Groundwater Exploration in Ago-Iwoye Area of Southwestern Nigeria, using Very Low Frequency Electromagnetic (VLF-EM) and Electrical Resistivity Methods

Abstract

Very Low Frequency Electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) method were used to delineate fracture zones for groundwater exploration within the permanent site of Olabisi Onabanjo University, Ago-Iwoye, Southwestern Nigeria which is underlain mainly by suites of gneissic rocks. The VLF-EM survey was made at 10 meters interval along eight (8) traverses at East - West direction ranging from 230 - 500 meters in length. The plot of filtered real and filtered imaginary identified eight (8) prominent fracture zones close to the surface or sub surface which was further delineated by VES method. Seventeen (17) VES soundings were carried out at locations of prominent VLF anomalies presumably typical of basement fracture using AB/2 of 100m. The results shows 3 distinctive geo-electric interpreted layers of sandy top soil, (0.6m to 8.6m, 107.8 m to 662.72 m), underlain by sandy clay/clayey sand (5.7m to 43.5m, 34.7Ωm to 346.8Ωm) which is underlain by fractured/fresh basement (484Ωm to 5651Ωm). The basement fractures identified from VLF-EM anomaly curves were confirmed by geo-electric interpretation of the VES, therefore, the use of the two methods help in identification and delineation of prominent prospective groundwater areas.