Groundwater Assessment of the Area between Medani & Sennar

Abstract

A combination of hydrogeological investigation and a geophysical survey (vertical electrical sounding) were carried out east and the west of Blue Nile between latitudes 14º 32' &13º 29’ and longitudes 33º 15'&34º 00. This study area covers about 5200km2. The resistively method was employed at two locations Daim Elmashykha and Rahad where the geological information is limited to identify the sedimentary sections and their depths to the Basement Complex Rocks and the water quality . From these sections the thickness of the sedimentary deposits at the western and northern part of the study area is larger than that at the south eastern part. This is due to the effects of the structural faults associated with the geology of the Blue Nile rift basins. The basins were subjected to tectonic movement that affected the central Sudan such as Central African Shearson (CASZ), The geological set up of the area is characterized by the Precambrian Basement Complex, the Mesozoic Nubian sandstone Foramation and the Tertiary to Quaternary deposits covered by the recent superficial deposits. The groundwater in the study area occurs in three different aquifers namely, The Nubian Sandstone Aquifer, Gezira Aquifer, Al Atshan Aquifer. The aquifer occur under confined and semi-confined condition. The direction of the groundwater flow follow the direction of the main surface drainage system (Blue Nile and its tributaries from South and Southeast to the north and northwest). The aquifer thickness is determined by the structural prexisting configuration of the Basement Complex Rocks which in turn control the borehole yields. The average transmissisivity values of the Nubian Sandstone Aquifers from the calculated method are 2x 10-3 m2/S and 5x 10-3 m2/S and from the estimated method are 2x 10-3 m2/S and 4 x 10-3 m2/S while the hydraulic conductivity values for the same aquifer from the calculated method are 1 x 10-3 m/S and 2 x 10-3 m/S and the estimated methods gives 1 x 10-3 m/S and 1 x 10-3 m/S for the Nubian Sandstone Aquifer east Wadmedani and east at Sennar respectively. 4 The average transmissisivity values of Gezira and Alatshan Aquifers from the calculated method are 5 x 10-3 m2/S and 4 x 10-3 m2/S respectively and 6 x 10-3 m2/S and 3 x 10-3 m2/S from the estimated method,on the other hand the average hydraulic conductivity values of Gezira and Alatshan from the calculated method are 2 x 10-3 m/S and 1 x 10-3 m/S and from the estimated method are 1 x 10-3 m/S and 1 x 10-3 m/S. The main source of recharge in the study area is the Blue Nile and the total annual recharge to the whole study area is estimated as 18 x 106m3 and the total abstraction from wells is estimated to be 15 x 106m3, hence there is an annual surplus of 3 x 106m3 that can be used in the future. The most dominant type of ground water within the study area is calcium and magnesium bicarbonate and the sodium bicarbonate water, and the ground water within the study area is characterized by soft to moderately soft, good to fairly good type that is dominated by class (C2–S1) medium salinity and low sodium hazard with an average 280 PPM total dissolved solids, the value of pH range from 7 to 8.5 which can be classified as neutral to alkaline,itis suitable for human uses. Owing to the above mentioned characteristics, it is possible to classify the study area as having rich groundwater resources which is characterized by good quality and quantity. Nevertheless regular monitoring of water levels and hydrochemical monitoring must be taken temporarily, realizing that the groundwater resource is the main source of water for human and animal consumption in the study area.