DIRECT CURRENT RESISTMTY METHODS FOR GROUNDWATER PROSPECTfNG 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 (pa) values between 1OO and 200 Ohmm characterise water bearing zones in hardrock terrains. Prolific water boreholes were drilled at locations with such apparent resistivity horizontal profiling values 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 can be estimated from VES data. Areas with high ground water yield are characterized by low Alpha and Conductance (S) values. Water-table topography was constructed from static water-level measurements taken in hand-dug wells, and were found to be similar to basement surface topography constructed from VES data acquired 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 lo 60mV. Deep basement combined with positive SP values often indicate high potential for optimum ground water yield. Induced polarization (IP) is not observed in clean sands devoid of clay.