Characterizing residual saltwater desalination behind subsurface dams influenced by seasonal groundwater fluctuations and hydraulic conductivity anisotropy in the coastal aquifers.

This article focuses on the dynamic behavior and natural desalination processes of residual saltwater behind subsurface dams in unconfined coastal aquifers, emphasizing the combined effects of hydraulic conductivity anisotropy and seasonal groundwater fluctuations. Using a numerical model, the study evaluates desalination efficiency through two indicators: the removal rate of residual salt mass (RRSM*) and the reduction rate of residual saltwater length (RRSL*). Results indicate that both hydraulic conductivity anisotropy—defined as the ratio of vertical to horizontal hydraulic conductivity (rk)—and seasonal groundwater level fluctuations significantly influence the critical dam height required to prevent seawater intrusion and affect the desalination efficiency of residual saltwater, often exhibiting a synergistic effect. The findings highlight that higher anisotropy and groundwater fluctuations can reduce desalination efficiency and cause preset subsurface dams to fail, underscoring the need for careful design and management of subsurface dams considering local hydrogeological and climatic conditions.