Author(s): Yonggang Zhang; Ping Wang; Jinhua Cheng
Linked Author(s):
Keywords: No keywords
Abstract: Riparian vegetation plays key roles in natural waterways and wetland ecology, interacting with both the water flow and sediment. However, the physical processes governing these interactions are still poorly understood especially for the nonuniform flow. This paper investigates how bedload transport responds to the presence of dense vegetated patch, and how this response is influenced by the vegetation drag coefficient Cdf in a nonuniform flow. Laboratory flume tests of both the fixed bed and mobile bed for different vegetation densities exposed to the constant flow rate were conducted, and the variation in the water surface was accurately measured. The Saint-Venant equation (SVE) was applied to explore the vegetation hydrodynamics, and a bed-load transport model was proposed to predict the bed-load transport rate Qs based on the turbulence theory under the condition of nonuniform flow. The results reveal that the calculated values of Cdf exhibit nonmonotonic variation with increasing Reynolds number along the streamwise direction due to the flow nonuniformity. There are two effects of blockage and sheltering in the flexible vegetated patch. However, for emergent vegetation on the mobile sand bed, drag coefficient Cd exhibits monotonic increase for different vegetation density and flow rate, which is influenced by both the water surface gradient and bed erosion degree. Qs increases with downstream streamwise distance. The increase of the vegetation-generated turbulence can in turn increase the bedload transport, thereby affecting the sediment transport process and bed slope. Finally, the new bed-load transport model can predict the Qs measurements for the vegetated patch in nonuniform flows. The results presented in this study can potentially support applications relating to the riverine restoration.
Year: 2022