Combined effect of subsurface dam and layered heterogeneity on groundwater flow and salinity distribution in stratified coastal aquifers

In this paper, for the first time, we investigated the combined effect of subsurface dams and a typical stratified aquifer (two high-permeability layers with a low-permeability layer between them) on groundwater flow and salinity distribution in a tidally influenced coastal unconfined aquifer. Subsurface dams can inhibit the invasion of saltwater, and the low-permeability layer (LPL) and tide action can increase the effect of subsurface dams and the removal rate of residual saltwater. Through sensitivity analysis, it was discovered that shifting the dam location towards the inland resulted in a reduction in the effective heights of the dam. The upper saline plume contracted with increasing dam height, and the upper boundary of LPL was moved to shallower regions. And the natural removal time increased significantly with increasing dam height and the bottom boundary of LPL was moved to deeper regions. In addition, if the dam location was close to the sea boundary and the bottom boundary of LPL was moved to deeper regions, we could increase the subsurface dam height to reduce the risks of control of saltwater intrusion. This study provides us a comprehensive understanding of the complex hydrodynamics of saltwater intrusion and provides guides for the design of subsurface dams aimed at saltwater intrusion control in stratified coastal aquifers.