Hydrogeophysical Investigation of Groundwater Systems in Otukpo, Benue State, North-Central Nigeria

Abstract

Hydrogeophysical investigation of groundwater systems in Otukpo, Benue State, Nigeria has been carried out using vertical electrical sounding (VES) technique to delineate the groundwater potentials across the study area. Ten (10) vertical electrical soundings were carried out during the geophysical survey using the Schlumberger configuration of electrical resistivity method with maximum current and potential electrode spacing of 600 meters and 80 meters respectively. The VES data was qualitatively and quantitatively interpreted using the conventional curve matching and computer iteration methods. The result of qualitative interpretation depicts that the VES curves obtained within the study area are mainly the QH and KQH which are typically indicative of a sedimentary terrain. The results of the quantitative interpretation reveal that the resistivity values from shallow subsurface to the depth of about 500 m of the VES stations ranges from 3 Ωm to 1250 Ωm. The VES results also show that the study is characterized by seven (7) different inferred lithological layers namely; topsoil, sand/silt, laterite, clay, shale, sandstone and the basement rock. The result also reveals that the depth to water-saturated unit ranges from 450 to 500 meters within the study area. Two distinguished aquifer types were obtained within the area namely; unconfined and confined aquifers. The findings reveal that the future borehole drillers should target the confined aquifers situated between the depths of 450meters to 500 meters beneath the surface for sustainable groundwater yield across the study area.