Simulated groundwater dynamics and solute transport in a coastal phreatic aquifer subjected to different tides

Abstract

A 2 D cross-shore transect model with variable density and saturation was established in FEFLOW to investigate the groundwater dynamics and solute transport under the influences of three tidal conditions. This study resulted in four major conclusions. The phreatic aquifer acted as a low-pass filter accompanied by a longer period in groundwater fluctuations. More obvious stability was observed in the solute transport at the lower water table of the tide-fixed, in the spring tide of tide-1, and in the valley stage of tide-2, the ranges of the fluctuations in solute concentrations showed a phenomenon of “reverse distance” and the morphologies showed a “bimodal wave” pattern under the variable-amplitude tides. The solute migration rates were hastened by tidal boundaries and flux patterns of solute transport presented fluctuations. Sensitivity analyses indicated that the solute concentration was insensitive to the boundary transformation when the hydraulic conductivity was low or the dispersivity was high. This model provides a reliable analogical approach for the management of pollutant dispersion in coastal areas lacking data.