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Influence of Vegetation Height on Turbulence Structure and Sediment Deposition

Author(s): Kazumasa Matsumoto; Taka-Aki Okamoto; Michio Sanjou

Linked Author(s): Michio Sanjou

Keywords: Open-channel flow over vegetation; Turbulence structure; Sediment deposition; Vegetation height; PIV

Abstract: In natural rivers, vegetation has various influences on flood risk and riverine environment. Therefore, it is important to understand the effects of riverine vegetation on flow field and sediment transport in order to predict changes in the aquatic environment. Especially, vegetation height is one of the most important parameters since there are a variety of plants in terms of species and growing conditions in a river channel. In this study, Particle Image Velocimetry (PIV) was performed for the open-channel flows over a vegetation patch. To investigate the effect of vegetation height on flow structure, two types of rigid, submerged vegetation models with different heights were considered. Results of PIV revealed the flow structure around vegetation. Reduction of the streamwise velocity within a patch and recovery in a wake region were slower in the case of taller vegetation than in the shorter vegetation case. Turbulence generation around the vegetation tips was the most significant in the case with moderate vegetation height. A quadrant analysis of the Reynolds shear stress demonstrates for the shorter vegetation, coherent motions of turbulent flow reach the bottom more frequently. Next, sediment deposition experiments were also conducted to explore effects of vegetation height on sediment transport processes. Observation of the sediment deposition suggests the changes in mean flow and turbulence structure with vegetation height affect the sediment transport and deposition within and around a vegetation patch.


Year: 2023

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