Characteristics, Assessment and Management of Groundwater Resources of the Coastal Aquifer inTokar Delta, Eastern Sudan

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Ahmed, Elgaily Mohamed Babiker
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University of Khartoum
An integrated approach of using vertical electrical sounding data, borehole data, hydrogeological, hydrochemical information and groundwater modeling has been employed in Tokar Delta to study the hydrogeological characteristics of the aquifer and to evaluate and manage its groundwater resources. A conceptual model based on the resistivity measurements is proposed which indicates the presence of four zones of different resistivity values which occur from the surface downwards: A zone of dry sediments of the overburden (the vadose zone) which consists of silt and sand with gravels marked by resistivity values of 10 to 1075 ]7;m and it has an average thickness of 15 m. The underlying zone is the lens-shaped freshwater aquifer having resistivity values of 20 to 140 ]7;m and a thickness between 10 and 80m. The surface area of the freshwater aquifer is 200 km2. The third zone is a transition zone of brackish water bearing layers marked by resistivity values between 5 and 18 ]7;m, and a thickness of a few meters to tens of meters. The brackish water zone is underlain by a zone of resistivity values below 5 ]7;m reflecting saline water-bearing formations or possibly clayey layers. The aquifer is composed of alluvial sediments of Khor Baraka. It is semi confined to unconfined with delayed yield. The average depth to the water table is 15m and the general groundwater flow is from SSW to NNE. The transmissivity of the aquifer is moderate (120 m2/d) to very high (4680 m2/d). The hydraulic conductivity ranges from moderate (33 m/d) to high (780 m/d). The aquifer has an average specific yield of 13%. The average yield of the boreholes is 40 m3/h, but the yield of the dug wells is low (5 to 10 m3/d). The aquifer is recharged annually by the flood water of Khor Baraka. The annual groundwater recharge was calculated as 31 million cubic meter and the annual groundwater discharge is 32 million cubic meters. Groundwater in storage is estimated to be 600 million cubic meters. The mesquite trees are the largest consumers of groundwater by evapotranspiration (79% of groundwater discharge). Historical data has shown that the aquifer has remained stable for the last two decades. The groundwater of the study area can be classified into three major groups: group A: (Na-Ca- HCO3) water type, it is characterized by relatively low salinity, abundance of bicarbonate anion and a relatively low concentration of Sr and B. The second group B (Na-Ca-Mix) water type is characterized by medium to relatively high salinity and a moderate concentration of Sr and B. The third group C: Na-Cl water type is characterized by high salinity indicating brackish or saline water and a slightly high concentration of Sr and B. Groundwater of group A is suitable for domestic and irrigation uses. The brackish groundwater of group B is not fit for domestic uses but can be used for irrigation purposes under certain agricultural management. Groundwater of group C is neither suitable for domestic nor for irrigation purposes. Groundwater flow simulation has shown that the system will be stable after 10 years under an assumed abstraction rate of 20000 cubic meters per day (7 million cubic meters per year). Under this condition the aquifer will be safe from contamination by saline water intrusion. Based on groundwater potential index (GWPI) an area located in the upstream part of the delta has been selected for future groundwater development projects
191 Pages
Socio-economic features;Post field phase;Regional geology of the Red Sea area;Cenozoic volcanics;Mesozoic Sediments;Tertiary Formations;Quaternary and Recent sediments;