Revisiting Surface-Subsurface Exchange at Intertidal Zone with a Coupled 2D Hydrodynamic and 3D Variably-Saturated Groundwater Model

A new high-performance numerical model (Frehg) is developed to simulate water flow in shallow coastal wetlands. Frehg solves the 2D depth-integrated, hydrostatic, Navier–Stokes equations (i.e., shallow-water equations) surface domain and 3D variably-saturated Richards equation subsurface domain. The two domains are asynchronously coupled surface-subsurface exchange. applied evaluate sensitivity a variety of simplifications that commonly adopted for wetland models, especially use diffusive wave approximation place traditional Saint-Venant flow. results suggest dynamic momentum preferred over wetlands marshes because latter fails capture unsteadiness. Under combined effects evaporation wetting/drying, using leads discrepancies modeled exchange flux intertidal zone where strong processes occur. It indicates models should be built with (i) timing inundation, (ii) complex topographic features render accurate spatial extent (iii) solver capable modeling moisture change due infiltration.