Delineation of Subsurface Groundwater Potential Zones Using 2D Electrical Resistivity Tomography (ERT): A Case Study of Tudun Wada, Kaduna State, Nigeria

Abstract

Groundwater constitutes a critical resource for domestic, agricultural, and industrial purposes in Nigeria's basement complex terrain, which covers approximately 60% of the country's landmass. However, groundwater occurrence in these terrains is highly erratic and largely controlled by the presence of weathered overburden and fractured crystalline rocks, making borehole siting notoriously difficult. This study applied 2D Electrical Resistivity Tomography (ERT) to delineate groundwater potential zones within Tudun Wada, Kaduna State, Nigeria. The primary aim was to characterize the subsurface hydrogeological conditions and identify areas with the highest probability of yielding adequate groundwater for domestic and institutional use. Ten ERT profile lines (K1–K10) were acquired using a multi-electrode resistivity meter with a Wenner-Schlumberger array configuration and a uniform electrode spacing of 5.00 m. The acquired data were processed and inverted using RES2DINV software, employing a smoothness-constrained least-squares algorithm. Both resistivity and chargeability (induced polarization) data were inverted to generate two-dimensional models of the subsurface. The inverted models revealed a typical basement complex subsurface architecture, consisting of a resistive lateritic top layer, a variable weathered zone, and fresh basement rock at depth. The weathered zone varied in thickness from about 5 m to over 30 m across the study area. Low-resistivity anomalies (below 100 Ωm) indicative of water-saturated weathered or fractured zones were identified in several profiles, particularly K1, K3, K6, and K8. Chargeability data provided complementary information that helped discriminate between clay-rich low-resistivity zones (high chargeability) and clean water-bearing zones (low chargeability), improving the reliability of aquifer identification. The study area was classified into high, medium, and low groundwater potential zones. High-potential zones, characterized by extensive low-resistivity zones more than 20 m thick at depths shallower than 40 m, were concentrated in the central and eastern parts of the study area (profiles K1, K3, K6, and K8). Medium-potential zones were identified in profiles K2, K4, K7, and K10, while low-potential zones dominated by high-resistivity fresh basement were found in the western and northwestern parts (profiles K5 and K9). The depth to fresh basement ranged from about 10 m to over 30 m, with the deeper weathering profiles corresponding to areas of higher groundwater potential. The findings of this study confirm that 2D ERT, particularly when integrated with chargeability data, is a reliable and cost-effective tool for groundwater exploration in basement complex terrains. The groundwater potential map produced from this research will serve as a practical guide for future borehole siting and water resource development in Tudun Wada and surrounding areas, contributing to reduced drilling failure rates and improved water supply for Kaduna Polytechnic and the surrounding residential communities.