Unveiling hidden Flows: Tracing submarine groundwater discharge in Punnakayal Estuary coastal region, Tamil Nadu, India, through radon (Rn) and GIS topology.

The precise quantification and understanding of submarine groundwater discharge (SGD) pose significant challenges, despite its critical role in the dynamics of coastal ecosystems. The present study conducted in the Punnakayal Estuary, Tamil Nadu, India presents an innovative approach to unveil hidden flows of groundwater discharge using a combination of radon (Rn) tracing and Geographic Information Systems (GIS) Topology. Radon (Rn), a radioactive gas that occurs naturally acts as a unique tracer for SGD due to its ability to partition between groundwater and surface water. In the present study, radon concentrations were measured systematically across the estuarine environment to identify areas of SGD influence. The data were then integrated into a GIS framework, where spatial topology was employed to analyze the intricate connectivity between surface water bodies, subsurface groundwater and SGD pathways. The results reveal a comprehensive view of SGD dynamics within the Punnakayal Estuary with the fresh SGD of 4.52 × 10 m/s through GIS modelling approach. Notably, the combination of radon tracing and GIS topology unveils previously concealed pathways of groundwater discharge. High-flow accumulation zones indicative of SGD was identified, shedding light on the spatial distribution of this vital hydrological process. SST of the region was also calculated to validate this approach. This research contributes to our understanding of coastal hydrogeology and ecosystem health in the Punnakayal region, with implications for sustainable coastal management and resource conservation. The integrated approach of radon tracing and GIS topology offers a robust methodology applicable to similar coastal environments globally, addressing the challenges associated with the hidden flows of submarine groundwater discharge. By uncovering the intricate subsurface interactions between groundwater and estuarine systems, was not only advances scientific knowledge but also provides valuable understandings to protect and preserve the delicate balance of coastal ecosystems.