Study of Suspended Sediment Diffusion Coefficients in Submerged Vegetation Flow

Abstract

The traditional profile model of the sediment diffusion coefficient (εs ${\varepsilon }_{s}$), which is parabolic along the water depth, cannot precisely predict the vertical distribution of εs ${\varepsilon }_{s}$ in vegetated flow. Therefore, in this study, a series of flume experiments were conducted to clarify the influence of submerged vegetation on the diffusion characteristics of suspended load particles. First, the submerged canopy increases the efficiency of momentum exchange but restrains the vertical diffusion of suspended sediment, indicating that the presence of submerged plants promotes the siltation of solid particles. Second, the depth‐averaged sediment diffusion coefficient (εstrue¯ $\bar{{\varepsilon }_{s}}$) monotonically decreases with increasing relative water depth, while the depth‐averaged momentum exchange coefficient (εmtrue¯ $\bar{{\varepsilon }_{m}}$) presents two opposite trends, likely owing to the dominant turbulence event changing from ejections to sweeps and the different variation tendencies of the velocity gradient and Reynolds shear stress with increasing vegetation density. Compared with the ratio (β $\beta $) of εs ${\varepsilon }_{s}$ to the momentum exchange coefficient in nonvegetated flow, β $\beta $ in submerged canopy flow is significantly less than 1, which means that the solid particles diffuse less readily than liquid particles because of the stem‐scale vortices generated by the vegetation. In addition, vertical profile models of εs ${\varepsilon }_{s}$ and suspended sediment concentration were proposed and validated by experimental data. The models exhibit a high accuracy, correlation and applicability and can provide critical information to promote research on riverbed deformation and nutrient dynamics in vegetated rivers, wetlands and estuaries.

A Study on the Influence of Submergence Ratio on the Transport of Suspended Sediment in a Partially Vegetated Channel Flow

“…(2022) and the present simulation results is clearly because the inlet averaged velocity of D. Li et al. (2022) is smaller than present cases and the particle diameter of Li is bigger than the present case. The other cases listed in Table 2 are used in the following discussion section.…”

“…Panel (d) is the normalized concentration profiles from D. Li et al. (2022) and the present simulation results under SRs around 20%.…”

“…Note that Xue's model is an a priori estimation to design reasonable and feasible simulation conditions. Then, after the simulations were achieved we obtain more information about the flow field and Xue's model is used again to test the reasonability of the simulation results, even though the authors have validated the simulation results by comparing the experimental results from Lu (2008) and D. Li et al (2022). The utilization of the Xue's model is given below.…”

“…The first is the lack of the experimentally measured data to validate the simulation results directly. In order to improve the reliability of the present simulation results, similar experimental results and concentration profiles in submerged vegetated channel flow from Lu (2008) and D. Li et al (2022) were added as a part of the validation and an additional data was set to discuss the influence of SR on the vertical concentration profiles. In future, corresponding experiments are still needed to validate some aspects of conclusion of the present work, like the high variance of PDF of the particles in the spanwise mixing layers.…”

“…Due to lack of experimental measured data of the precise present numerical simulations flow conditions, the current numerical simulation approach is validated by comparing with similar experimental results from Lu (2008) and D. Li et al (2022). Lu (2008) and D. Li et al (2022) conducted suspended sediment transport studies in laboratory channels fully covered by submerged rigid vegetation with SR ranges from 20% to 50%. The detailed experimental parameters are listed in Table 2.…”