ABSTRACT
The Southern African Development Community (SADC) 1 Hydrogeological Map and Atlas (HGM) project produced a comprehensive, interactive web-based general hydrogeological map at a scale of 1: 2 500 000. The SADC-HGM provides information on the extent and geometry of regional aquifer systems, and primarily serves as a base map for hydrogeologists and water-resource planners. The hydro-lithology base map was compiled from the SADC geology map prepared by the South African Council for Geoscience. This was done through linking the stratigraphy to the rock types which simplified the 12 hydro-lithological classes that had been mapped. The identified hydro-lithologies were grouped into aquifer types: A. Unconsolidated intergranular aquifers; B. Fissured aquifers; C. Karst aquifers; and D. Lowpermeability formations. The aquifer types were grouped into eight classes according to aquifer productivity. The step of assigning aquifer productivity was a lengthy process where all available geological and hydrogeological materials were considered for each area (in map terms, a polygon or a set of polygons). In effect, the rock-type polygons were overlain, using a GIS or manually, with relevant reference layers (primarily the scanned national hydrogeological maps), and an essentially ‘manual’, expertise-based decision was made for each area. This was followed by national contact persons from SADC Member States to verify and update pertinent data to improve the hydrogeological map, reassigning production classes according to improved knowledge, or even re-defining them if necessary. The SADC Hydrogeological Mapping Project has delineated 14 transboundary aquifer systems on the basis of inferred continuous and transmissive aquifers, SADC hydro-lithological boundaries, and sub-basin river boundaries. The map should be used to guide policy-making and to influence political decision-making on water-resource issues and assist transboundary groundwater planning and management by water-resource planners.
