Coastal dynamic forces, such as waves, tides and evaporation, altogether drive groundwater circulation and salt transport in the intertidal zone. However, few numerical studies have ever considered the combined effects of waves, tides and evaporation in the field. Here we show two case studies to quantify these effects in aquifers in southern coastline of Laizhou Bay.

In the first case study, the fluctuations of wave height are identified together with tidal level using an Iterative Least-squares Fitting Method, in which the wave height can be acquired from measured sea level in the surf zone, and this fitted wave height is further verified by wind speed. Groundwater flow and salt transport were then simulated using the MARUN code to evaluate the impacts after considering wave effect. The simulated equivalent freshwater head and salinity of the model with wave effect presented less difference with the measured data compared with the simulated results of the model without wave effect. After incorporating the wave effect in a model, submarine groundwater discharge (SGD) was increased, among which recirculated SGD grew more rapidly than the fresh, leading to the proportion of the fresh SGD accounting for a small proportion. The water influx and efflux rates increased greatly especially during the period of high wave height. Most of the influx occurred in the intertidal zone, while a considerable amount of efflux occurred in the subtidal zone. The iterative algorithm to separate the wave height from the mixed field data can be employed to identify and quantify the respective effects of tides and the combined effects of waves and tides on the density-dependent beach groundwater flow.

In the second case study, both field observations and numerical modeling were applied to investigate the effects of evaporation on the beach surface on groundwater flow and solute transport in an multi-layered aquifer-aquitard-aquifer system under a tidal flat with large‐scale seepage faces. Results showed that seepage-face evaporation increased groundwater salinity landward and promoted groundwater and salt exchange within the intertidal zone significantly in comparison to the case without evaporation. A groundwater circulation cell was formed near the slope break by seawater infiltrating landward of the slope break and discharging seaward. The aquitard prevented approximately 85% of inland freshwater discharge near the slope break, resulting in the formation of two atypical freshwater discharge tubes in the upper and middle intertidal zones. Two additional groundwater circulation cells developed in the lower intertidal zone due to the spring‐neap tidal cycle. The outflow and inflow fluxes over a spring‐neap tidal cycle were numerically estimated to be 1.46 and 1.27 m2/d, respectively, with evaporation accounting for 45% of the outflow flux.

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