uganda. This data is analysed and stored by the Directorate of Water Resources Management. Monitoring is carried out bi-weekly and the following data are collected:

  • pH, temperature, electrical conductivity, dissolved oxygen and hardness
  • Major ions (e.g. Ca, Ma, K, Na, SO4, Cl, HCO3)
  • Selected problem ions (e.g. Fe, NO3, F)
  • Selected stable isotopes (e.g. 2H, 18O)

References

Many of the references below, and others relating to the hydrogeology of Uganda, can be accessed through the Africa Groundwater Literature Archive.

Geology: Key references

Department of Lands and Surveys. 1969. Uganda Geology map: 1:1,500,000 scale. Compiled by R. MacDonald and drawn by the Dept. of Geological Survey and Mines, Uganda, 1966.

Westerhof ABP, Harma P, Isabirye E, Katto E, Koistinen T, Kuoasmanen E, Lehto T, Lehtonen MI, Makitie H, Manninen T, Manttari I, Pekkala Y, Pokki J, Saalmann K and Virransalo P. 2014. Geology and Geodynamic Development of Uganda with Explanation of the 1:1,000,000 scale Geological Map. Geological Survey of Finland, Special Paper 55, 387p.

Lehto T, Westerhof AB, Lehtonen MI, Manninen T, Mäkitie H, Virransalo P, Pokki J, Härmä P, Koistinen T, Saalmann K, Kuosmanen E, Mänttäri I, Katto E, B guma Z, de Kock G and Elepu D. 2014. Geological Map of Uganda, Scale 1:1 000 000. Geological Survey of Finland, Espoo, Finland.

Hydrogeology: Key references

Key information sources

The Ministry of Water and Environment, Uganda.

Outputs from the Mapping of Groundwater Resources Programme.

Literature

Directorate of Water Resources Management. 2012. Kole District Groundwater Report: Mapping Groundwater Resources in Uganda. Ministry of Water and Environment, Uganda.

Ministry of Water and Environment. 2010. Uganda Water Supply Atlas.

Tindimugaya C. 2004. Groundwater mapping and its implications for rural water supply coverage in Uganda. Presentation at 30th WEDC International Conference, Vientane, Lao PDR.

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