Assessment of the Subsurface for Identification of Borehole Sites for Irrigation at Challawa-Gorge Dam, North West Basement Complex, Nigeria

A geo-electric survey using 1-D carried out to identify suitable sites and construction of boreholes that will give water supply for large irrigation work at Challawa-Gorge Dam, North West Basement complex, Nigeria. The data was acquired using Schlumberger technique at points chosen across the study area. The data analyzed with IPI2WIN software, information from a borehole where use as control for delineation of virtual geologic model of the study area. Th eresults suggest 4-5 geo-electric layers exist in the study area. The topsoil layer having resistivity range between 158 ohm m to 417 ohm m and thickness range between 0 m to 3 m. Sand layer having resistivity range between 58 ohm m to 107 ohm m and thickness range between 7 m to 14 m. Weathered rock layer having resistivity range between 122 ohm m to 192 ohm and thickness range between 7 m to 9 m. Moderately fractured layer having resistivity range between 166 ohm m to 317 ohm m and thickness range between 28 m to 31 m. Fresh bedrock layer having resistivity greater than 1000 0hm m and infinite thickness. Lithological units suggest weathered and underlain by partially weathered, fractured basement as the aquifer zone where it is extensively thick and suitable points for borehole selected based on the depth and thickness range of the aquifer layers.