A multi approach study of Groundwater level fluctuation, Sea surface temperature anomaly and Physicochemical parameters to assess Seawater Intrusion and Submarine Groundwater Discharge along Odisha coast, India.

Abstract: Seawater Intrusion (SWI) and Submarine Groundwater Discharge (SGD) are two opposite natural processes which plays significant role in sustainable management of coastal groundwater resources. Thus site specific investigation is necessary to comprehensively evaluate the timing and magnitude of SWI and SGD along water stressed coastal regions. The present study attempts to locate the potential SWI and SGD zones along the central Odisha coast which is experiencing water stress due to overexploitation, groundwater salinization as well as fresh groundwater loss through natural discharge. In this study groundwater level fluctuations along the coastal tract (below or above to mean sea level) and sea surface temperature anomalies (thermal contrast in sea water through LANDSAT -8 TIR imagery) were used as holistic approach to draw inferences about probable SWI and SGD sites before our field investigations. Further during post monsoon 2021 a total number of 93 water samples (34 pore water, 34 sea water and 25 groundwater) were collected along ∼145 km stretch coastline of Odisha state. The in-situ physicochemical parameters of pore water and sea water (pH, EC, TDS, salinity and temperature) were measured at every 1km gap along the coastline except the inaccessible sites using HANNA made portable multi-parameter water quality kit. The physicochemical anomalies observed in water samples were used as evidences for our initial holistic approach to identify SWI and SGD zones. The EC of groundwater sample varied from 99 to 6440 μS/cm with Mean±SD of 1238.6±1668.5, the EC of porewater varied from 8.25 to 44.47 mS/cm with Mean±SD of 39.0±7.4 and the salinity of porewater varied from 4.59 to 28.89 ppt with Mean±SD of 24.97±4.95. Groundwater samples with EC > 3000 μS/cm were considered as potential SWI zones and porewater samples with salinity < 25 ppt and EC < 35 mS/cm were considered as suspected SGD zones. A total number of 3 SWI zones and 6 SGD zones were identified in present work and this preliminary study will act as a baseline for detailed investigation of groundwater-seawater interaction process along the coast.

Keywords: Groundwater level fluctuation, Sea surface temperature, Pore water, Seawater Intrusion, Submarine Groundwater Discharge