To understand the influence of aquatic vegetation on flow structures and sediment deposition, field experiments were conducted in a floodplain with water movement dominated by unidirectional current. Flow velocity, suspended sediment concentration, and sediment deposition were measured within and without vegetation at four sites covered by Phragmites communis (reed), Artemisia selengensis, Carex cinerascens, and a mix of them. Results show that the presence of vegetation reduced the time-averaged velocity and turbulent kinetic energy (TKE) and altered vertical distributions of the time-averaged velocity and TKE. For emergent conditions, both the time-averaged velocity and the TKE were uniformly distributed through the entire water column. Two layers were separated at the top of vegetation for submerged conditions. Within vegetation both the time-averaged velocity and TKE were decreased and uniformly distributed, similar to observations under emergent conditions. The discontinuity of drag force at the top of vegetation generated a region with rapidly increased velocity near the vegetation interface. TKE reached its maximum near the top of vegetation and decreased gradually toward both bed bottom and water surface. In present study, canopy with larger frontal area caused bigger reduction of time-averaged velocity and TKE within vegetation. By reducing the mean and turbulent velocities, the presence of vegetation decreased the depth-averaged suspended sediment concentration by 30-50% and increased the thickness of sediment deposited over one flood season by as high as 190% when compared with bare bed.
JOURNAL OF HYDROLOGY 卷: 584 文献号: 124644 出版年: 2020