The hydrogeology map shown here was developed by the British Geological Survey as part of a series of continent-scale quantitative groundwater maps showing aquifer productivity, saturated aquifer thickness, and aquifer flow and storage type, which were presented by MacDonald et al. (2010; 2012). It is based on a 1:5,000,000 (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.
This new hydrogeology map combines geology, aquifer productivity, and aquifer flow/storage type. It provides a geologically based view of the overall hydrogeological environment, reflecting the overall 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 distinguishes the following major aquifer groups, or hydrogeological environments:
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.
These include both volcanic and intrusive rocks (such as granites). Across much of Africa, most large outcrops of igneous rocks shown on this map are volcanic. 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 very 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.
Country-scale hydrogeology maps
The continent-scale hydrogeology map was used as the basis of new country-scale hydrogeology maps for each country in Africa, which are presented in this Atlas. Because the map is based on 1:5 million scale linework, it is not always appropriate or accurate at the scale of individual countries. Where this is the case, the country maps have, wherever possible, been updated in collaboration with experts in the country's hydrogeology, to better reflect the geology at a country scale.
- MacDonald AM, Bonsor HC, Ó Dochartaigh BE and Taylor RG. 2012 Quantitative maps of groundwater resources in Africa. Environmental Research Letters, 7 (2), 024009. 10.1088/1748-9326/7/2/024009
- MacDonald AM, Ó Dochartaigh BE, Bonsor HC, Davies J and Key R. 2010. Developing quantitative aquifer maps for Africa. British Geological Survey Internal Report IR/10/103, Nottingham, UK.
Further Sources of Information
The World-wide Hydrogeological Mapping and Assessment Programme (WHYMAP) was launched in 2000 to provide data and 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 from the WHYMAP website.