Integrated ERT and PQWT Investigation for Sustainable and Climate-Resilient Groundwater Development in the Basement Complex Terrain of Oban Farmland, Southeastern Nigeria

Abstract

Groundwater is essential for agricultural development, particularly where surface-water resources are limited. However, groundwater occurrence in crystalline basement terrains is difficult to predict because lithology and geological structures vary considerably over short distances. This study evaluated the groundwater potential of Oban Farmland, Akamkpa Local Government Area, Cross River State, Nigeria, using integrated Electrical Resistivity Tomography (ERT) and Portable Quantum Water Detector (PQWT) surveys. ERT delineated vertical and lateral variations in subsurface resistivity, while PQWT provided reconnaissance information for identifying favourable groundwater zones. Two ERT profiles were acquired, processed, and inverted using RES2D software. Resistivity values ranged from 50.70 to 11,830.00 Ωm along ERT-01 and from 20.50 to 1,140.00 Ωm along ERT-02, indicating substantial subsurface heterogeneity. Low-resistivity zones were interpreted as weathered, potentially water-bearing materials, whereas very high-resistivity zones represented relatively dry lateritic deposits and fresh crystalline basement. The subsurface comprises lateritic topsoil, weathered materials, fractured basement, and fresh basement rock. Weathered-zone thickness ranged from approximately 24 to 78 m. Weathered and fractured basement units constitute the principal aquifers because they provide groundwater storage and flow pathways. Fractured zones with resistivity values of approximately 852–1,165 Ωm were identified as promising drilling targets. Integrated interpretation indicated suitable borehole depths of approximately 70–135 m, especially where thick weathered materials coincide with fractured basement structures. The results demonstrate that combining ERT and PQWT significantly improves borehole siting and reduces groundwater-exploration uncertainty in complex basement environments. Borehole logging, pumping tests, and water-quality analyses are recommended to validate aquifer conditions and support sustainable agricultural groundwater development.