Transverse distribution of the streamwise velocity for the open-channel flow with floating vegetated islands

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 effects of boundary friction, drag force of vegetation, transverse shear turbulence, and secondary flow is established to predict transverse variation of depth-averaged streamwise velocity for the open-channel flow with FVIs using Shiono and Knight method. The simulation results with suitable boundary conditions successfully predicted lateral profile of the depth-averaged streamwise velocity compared with the experimental results of symmetrical and unsymmetrical arrangements of FVIs. Hence, the presented model can provide guidance for investigating flow characteristics of rivers with FVIs.

An analytical model for transverse velocity distributions of overbank flows with submerged and emergent vegetated floodplains

“…The $$$ \overline{\varepsilon_a} $$$ of the proposed model was within ±0.005 m/s for all cases; meanwhile, the maximum $$$ \overline{\varepsilon_a} $$$ was as high as 0.021 m/s in the previous models. The $$$ \overline{\varepsilon_r} $$$ of the proposed model was less than 7% (5%) in 8 (Fu et al, 2021) cases. However, in previous models, the $$$ \overline{\varepsilon_r} $$$ value was more than 5% (except for cases Run05 and Run06), and its values in case Run04 peaked at 12.16%.…”

“…In addition, the simulated U d exceeds that of the measured data in both our model and a previous SKM model when the secondary current is neglected (Figure 8a–d). Over‐prediction without considering secondary currents is well known in previous modified SKM models (e.g., Fu et al, 2021; Liu, Luo, Liu, & Yang, 2013; Tang & Knight, 2009b). The same mechanism was also observed in our model.…”

“…Despite their contributions towards reproducing and forecasting the vegetated overbank flow, all of these models incorporate a large number of complex calculations to solve the Navier–Stokes equation. Recently, several researchers have developed analytical models for both emergent and submerged rigid vegetation (Fu et al, 2021; Huai et al, 2009; Huthoff et al, 2007; Konings et al, 2013; Shi et al, 2019; Tang, 2019; Tinoco et al, 2015; Wang et al, 2019; Yan et al, 2022; Yang et al, 2020); these can effectively estimate overbank flow characteristics in a simple manner.…”

“…The change in λ value has almost no influence on the simulation accuracy, except near the sidewall. This is consistent with previous models that consider the dimensionless eddy viscosity as a constant (e.g.,Fu et al, 2021;.4.3.5 | Contribution of each hydrodynamic mechanism for U d U d is not sensitive to variations in vegetation porosity θ. Therefore, the contribution of θ for U d is not discussed.…”

Dip-phenomenon and analytical model for velocity profile in open-channel bends

“…Accurate predictions of the profile of velocity are essential to problems related to the dispersion of nutrients and mixing processes of pollutants as well as the transport of sediments (Termini and Moramarco 2020;Fu et al 2021). Due to its practical implications, the velocity distribution of openchannel flows has interested engineers and researchers for many years (Stearns 1883;Nikuradse 1950;Coles 1956;Yang et al 2004;Guo 2008;Mahananda et al 2019).…”