Electrical Resistivity Tomography for Groundwater Exploration in Kebbi State

This study applies electrical resistivity tomography to delineate aquifer zones suitable for borehole siting in Kebbi State, North West Nigeria. Access to potable groundwater remains a persistent challenge across rural Kebbi State, where over 60 percent of communities depend on unprotected shallow wells and seasonal rivers. Electrical resistivity tomography provides a non-invasive, cost-effective technique for imaging subsurface lithology and identifying permeable formations at depth. This study acquires ERT data along six profiles in Argungu, Jega, and Birnin Kebbi local government areas using a Wenner-Schlumberger electrode array with 56-electrode spread and 5-metre electrode spacing. Two-dimensional inversion is performed using RES2DINV software. Apparent resistivity sections are interpreted against available geological and borehole logs from the Kebbi State Rural Water Supply and Sanitation Agency. Findings reveal low-resistivity anomalies in the range of 10 to 45 ohm-metres at depths between 25 and 60 metres, interpreted as water-saturated sandy and gravelly alluvial sediments overlying the crystalline basement complex. High-resistivity zones above 500 ohm-metres correspond to fresh bedrock and laterite. Three borehole targets are delineated with estimated aquifer thicknesses between 12 and 28 metres. Post-drilling confirmation from one borehole commissioned by the LGA validates the interpreted target at 34 metres depth with an initial yield of 4 litres per second. The study recommends ERT profiling as a prerequisite to all community borehole programmes in crystalline basement terrains of North West Nigeria.

Keywords: electrical resistivity tomography, groundwater, aquifer delineation, Kebbi State, ERT inversion.