ABSTRACT

Vegetation has great influence on flow structure and sediment transport, which will further affect the pollution diffusion and the eco-system. Laboratory experiments were carried out in this paper to investigate the effects of submerged rigid vegetation on sediment transport under waves, currents and combined wave-current flows. The flow structure and sediment concentrations affected by the submerged rigid vegetation were measured by using Acoustic Doppler velocimetry (ADV) and Optical Backscattering turbidity sensor (OBS). The effects of vegetation on the flow velocities, turbulence kinetic energy (TKE) and sediment distributions were analyzed. According to the results, it was founded that flow velocity was reduced by vegetation due to the obstruction of vegetation stem, and the velocity gradient was the largest near the top of the canopy. TKE increased at the bottom under the unidirectional flow, which was mainly caused by wake turbulence around vegetation stems. Under the regular waves and combined wave-current flows, more than one inflection points were found in the vertical profiles of TKE, because of the combined effects of shear turbulence (canopy-scale) and wake turbulence (stem-scale). The near bed sediment concentration was higher in case with denser vegetation. In flow with vegetation, the bed shear stress could no longer be used as an index to judge the incipient motion of sediment, but the wake turbulence around the vegetation stem was the main influencing factor.

INTRODUCTION

Wetland is an important part of natural ecosystem, which has great environmental functions and economic benefits, and plays an irreplaceable role in flood control, waterlogging reduction, runoff regulation, environmental purification and soil erosion reduction. (Shang et al. 2018; Wang et al. 2020). Aquatic vegetation commonly exists in the wetland ecosystem, which can affect the flow velocity, sediment transport, as well as the pollutant diffusion. Therefore, it is of great significance to study the flow structure and sediment transport under the influence of vegetation, which can provide useful information for wetland management.

This content is only available via PDF.
You can access this article if you purchase or spend a download.