Water Table Depth Mapping Using Electrical Resistivity in Kwara State

Accurate determination of water table depth across Kwara State, North Central Nigeria, is critical for agricultural groundwater utilisation, borehole construction planning, and environmental vulnerability assessment in a state where basement and sedimentary rocks of contrasting hydrogeological properties coexist. This study maps the spatial variability of water table depth using vertical electrical sounding data collected at systematically distributed stations across three local government areas in Kwara State. The Schlumberger array was deployed at seventy sounding stations, with current electrode spacing extended to a maximum of three hundred metres to resolve the depth range of interest. Sounding curves were interpreted using computer-assisted partial curve matching and one-dimensional forward modelling. Interpreted aquifer depths were validated against water level measurements from existing boreholes and hand-dug wells obtained through community enumeration. Contour maps of water table depth were constructed using ordinary kriging interpolation. Results reveal a statistically significant contrast in water table depth between communities overlying basement rocks in the east and those on sedimentary cover in the west, with implications for relative borehole installation costs. The study further identifies shallow water table zones vulnerable to surface contamination from agricultural inputs and open sanitation. Findings are delivered to the Kwara State Water Corporation and Department of Rural Development for integration into water infrastructure investment planning. Keywords: water table, electrical resistivity, vertical electrical sounding, Kwara State, hydrogeology.