Hydrogeophysical investigation for groundwater potential of Ishara/Ode-Remo geological transition zone,southwestern Nigeria

Geological transition zones are noted to be problematic in groundwater potential and development, due to their erratic and complex nature as well as characteristic of the subsurface lithologies. There were several occurrences of reported borehole failures and dry wells in these zones in Nigeria as a result of very scanty information that could serve as database for studying its groundwater potential. This study was therefore designed to generate hydrogeophysical data that could serve as baseline information on the groundwater potential in the study. In addition, to also delineate various subsurface lithologies present. Electrical resistivity survey for geophysical investigation was carried out using vertical electrical sounding (VES) technique. A total of 150 VES stations were purposively probed using Schlumberger electrode array. The interpreted data were used to produce geoelectric subsurface lithologies and to draw the geological section across the entire area. Various subsurface lithologies with their resistivities (Ωm) were delineated for basement complex (BC), transition zone (TZ), and sedimentary terrain (ST). In BC were topsoil, weathered zone, and fresh bedrock and in TZ were topsoil, sandy, laterite/clay, dry sand, sandstone, and fresh bedrock delineated while in the ST, topsoil, lateritic and sandy clay, dry sand, and the sandstone were delineated. In conclusion, the groundwater potential of the study area is largely been affected by the topography and the nature/composition of the Abeokuta Group that underlie the sedimentary part of the study area and the presence of thick laterite/clay unit of the basement complex portion of the study area.