Hydrogeology of Rwanda

From Earthwise
Jump to navigation Jump to search

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

Rwanda is a small and quite densely populated country in the Great Lakes region of central Africa. It is also known as "The Land of a Thousand Hills". Rwanda has been a distinct entity from pre-colonial times. It was colonised by Germany in 1884, as part of what was called German East Africa, then by Belgium in 1916, before achieving independence in 1962. Ethnic tensions between the Hutu and Tutsi cultural groups led to periodic episodes of violence, including the 1994 genocide. In the aftermath of the genocide there was a period of reconciliation and justice with associated improvement in economic, health and social indicators.

Tea and coffee cultivation are the major cash crops and growth agricultural industries, facilitated by Rwanda's climate and geography. Mining is a significant contributor to export income. The services sector has started to recover after the late 2000s recession, including banking and communications, and particularly tourism, which is now the main source of foreign income and is supported by government. This sector is boosted by the presence of mountain gorillas in uplands areas.

Rwanda has relatively high rainfall and both surface water and groundwater resources. Two major river basins cover Rwanda – the Nile and the Congo basins – and there are many lakes and wetlands. Groundwater is the main source of water supply in rural and some urban areas: in mountain areas from springs, and in other areas from boreholes.


Compilers[edit]

Mr Francois-Xavier Tetero, Rwanda Water and Forestry Authority

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

Dr Imogen Bellwood-Howard, Institute of Development Studies

Please cite this page as: Tetero, Upton, Ó Dochartaigh and Bellwood-Howard, 2018.

Bibliographic reference: Tetero F, Upton K, Ó Dochartaigh BÉ and Bellwood-Howard, I. 2018. Africa Groundwater Atlas: Hydrogeology of Rwanda. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Rwanda

Terms and conditions[edit]

The Africa Groundwater Atlas is hosted by the British Geological Survey (BGS) and includes information from third party sources. Your use of information provided by this website is at your own risk. If reproducing diagrams that include third party information, please cite both the Africa Groundwater Atlas and the third party sources. Please see the Terms of use for more information.

Geographical Setting[edit]

Rwanda. Map developed from USGS GTOPOPO30; GADM global administrative areas; and UN Revision of World Urbanization Prospects. For more information on the map development and datasets see the geography resource page.

General[edit]

Capital city Kigali
Region Eastern Africa
Border countries Uganda, Tanzania, Burundi, the Democratic Republic of the Congo
Total surface area* 26,340 km2 (2,634,000 ha)
Total population (2015)* 11,610,000
Rural population (2015)* 8,029,000 (69%)
Urban population (2015)* 3,581,000 (31%)
UN Human Development Index (HDI) [highest = 1] (2014)* 0.4832

* Source: FAO Aquastat


Climate[edit]

Rwanda's climate is classed as tropical savannah. Temperature does not vary significantly throughout the year but there are two distinct rainy seasons (February to May and October to December). Rainfall varies across the country, with drier conditions in the eastern savannah regions and much wetter conditions over the central plateau and western mountains.

Koppen Geiger Climate ZonesAverage Annual PrecipitationAverage Temperature

Average monthly precipitation for Rwanda showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Rwanda 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)

These maps and graphs were developed from the CRU TS 3.21 dataset produced by the Climatic Research Unit at the University of East Anglia, UK. For more information see the climate resource page.

In Rwanda, rainfall data are collected by MeteoRwanda. More detailed information on rainfall at a catchment scale is described in the Rwanda Water Resources Master Plan (MINIRENA/RNRA 2015).

Surface water[edit]

Rwanda is divided into two major river basins: the Nile in the east and centre, and the Congo in the west. Both are shared with neighbouring countries.

Within the Nile and Congo basins in Rwanda, nine 'Level 1' surface water catchments have been classified for management purposes (see the Rwanda Water Resources Master Plan (MINIRENA/RNRA 2015)). The Akagera River, and its tributary the Nyabarongo, are two of the main rivers, both part of the upper Nile basin, and both subdivided into upper and lower reaches for the purposes of Level 1 catchment management. The other Level 1 surface water catchments are the Rusizi, Akanyaru and Muvumba rivers, and Lake Kivu. Parts of some of the Level 1 river catchments are shared with neighbouring countries (Burundi, Tanzania, Uganda or the DRC). There are many smaller lakes, rivers and associated wetlands.

