Laboratory investigation on flow structure and turbulent characteristics in low sinuous compound channels with vegetated floodplains

The flow-vegetation interactions and management of floodplain vegetation can be helpful for morphological stability and ecological maintenance of the rivers. Experiments were conducted in a fluvial hydro-ecological laboratory to study the hydrodynamic behavior of the compound meandering channel of low sinuosity with different layouts of flexible vegetation on floodplain. The presence of high density of floodplain vegetation resulted in increase of streamwise velocity up to 23% in main channel as compared to other vegetation layouts. The floodplain vegetation enhanced the streamwise velocities along the curvature, but the magnitude of the increase was dependent on the flow depth. The shear layer at the interface of the vegetated floodplain is expanding laterally towards the main channel with varying vegetation density. At the channel-floodplain interface, the velocity gradient in the lateral direction increases with increasing vegetation density, generating a strong shear layer at that position. The turbulent structures near the channel-floodplain interface are observed to increase with increasing vegetation density. This resulted in an increase in turbulence parameters such as turbulence intensity, Reynold's shear stresses and turbulent kinetic energy showing its peak near the inner bank. The variability of flow angle at apex, bend and crossover region is observed to be less dominant in emergent conditions than vegetation configurations in submerged conditions. These findings provide insights of the shear layer dynamics and other turbulent structures in a low sinuous channel with the effect of floodplain vegetation.