INTEGRATED APPROACH FOR IDENTIFICATION OF POTENTIAL GROUNDWATER ZONES IN IRE-AKARI ESTATE, ORITA OBELE, AKURE, SOUTHEWSTERN NIGERIA

Abstract

An integrated geophysical and hydrogeological approach has been used to investigate the groundwater potential over the crystalline basement complex rocks of Ire – Akari Estate, OritaObele, Akure, Southwestern Nigeria.This is with a view to characterise the study area into groundwater potential zones. The continuous failure of pipe borne water supply and the tremendous increase in population in the study area in the last ten years has stretched the available water facilities to their limits. Based on this,the inhabitants of the study area depend mainly on groundwater from hand dug wells and some functioning boreholes for their daily water needs hence a growing demand for more groundwater. The geophysical investigation involved the Very Low Frequency Electromagnetic (VLFEM) and the Electrical Resistivity Methods using the Dipole-Dipole and the Vertical Electrical Sounding (VES) techniques.The VLF-EM and the dipole-dipole profiles were conducted along the established six traverses in an approximately east-west direction,ninety six (96) VES was conducted while static water level measurements were carried out in sixty hand dug wells across the study area. Both the 2-D resistivity structure and the geoelectric sections revealed subsurface geologic units consisting of the topsoil, laterite, weathered layer, fractured basement and the fresh basement bedrock. Their resistivity values generally range from 12 – 372 ohm-m,39 – 617 ohm-m, 12 – 576 ohm-m, 51 – 714 ohm-m and305 – ∞ ohm-m respectively while the thickness values vary from 0.5 – 4.9 m, 1.8 – 17.6 m, 2.5 – 30 m, 4.8 – > 40 mrespectively. The depth to basement bedrock range from5 – 37.8 m. The conductive zones delineated by the VLF-EM method, the weathered layer and the fractured basement constitute the main aquifer units within the investigated area.The static water level measurement for the peaks of dry and raining seasons generally varies from 1.3 – 9.9 m and 1.8 – 10.7 m respectively. In conclusion, the groundwater potential map generated for the investigated area was used to characterize the study area into low, medium and high groundwater potential zones.