Experimental study of the impact of the floating-vegetation island on mean and turbulence structure

The floating-vegetation island (FVI) is widely used in river restoration projects for its decontamination effect for the pollutants. A physical experiment is conducted in this paper to study the flow regime near the FVI to better understand the role played by the FVI in the river systems. According to the observed data concerning the mean and turbulent flow characteristics, the flow field can be subdivided into four regions: the incoming flow adjustment region, the initial adjustment region, the shear layer developing region and the fully developed region. The variation of the velocity profile can be described as follows: a “J” shape in the incoming flow adjustment region evolves to an “S” shape in the shear layer developing and fully developed regions. The velocity in the interface between the canopy and the flow in the fully developed region obeys the rule of a mixing layer theory. Based on the experiment data, a three-layer model for estimating the vertical velocity distribution in the fully developed region is established and it performs well as compared with the laboratory findings.