Inadequacies in theTechnique of Resistivity Method for Location of Waterwell Sites in Hard Rock Areas

Large scale exploratory work for groundwater in hard rock region of South India has been carried out by the authors during the last ten years, using electrical resistivity method. The standard methods of data interpretation were found to be inadequate in locating water well sites and determining the existence and depth of occurrence of water bearing fractures and joints. Wenner and Schlumberger type vertical electrical sounding (VES) curves were interpreted by matching against theoretical model curves and also by inverse slope method. The interpreted results were correlated with the actual driller's logs. No satisfactory correlation could be observed either between the geoelectrical interpreted layer boundaries and the layer boundaries from the wells or between the resistivity in the hard rock and the water yield. A more pragmatic approach to the problem is desirable to minimize the failures of wells in hard rock terrain.