Using Floating Vegetation to Control Transport Processes in Streams.

Abstract Submission: Patches of floating vegetation change the hydrodynamic field through and past the submerged plants’ biomass. Physical properties of submerged branches, leaves, and/or roots determine the changes in mean velocities, stresses, and turbulent features of the flow. The size, relative submergence, rigidity, and area obstructed by plant material can create regions of relatively high speed near the bed and low-speed recirculation areas through the plants. We conducted a series of laboratory experiments on a recirculating racetrack flume to characterize the effects of floating vegetation patches on two fundamental transport processes in streams: a) changes in erosion and deposition patterns on a mobile bed below the patches, and b) the transport of downstream drifting near-neutrally buoyant particles through the floating patches. By testing different vegetation types under a wide range of velocities and water depths, we identify trends in transport of drifting particles based on both the velocity differential between the lower and upper layers created by the plants, and the turbulent eddies at the canopy- and stem-scale. Enhanced near-bed velocities and turbulence for denser, highly submersed roots, locally increase sediment motion, resulting in potential downstream accumulation at the trailing edge of the patch. The results provide new insights for the design of nature-based infrastructure for river management and restoration, such as floating wetlands for the control of sediment and the creation of habitat for particular species.

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