Characteristics of Seawater Intrusion in Coastal Aquifers Due to Seawater Flooding: A Numerical Study

In typical coastal aquifers, dense brine infiltrates under freshwater in a wedge form. However, during seawater flooding due to storm surges or tsunamis, dense brine infiltrates from the surface into the ground. In this study, to investigate the characteristics of seawater intrusion in coastal aquifers. we simulated seawater intrusion by seawater flooding using the Navier-Stokes solver based on the porous body model. The numerical analysis results showed that when the hydraulic gradient of the coastal aquifers was small, salt diffusion by seawater flooding occurred throughout the groundwater, and the infiltrated seawater remained in the freshwater layer for a long time. However, when the hydraulic gradient of the coastal aquifers was large, the salt damage by seawater flooding was relatively small, and the amount of infiltrated seawater that escaped into the sea through the groundwater flow increased. In other words, a larger hydraulic gradient of coastal aquifers leads to a lower salt diffusion in the groundwater by seawater flooding and a faster recovery. The results of this study will be useful for the preservation of coastal aquifers in the event of tsunamis and flooding.