Direct Current Resistivity Methods for Groundwater Prospecting in Hardrock Terrains: A Viable Approach to Providing Sustainable Potable Water

Abstract

Wide- spread application of direct current resistivity prospecting methods can result in providing sustainable potable water. Apparent resistivity (ρa) values between 100 and 200 Ωm characterise water bearing zones in hardrock terrains. Prolific water boreholes are drilled at locations with such ρa profiling at Awi campus of College of Education in Cross Rivers State of Nigeria. Sounding curves prepared from VES (vertical electrical sounding) data reveal the presence of water- bearing fractures. Longitudinal unit conductance (S) and transverse anisotropy (λ) can be estimated from VES data. Areas with high ground water yield are characterized by low λ and S values. Water table topography was constructed from static water-level measurements taken taken in hand dug wells, and was found to be similar to basement surface topography constructed from VES data in Saukakahuta suburb in Minna, Nigeria. This demonstrates the potential of VES data for constructing groundwater flow pattern. Convergence zones identified from flow pattern are sites for prolific water boreholes. VES data collected in Chanchaga suburb in Minna reveals that the basement is deep in north-eastern and southern portions of Chanchaga. Spontaneous Potential (SP) values obtained in these areas ranges from 20 to 60 mV. Deep basement combined with positive SP values often indicate high potential for optimum ground water yield. Induced polarisation (IP) is not observed in clean sands devoid of clay.