A pre-storage, subgrid model for simulating flooding and draining processes in salt marshes

• A subgrid model is developed for simulating flooding and draining processes in salt marshes.
• High-resolution subgrid effects are accounted for in the coarse grid computations.
• A pre-storage method is proposed to improve the model efficiency.
• The model is validated with an idealized case and applied in a salt marsh.
• The model is able to obtain comparable results with regular grid model at much lower computational cost.

We present the development of a high-efficiency and high-resolution subgrid model for simulating flooding and draining processes in salt marshes or tidal flats. The model integrates the concepts of Defina's (2000) subgrid model and the ideas of Volp et al. (2013) on treatment of the feedback of fine grid effects into coarse grid calculations. A pre-storage method is proposed to pre-calculate coarse cell-wise integrated variables associated with high resolution bathymetry data in order to further improve the model efficiency. Model validations are conducted in an idealized channel-flat system as well as a meso-tidal salt marsh. Results show that the subgrid model is capable of obtaining results which are comparable to those from the full grid model running directly on the high-resolution grid, but the computational cost can be orders of magnitude smaller than the full grid model due to the reduction in the number of computational cells and the increase in time-step size. Flows over subgrid micro-topography features like narrow channels and creeks can also be modeled, which is crucial for simulating flow routing in marsh networks. With the increasing availability of high-resolution coastal topographic data and the need for high-resolution modeling, the model is promising for applications to large-scale salt marsh modeling.