Multi-Dimensional Assessment of Submarine Groundwater Discharge and Seawater Intrusion Between Mangaluru and Udupi Coast of Karnataka, India

Abstract

Submarine Groundwater Discharge (SGD) and Seawater Intrusion (SWI) are critical, interlinked processes impacting coastal groundwater sustainability. Increasing population density, rapid urbanization, and unsustainable agricultural practices contribute to groundwater stress along coastal regions, especially from the Mangalore and Udupi coasts of Karnataka, India. This study investigates SGD and SWI dynamics using groundwater level (GWL) fluctuation, in-situ water quality parameters assessment, and Sea Surface Temperature (SST) anomalies. The Historical and in-situ GWL data has been used to locate possible SGD and SWI-prone areas. The same has been validated with the key indicators Salinity, Electrical Conductivity (EC), and Total Dissolved Solids (TDS) of Groundwater, Porewater, and Seawater samples, and also from thermal image-derived SST. The integrated analysis identified zones of SGD and SWI. Surathkal Hejamadi, Padubidri, Tenka, Bada, kaiparjal, and Mattu, emerged as potential SGD areas, with GWL > 7.5 m above MSL, salinity < 1.5 PPT, EC < 1000 µS/cm, and TDS < 1500 mg/L. SWI-prone locations, such as Sasihithlu, displayed elevated TDS (up to 6770 mg/L) and GWL < 2.5 m above MSL. Malpe Beach exhibited clear SGD indicators with TDS < 400 mg/L and groundwater flow directed seaward. EC values varied from 200 µS/cm in SGD regions to over 2000 µS/cm in SWI zones, while salinity peaked at 10 PPT in Padubidri. SST anomalies validated SGD presence at Hejamadi and Surathkal, supported by hydrological and hydrochemical data. This comprehensive approach offers an effective methodology for delineating SGD and SWI zones, contributing to sustainable coastal aquifer management. © The Institution of Engineers (India) 2025.