Suspended sediment concentration within submerged vegetation canopies: An improved method

Aquatic vegetation plays a crucial role in regulating sediment transport and maintaining the stability of aquatic ecosystems. To investigate the turbulence structure and suspended sediment distribution under the influence of natural flexible submerged vegetation, this study selected Vallisneria natans (eelgrass), a representative flexible submerged plant, as the experimental material. Systematic measurements of flow structure and suspended sediment concentration (SSC) were conducted under submerged vegetation conditions. The experimental results demonstrated that the presence of flexible vegetation significantly altered the vertical distribution of flow velocity and turbulence characteristics. Under different vegetation densities, noticeable variations were observed in time-averaged velocity, lateral and vertical Reynolds stresses, and turbulent kinetic energy (TKE), with particularly pronounced changes in the near-bed and canopy regions. Compared to the bare bed condition, SSC in vegetated flows was significantly reduced, and the reduction became more evident with increasing vegetation density. To predict the SSC profiles under flexible vegetation conditions, the vertical distribution of the turbulent diffusion coefficient was calculated. Results showed that the coefficient exhibited a linear distribution within the canopy, reaching a maximum near the canopy top. Based on this distribution pattern, an improved Rouse equation applicable to submerged flexible vegetation conditions was proposed. The modified Rouse model was validated against measured SSC profiles under various vegetation densities and hydraulic conditions, demonstrating its ability to accurately predict the vertical distribution of suspended sediment. This study provides theoretical support for sediment transport modeling, hydrodynamic regulation, and ecological restoration in vegetated riverine and lacustrine environments. It also lays a foundation for advancing the understanding of the coupled interactions among flow, sediment, and vegetation.