HYDROGEOPHYSICAL INVESTIGATION In El BAGAIR AREA Gezira State

Abstract

Abstract The study area is coverd by recent deposits, overlying Gezira Formation. The water bearing strata comprises two separated aquifers; the upper is the Gezira Fonnation and the lower aquifer is the Nubian sandstone Formation and they are separated by a thick layer of clay or mudstone. The Nubian aquifer is mainly composed of medium to coarse sand and gravels, the aquifer recharges directly from the Blue Nile. The Gezira aquifer consists of unconsolidated clays, silts, sands and gravels which represent alluvial fan deposits carried out from Ethiopia by the Blue Nile system. The aquifer geometry was ascertained by geo-electric investigation coupled with data from existing boreholes. From pumping test the hydrogeological parameters were calculated using different methods. The transmisivity values are in the range of 100 ml/d -3000 m’/d, and the average hydraulic conductivity between 3.53xl0" and 1.03x10'l m/day, and the storativity varies between 1x10" _ hl0_l .The chemical quality of the ground water is generally good and in general the groundwater of the area is suitable for all purposes, the TDS ranged from 168-800 mg/l. The saturation state of groundwater showed that it is saturated with carbonate minerals. About 51 Vertical Electrical Soundings (VES) were conducted along 12 profiles to delineate aquifer extents, its lithological characteristics as well as the lenses of basalt in the area. Results of the VESs have shown variations in depth, thickness and resistivity of the saturated zones indicating inhomogenity of the aquifer. The resistivity of aquifer ranges between 40 - 200 Qm, while its thickness varies from 40 m to 320 m. Though it's rather ambiguous to map basalts, lenses intruded in the Nubian sandstone Fomiation, basalt has been detected in a number of boreholes in El Bagair area. It is massive rock and black in colour, and non-water bearing.