Bathymetric changes in reaches with emergent vegetation in response to repeated flood flows

Flume experiments were conducted to evaluate the impact of an isolated, emergent vegetation patch on channel bed morphology and adjustment during steady and unsteady flow sequences in which low flows and hydrographs were alternated over sand/gravel and sand/silt beds. In all experiments, vegetation presence enhanced topographic variability at the reach-scale. Vegetation stem density and sediment mixture impacted the processes by which the channel approached a dynamically stable state during unsteady flow sequences. Results indicated a limited subset of patch, sediment, and unsteady flow conditions in which an in-channel emergent vegetation patch enhanced channel bed stability. In all other cases, the highly mobile nature of the transport events inhibited dynamic stability at the reach-scale or significant scour at the patch location occurred, indicating an erosive morphology around the vegetation that could promote erosion of the individual stems or the entire patch.