Electrical resistivity technique for assessing groundwater tables in an unconfined aquifer system and the importance of Dar-Zarrouk parameters in aquifer investigation: a case study from Walajabad block, Tamil Nadu, India

Groundwater occurrence in Walajabad block, Tamil Nadu, is influenced by variations in geological formations and subsurface conditions, making detailed characterization important for groundwater exploration and management. This research explores the groundwater characteristics and subsurface resistivity patterns for this block. In this study, 110 vertical electrical sounding (VES) points were conducted using the Schlumberger electrode array to investigate the subsurface resistivity distribution and groundwater conditions. The VES data were interpreted using IX1D software, and spatial maps were prepared using ArcGIS 10.2. A good correlation (R 2 = 0.8854) between the observed and predicted groundwater levels supports the reliability of the resistivity-based estimation. Dar-Zarrouk parameters provide quantitative information on the electrical and geometrical characteristics of subsurface layers and are useful for interpreting vertical electrical sounding (VES) data in geophysical and hydrogeological investigations. The interpreted longitudinal resistivity ranges from 2.6 to 20,756 Ω m, while transverse resistivity ranges from 2.7 to 6190 Ω m. Longitudinal conductance (S) varies from 0.00034 to 14.4 S, and total transverse resistance (T) ranges from 37 to 390,169 Ω m 2 . The unconfined aquifer thickness ranges from 2.5 to 46 m, with an average of about 10 m. Groundwater levels are less than 5 m below ground level over a substantial part of the study area, while depths greater than 10 m occur mainly in the eastern region. The spatial distribution of resistivity, S, T, and anisotropy reflects variations in clay-rich materials, unconsolidated sediments, weathered zones, and hard-rock formations. These results provide useful information for groundwater exploration, preliminary bore-well siting, and groundwater management in Walajabad block.