Sediment deposition in a channel with floating vegetation based on a random displacement model

Abstract

In open channels, floating vegetation canopies (e.g., E. crassipes) reduce the flow velocity within canopies and increase the velocity in the free-flow region below canopies. The variation in the flow structure below the canopies impacts both sediment resuspension and deposition onto the channel bed. Combining the random displacement model with the sediment deposition probability, a new model was proposed for predicting the longitudinal distribution of sediment deposition below floating vegetation canopies. The deposition distributions were measured below floating canopies of model vegetation (rigid cylinders) and real vegetation (E. crassipes). The measurements agreed well with the predictions of the proposed deposition model. With the use of the proposed model, the impacts of floating E. crassipes canopies on the deposition distribution were examined for different upstream mean flow velocities (U₀), relative flow depths (h_g/H), vegetation densities (a) and sediment sizes (d_s). The results suggested that net deposition below floating canopies decreased with increasing U₀ and a and with decreasing h_g/H. Under the same flow and vegetation conditions, smaller sediment particles were more likely to become resuspended, resulting in less net deposition below the floating canopies. These results can improve the fundamental understanding of vegetation-based river management and ecological restoration.