GEOMORPHIC CONTROL ON OCCURRENCE OF FRESH GROUNDWATER IN A SALTWATER INTRUDED COASTAL AQUIFER

Intrusion of saltwater into coastal aquifer deteriorates the groundwater quality and affects the freshwater availability in the coastal regions. A study has been conducted with the aim to (i) demarcate the potential fresh groundwater zones, and (ii) determine the processes that control fresh groundwater availability in the coastal areas of Puri district of Indian state of Odisha. Sixty-eight groundwater samples were collected from tube wells extending up to 10 km inland along 120 km stretch of the coast. Various physico-chemical parameters such as Electrical Conductivity (EC), Total Dissolved Solids, pH and concentrations of major ions were determined. Majority of the collected water sample (56%) falls in brackish water category, as their EC values higher than 1500 µs/cm has been registered. The major ion composition of the collected water samples indicate the intrusion and mixing of saltwater with the fresh groundwater in the inland areas up to an extent of 5-7 km. Interestingly, the water samples close to shoreline show freshwater characteristics and fall in Ca-Mg-HCO₃ field of the Piper diagram. With the help of Enhanced Thematic Mapper Plus (ETM +) Pan Mosaic images and digital elevation model, it has been identified that these freshwater patches exist on buried paleochannels and sand dunes, which act as perched aquifer to store fresh groundwater. The demarcation of perched aquifers for groundwater exploration may provide an immediate solution to deal with the problem of freshwater scarcity in the coastal areas.