Impact of sea level rise and tidal effects on flux-controlled and partially isolated shallow aquifer on the southeast coast of India.

A rise in sea level is the most important threat to the coastal aquifers in which the intensity of threat also depends on the local hydrogeological settings. The present study seeks to identify the impacts of sea level rise and tidal effects on the shallow and complex aquifer located south of Chennai, India. The aquifer geometry is isolated dune surfaces due to the presence of enclosing saline surface water. The freshwater is available as an elongated lens, and replenishment occurs by rainfall, with limited regional influx. Numerical simulation was carried out to understand the response of groundwater table to sea level rise until the year 2100. Initially, the tidal effects were investigated for the duration of 3 years. A sinusoidal fluctuation of groundwater table is noticed only in the northern part and the tidal impact seems infinitesimal because of steep hydraulic gradient in the south. Simulation of groundwater table without considering sea level rise predicts a decline in the elevation of groundwater table/freshwater lens by - 0.35 m in the dune surfaces. The simulation with reported sea level rise of 2 mm year with the same rate of groundwater pumping results in a total increase of 0.5 m in groundwater table. The study infers that the tidal effects are high in the shallow groundwater gradient, and sea level rise will be beneficial to the isolated coastal freshwater aquifers by increasing the elevation of groundwater table/freshwater lens and further deepening the interface between seawater and freshwater.