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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Resource Pages]] >> Hydrogeology Map


== Dataset Description ==
The hydrogeology map presented in this Atlas was developed by the British Geological Survey. It is based on a 1:5,000,000 (5 million) scale geology map, [[Geology|described here]], which was attributed with quantitative and qualitative hydrogeological information derived from published hydrogeological maps and studies of aquifer properties.
This hydrogeology map was originally developed as part of a [https://www.bgs.ac.uk/research/groundwater/international/africanGroundwater/maps.html project to produce quantitative groundwater maps for Africa] showing aquifer productivity, saturated aquifer thickness, and aquifer flow and  storage type (MacDonald et al. 2010, 2012). More information on these parameters can be found on the [[Aquifer properties | aquifer properties]] page.
This hydrogeology map combines geology, an assessment of aquifer productivity, and aquifer flow and 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.
[[File: Hydrogeology.png | 500px]] [[File: Hydrogeology_Key.png | 500x195px]]
The hydrogeology map distinguishes the following major '''aquifer groups'''. More information on these groups can be found on the [[Hydrogeological environments of Africa | hydrogeological environments]] 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.
===Country-scale hydrogeology maps===
The new Africa-wide hydrogeology map described above was used as the basis of new country-scale hydrogeology maps for each country, presented in this Atlas. Where possible, the Africa-wide map has been updated in collaboration with experts in the country's hydrogeology, to better reflect the hydrogeology at a country scale.
===Further information and Citations===
: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. [https://nora.nerc.ac.uk/501779/ Developing quantitative aquifer maps for Africa]. British Geological Survey Internal Report IR/10/103, Nottingham, UK.
====Other Hydrogeology Maps ====
'''[https://www.whymap.org/whymap/EN/Home/whymap_node.html WHYMAP]'''
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 [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://www.bgr.de/cgi-bin/ms481/mapserv.exe?MAP_LEGEND_STATUS=ON&MAP_REFERENCE_STATUS=%5BMAP_REFERENCE_STATUS%5D&ADMIN_CHECK=OFF&java=off&imgext=-20040000.000000+-19038000.000000+20040000.000000+19038000.000000&map=f%3A%5Cwww%5CAnwendungen%5Cfishy%5Cwhymap%5Cwhymap.map&mapext=shapes&mode=browse&zoomsize=2&zoomdir=1&imgxy=450.0+427.5&imgbox=-1+-1+-1+-1&jump=&help=&map_size=900+855&layer=Hydrogeo1&layer=Lake&layer=Saltlake&layer=ice&layer=admin&layer=conti&layer=Grid&layer=relief&img.x=504&img.y=461 WHYMIS] application. These national maps are also indexed in the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
'''[https://www.brgm.eu/ BRGM]'''
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.
'''[https://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA500854 International Hydrogeological Map of Africa]'''
This map, at 1:5 Million scale, is not available digitally but is described in the report Gilbrich and Struckmeier (2014).
Gilbrich WH and Struckmeier WF. 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).
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Additional resources]] >> Hydrogeology Map

Latest revision as of 10:15, 9 January 2019