Effect of Bed Slope on Seawater Intrusion into Confined Coastal Aquifer

Excessive exploration of groundwater causes seawater intrusion (SWI) in coastal aquifers. The purpose of this study is to investigate the effect of aquifer bed slope on SWI characteristics including salt wedge toe position, thickness of mixing zone and seawater volume in the aquifer. Different scenarios under various bed slope values and directions are defined and numerical dispersive SEAWAT code is used for modeling. Two different boundary conditions (i.e. constant head and constant flux) are also applied to freshwater inflow at landside. The simulation results demonstrate that in the confined aquifers with landside constant flux, the SWI extent and thickness of mixing zone have increased when the slope changes from a positive value (i.e. longitudinal slope toward the sea) to negative amount (i.e. longitudinal slope toward the land). The results of this study show that when the aquifer bed is considered flat, the SWI specifications including salt wedge toe position, mixing zone thickness at bed and saline water volume are less estimated than those in cases with negative slope and are more predicted than positive slope cases. Type of freshwater inflow at landside boundary also influences the results. In confined aquifers, when landward boundary condition is changed from constant flux to constant head, salt wedge characteristics were not significantly changed. Variation in the aquifer bed slope will affect the gravity factor (potential head) in the related equations that is accompanied with pressure head, which plays a key role on SWI specifications in confined coastal aquifers.