Modeling streamwise velocity and boundary shear stress of vegetation-covered flow

Suspended vegetation floating in open channel alters the flow structure and generates vertically asymmetric flow because of the different roughnesses of the river bed and vegetation cover. Moreover, its typical profile of streamwise velocity can be used for a rough estimation of the fate of solute transportation. In this study, a two-power law expression was adopted to predict the vertical profile of streamwise velocity. The influence of roughness of the floating vegetation patches and channel bed was also analyzed. To verify the model, the vertical distribution of longitudinal velocity and shear stress of a vegetation covered flow was investigated by laboratory measurements. Results showed that the location of the maximum streamwise velocity was close to the smooth boundary (i.e., the vegetation cover). The vertical profile of shear stress indicated that the turbulent structure was intensively influenced by the presence of vegetation cover and its roughness characteristics. In addition, the turbulence intensity values were amplified in the vicinity of simulated vegetation cover but reduced near the channel bed. The location of the maximum values of shear stress was close to the vegetation cover. The large values of shear stress near the vegetation canopy indicate the high turbulent levels because of the perturbation resulting from vegetation drag and the canopy gap.