Finite element modelling to assess the submarine groundwater discharge in an over exploited multilayered coastal aquifer

A three-dimensional variable-density finite element model was developed to quantify the impact of groundwater over use on submarine groundwater discharge (SGD). The model was applied to the Arani-Korttalaiyar river basin, north of Chennai, India. This region has an upper unconfined and lower semi-confined aquifer extending up to 30 km inland from the coast and beyond this distance; the two aquifers merge and become a single unconfined aquifer. The model simulated that during the period from 2000 to 2012, the flux of seawater to the aquifer has increased from 17,000 to 24,500 m(3)/day due to over-exploitation of groundwater from the semi-confined aquifer. Where as in the unconfined aquifer, SGD has been taking place. Scenarios showing the impact of newly constructed managed aquifer recharge structures, 10% additional increase in rainfall recharge, and termination of pumping from five well-fields on the groundwater conditions in the area were studied. The model predicted a SGD of 85,243 m(3)/day from the unconfined aquifer and 22,414 m(3)/day from the semi-confined aquifer by the end of 2030. By adopting managed aquifer recharge methods, seawater intrusion (rate of 4,408 m(3)/day) can be reduced and SGD (rate of 22,414 m(3)/day) increased. The rate of SGD increase and the movement of seawater to aquifer can be completely prevented in the semi-confined aquifer by adopting these management options by 2030. Findings from this study have enhanced the understanding of SGD and water budget, which can be used by decision-makers for the sustainable management of groundwater resources in coastal aquifers.