Surface water resources, as other water resources in Rwanda, are managed by the Rwanda Water and Forestry Authority, previously the Rwanda Natural Resources Authority, which is affiliated to the Ministry of Environment. Surface water monitoring is generally at good detail for the large catchments, but less well established for smaller catchments (MINIRENA/RNRA 2015). Monitoring data are collected and stored as part of the Water Management Information System. Data from 73 surface water monitoring stations (as of 2021) is available via the Rwanda Water Portal, including real time data for some river level gauges, available from the Rwanda Water Portal. Summary data are presented in monitoring reports and annual water status reports available from the Rwanda Water Portal.

Major surface water features of Rwanda. Map developed from World Wildlife Fund HydroSHEDS; Digital Chart of the World drainage; and FAO Inland Water Bodies. For more information on the map development and datasets see the surface water resource page.

Soil[edit]

Soil Map of Rwanda, from the European Commission Joint Research Centre: European Soil Portal. For more information on the map see the soil resource page.

Land cover[edit]

Land Cover Map of Rwanda, from the European Space Agency GlobCover 2.3, 2009. For more information on the map see the land cover resource page.


Water statistics[edit]

2000 2005 2014 2015
Rural population with access to safe drinking water (%) 71.9
Urban population with access to safe drinking water (%) 86.6
Population affected by water related disease No data No data No data No data
Total internal renewable water resources (cubic metres/inhabitant/year) 818.3
Total exploitable water resources (Million cubic metres/year) No data No data No data No data
Freshwater withdrawal as % of total renewable water resources 1.128
Total renewable groundwater (Million cubic metres/year) 7,000
Exploitable: Regular renewable groundwater (Million cubic metres/year) No data No data No data No data
Groundwater produced internally (Million cubic metres/year) 7,000
Fresh groundwater withdrawal (primary and secondary) (Million cubic metres/year)
Groundwater: entering the country (total) (Million cubic metres/year) No data No data No data No data
Groundwater: leaving the country to other countries (total) (Million cubic metres/year) No data No data No data No data
Industrial water withdrawal (all water sources) (Million cubic metres/year) 20.5
Municipal water withdrawal (all water sources) (Million cubic metres/year) 61.4
Agricultural water withdrawal (all water sources) (Million cubic metres/year) 102
Irrigation water withdrawal (all water sources) 1 (Million cubic metres/year) No data No data No data No data
Irrigation water requirement (all water sources) 1 (Million cubic metres/year)
Area of permanent crops (ha) 250,000
Cultivated land (arable and permanent crops) (ha) 1,400,000
Total area of country cultivated (%) 53.15
Area equipped for irrigation by groundwater (ha) 85
Area equipped for irrigation by mixed surface water and groundwater (ha) No data No data No data No data

These statistics are sourced from FAO Aquastat. They are the most recent available information in the Aquastat database. More information on the derivation and interpretation of these statistics can be seen on the FAO Aquastat website.

Further water and related statistics can be accessed at the Aquastat Main Database.

1 More information on irrigation water use and requirement statistics

Geology[edit]

The geology map shows a simplified overview of geology at a national scale (see the Geology resource page for more details). More information is available in the report UN (1988) (see References section, below).


Geology of Rwanda at 1:5 million scale. Based on map described by Persits et al. 2002/Furon and Lombard 1964. For more information on the map development and datasets see the geology resource page.


Geological environments
Key formations Period Lithology
Unconsolidated sedimentary
Alluvium and lake sediments Quaternary Unconsolidated alluvium infilling valleys and forming floodplains; and lake sediments, which mainly comprise sands, silts, gravels and clays. The most significant alluvial sediments occur in the Akagera River floodplain along the eastern border with Tanzania. Smaller outcrops of alluvium are also present in river valleys across the rest of the country, but are too small to be shown on this map.
Volcanic rocks
Northern lavas; Southwestern basalts Cenozoic (some possibly Cretaceous) Volcanic rocks crop out in the north and the far west of the country, largely lava flows. Schlüter (2006) divides them into northern lavas (of Quaternary age) and southwestern basalts (of Cenozoic-Cretaceous age).
Precambrian

A number of different units within the Precambrian are named, with complex outcrops across the country (e.g. see Schlüter 2006). These are not distinguished on this geology map because of its small scale. The main divisions are described below.

Metasedimentary rocks, including the Burundian Supergroup Middle Proterozoic Metasedimentary rocks, largely quartzites, metamorphosed sandstones and shales of the Burundian Supergroup, which are locally intruded by granite. These are seen across much of the country. Named geological units within the Burundian Supergroup are the Byumba, Miyove and Lower series (Schlüter 2006).
Granites and associated other basement rocks Lower Proterozoic These are sometimes called 'older granites', along with granitic-gneisses and migmatites. They are seen in parts of eastern and southern Rwanda.

