Experimental Study On Water And Sediment Transport In Open Channel Flow With Vegetation

River with vegetation is an essential part of natural ecology. The characteristic of water flow and sediment transport in rivers with vegetation is a difficult issue among river dynamics problems. The research status of flow with vegetation is systematically summarized, and indoor flume tests on water and sediment transport in open channel flow with vegetation are conducted by using three artificial flexible plants (plant with no grass, submerged flexible plant, and non-submerged flexible plant). The research is divided into three aspects:1. Characteristics of flow resistance in open channel flow with different plants.Variation regularity of the flow resistance of the three plants are researched through flume tests, and the variations of one-way water surface slope and drag coefficient of open channel with the three plants are analyzed. It’s found that the variation of drag coefficient of each plant is similar with Nikuradse curve in general. Turbulent flow range c can be divided into turbulent smooth zone, turbulent transition rough zone, and turbulent drag rough zone. The crown heights of plants beat down by water impact are counted and the relationship between flow resistance coefficient and roughness for each plant is obtained accordingly. Regression analysis on the relationship verified that the method can be applied to deduce the resistance coefficient of open channel flow with plants.2. Hydrodynamic properties of open channel flow with different plants.Flume test results reveal that the flow velocity variation in a certain area above the crown top of submerged plant is similar with that of plant with no grass. The longitudinal velocity for non-submerged plant distributes in "S" shape along the depth direction with clear stratification. Turbulence intensity exhibits different characteristics with the variation of plant morphology, one-way distribution and distance to the side wall.-(uv+uv)/u2*is the important factor characterizing flow variation. It is closely associated with plant morphology and one-way distribution in the presence of plants. Moreover, it regularly adjust along with the changes of plant morphology and one-way distribution.3. Regularity of sediment transport in open channel flow with different plants.Flume test result shows that the vertical distribution of sediment concentration gradient is in positive correlation with flow turbulence intensity, and the relationship between the two is fitted. The particle size of sediment decreases upwards, presenting an obvious stratification. The impact of the same plant on the vertical distribution of fine sediment is smaller than that on coarse sediment. Plants have a stronger effect of blocking coarse sediment in open channel but have little effect of blocking fine sediment, which is similar with the variation of sediment concentration in the downstream river after the operation of the Three Gorges Project. Momentum diffusion coefficient, sediment diffusion coefficient, and β(the ratio of the former to the latter) change in vertical direction. They are all functions of spatial location (regions and relative water depth) and vary with the changes of spatial location. In general, momentum diffusion coefficient distributes in parabolic shape in vertical direction, and increases before decreases with the increase of relative water depth. Sediment diffusion coefficient gradually reduces with the increase of relative water depth in the presence of different plants. The value of β ranges from0.14to10.0, most of which is significantly larger than1. This is because lightweight model sand used in the experiment is beneficial to sediment diffusion and the sediment diffusion coefficient is large.