Abstract

Resistivity depth soundings integrated with the very low-frequency electromagnetic (VLF-EM) profiling and some hydrogeologic measurements were conducted at Bamikemo, Nigeria. The exercise attempted to evaluate the groundwater potential of the main water supply area. The integrated approach enabled the delineation of the regolith/weathered layer containing the overburden aquifers from the hard rock housing the bedrock aquifers. The study reveals that the thickness of the overburden/weathered layer ranges from 2.4 to 24.5 m, with average value of 12.6 m. Static water level also varies from 0.2 to 14 m in the area. The potentiometric surface map constitutes groundwater occurrence guide for the area. In all the fifteen electromagnetic (EM) profiles established, prominent fractures in varying magnitudes were only in two profiles. A comparative correlation with the appropriate geoelectric sections show that resistivity parameters around the EM-delineated bedrock fractures within the granite/granite-gneiss bedrock in the area which reveals that the bedrock is not considerably decomposed or fractured to hold significant quantities of groundwater. The prominent EM anomalies at these locations are apparently attributable to fairly thick unconsolidated weathered mantle. Consequently, the weathered overburden in the area, especially the central/western segment is considered groundwater prospect specific area. Beyond the results concerning the main objectives of the survey, the study also justified the reliability in integrated application of hydrogeologic, VLF-EM and depth sounding data in locating groundwater prospect specific areas in hard rock terrains.

Key words: Electromagnetic profiling, depth sounding, overburden/weathered layer aquifers, bedrock aquifers, potentiometric surface.