Hydrogeology[edit]

The hydrogeology map below shows a simplified overview of the type and productivity of the main aquifers at a national scale (see the hydrogeology map resource page for more details).

Information on the hydrogeology of Rwanda is still relatively limited, but further detail can be found in the reports listed in the references section below. An Annual Water Status Report produced for 2016/17 is available through the Water Portal (Rwanda Water and Forestry Authority, 2017), which contains a small image of a more detailed hydrogeological map of the country.

Hydrogeology of Rwanda at 1:5 million scale. For more information on how the map was developed see the hydrogeology map resource page.


Summary

The most widespread aquifer in Rwanda is fractured, weathered Precambrian basement. Small outcrops of volcanic rocks form aquifers in the Western Province, in the far west and on the northern border. There are many local Quaternary unconsolidated alluvial aquifers, which are generally narrow and shallow along river valleys, with the largest outcrops in the east of the country.


Unconsolidated[edit]

Aquifer Productivity Named Aquifers and General Description Recharge
High Productivity Most of the Quaternary unconsolidated aquifers are alluvial, forming narrow linear aquifers along river valleys. Their aquifer properties are variable, depending largely on lithology, but where alluvium is dominated by coarser grained sediment (gravel and coarse sand), storage capacity and transmissivity can be high. These aquifers are usually unconfined with a shallow water table (<15 mbgl). They are locally important water supply sources, and are often heavily exploited because their high productivity and shallow water tables mean easy access to groundwater. Recharge is generally high due to close connection with rivers and wetlands.

Volcanic[edit]

Aquifer Productivity Named Aquifers and General Description
Moderate Productivity Little is known about groundwater in the volcanic rocks in Rwanda, but they are known to have complex hydrogeology. Groundwater storage and flow is likely to be mainly through fractures in the rocks, and possibly also through weathered zones at the junctions of formed lava flows. The permeability of the aquifer will depend on the density and interconnection of fracture networks, and can be variable, with locally more productive areas interspersed with low productivity zones. One place for which some information exists is the Sebeya catchment in north-west Rwanda, in which highly permeable basalt layers have been documented (Water for Growth Rwanda, 2018c).

Weathered, Fractured Precambrian Basement[edit]

Aquifer Productivity Named Aquifers and General Description
Variable Productivity (generally Low to Moderate) The productivity of the basement aquifer depends on the localised nature and extent of fracturing and weathering - the thickness of the near-surface weathered zone, and the density and interconnectivity of fractures. The simplified hydrogeology map shown here does not subdivide the Precambrian basement rocks, but the hydrogeological map shown in the (Annual Water Status Report 2016-2017 (Rwanda Water and Forestry Authority, 2017) subdivides the basement rocks into four different hydrogeological zones depending on lithology:

- relatively low productivity granite and gneiss, which covers a large part of the south-centre and north-east;

- low permeability schist and metaschist, which occurs in belts in different parts of the country;

- permeable quartzite on a schist base, which occurs in belts across much of the east of the country; and

- semi-permeable schist, mica and quartzite, across much of the centre and parts of the south-west.

Generally, only quartzite shows moderate productivity. The other basement lithologies typically have low productivity .

Groundwater use and management[edit]

The Ministry of Environment and the Rwanda Water and Forestry Authority (RWFA) have responsibilities for managing water resources in Rwanda. The Rwanda Water Resources Master Plan (2015) contains detailed recommendations for integrated water resources management, including setting up and operating a groundwater monitoring network. In 2017, RWFA had begun inventorising groundwater abstraction boreholes, and geophysical investigations of groundwater resources for potential future development, but overall groundwater availability in the country was not yet well understood (Rwanda Water and Forestry Authority (2017)). The Water Resources Master Plan estimated that total groundwater storage in Rwanda is around 162,176 million cubic metres.

There are no reliable estimates of total groundwater abstraction, but in 2005, groundwater was reported to account for 86% of safe drinking water supply in rural areas (Ministry of Natural Resources 2011). In the Eastern and parts of the Southern Province, most people depend on groundwater from boreholes. As of 2009, there were at least 400 boreholes and wells in various parts of the country (Ministry of Natural Resources 2011). In upland areas, groundwater from springs is a key resource, including via many piped water supply schemes. The locations of some - probably large - water abstractions (both surface water and groundwater) are shown in the Rwanda Water Portal.

