Fast Modeling of Vegetated Flow and Sediment Transport Over Mobile Beds Using Shallow Water Equations With Anisotropic Porosity

Abstract

A two‐dimensional shallow water model based on the anisotropic porosity method is developed for predictions of water flows, sediment transport and bed morphological changes through rigid vegetation. Effects of the vegetation resistance and the spatial occupation are accounted for by adding an extra vegetation drag force and introducing porosity parameters. By defining a cell‐based porosity for the volumetric occupation and an edge‐based porosity for the flux exchange, the anisotropic property of the preferential flow can be well captured. Based on the finite volume method, the model is solved explicitly with a hybrid local time step/global maximum time step method and is parallelized using the Open MP techniques. The numerical grid convergence and quantitative accuracy of the model have been tested against a series of flume experiments for various configurations of rigid emergent vegetation over fixed or mobile beds. It is shown that using shallow water equations with anisotropic porosity, a constant drag coefficient can lead to numerical solutions of comparable accuracy as those complex empirical relations. Moreover, appropriate quantification of the stem‐scale turbulence effects brings significant improvement in modeling of the vegetation‐affected sediment transport.