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| [[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Additional resources]] >> Hydrogeology Map
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| ==The hydrogeology maps in the Africa Groundwater Atlas==
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| The hydrogeology maps for each country shown in this Atlas were developed by the British Geological Survey. They are based on a 1:5 million scale [[Geology | '''geology''' map]]. This was was attributed with quantitative and qualitative hydrogeological information from published hydrogeological maps and studies of aquifer properties.
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| This hydrogeology map was originally developed as part of the [https://www.bgs.ac.uk/research/groundwater/international/africanGroundwater/maps.html '''Quantitative Groundwater Maps for Africa'''] project (MacDonald et al., 2010, 2012). This project produced three '''groundwater maps for Africa''':
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| ; Groundwater (aquifer) productivity
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| ; Groundwater storage
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| ; Depth to groundwater
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| These three Africa-wide maps can be freely downloaded in digital form as a 5 km resolution grid (xyz ASCII file), which can be used in GIS. They are also available as high resolution PDF files. [https://www.bgs.ac.uk/research/groundwater/international/africangroundwater/mapsDownload.html '''Download the Africa groundwater maps here'''].
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| Information from these groundwater maps was incorporated into a new single hydrogeology map for Africa that combines information on geology, aquifer productivity, and aquifer flow and storage type. The map gives a geologically based overview 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. Background information on aquifer productivity and other aquifer hydraulic parameters can be found on the [[Aquifer properties | aquifer properties]] page.
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| This Africa-wide hydrogeology map was used to produce hydrogeology maps for each country in Africa. For some countries, the country map was extracted from the Africa-wide map with no further modifications. For others, further modifications have been made that 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.
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| Like all maps, the hydrogeology maps of Africa are a two-dimensional representation of the complex three-dimensional geological reality. They show the uppermost aquifer only. If there are other aquifers at depth, these are not shown on the maps. Also, if a major aquifer is overlain by unconsolidated sediments that don't form a major aquifer, the overlying sediments are not shown on the hydrogeology maps.
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| [[File: Hydrogeology.png | 500px| thumb| Hydrogeology map of Africa, 1:5 million scale]]
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| [[File: Hydrogeology_Key.png | thumb| Legend for hydrogeology map of Africa| 500x195px]]
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| The hydrogeology maps distinguish the following major '''aquifer groups'''.
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| More information on these aquifer groups can be found on the [[ Overview of Groundwater in Africa | Overview of Groundwater in Africa]] page.
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| ; Basement aquifers
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| These incorporate all crystalline basement complex rocks, most of which are Precambrian in age. These develop distinctive local weathered (also called regolith) and fractured aquifers.
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| ; Igneous aquifers (largely volcanic)
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| 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.
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| ; Consolidated sedimentary aquifers
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| These have been subdivided according to the dominant groundwater flow type – fracture, intergranular, or a combination of fracture and intergranular.
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| ; Unconsolidated sedimentary aquifers
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| 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.
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| ===Sources===
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| MacDonald, A M, Bonsor, H C, Ó Dochartaigh, B É, and Taylor, R G. 2012. [https://nora.nerc.ac.uk/id/eprint/17892/ Quantitative maps of groundwater resources in Africa]. Environmental Research Letters, 7 (2), 024009. 10.1088/1748-9326/7/2/024009
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| MacDonald, A M, Ó Dochartaigh, B É, Bonsor, H C, Davies, J, and Key, R. 2010. [https://nora.nerc.ac.uk/501779/ Developing quantitative aquifer maps for Africa]. British Geological Survey Internal Report, IR/10/103.
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| ==Other hydrogeology maps for Africa==
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| ===[https://www.whymap.org/whymap/EN/Home/whymap_node.html WHYMAP]===
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| 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
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| download (as pdf or image files) from the [https://www.whymap.org/whymap/EN/Downloads/downloads_node_en.html WHYMAP website]. These include a [https://www.whymap.org/whymap/EN/Downloads/Continental_maps/gwrm_africa_pdf.pdf?__blob=publicationFile&v=2 groundwater resources map of Africa]; and many scans of national hydrogeological maps across Africa through the [https://produktcenter.bgr.de/terraCatalog/OpenSearch.do?search=WHYMAP+infoMapAccessService&type=/Query/OpenSearch.do WHYMIS] application. These national maps are also indexed in the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
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| ===[https://www.brgm.eu/ BRGM]===
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| In 2008, BRGM published a [https://www.brgm.eu/projects/hydrogeological-map-of-africa 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.
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| ===[https://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA500854 International Hydrogeological Map of Africa]===
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| This map, at 1:5 Million scale, is not available digitally but is described in the report by Gilbrich and Struckmeier (2014).
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| Gilbrich, W H, and Struckmeier, W F. 2014. [https://unesdoc.unesco.org/images/0023/002310/231066e.pdf 50 Years of Hydro(geo)logical Mapping Activities]. German Federal Institute for Geosciences and Natural Resources (BGR) and UNESCO International Hydrological Programme (UNESCO-IHP).
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| [[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Additional resources]] >> Hydrogeology Map
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| [[Category:Additional resources]]
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| [[Category: Overview of Groundwater in Africa]]
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| [[Category:Africa Groundwater Atlas]]
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