Turbulence and Sediment Deposition in a Channel with Floating Vegetation

Floating canopies of vegetation alter the vertical profile of flow velocity within and below canopies, which in turn impacts sediment deposition below canopies. This study explored the impacts of channel-average velocity (U0), U 0 ), vegetation density (a), a ), and relative flow depth (hg/H, h g / H , where hg g is the height of the free flow region below the floating canopy and H is the entire flow depth) on the longitudinal distributions of near-bed turbulent kinetic energy (TKE) TKE ) and sediment deposition in a channel with a floating vegetation canopy. Below a floating canopy, sediment deposition was correlated with the near-bed TKE. . For the low-density and low-velocity cases, sediment deposition was spatially uniform across the entire channel because the near-bed TKE was lower than the critical value for sediment resuspension. As the vegetation density and channel-average velocity increased, the near-bed TKE increased and surpassed the critical TKE, , which caused resuspension and reduced deposition below the canopy relative to the upstream reference. For the same vegetation density and channel-average velocity, a lower relative flow depth (hg/H) h g / H ) produced a higher below-canopy depth-averaged velocity and near-bed TKE, , resulting in less deposition below the canopy. A model was proposed for predicting the longitudinal evolution of near-bed TKE based on the predicted flow velocity below the canopy throughout the channel. The longitudinal evolution of deposition below a floating canopy was predicted by combining the predicted near-bed TKE with the deposition probability. The predicted near-bed TKE and deposition matched laboratory measurements. Finally, the proposed model can be used to predict the longitudinal profile of deposition below a real Eichhornia crassipes canopy.