A surface porosity approach for eliminating artificial ponding in coastal salt marsh simulations

Abstract

Hydrodynamic processes over marsh topography are significantly affected by surface defects such as cuts and rills on channel berms and platforms. These meter-scale features are often missing in the model representation due to the spatial resolution available from data sources, as well as incomplete resolution in the model grid itself. To minimize the artificial hydraulic isolation in the numerical models, we propose implementing an effective porosity algorithm on the marsh surface by considering the fine-scale topography over marsh depressions that control the drainage process. The modification is carried out to eliminate artificial ponding effects observed in model simulations in Bombay Hook National Wildlife Refuge, DE, USA using the original FVCOM code. Results from the revised and original FVCOM models are compared with pressure gauge data collected from an isolated depression in the marsh platform. The new implementations for proper wetting and drying are efficient and accurate for hydrodynamic modeling inside a complex salt-marsh system, which constitutes a major breakthrough in the context of increasing need for better understanding of physical and morphological changes in valuable coastal ecosystems. • A permeable-seabed technique is proposed to improve wetting and drying in artificial hydraulic depressions over salt marsh surfaces. • A new set of the formula is implemented in a widely used coastal ocean model FVCOM and tested the model performance in a salt marsh system. • The detailed comparison against the traditional approach showed a substantial improvement in the marsh flooding and draining accuracy.