Integrated electrical resistivity and isotopic approach for delineating groundwater potential zones in a coastal...

Understanding recharge processes and surface-groundwater interactions in rapidly urbanizing coastal regions is essential for sustaining freshwater availability under growing climate and anthropogenic pressures. The objective of this study was to evaluate surface water-groundwater interactions and delineate groundwater potential zones (GWPZ) in coastal regions of Chengalpattu district, Tamil Nadu, using an integrated approach of water stable isotope analysis (δ¹⁸O, δ²H), analytical hierarchy process (AHP) and electrical resistivity survey (ERS). For the isotopic analysis, we collected precipitation, surface water, and groundwater samples for the pre-monsoon, monsoon, and post-monsoon seasons. The ERS was conducted to identify the aquifer geometry, fractures, and lineament for identifying the GWPZ. Seasonal variations in isotopic compositions were observed, with a depletion in isotopic compositions during the monsoon season in wells and lake waters, indicating a surface and groundwater interaction, and an isotopic enrichment during the pre-monsoon and post-monsoon seasons due to evaporation. Based on the δ¹⁸O-δ²H plot, two sources of groundwater recharge were discerned, (i) direct recharge from precipitation; (ii) recharge from the lakes. Using a conservative isotope (δ¹⁸O) mixing model, the contribution of lake to the groundwater was estimated. The average contribution from lake water to groundwater was found to be nearly 25 %. ERS using vertical electrical sounding identified true resistivity ranging from 13.10 to 59.49 Ω·m with an average resistivity value of 20.68 Ω·m. The integrated isotopic-geophysical approach provides an effective framework for understanding recharge dynamics and managing groundwater in coastal semi-urban environments.