Geoelectric Characterization and Groundwater Potential Mapping of Nguru Local Government Area, Chad Basin, Northeastern Nigeria

Abstract

The geoelectric investigation was carried out in Nguru Local Government Area (LGA), Yobe State, within the Chad Basin of Northeastern Nigeria, to evaluate groundwater potential and delineate subsurface lithology. The study area is underlain predominantly by the Chad Formation, comprising unconsolidated to weakly consolidated sand, clay and sandy-clay deposits of fluvial and lacustrine origin. These alternating permeable and relatively low-permeability units form the principal aquifer–aquitard framework of the area. One hundred (100) Vertical Electrical Soundings (VES) were carried out using the Schlumberger electrode configuration with a maximum current-electrode half-spacing (AB/2) of 200 m. WinResist software was used for partial curve matching and one-dimensional forward modelling. The results revealed five to six geo-electric strata with resistivity values ranging from 0.5 to 1941.3 Ωm. Seventeen curve types were identified, with KHK (19%) and KQH (19%) being the most common. The lithological categories identified were topsoil, lateritic/hard clay, clay, sandy clay and sand. A major NW–SE-trending sand-rich buried channel-like feature was delineated, with maximum interpreted sand-bearing thickness of 88.7 m at Yamdugu (VES 86). The Groundwater Potential Index classified the area into HIGH (5%), MODERATE (70%) and LOW (25%) zones. Sixteen priority locations were identified for further borehole investigation. Validation data supplied from 25 borehole logs were compared with the VES interpretations; the existing scatter plot contains 10 numerical paired observations and gives r = 0.993 and R² = 0.985. The study provides a regional geoelectrical framework for groundwater exploration in Nguru LGA.