Settling of Fine Sediment in a Channel with Emergent Vegetation

The potential for enhanced removal of sediment from flowing water in a channel by means of settling on vegetation was studied theoretically and experimentally. Settling on vegetation was modeled as a distributed sink of sediment with vegetation spread throughout depth and length of the channel. Sediment-capture experiments were performed in a laboratory channel using model vegetation and well-sorted silt. The theory predicts that settling on vegetation has the potential to increase sediment-capture efficiency considerably, and this was demonstrated in the experiments. The enhancement of sediment removal was greater for artificial vines than for inclined strips. For the runs with flow velocities >10 mm/s the sedimentation efficiency was less than predicted. The reduced efficiency could be related to bed destabilization (which was observed in some runs), re-entrainment from the vegetation, or sediment sliding off the vegetation.