HYDROGEOPHYSICAL INVESTIGATION OF GROUNDWATER POTENTIAL OF OLORUNDA-ABAA AREA, IBADAN, SOUTHWESTERN NIGERIA

Abstract

Integrated hydrogeological and geophysical methods involving Very Low Frequency Electromagnetic (VLF-EM), Vertical Electrical Sounding (VES), Multi-criteria Decision Analysis (MCDA) data mining technique and statistical modeling had been utilized with the aim of delineating the groundwater potential of Olorunda-Abaa area, Ibadan, Southwestern Nigeria. A total of five (5) traverses were established across the study area. VLF-EM data were acquired at a station interval of 10 m along the five traverses while fifty-three (53) VES data were collected in the study area using Schlumberger array with a total length spread of 100 m – 150 m. The VLFEM interpretation results delineated conductive zones along the profiles that are typical of geological structures. The VES result delineated four subsurface geoelectric units consisting of the topsoil, weathered layer, partly weathered/fractured basement and fresh basement rock. The layer resistivity values generally ranged from 36 – 584 Ωm, 46 - 488 Ωm, 51 – 263 Ωm and 135 – 1120 Ωm respectively while the thickness values generally varied from 0.6 – 1.2 m, 3.9 – 47.1 m and 6.2 - 49.5 m respectively. The AHP technique was used to integrate all the factors considered influencing groundwater occurrence for the development of groundwater potential map. The investigated area was subsequently characterized into high, medium, low and very low potential zones. The study concluded that the integration of hydrogeological and geophysical data with Multi-criteria Decision Analysis (MCDA) data mining technique can provide a robust result in developing a model groundwater potential map for groundwater resources management in the study area.