Geoelectrical Investigation of Groundwater Potential in the Hard Rock Terrain: A Case Study from Lokapavani River Basin, Mandya District, Karnataka

Abstract

Groundwater in crystalline basement regions is mainly stored in weathered and fractured zones due to the low permeability of fresh bedrock, making its distribution highly variable and dependent on subsurface structural features. Accurate identification of these aquifer zones is therefore essential for sustainable groundwater exploration and management in hard rock terrains. The present study investigates groundwater potential in the hard rock terrain of the Lokapavani River Basin, Mandya District, Karnataka, using the Vertical Electrical Sounding (VES) technique. Twenty-one VES stations were conducted employing the Schlumberger electrode configuration using a resistivity meter (SSR-MP-ATS), with fixed potential electrode spacing (MN/2 = 5 m) and current electrode spacing (AB/2) varying from 10 m to 100 m. Apparent resistivity data were analyzed qualitatively through comparative log–log sounding curves to delineate subsurface geoelectrical variations associated with groundwater occurrence. The interpreted apparent resistivity values range from less than 30 Ωm to greater than 7000 Ωm, reflecting considerable lateral and vertical heterogeneity in subsurface conditions. The VES curves revealed predominantly three- to four-layer geoelectrical models characteristic of crystalline basement terrains. The interpreted subsurface conditions indicate the presence of conductive clayey layers, moderately resistive weathered/fractured basement zones and highly resistive fresh basement formations. Locations characterized by moderate resistivity increase with depth are interpreted as favorable groundwater zones, whereas zones exhibiting very high resistivity values correspond to compact basement rocks with low groundwater potential. The study demonstrates that electrical resistivity sounding is an effective and economical technique for groundwater exploration in hard rock terrains and provides valuable information for sustainable groundwater resource development in the study area.