Groundwater Investigation in Markandahalla Basin Using Vertical Electrical Sounding Data

This study employs the electrical resistivity technique to investigate groundwater potential zones in the hard rock terrain of the Markandahalla basin, Kolar district, Karnataka. Fifty-two Vertical Electrical Soundings (VES) were conducted using the Schlumberger array with maximum AB/2 electrode spacing of 360 m. curves were interpreted by standard curve-matching against Rijkswaterstaat (1975) master curves and 1D inversion using IPI2WIN software, accepting models with root-mean-square error (RMSE) ≤ 5%. Isoresistivity maps at AB/2 = 45, 90, 180, and 360 m were generated to delineate subsurface lithology and aquifer zones. Results show that weathered and semi-weathered zones with moderate resistivity values (50 - 250 Ωm) favour groundwater occurrence. Depth to bedrock varies from 1.9 to 27.8 m; Total longitudinal conductance ranges from 0.01 to 1.41. Geophysical interpretations were validated against borehole yield data from 18 existing wells, confirming that sites with ρ₂ < 200 Ωm and S > 0.3 Siemens consistently yield > 1.0 lps. The study identifies the central and north-western portions of the basin as the most prospective groundwater target zones.