Saltwater intrusion hydrodynamics in a tidal aquifer

The saltwater freshwater interface at the intertidal zones of surficial aquifers is continuously influenced by tidal effects. The numerical solution of this continuously changing intertidal saltwater interface profile is difficult. To simulate this dynamic system correctly appropriate definition and use of seaside boundary conditions are necessary. The estimation of submarine groundwater discharge may vary significantly depending on the way these boundary conditions are handled on the intertidal zone. In this study we have investigated this problem numerically to evaluate the effect of the use of different intertidal zone boundary conditions on the magnitude and the direction of submarine groundwater discharge as well as their effect on saltwater interface profiles. Our findings indicate that the numerical results are sensitive to density differences between the freshwater and seawater phases along with the type of boundary condition used at the intertidal zone. Based on these results, we conclude that the adaptable free exit boundary condition introduced by Frind in 1988 is the proper boundary condition to use on the advection dominant intertidal zone boundary. This approach necessitates the use of nontraditional boundary conditions in the transport model to prevent the artificial accumulation of saltwater mass underneath this boundary. The use of an improper boundary condition at this boundary may lead to the development of artificial fingering due to the accumulation of saltwater mass in the intertidal zone.