Hydrogeophysical Characterisation of Aquifer Systems Using Vertical Electrical Sounding in Parts of Obio-Akpor LGA, Niger Delta, Nigeria

Abstract

The geology of the Niger Delta region, including Obio-Akpor Local Government Area of Rivers State, is dominated by coastal plain sands interbedded with clay and shale formations, giving rise to multilayered aquifer systems with variable hydraulic properties and productivity. Rapid urbanisation, oil and gas exploration, and infrastructure expansion have heightened groundwater demand while also raising concerns regarding aquifer vulnerability and environmental contamination. Despite growing dependence on groundwater resources in Obio-Akpor Local Government Area, detailed hydrogeophysical investigations focusing on aquifer characteristics, groundwater potential, and subsurface lithological distribution remain limited.  This study presents a hydrogeophysical investigation of groundwater potential and aquifer characteristics in parts of the Obio-Akpor Local Government Area, Rivers State, Nigeria, using electrical resistivity methods. Vertical Electrical Sounding (VES) employing the Schlumberger array was conducted at five locations to delineate subsurface lithology, aquifer depth, thickness, and groundwater potential zones. Resistivity data were analysed descriptively and interpreted hydrogeophysically. The geoelectric layer parameters obtained from the VES stations show apparent resistivity values ranged from approximately 12 Ωm to 980 Ωm, indicating heterogeneous sedimentary sequences dominated by clay, sandy clay, fine sand, and coarse sand units typical of the Niger Delta coastal plain sands. Aquifer horizons were identified at depths of 32-65 m, with thicknesses of 19-28 m. High resistivity values correspond to coarse sand formations characterised by enhanced permeability and groundwater storage capacity, whereas low resistivity values indicate clayey confining layers. The results indicate favourable groundwater potential within the deeper sandy stratigraphic units, which appear to constitute viable aquifer horizons. However, comprehensive hydrochemical characterisation is recommended to validate water quality parameters and to assess the long-term sustainability of abstraction from these units. Such integrated evaluation would enable a more robust appraisal of aquifer suitability for potable and agricultural use. Overall, the findings furnish essential baseline hydrogeophysical data to inform groundwater exploration and development strategies. They offer a scientific basis for optimising borehole siting, guiding sustainable abstraction practices, and supporting integrated water resource management initiatives within the Niger Delta region.