Application of Electrical Resistivity Method for Groundwater Exploration in Oba and Environs, Anambra State, Nigeria

Abstract

Thirteen Schlumberger Vertical Electrical Soundings were carried out using the Abem Terrameter SAS1000 in Oba and environs of Anambra State, Nigeria in order to investigate the subsurface layering with the aim of defining the aquiferous units within the study area by determining their resistivities, depths and thickness thereby providing a scientific basis for identifying areas where boreholes can be sited using a maximum current electrode spacing of 225m. The study area lies between latitudes 7^o 00^I N to 7^o 05^I N and longitudes 6^o 48^I E to 6^o 53^I E and is located within the Anambra Basin which is one of the sedimentary basins in Nigeria. The main geological formation in the study area is Ogwashi-Asaba Formation which constitute of sand and lignite. The data obtained were interpreted and evaluated using One Dimensional Interpex Version-3 software.  The result revealed four to six geo-electric units across the study area. It also revealed that the depth to water-bearing formation ranges from 48.3m to 114.2m, thickness of aquifer ranging from 48.3m to 122.9m and resistivity values range from 233.6ohm-m to 4934ohm-m. Aquifer characteristics derived from the sounding results such as transmissivity and hydraulic conductivity ranged from 0.397m²/hr to 5.594 m²/hr and 0.0823cm/s to 15.4110cm/s respectively. The water-table map showed a NW-SE principal groundwater flow direction in the area. From these results it can be seen that at Ogwugwu village in Oba, aquifer thickness of 122.90m presents the best prospect for groundwater in the study area.

Keywords: Schlumberger array, Apparent resistivity, Water Saturated layer, Transmissivity and Hydraulic Conductivity and Oba