Extensive borehole drilling and shallow well construction have been done, mostly in the Eastern Province, since 1994. A major project investigating groundwater in the Eastern Province was reported on in Rwanda Water and Forestry Authority (2019). The aim of the project was to identify or confirm the main aquifers, understand their hydrodynamic behaviour, groundwater resource potential and recharge mechanisms. The project report provides much detailed hydrogeological data and interpretation (Rwanda Water and Forestry Authority, 2019)

Some threats to groundwater include the effects of deforestation and erosion, which can damage spring supplies. Noted problems with water quality generally (mostly related to surface water but also likely to affect groundwater) are usually caused by poor agricultural and mining practices, or by wastewater discharge from both domestic and industrial sources (Rwanda Water and Forestry Authority (2017)).

Groundwater monitoring[edit]

Groundwater Quality[edit]

Groundwater quality is monitored by the Rwanda Water and Forestry Authority (RWFA). Most ongoing water quality monitoring is of surface waters: monitoring data is available from the Rwanda Water Portal, and a summary of results is in Rwanda Water and Forestry Authority (2017). A recent study commissioned by the RWFA collected detailed water quality data for 36 water bodies in Rwanda, including groundwaters, to establish a water quality baseline to support future monitoring. Detailed data from this study are available in Rwanda Water and Forestry Authority (2019).

Groundwater levels[edit]

In 2021 the national groundwater level monitoring network included 24 boreholes. At least 8 of these monitoring boreholes are equipped with automatic water level monitors (pressure transducers). The locations of monitoring boreholes can be seen on an interactive map in the Rwanda Water Portal, and monitoring data can be downloaded from the Rwanda Water Portal. A summary of groundwater level monitoring results is given in the Annual Water Status Report 2016/17 (Rwanda Water and Forestry Authority, 2017).

Transboundary aquifers[edit]

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

References[edit]

References with more information on the geology and hydrogeology of Rwanda may be available through the Africa Groundwater Literature Archive.

Online resources[edit]

Further information on Rwanda's water and groundwater resources can be found via:

Rwanda Water Portal

Rwanda Water and Forestry Authority]

Water for Growth Rwanda - a joint Rwanda-Netherlands Initiative to promote improved integrated water resources management in Rwanda; information at project partner webpages including FutureWater and SNV.

Ministry of Environment

Further geological information is held by the Rwanda Mining Board.

Documents[edit]

Hulsbosch N, Van Daele J, Reinders N, Dewaele S, Jacques D and Muchez P. 2017. Structural control on the emplacement of contemporaneous Sn-Ta-Nb mineralized LCT pegmatites and Sn bearing quartz veins: Insights from the Musha and Ntunga deposits of the Karagwe-Ankole Belt, Rwanda. Journal of African Earth Sciences 134, 24-32. Doi: 10.1016/j.jafrearsci.2017.06.004

MINERENA / RNRA. 2015. Rwanda National Water Resources Master Plan. Ministry of Environment (formerly Ministry of Natural Resources of Rwanda) / Rwanda Natural Resources Authority. October 2015.

Rwanda Natural Resources Authority (RNRA). 2014. Consultancy services for development of Rwanda National Water Resources Master Plan. Tender Number 021/RNRA/2011-2012. Master Plan Report: Main Volume. Final Version May 2014. Prepared by SHER Ingénieurs-Conseils s.a.

Rwanda Ministry of Natural Resources. 2011. Water Resources Management Sub-Sector Strategic Plan (2011-2015).

Rwanda Water and Forestry Authority. 2017. Annual Water Status Report 2016-2017

Rwanda Water and Forestry Authority. 2019. Water quality monitoring in Rwanda: final report. IWRM Programme Rwanda, April 2019.

Rwanda Water and Forestry Authority. 2019. Ground Water Recharge and Storage Enhancement in Eastern Province. Rwanda IWRM Programme, April 2019.

Schlüter T. 2006. Geological Atlas of Africa.

Water for Growth Rwanda. 2018a. IWRM Programme Rwanda: Upper Nyabarongo Catchment Plan 2018-2024.

Water for Growth Rwanda. 2018b. IWRM Programme Rwanda: Nyabugogo Catchment Plan 2018-2024.

Water for Growth Rwanda. 2018c. IWRM Programme Rwanda: Sebeya Catchment Plan 2018-2024.

Water for Growth Rwanda. 2018d. IWRM Programme Rwanda: Muvumba Catchment Plan 2018-2024.

Theunissen K, Hanon M and Fernandez N. 1991. Carte geologique du Rwanda (scale 1:250,000). Service Geologique du Rwanda et Musee Royale de l'Afrique Centrale, Tervuren.

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


Return to the index pages: Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Rwanda