Wave effect from sea level dynamics on density-dependent groundwater flow at a sandy beach

Dynamic coastal forces, such as waves and tides which are typically coexisting in coastal environments, impact groundwater flow and salt transport in the intertidal zone. In this study, firstly, an iterative least-squares fitting method for tidal level and wave height was introduced, and the wave height can be acquired from measured sea level and then further verified by wind speed. Groundwater flow and salt transport were then simulated using a code called MARUN under different seaward boundary conditions with and without wave effects. Comparison of measured and simulated water level and salinity indicates that the model which included wave setup can accurately reproduce the measured data in the observation wells. Simulation results show that water and salt fluxes across the aquifer-ocean interface are increased and the groundwater circulation in the intertidal zone is more active after considering wave setup. Most of the influx occurs in the intertidal zone, while a considerable amount of efflux occurs in the subtidal zone, and the maximum influx of water and salt moves toward the high tide line compared to the model results without wave setup. The water influx and efflux rates increase greatly especially during the period of high wave height. After wave effects considered, fresh submarine groundwater discharge only takes up a small proportion of submarine groundwater discharge, which is dominated by recirculated seawater. It is concluded that the presence of waves significantly increases the amount of seawater circulation.