An appraisal of ground water resources of Zalengei area, Darfur Province, Sudan

Abstract

Zalengei area, Darfur Province, Sudan, a semi-arid area, appears favorable in many respects for future agricultural development. The cultivation of new cash crops depends on the availability of adequate supplies of ground water of satisfactory quality to irrigate these crops. The principal aquifer in the area is unconfined in the valley fill sediments which form the Lower Terrace and the Flood Plain formations. The average thickness of the aquifer is some 90 feet, and its average transmissivity and storage coefficient are 100,000 gallons/day/foot, and 0.2 respectively. The storage capacity of the ground water reservoir is some 140,000 acre feet. Ground water is discharged from the basin by evapotranspiration, effluent seepage, and underflow out of the basin. Recharge to the ground water is from direct precipitation over the basin area, by influent seepage, and by underflow into the basin. The ground water supplies of the area have small amounts of dissolved solids, mostly bicarbonates and, carbonates. The waters that underlie Wadi Aribo are generally rich in calcium and magnesium bicarbonates, whereas those underlying Wadi Azum are rich in sodium carbonates and bicarbonates. The ground water underlying Wadi Azum is an approximate blend of the waters supplied by its tributaries and the water of the Large Dariba Lake. This lake has the highest content of fluoride yet known in natural waters. The arable land in the area is 7200 acres. The amount of ground water needed to irrigate these lands is about 21,600 acre-feet per year. About 20 per cent of this amount can be recharged to the ground water body from the annual precipitation over the basin area; the rest can be recharged by influent seepage from the wadis during flood time. Most of the water supplies are of excellent to good quality for irrigation and domestic uses.