Eliminating the effect of artificial ponding in salt marsh flooding and draining

The stability and long-term sediment flow in a tidal salt marsh wetland system largely depend on the marsh platform wetting and drying. Flow exchange between channel and marsh flats has a significant control on the overall hydrodynamics, net volume exchange and sediment transport. Hydrodynamic processes over marsh topography are significantly affected by surface defects such as cutsand rills on channel berms and creeks on the platform. These meter-scale features are often missing in the model representation due to the spatial resolution available from data sources such as LiDAR, as well as incomplete resolution in the model grid itself. Inadequate representation of these features can lead to the artificial hydraulic isolation of depressions in the marsh surface, leading to artificial ponding and resulting inaccuracies in predictions of sediment flux onto platforms, hydroperiod and average inundation depth. In order to improve the representation of wetting and drying in artificially isolated depressions, we introduce an effective surface porosity effect in the mass conservation equation, using the FVCOM model as a framework. The modification is verified using observations of water levels on marsh platforms in Bombay Hook National Wildlife Refuge, DE. We use model simulations with and without the correction in order to estimate the effect of ponding on volumetric exchanges and tidal asymmetry in the complex Bombay Hook marsh system.