Hydrogeology of Shagora Basin with Reference to the Water Supply of El Fasher Town

Abstract

The geological formations in Shagora basin include the superficial deposits, Tertiary volcanics, Nubian Sandston Formation and the Basement Complex. The principal aquifer is mostly confined in the pebbly beds of the Nubian Sandstone. However, groundwater in small amounts is tapped in the weathered Basement Complex, superficial deposits, and the jointed volcanics. Groundwater is struck in the Nubian aquifer at a depth ranging from 300 to 700 feet whereas the standing water level ranges from 150 to 205 feet below ground level. In some localities within the basin leakage occurs from the overlying aquifer of the superficial deposits to the Nubian aquifer. Groundwater movement is generally in the south direction coinciding with the direction of surface flow of Wadi El Ku. The mean value of the transmissibility of the Nubian aquifer is about 14,000 g/d/ft while the coefficient of storage is 2x10–4. The total groundwater in storage has been estimated as 1.03x109 gallons whereas the annual recharge is estimated as 2.4x108 gallons. The recharge occurs mainly from the Nubian trough around Barboja jointed volcanics along Wadi Tawilla and the weathered Basement Complex underlying Wadi Magdub. Groundwater abstraction from the such an amount forms about 65 per cent annual recharge to the groundwater basin. The present annual demand for El Fasher town water supply is generally 2.6x108 gallons which falls within the safe yield of the aquifer. Such an amount can be tapped from six wells only and therefore, there is no need to drill more production wells. The groundwater in the Nubian aquifer contains total dissolved solids ranging from 200 to 870 ppm. It is classified as fresh water chemically fit for human and animal consumption. In groundwater the sodium hazard is low while the salinity hazard is medium. Such type of water can be used safely for supplementary irrigation.