Groundwater potential evaluation in the basement complex terrain of Ilawe-Ekiti, Nigeria, using GIS-weighted overlay and transmissivity-based validation

ABSTRACT The rising demand for water in Ilawe-Ekiti necessitates sustainable groundwater management, particularly within its fracture-controlled basement complex aquifer system. This study employed an integrated geospatial and geophysical approach to delineate groundwater potential zones. Four hydrogeological factors – drainage density, slope, land use/cover, and elevation – were analysed and weighted (40, 25, 20, and 15, respectively) using an expert-judgement scheme informed by similar basement terrain studies. These thematic layers were integrated within a geographical information system weighted-overlay framework to generate an initial groundwater potential map (GWPM-1). To enhance the spatial model, thirty vertical electrical soundings were conducted using the Schlumberger configuration, enabling estimation of aquifer transmissivity from resistivity and thickness parameters. These were integrated with GWPM-1 to produce an enhanced map (GWPM-2). Results classify the study area into high (36%), moderate (42%), low (19%), and very low (3%) groundwater potential zones, indicating overall moderate-to-high potential. Model validation, based on spatial agreement between classified groundwater potential zones and established transmissivity frameworks, showed agreement ranges of 52.7–64, 62–82, and 35.3–44% with Offodile, Krásný, and Jetel–Krásný classifications, respectively. The findings underscore the need for targeted groundwater conservation strategies and recommend the incorporation of additional surface indicators to further improve groundwater characterization accuracy.