Modeling of velocity and shear stress profiles in the ecological channel with floating vegetation

Abstract

Floating vegetation occurs in various environments, such as artificial floating islands, wetlands, river courses, and lakes, which constitute an important part of the river landscape and ecological restoration. The vertical distribution of the streamwise velocity of the channel flow with floating vegetation is of the utmost importance, and therefore, it is the basis for research on bed erosion and pollutant transport. Laboratory experiments on an open-channel flow covered by floating vegetation with unanchored roots have shown a two-layer structure of the velocity profile and a rapid decrease in the Reynolds stress across the interface in the vegetation layer but gradual in the non-vegetation layer. The flow was divided into four subzones in a vertical direction according to the organized flow structure in the experiment as follows: (I) the uniform region deep within the non-vegetation layer, (II) the outer region in the non-vegetation layer, (III) the inner region in the vegetation layer, and (IV) the uniform region deep within the vegetation layer. An analytical model based on the momentum balance in each subzone was developed to predict the profiles of velocity and Reynolds stress. The predictions from analytical models agree well with those from laboratory studies of floating vegetation and lay the theoretical foundation for future studies on water eutrophication and the transport of pollutants, sediments, and algae.

Keywords: A two-layer structure; Analytical model; Floating vegetation; Momentum balance; Reynolds stress profiles; The vertical distribution of the streamwise velocity.