A study on the differences of turbulent flow properties along the open channel with submerged rigid vegetation

Submerged rigid vegetation causes uneven vertical distribution and streamwise differences of hydraulic parameters such as time-averaged flow velocity, turbulence intensity, and Reynolds stress by altering the flow structure. ADV is adopted to measure the flow velocity under three submergence ratios of 3.0, 4.0, and 5.0, combined with statistical methods, the differences in velocity and turbulence characteristics within the vegetation section and its upstream and downstream transition sections are systematically analyzed. The results show that vegetation significantly enhances water flow turbulence, and the values of turbulence characteristics are positively correlated with submergence ratios. Within the vegetation segment, the differences in velocity are more significant in the two vertical zones: one is the vegetation layer under low submergence and the other is the free flow layer under high submergence. Furthermore, the values of turbulence characteristics are enhanced along the path, and the vertical distribution has similarity, with the location of maximum point is near the top of the canopy. When the submergence ratio meets the formation and development conditions of KH vortices, the turning point appears gradually in the vertical distribution curves of turbulent characteristics within the vegetation segment, near which the gradient value sharply decreases and approaches 0. In addition, the number of cross sections with turning points increases with submergence ratios increasing. It is verified that this point can serve as the upper boundary point of KH vortices in the fully developed turbulent flow region.