Wave and vegetation effects on flow and suspended sediment characteristics: A flume study

- Flume experiments using real vegetation (Scirpus Mariqueter) and suspended sediment under current-wave condition were performed.
- The combination of wave and vegetation greatly increase the turbulence intensity, and the velocity changes mostly above the top of the canopy.
- The wave attenuation rate and the drag coefficient CD have been investigated.
- Waves increase the capacity of sediment-carrying compared to current-only flows.

Vegetation in tidal flats can alter flow dynamics by increasing the velocity gradient and attenuating the wave energy. In this study, a flume experiment was performed using the pioneer plant Scirpus mariqueter and suspended sediment. Two cases are analysed: current-only and current-wave conditions with a regular wave. A statistical method is used to analyse the average velocity and the turbulence intensity. Results demonstrate that the plants can cause a velocity decrease in the vegetation region and an increase in the turbulence intensity below the top of the canopy. The combined effect of waves and vegetation on turbulence dramatically increases the flow velocity above the average water depth as well as the turbulence intensity profiles. In this study, the attenuation efficiency of the wave height is 0.0448 m-1, which is identical to results using artificial plants with the same relative submerged depth. The drag force in current-wave conditions is almost twice of that observed in current-only conditions. The spectral analysis shows that only waves can influence high-frequency motion. In addition, an increase is observed in the bottom shear stress, mean grain size, and suspended concentration of the sediment during current-wave conditions.

The relationship between Reynolds number and the period-averaged drag force coefficients, including the experimental results from literature.136