Insights into Groundwater-Seawater Interaction using Magnetic and Electromagnetic Data along the Western Coast of India

Coastal basaltic aquifers are inherently heterogeneous, making the identification of groundwater-seawater interactions and submarine groundwater discharge (SGD) zones challenging using conventional hydrogeological approaches. SGD represents a critical pathway for nutrient transport, contaminant dispersion, and freshwater flux into coastal environments. Limited subsurface exposure and complex fracture-controlled flow systems further increase uncertainty in delineating these zones along basaltic coastlines. To address these challenges, this study integrates Very Low Frequency Electromagnetic (VLF-EM), Transient Electromagnetic (TEM), and magnetic methods to characterize groundwater–seawater interactions along Western Coast Beach in the Raigad district, Maharashtra, India. The study area lies within the Deccan Traps, the largest basaltic lava province in India. VLF-EM and TEM surveys were employed to identify conductive structures associated with coastal aquifers and saline water intrusion, while ground magnetic data were analyzed to delineate structural controls and zones of reduced magnetic susceptibility. These integrated geophysical interpretation reveals preferential groundwater flow pathways connecting onshore aquifers to the coastal zone, indicating areas of active groundwater–seawater exchange. The study demonstrates that the combined use of electromagnetic and magnetic methods effectively reduces uncertainty in coastal groundwater investigations and provides a robust framework for identifying SGD zones, thereby supporting sustainable coastal groundwater management.