GROUNDWATER POTENTIAL EVALUATION AND VULNERABILITY ASSESSMENT OF AQUIFER LAYERS AT NORTH WESTERN PART OF AKURE, SOUTHWESTERN, NIGERIA.

Abstract

Groundwater Potential and Aquifer Vulnerability of the North-Western part of Akure, Nigeria was investigated using Electrical Resistivity Method, involving vertical electrical sounding. The research was carried out with the aim of delineating the Groundwater Potential and Aquifer Vulnerability of the area. Geology and elevation maps were obtained from the existing geology and topographic map of the area. Two hundred and twenty four (224) VES was carried out using Schlumberger array technique. The VES data were interpreted qualitatitively and quantitatively using a partial curve matching from which aquifer layers, resistivity and thickness values and the overlying layers, resistivity and thickness and bedrock relief values were obtained. The additive model was modelled using surfer software and the model was utilized for this study both for the groundwater potential evaluation (GERRT) and aquifer vulnerability assessment (GERT). The results delineated fifteen different curve types like KH, HA, H, A and AA across the area. Three to five geo-electric layers were delineated across the area. The resistivity of the layers vary respectively as 6.9 - 550 ohm-m, 60 - 2500 ohm-m, 20 - 650 ohm-m and 220 - 7900 ohm-m in the topsoil, weathered layer, partially weathered basement/partially fractured basement and presumed fresh basement and thickness values also vary respectively as 0.4 - 4.0 m, 0.7 - 19.0 m and 4.0 - 60 m. Geo-electric derived data and geomorphologic data were modeled and synthesized to generate GERRT map of about 60% characterized as low groundwater potential, about 30% as moderate potential and about 10% high potential and was validated with functional hand-dug wells and boreholes in the area and also generated GRET map of about 60% characterised as high vulnerability, about 35% as moderate and 5% as low vulnerable area. It was recommended that the high and moderate groundwater potential zones should be accorded priority for any future groundwater development effort in the study area and should be protected through grouting