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 ?m along ERT-01 and from 20.50 to 1,140.00 ?m 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 ?m 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.

Introduction

The text examines groundwater potential at Oban Farmland, Oban Community, Akamkpa LGA, Cross River State, Nigeria, with emphasis on groundwater exploration in crystalline basement terrain.

• Groundwater is essential for domestic use and agriculture, particularly where surface water is seasonal or inadequate. In crystalline basement environments, groundwater is mainly stored and transmitted through weathered layers, fractures, joints, and faults, since fresh basement rocks have very low primary porosity and permeability.
• Reliable groundwater is especially important for irrigation because it helps farmers maintain crop production during dry periods and reduces the impacts of rainfall variability. However, unsuccessful borehole drilling can cause significant financial and resource losses, making detailed subsurface investigation necessary.
• The study uses Electrical Resistivity Tomography (ERT) as the primary geophysical method and the Portable Quantum Water Detector (PQWT) as a supplementary reconnaissance method. ERT was selected because it can map lateral and vertical resistivity variations and identify weathered and fractured zones that may contain groundwater.
• Oban Farmland covers approximately 0.882 km² and is located within a humid tropical rainforest environment. The area is predominantly underlain by Precambrian granite of the Nigerian Basement Complex, with groundwater potential controlled by weathering and basement fracturing.
• Two ERT profiles, ERT-01 and ERT-02, each about 300 m long, were surveyed using a Wenner configuration. The resulting resistivity models revealed three broad subsurface conditions: weathered regolith, fractured/partly weathered basement, and relatively fresh basement.
• ERT-01 showed resistivity values of about 50.70–1,183 Ω·m, while ERT-02 ranged from approximately 20.50–1,140 Ω·m in the reported results. Low-resistivity zones were interpreted as potentially weathered, clay-rich, moist, or saturated materials, while moderate-to-high resistivity zones were associated with fractured or partly weathered basement.
• The most promising groundwater targets are not necessarily the lowest-resistivity zones. Instead, favourable targets are areas where a sufficiently thick weathered layer is hydraulically connected to open and interconnected basement fractures.
• Eight PQWT measurements were conducted. The strongest anomalies that coincided with ERT-identified weathered or fractured zones were considered more favourable groundwater targets. However, PQWT results were treated cautiously because conductive responses can also arise from clay-rich or highly weathered materials.
• The integrated ERT–PQWT interpretation provides a stronger basis for selecting potential borehole locations and reducing drilling risks. Nevertheless, the identified targets require exploratory drilling, borehole logging, pumping tests, and water-quality analysis to confirm aquifer thickness, groundwater yield, lithology, and water suitability.

Conclusion

This study assessed the groundwater potential of Oban Farmland, Akamkpa Local Government Area, Cross River State, using an integrated ERT and PQWT approach. The ERT models revealed variations in subsurface resistivity, ranging from approximately 50.70 to 1,183.50 ?•m along ERT-01 and from 20.50 to 1,140.00 ?•m along ERT-02. These variations enabled the subsurface to be characterized into conductive weathered regolith, fractured or partly weathered basement, and relatively fresh crystalline basement. The most favourable groundwater conditions were associated with thick weathered materials that appeared hydraulically connected to fractured basement structures. These formations can provide groundwater storage within the regolith and secondary pathways for movement through interconnected fractures. The PQWT survey identified anomalies corresponding with several conductive and structurally disturbed zones delineated by ERT. Agreement between both datasets strengthened the selection of potential groundwater targets, although it did not independently confirm aquifer occurrence or productivity. Overall, integrating ERT with PQWT improved subsurface characterization and provided a defensible basis for prioritizing prospective borehole locations in the crystalline basement terrain. However, the interpreted targets should be validated through exploratory drilling, lithological and geophysical borehole logging, pumping tests, and hydrochemical analyses. These investigations are required to confirm aquifer depth, thickness, yield, hydraulic properties, and water quality and to support sustainable groundwater development for agricultural activities within Oban Farmland.

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Copyright © 2026 Mfoniso U. Aka, Okechukwu E. Agbasi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.