Numerical Simulation of Flow and Suspended Sediment Deposition Within and Around a Circular Patch of Vegetation on a Rigid Bed

Flow and sediment transport around the patch of vegetation are closely linked to landform evolution, and the understanding of such processes allows effective river restoration and management. Numerical investigation of flow and suspended sediment (with size, d(s), ranging between 10 and 40 mu m) deposition within and around a circular patch of emergent vegetation was conducted using a two-dimensional model, in which the vegetation was assumed as a porous zone. A von Karman vortex street formed due to the interaction of the separated shear layers at solid volume fraction >= 0.1. As the flow blockage increased, the distance from the back of the patch (where the recirculation and large-scale vortices developed) decreased. The suspended sediment deposition was observed within and downstream of the patch, where the velocity and turbulence were diminished. When the flow blockage was low, deposition in the wake region occurred over a long distance. When the flow blockage was large enough to develop the vortex street, the enhanced deposition occurred in two regions immediately downstream of the patch and within the recirculation zone. For sufficiently high flow blockages, however, the recirculation zone was the only location of enhanced deposition in the wake region. The region of enhanced deposition was observed both in the patch and the wake region as 0.84 <= u(*)/u(*c) (ratio of the friction velocity to the critical friction velocity) <= 1.35, whereas reduced deposition occurred in the wake region as u(*)/u(*c) (associated with sediment size) decreased. The deposited region in the wake region corresponded to the length scale of vortex formation regardless of sediment size.