Assessment of hydrogeophysical delineation of groundwater zones using vertical electrical sounding (VES) in Jeypore Block, Koraput District, Odisha

Abstract

Groundwater occurrence in hard-rock terrains is complex and spatially heterogeneous, controlled by weathered and fractured zones with limited surface expression. This research integrates Vertical Electrical Sounding (VES) with remote sensing, GIS and Analytical Hierarchy Process (AHP) for groundwater potential mapping of Jeypore Block, Koraput District, Odisha. This area is underlain by Eastern Ghats Mobile Belt rocks such as khondalites, charnockites, and granite gneisses. Fifteen VES surveys using Schlumberger configuration were conducted across the study area, with electrode spreads up to 800 m. Resistivity data were interpreted using IPI2WIN software, producing one-dimensional resistivity models and Dar-Zarrouk parameters. Subsurface profiling revealed distinct lithological layers consisting of topsoil, laterite, sandstone, weathered/fractured granite, and compact bedrock. Layer thicknesses ranged from 0.6 to 20.4 m in the first layer to 99.5 m in the third layer. Iso-resistivity maps generated using Surfer-25 showed significant lateral heterogeneity. Low-resistivity zones (2.6–105.2 Ωm) indicated saturated formations, whereas high-resistivity values (> 150 Ωm) represented compact basement rocks. Curve-type analysis identified predominantly AAA-type curves, which indicate increasing resistivity with depth. HA-type curves observed at two locations suggested the presence of conductive, water-saturated layers favourable for aquifer development. VES-derived parameters were integrated with twelve geospatial thematic layers, including geology, geomorphology, soil, NDVI, lineament density, drainage density, rainfall, slope, physiography, land use, groundwater fluctuation, and hydrogeology, using the AHP framework. The consistency ratio of the model was 2.36%, indicating reliable thematic weighting. Validation via pumping tests and ROC analysis (AUC = 0.86) confirmed model reliability. This approach offers a scientifically robust framework for sustainable groundwater management in structurally complex hard-rock terrains.