Geoelectric Investigation for Groundwater Development in Oroki Estate, Osogbo, Southwestern Nigeria

Abstract

The rapid development of Oroki Estate in Osogbo, Osun State has warranted the need to develop the water supply in the area. The area lies within the Basement Complex terrain of southwestern Nigeria typified by quartzites/quartz schist. This study was carried out to characterize the aquifer units for evaluation of groundwater development in the area. Twenty Schlumberger vertical electrical soundings were carried out to determine the different subsurface lithounits with the aim of delineating the thickness and continuity of the aquiferous zone. Hydro-resistivity maps such as Isoresistivity of topsoil, weathered layer, basement and overburden thickness maps were generated. Interpretation of the twenty Schlumberger vertical electrical soundings data generally show a system of three to four layered earth structure notably topsoil, saturated/sandy/lateritic clay and weathered basement and fractured/fresh basement which are mostly of the type “H” curve. Overburden isopach map revealed that the depth to bedrock varies from 9.5 to 37.8m indicating some degree of deep weathering. The main water-bearing unit in the area of study is the weathered and fractured basement which is within the second/third and the last geoelectric layers respectively. The weathered/fractured basement resistivity values vary from 16 Ohm-m and 84 Ohm-m with thickness values ranging from 3.8 m to 37.3 m. Locations with thick weathered/fractured basement were delineated to be the most promising sites for borehole drilling at the estate.