Flow-Vegetation-Sediment Interaction in a Cohesive Compound Channel

The purpose of this study was to quantify how vegetation influences the flow and sediment processes relevant to the design and management of environmental compound channels. Therefore, a two-year field investigation was conducted in a cohesive two-stage channel, focusing on the flow resistance and net deposition in five subreaches with different floodplain vegetation conditions. In the grassy subreaches, the cross-sectional blockage factor was the key vegetation property governing the flow resistance, with a process-based model providing reliable estimates under widely variable hydraulic and vegetative conditions. The net deposition of cohesive sediment was best explained by vegetation height while high stand length and density created supply-limited conditions on the inner floodplain. These results showed that the two-stage approach offers potential for controlling the sediment processes through appropriate vegetation maintenance. The novelty of this research is that straightforward analyses accompanied by a physically-based parameterization of the floodplain plant stands were successfully used to characterize the flow-vegetation-sediment interaction in a practical engineering application. The results are expected to be helpful in designing and managing comparable channels. (C) 2015 American Society of Civil Engineers.