Evaluation of sharp-interface simulation of saltwater intrusion into the multi-layered coastal aquifers exposed to pumping

Population growth and scarcity of coastal freshwater resources have increased the stresses on many coastal aquifers, leading to aquifer storage decline and salwater intrusion (SWI). Investigation of coastal aquifers routinely involves the application of SWI models, which can be divided into two categories, namely sharp-interface and dispersive-interface approaches. There is no mixing between freshwater and saltwater at sharp-interface approaches. This makes them computationally more efficient while dispersive-modeling approaches are more numerically challenging, but allow for freshwater-saltwater mixing. Most coastal aquifers comprise overlying sequences of geological strata, resulting in SWI characteristics that may differ significantly to those of homogeneous cases. The layered coastal aquifers have received significantly less attention than the more simplified single-layer case, despite the fact that stratified aquifers are widespread. In this study, a sharp-interface approach (named as SHI-SWIM) was developed using FORTRAN programming code. The model is first validated and then applied for the simulation of sand-tank experiment and field-scale multi-layered aquifers exposed to pumping in order to evaluate the strength and limitation of the developed model. SHI-SWIM model produced better result for higher pumping rates. Additionally, the results of fully penetrating wells and closer position 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.