Abstract
Floating vegetation islands (FVIs) have been widely utilized in various river ecological restoration projects due to their ability to purify pollutants. FVIs float at the surface of shallow pools with their roots unanchored in the sediment. Biofilm formed by roots under islands filters nutrients and particles in the water flowing through it. Flow field disturbance will occur, and transverse distribution of flow velocity will change due to the existence of FVIs. Transport efficiency of suspended solids, nutrients, and pollutants will also be altered. A modified analytical model that considers the effects of boundary friction, drag force of vegetation, transverse shear turbulence, and secondary flow is established to model the transverse distributions of depth-averaged streamwise velocity for the open-channel flow with FVIs using the Shiono and Knight Method. The simulation results with suitable boundary conditions successfully modeled the lateral profile of the depth-averaged streamwise velocity compared with the experimental results of symmetrical and unsymmetrical arrangements of FVIs. Hence, the presented model is of guiding significance to investigate the flow characteristics of rivers with FVIs.
Highlights
Floating vegetation islands (FVIs) are widely used in river ecosystem recovery projects due to their satisfactory pollutant purification ability
The water depth is adjusted using a tailgate with the discharge regulated by an electromagnetic flowmeter installed upstream of the channel, and the point velocity is measured with a SonTek 3D Acoustic Doppler Velocimeter (ADV)
The channel cross section is subdivided into different subregions and suitable secondary flow coefficients are applied to each subregion using Eqs. (12)–(15) to establish the lateral distribution model of
Summary
Floating vegetation islands (FVIs) are widely used in river ecosystem recovery projects due to their satisfactory pollutant purification ability. The transverse distribution of the streamwise velocity in the open channel with FVIs can be acquired according to the depth-averaged Navier–Stokes (N–S). The majority of studies on the transverse distribution of the streamwise velocity in the channel have focused on the flow through submerged and emergent canopies, typically introduced the term of vegetation drag force into the N–S equation while considering the effect of the canopy, and applied different methods to improve the model. Studies concentrating on the transverse distribution of the depth-averaged streamwise velocity of the open-channel flow with FVIs are limited. (Shiono and Knight 1991) and secondary flow theory (Ervine et al 2000) for predicting the transverse distribution of the depth-averaged streamwise velocity in the open channel with.
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