Critical Flow Velocity for Incipient Sediment Motion in Open Channel Flow with Rigid Emergent Vegetation

In vegetated open channel flow, sediment transport is affected by both boundary shear and vegetation-induced turbulence. This study presents a theoretical derivation of the critical flow condition for incipient sediment motion, which is evaluated in the reach scale in the presence of emergent vegetation simulated with cylindrical rods. To take into account the combined effects of both mean flow and turbulence on sediment motion, a spatiotemporal average is applied to the force balance equation. The analysis shows that the critical condition can be formulated in terms of the dependence of the densimetric Froude number on the vegetation concentration for the condition of hydrodynamically rough turbulent flows. The derived theoretical formula is consistent with laboratory measurements reported in previous studies.