Abstract
Vegetation canopies control mean and turbulent flow structures as well as suspended sediment processes in the coastal wetlands. In this study, a three-dimensional hydrodynamic and sediment transport model is developed for studying flow/wave-vegetation-sediment interactions. The model is based on the non-hydrostatic model NHWAVE. The vege- tation effects on turbulent flow are accounted for by introducing additional formulations associated with vegetation- induced drag and turbulence production in the governing equations. The sediment concentration is obtained by solving the advection-diffusion equation with sediment exchange at the bed. The turbulent flow and suspended sediment are simulated in a coupled manner. The model is validated against the laboratory measurements of partially vegetated open channel flows. It is shown that the model can well predict the vegetation effects on the flow field. The model is then employed to study nearshore sediment suspension influenced by a patch of vegetation, which is located in the surf zone. The turbulence generated by wave breaking is greatly damped by the vegetation patch, resulting in considerably less sediment pickup from the bottom in the surf zone. Within the vegetation patch, most suspended sediments are restricted in a thin layer near the bottom. The net sediment transport is in the shoreward direction, in contrast to the seaward net transport of sediments in the unvegetated surf zone.
Highlights
Aquatic vegetation play a significant role in controlling mean flow, turbulence as well as sediment processes
Due to the enhanced resistance associated with the plants, the mean flow is greatly reduced within the vegetation patch, compressing turbulence level (Nepf, 1999) and promoting sedimentation and the retention of suspended sediments (Lopez and Garcia, 1998; Sharp and James, 2006; Zong and Nepf, 2010)
We have developed a three-dimensional hydrodynamic and sediment transport for studying flow/wave-vegetation-sediment interactions
Summary
Aquatic vegetation play a significant role in controlling mean flow, turbulence as well as sediment processes. Due to the enhanced resistance associated with the plants, the mean flow is greatly reduced within the vegetation patch, compressing turbulence level (Nepf, 1999) and promoting sedimentation and the retention of suspended sediments (Lopez and Garcia, 1998; Sharp and James, 2006; Zong and Nepf, 2010). Sharpe and James (2005) performed a series of laboratory experiments to study how emergent vegetation promotes sediment deposition They found that the suspended transport and the extent of longitudinal deposits from suspension within emergent stems is enhanced by increased flow depth and reduced by increased sediment grain size and stem density. Their studies revealed the existence of a diverging flow at the leading edge of the vegetation patch and a shear layer with large-scale coherent vortices at the lateral interface between the patch and adjacent open channel, which have significant effects on sediment deposition within the patch
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