Subsurface Dams as a Mitigation Measure for Saltwater Intrusion and Recharge of Shallow Water Aquifer in Puducherry, India

Groundwater is the key water resources for farming and drinking in Puducherry (union territory), India. Salt water intrusion where sea water infiltrates in to a coastal aquifer impacting the ground water. In Puducherry, India, water quality of the groundwater abstracted from the tube wells deteriorated in the recent years possibility due to excess pumping, urbanization, industrial waste disposal, sea level rise, subsidence, decrease in recharge, and reduction of water level in the aquifer. As the coastal aquifers are generally connected hydraulically to the sea with lateral or horizontal intrusion and through which the seawater being slightly denser initially intrudes at the bottom of the aquifer and the fresh water is present at the top. Over exploitation of groundwater from such coastal aquifers to meet the increasing demand accelerates the progress of seawater intrusion. Coastal region of Puducherry is facing problem due to the ingress of seawater into the tube wells, up to a distance of 5 to 7 km from the coast. Any further extraction of groundwater has to be done only beyond this distance. In order to improve the conditions in Puducherry underground coastal reservoir is seen as an option as the mitigation measure for salt water intrusion. The main idea of creating a barrier is to reduce or prevent saline water intrusion into the coastal region.

In this work, groundwater modelling will be set-up up for the study area in order to simulate the saline water intrusion and relevant modelling scenarios for the coastal region of Puducherry, India. This study assesses the seawater intrusion vulnerability in coastal areas of Puducherry and further study the shallow groundwater hydrochemistry and its variations from sea coast with regards to the ground water quality parameters comparing it to with WHO (World Health Organization) drinking water standards for drinking and farming purposes. Implementation of a sub-surface reservoir by introducing a subsurface structure in the form of a cut-off wall in the groundwater model is recommended as a mitigation measure. The Horizontal Flow Barrier (HFB) package in MODFLOW which is used to simulate the effects of sheet piles, slurry trenches will be employed for this study to model the sub-surface barrier and study its effect on the reservoir.

Keywords: Water, Aquifer, Groundwater, Saltwater, Underground dams, Barriers, Subsurface Reservoir, MODFLOW.