Predictive Simulation of Seawater Intrusion Control Measures in a Coastal aquifer

Abstract

Many coastal aquifers are facing seawater intrusion due to overexploitation of freshwater. In this study, the groundwater flow and solute transport in a coastal aquifer of Minjur in India were simulated considering the possible cases of aquifer recharge, freshwater draft, relocation of pumping wells, etc., using numerical modelling software. The groundwater flow model MODFLOW and solute transport model MT3D were calibrated for seven years period and validated against the dataset for two years, which gave satisfactory results . The sensitivity analysis of model parameters revealed that the horizontal hydraulic conductivity greatly influenced the hydraulic head. The model was used to predict the response of the coastal aquifer to four potential scenarios like aquifer recharge, reduced pumping, relocation of pumping wells, and a combination of these scenarios. The effectiveness of various management scenarios was evaluated based on their ability to improve groundwater level and salinity in observation wells/piezometers, reduce the affected area and restrict the advancement of the seawater-freshwater interface. The result of predictive simulation indicated that a combination of scenarios such as reduction in groundwater pumping by 25% from the semi-confined aquifer, increased pumping by 25% from the unconfined aquifer, and increased recharge from rivers by constructing check dams have the potential to restrict the seawater-freshwater interface movement and improve groundwater quality in Minjur aquifer. These control measures would effectively shift the interface towards the coast by 1.0 km in the unconfined aquifer and 1.5 km in the semi-confined aquifer by 2025.