Impact of emergent vegetation on three-dimensional turbulent flow properties and bed morphology in a partially vegetated channel

Abstract

The study aimed to explore three-dimensional turbulent flow properties and bed morphology in a partially vegetated channel with sand bed conditions. Presence of flexible vegetation in the river and its interaction with the flow are of great significance in understanding the momentum and mass transport in the flow. Experiments were conducted in a straight, tilting rectangular flume with staggered emergent vegetation covering half of the channel width. The results show that the presence of vegetation diverts streamwise velocity from the vegetated side to the non-vegetated side. The study reveals that the presence of vegetation leads to an increase in turbulent intensity, turbulent kinetic energy, and Reynolds shear stress at the transition area between the vegetated and non-vegetated sides of the channel. This increase is attributed to higher transverse flow and momentum exchange in the transition area between the vegetated and non-vegetated sides. In the vegetated side, the vegetation serves as an obstruction, reducing turbulent intensity, turbulent kinetic energy, and Reynolds shear stress compared to the transition area between the vegetated and non-vegetated sides. This reduction in turbulence supports the stability of bed materials and promotes sediment deposition. The presence of vegetation significantly alters the secondary current in the channel. Scour depth along the non-vegetated side was higher than the vegetated side, mainly because the flow concentrated in the centre and non-vegetated side of the channel. The investigation determines that the existence of vegetation on the vegetated side effectively protects against bed erosion and sediment transport. Understanding the impact of emergent flexible vegetation on flow properties and sediment transport can inform decisions about vegetation layouts in river ecosystems.