Bedload transport through emergent vegetation: current status and its future prospect

Vegetation present in the water streams, on the banks and in the floodplain areas largely affects the river hydraulics. Indeed, river vegetation significantly influences hydrodynamics, sediment transport, bedforms, and pollutant transport. Environmental management of rivers requires an understanding of the various processes and predictive capabilities of models. In the past, many studies were conducted, especially in laboratory settings, in order to quantify flow resistance due to vegetation. It is only recently that the effects of vegetation on sediment transport came to the attention of researchers. In particular, both suspended and bedload transport were considered. This paper reviews recent works conducted on the effect of vegetation on incipient sediment motion and bedload transport. With regard to the incipient sediment motion, methods based on critical velocity, turbulence, vegetation drag, and velocity in the bed roughness boundary layer have been discussed. For bedload transport, methods based on bed shear stress, turbulent kinetic energy, a revisiting of classical formulas for estimating bedload transport in non-vegetated channels, and estimation from erosion around a single vegetation stem are analyzed. Finally, indications on further research and new development are provided.