Abstract
The main purpose of this study is to investigate the effects of aquatic plants with no leaves (L0), 4 leaves (L4), 8 leaves (L8), and 12 leaves (L12) on the mean streamwise velocity, turbulence structure, and Manning’s roughness coefficient. The results show that the resistance of submerged aquatic plants to flow velocity is discontinuous between the lower aquatic plant layer and the upper free water layer. This leads to the difference of flow velocity between the upper and lower layers. An increase of the number of leaves leads to an increase in the flow velocity gradient in the upper non-vegetation area and a decrease in the flow velocity in the lower vegetation area. In addition, aquatic plants induce a momentum exchange near the top of the plant and increase the Reynold’s stress and turbulent kinetic energy. However, because of the inhibition of leaf area on the momentum exchange, the Reynold’s stress and turbulent kinetic energy increase first and then decrease with the increase in the number of leaves. Quadrant analysis shows that ejection and sweep play a dominant role in momentum exchange. Aquatic plants can also increase the Reynold’s stress by increasing the ejection and sweep. The Manning’s roughness coefficient increases with the increasing number of leaves.
Highlights
Aquatic plants are an important component of river ecosystems
In different responsenumbers to this of leaves onpurpose the mean streamwise velocity, turbulence structure, roughness need, the main of this study is to study the effects of aquatic plants and with Manning’s different numbers of coefficient
This study investigates the variation in flow characteristics with the number of leaves in an openchannel flume using acoustic Doppler velocimeter (ADV), and some important conclusions can be drawn from this study: (1) The mean streamwise velocity profile in the upper layer obeys the logarithmic distribution law, and the velocity gradient increases with the increasing number of leaves
Summary
Aquatic plants are an important component of river ecosystems They can affect water chemical and physical parameters, but, more importantly, they can change flow velocity and momentum exchange, and affect the transport of pollutants and sediments in rivers [1,2,3,4,5]. The acoustic Doppler velocimeter (ADV) has been widely used in both laboratory and field settings for the measurement of flow velocity [1,3,6]. ADV is based on based on the Doppler effect and can accurately measure the mean velocities and turbulent statistical parameters [7], especially the flow characteristics under the influence of aquatic plants [1,3]. Zhang et al [10]
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