Variation in vulnerability to seawater intrusion with response to change in groundwater level in the coastal region of Sankaraparani river basin, India

Increasing urbanisation and dependency on groundwater in the coastal regions has increased the vulnerability of the coastal aquifer to seawater intrusion. The objective is to understand the variation in vulnerability to seawater intrusion with response to change in groundwater level in the coastal region of Sankaraparani river basin, located in the southeast coast of India. The hydrogeology of the coastal region of Sankaraparani river basin is comprised of alluvium formation as upper aquifer and sandstone formation as lower aquifer which is separated by clayey formation. Nearly 33 groundwater samples were collected from the different depth in the coastal region during June 2019. The GALDIT index was used to calculate the vulnerability of the coastal aquifer to seawater intrusion using the parameters such as aquifer type, hydraulic conductivity, groundwater level, distance of pumping wells from the sea, impact of seawater intrusion and thickness of aquifer. Based on the GALDIT index, about 3 km² of the coastal region is highly vulnerable to seawater intrusion, whereas 276 km² of the coastal region is moderately vulnerable to seawater intrusion during June 2019. The sampling wells located at a distance of less than 500 m are highly vulnerable to seawater intrusion. The variation in vulnerability of coastal aquifer to seawater intrusion is calculated with a decrease and increase in groundwater level. Nearly, 10 km² of the coastal region is found to be highly vulnerable to seawater intrusion if the groundwater level is decreased by 3 m, while about 350 km² of the coastal region is moderately vulnerable. The coastal region is predicted to be low vulnerable to seawater intrusion if the groundwater level is increased by 1 m. This indicates that the increase in groundwater level by increasing the groundwater recharge will decrease the impact of seawater intrusion in the coastal aquifers.