Assessment of sharp-interface approach for saltwater intrusion prediction in an unconfined coastal aquifer exposed to pumping

Water over-exploitation becomes a common problem in coastal aquifers as it disarranges the dynamic equilibrium of saltwater and freshwater and causes saltwater intrusion (SWI). Mathematical simulations become a necessary tool nowadays to predict SWI under future pumping scenarios. This study aims to assess the validity of sharp-interface approach for an unconfined coastal aquifer subjected to pumping by comparison with sand-tank observation and dispersive approach results. The comparison was in terms of (1) transient movement of saltwater toward the well screen and (2) prediction of well salinity in times. The sharp-interface approach produced acceptable results, although it over-predicted the toe position of saltwater wedge. Salinity of extracted water was less predicted by sharp-interface modeling. The sharp-interface approach was then applied for a synthetic field-scale unconfined aquifer in steady condition with different pumping rates and well placements to explore the sensitivity of the modeling. The results were compared with salinity contours of dispersive modeling. The sharp-interface approach produced better result for higher pumping rates where the saltwater was reached to the well screen. Additionally, the results of fully penetrating wells (compare to partially penetrating one) and also closer location of well to shoreline matched better with the dispersive modeling outputs. In real cases, where the saltwater may wend a long distance toward the well screen, the sharp-interface modeling weakly matched with the dispersive modeling specially in terms of well salinities that is attributed to wider mixing zone.