Experimental study on hydraulic behaviors of steady uniform flow in open channel with submerged flexible vegetation

The 3-D acoustic Doppler velocimeter was applied to measure the steady uniform flow in open channel with submerged flexible vegetation in model test.The vegetation was simulated by using feathers.The 3-D flow velocity distribution for different vegetation densities,different flow depth-vegetation height ratios and flow discharge were measured and the vertical distributions of Reynolds stress of the flow were obtained accordingly.The experimental results show that the longitudinal flows in the depth over the vegetation and within the height of vegetation exhibit different hydraulic characteristics.The Reynolds stress of the flow over the vegetation is linearly distributed along the depth,and the distribution of velocity obeys the logarithmic law.Whereas,in the depth within the height of vegetation the longitudinal flow velocity exhibits S type distribution.On the basis of the analysis on the relationship between Reynolds stress and longitudinal flow velocity a theoretical expression for distribution of longitudinal velocity is deduced based on the Prandtle's mixing length theory.The formula is in good agreement with experimental data.