Effect of tall vegetation on sediment transport by channel flows

Results of an experimental study on sediment transport by channel flows with tall rigid stems are presented. The experiments were conducted for various stem areal densities, channel slopes and sediment sizes with uniformly distributed unsubmerged cylindrical rigid stems forming a regular square staggering pattern in plan. The rates of sediment transport in the presence of simulated vegetated surfaces were observed to be significantly smaller than those without the vegetation. A method is proposed to determine the effective (grain) shear stress in presence of vegetation under the condition that the apparent shear stress is available from easily measurable flow parameters. The present data along with literature data are used for quantification of the reduction in the rate of sediment transport by the rigid tall stems. The grain shear stress rather than the apparent shear stress is observed to better describe the variations in the rate of sediment transport by vegetated flows.