Vertical electrical sounding (VES) methods to delineate potential groundwater aquifers in Akobo area, Ibadan, South-western, Nigeria

Abstract

Vertical electrical resistivity soundings were conducted in order to delineate groundwater potential aquifers in Akobo area, Ibadan, South western, Nigeria. Twenty-one vertical electrical soundings were conducted using the Schlumberger configuration, covering the area. The data were interpreted with the help of Abaque (master) curve. The geoelectrical sections for the study area were: the topsoil, the clayey sand, sandy clayey, shale/clay basement and the fresh basement. The dominant rocks comprise suites of quartz schist and pegmatite. Interpretations of vertical electrical sounding (VES) were used to generate longitudinal conductance map. Isoresistivity contour map was prepared and interpreted in terms of resistivity and thickness of sub-surface layer at 56 m spacing using computer software (SURFER), and resistivity results were correlated with the existing lithology. Similarly, aquifer unit(s) thickness map was also prepared, in which good, moderate and poor zones are classified. The study reveals that the weathered and fractured horizons that occur in the easternmost part of the area constitute the productive water-bearing zones referred to as good groundwater potential aquifers with a thickness value greater than 20 m. Key words: Electrical resistivity, fractured horizon, groundwater potential aquifers, vertical electrical soundings, weathered horizon.