Aquifer systems in Kordofan, Sudan: Subsurface lithological model

Subsurface lithological/hydrogeological investigations were conducted in west-central Sudan to define aquifer systems, their quality and extensions. Separated by a low-lying central base dome, the Bara and Kosti Basin Complexes accommodate thick clastic sedimentary rocks and provide a supply of groundwater. An examination of numerous boreholes from the database of the National Corporation for the Development of Rural Water Resources (NCDRWR) has revealed two aquifer systems: upper and main. The main aquifer system is semi-confined and most often lies under hydraulic pressure created by an overlying aquitard of a clayey nature, whereas the upper system is a water table aquifer. The upper aquifer extends from the north of the study region to the latitude 13 degrees 10' north and is composed predominantly of well-sorted sand dunes in the upper part and partially of the Umm Rawaba Formation in its lower part. The Umm Rawaba Formation, which is Late Tertiary-Pleistocene unconsolidated fluviolacustrine sediments, forms the main aquifer system. The average hydraulic conductivity and thickness were estimated to be 9.89 center dot 10(-5) m/sec and 70 m and 6.8 center dot 10(-6) m/sec and 150 m for the upper and main aquifer, respectively. Groundwater generally flows along the axial troughs of the Bara and Kosti Basins from the northwest to the southeast showing progressive increase in salinity owing to an ironic exchange with abundant evaporite minerals down the gradient. Based on water quality and availability, west-central Sudan is divided into three zones: western, central and eastern. In the western zone where groundwater is shallow and recharge is adequate, water exploitation is unchallenging. Water exploration in the central and eastern zones should be aided by geophysical methods. High salinity in the eastern zone requires a careful selection of productive zones and the sealing saline zones.