Assessment of Sea Water Intrusion in Coastal District of Southern India

Abstract

Coastal aquifers are increasingly threatened by seawater intrusion due to increased urbanization, groundwater exploitation, and global sea-level rise. Pattern diagrams, which constitute the outcome of several hydro-geochemical processes, have traditionally been used to characterize vulnerability to seawater intrusion. However, the formats of such diagrams do not facilitate the geospatial analysis of groundwater quality, thus limiting the ability of spatio-temporal mapping and monitoring. This raises the need to transform the information from current pattern diagrams into a format that can be readily used under a GIS framework to define vulnerable areas prone to seawater intrusion. A total of 162 no. of ground water samples were collected during May 2017 and analyzed for ionic properties. Among the 13 blocks of Cuddalore district, only 4 coastal blocks viz., Parangipettai, Kumaratchi, Kurinjipodi and Bhuvangiri blocks were assessed for sea water intrusion. These blocks were located from seashore to 30 km inland distance and around 52 nos. of ground water samples were collected from these coastal areas. Among the 4 coastal blocks studied, Melathirukallipalai and Kavarapattu locations of Parangipettai block and Ammapettai, Erukkankattu padugai and Karuppur locations of Kumaratchi block  of Cuddalore district, Tamilnadu were suspected for sea water intrusion based on their hydro geology parameters and molar ratios. Regarding sea water intrusion, the high Mg/Ca ratio (> 5.4) may be indicative of sea water contamination in these locations. According to Cl /CO₃^2-+HCO₃^-  ratio ( > 6.6 ) the screened locations have highly contaminated ground water (near sea water). Based on Na/Cl ratio (<0.86), the contamination may be due to marine source of origin. Hence, construction of check dams in these areas across the rivers at frequent intervals will assist in mitigating the problems of sea water intrusion by increasing ground water recharge.