Aquatic vegetation

as a key part of open-channel and lake ecosystems

plays critical ecological roles. It impacts flow turbulence and sediment suspension in a water body

thereby altering its turbidity—a basic indicator of aquatic ecosystem health. However

the mechanism of turbidity altered by natural aquatic vegetation remains complicated. This study conducts a flume experiment using Vallisneria natans arranged in a rectangular pattern

to observe vertical variations in the flow velocity and sediment concentration of water flows under different flowrates and densities of natural flexible submerged vegetation. Analysis on the measured vertical profiles shows the morphology of flexible vegetation markedly alters the flow velocity pattern and turbulence structure. Under different vegetation densities

the time-averaged velocity

lateral and vertical Reynolds stresses

and turbulent kinetic energy all vary significantly

particularly in the near-bed and canopy layers. A turning point of the mean velocity profile occurs at the canopy top; similar vertical patterns are observed in turbulent kinetic energy and Reynolds stresses

with the maximum values located near the top of the vegetation canopy. Compared with the flow on a bare bed

suspended sediment concentration is reduced significantly in the vegetation condition

and decreases further with the vegetation density increasing. Flow rate and density conditions impact the canopy layer remarkably. Thus

we demonstrate that the primary reason for the reduction of suspended sediment in the flow on a submerged vegetation riverbed is that vegetation lowers the time-averaged flow velocity within the canopy and thereby suppresses sediment suspension.