Hydrogeology map of Africa
The hydrogeology map of Africa presented in this Atlas was developed by the British Geological Survey. It is based on a 1:5 million scale geology map, described here, which was attributed with quantitative and qualitative hydrogeological information derived from published hydrogeological maps and studies of aquifer properties. The map shows the nature of the uppermost aquifer present below the ground.
This hydrogeology map was originally developed as part of a project that produced a series of quantitative groundwater maps for Africa showing groundwater (aquifer) productivity, groundwater storage, and depth to groundwater (MacDonald et al., 2010, 2012). More information on these parameters can be found on the aquifer properties page. Each of these groundwater maps is available to download as a 5 km resolution grid (xyz ASCII file), which can be used in GIS; and also as a high resolution PDF file.
The new hydrogeology map of Africa combines information on geology, aquifer productivity, and aquifer flow and storage into a single map. It provides a geologically based view of the hydrogeological environment, reflecting the dominant control that the geological environment has on the presence and movement of groundwater in aquifers, and indicates the relative aquifer productivity, from very high to very low.
It should be remembered that like all maps, this is a two-dimensional representation of the complex three-dimensional geological reality. The hydrogeology map of Africa shows the uppermost aquifer. If a major aquifer is overlain by unconsolidated sediments that don't form a major aquifer, the overlying sediments are not shown on the map.
The hydrogeology map distinguishes the following major aquifer groups. More information on these groups can be found on the Overview of Groundwater in Africa page.
- Basement aquifers
These incorporate all crystalline basement complex rocks, most of which are Precambrian in age. These develop distinctive, often local, weathered (also called regolith) and fractured aquifers.
- Igneous aquifers (largely volcanic)
These are dominantly volcanic rocks, but in some areas incorporate intrusive igneous rocks, such as granites. These form fractured, weathered aquifers that are often strongly controlled by the geometry and weathering of former lava flows.
- Consolidated sedimentary aquifers
These have been subdivided according to the dominant groundwater flow type – fracture, intergranular, or a combination of fracture and intergranular.
- Unconsolidated sedimentary aquifers
These are largely Quaternary but can also include Tertiary age sediments. They are highly variable in their distribution, thickness, geometry and lithology, and therefore in their hydrogeological characteristics. The hydrogeology map shows some of the most hydrogeologically significant outcrops of unconsolidated deposits in Africa, particularly where these overlie lower productivity bedrock aquifers. However, it does not show all unconsolidated deposits. Particularly, over some of the major consolidated sedimentary basins, unconsolidated deposits of hydrogeological significance are not always shown, because the underlying consolidated sedimentary rocks form more productive and significant aquifers.
MacDonald, A M, Bonsor, H C, Ó Dochartaigh, B É, and Taylor, R G. 2012. Quantitative maps of groundwater resources in Africa. Environmental Research Letters, 7 (2), 024009. 10.1088/1748-9326/7/2/024009
MacDonald, A M, Ó Dochartaigh, B É, Bonsor, H C, Davies, J, and Key, R. 2010. Developing quantitative aquifer maps for Africa. British Geological Survey Internal Report, IR/10/103.
Country hydrogeology maps
The hydrogeology map of Africa described above was used as the basis for producing a hydrogeology map for each country in Africa for this Atlas. For some countries, the country map was extracted from the Africa-wide map with no further modifications. For some other countries, further modifications have been made to better represent the hydrogeology at a national scale. These modifications were made in collaboration with the co-authors of the relevant country pages, who are experts in the hydrogeology of the respective countries.
Other hydrogeology maps for Africa
The World-wide Hydrogeological Mapping and Assessment Programme (WHYMAP) was launched in 2000 to provide summary information about global groundwater resources. Several global and continental scale maps related to groundwater resources, groundwater basins, large aquifer systems, and transboundary aquifers are available to download (as pdf or image files) from the WHYMAP website. These include a groundwater resources map of Africa; and many scans of national hydrogeological maps across Africa through the WHYMIS application. These national maps are also indexed in the Africa Groundwater Literature Archive.
In 2008, BRGM published a hydrogeological map of Africa at a scale of 1:10 Million, the first of its kind at this scale. The map is produced as a hard copy and in GIS form. It was developed by combining two categories of data: groundwater reservoir (or aquifer) type; and the proportion of precipitation available to recharge to aquifers. BRGM used extensive data to develop the map, which distinguishes eleven major hydrographic units.
This map, at 1:5 Million scale, is not available digitally but is described in the report by Gilbrich and Struckmeier (2014).
Gilbrich, W H, and Struckmeier, W F. 2014. 50 Years of Hydro(geo)logical Mapping Activities. Published by the Germal Federal Institute for Geosciences and Natural Resources (BGR) and UNESCO International Hydrological Programme (UNESCO-IHP).