Hydrogeology of the Gedaref Basin (East Central Sudan).

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Omer Mohammed, Kheir
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The Gedaref area consists of a flat clay plain with central low ridges and scattered inselberges. The geological formations, in the order of their occurrence from the base to the top, are the Basement Complex rocks of assumed Precambrian age, Mesozoic Nubian Sandstone Formation, Tertiary volcanics and Quaternary Superficial Deposits. Groundwater occurs mainly in the sandstone beds of the Nubian Formation under artesian and semi-artesian conditions. It also occurs in the weathered, jointed and fractured Tertiary lava flows mainly under free water table conditions. Groundwater is recharged through the seasonal stream beds and groundwater flow directions generally coincide with the directions of the surface flow drainage lines. Leakage occurs from the overlying thin lava flows at the peripheries of their thick parts to the Nubian aquifer. The average thickness of the Nubian Formation is about 700 feet (214 meters), and its average aquifer thickness is approximately 200 feet (61 meters). Depth to the static water level ranges from 23 feet (7 meters) and 400 feet (122 meters) in the Nubian aquifer, and it rarely exceeds 100 feet (30 meters) in the basalt aquifer. The average coefficient of transmissivity of the Nubian aquifer is 1500 gpd (18.6 m2 /day).. The storage coefficient ranges between 6.3X10-2 and 2.0X10-7, while the coefficient of permeability varies between 0.3-2 gpd/ft (0.01 m / day) and 23.7 gpd/ft2 (1.0 m/day). The total annual groundwater outflow is approximately 9.8X 106 cubic meters per year and the total artificial groundwater discharge through deep wells is estimated as 1.6X102 cubic meters per year. The total groundwater reserves in the Nubian multilayered aquifer is approximarely61.5X109 cubic meters.
The Hydrogeology of the Gedaref Basin (East Central Sudan).