HR: 17:00h
AN: H44B-05    [Abstracts]
TI: The effects of emergent vegetation on sediment transport and channel morphology
AU: * Yager, E M
EM: eyager@uidaho.edu
AF: Center for Ecohydraulics Research, Department of Civil Engineering, University of Idaho, Boise, ID 83702,
AU: Schmeeckle, M W
EM: mark.schmeeckle@asu.edu
AF: School of Geographical Sciences, Arizona State University, Tempe, AZ 85287,
AB: Riparian vegetation in rivers and on channel banks can significantly influence flow, sedimentation and channel width. For example, emergent vegetation on banks will locally increase drag and sediment deposition, which may cause the channel to narrow. Alternatively, depending on the location, size, and density of vegetation within a channel, it may enhance local and lateral channel erosion. Current models cannot accurately predict sediment transport rates through fields of emergent vegetation. We conducted a set of flume experiments to gain a mechanistic understanding of the influence of vegetation on flow and sediment transport. In our experiments, sand was transported through regular arrays of cylinders for a range of cylinder densities and flow discharges. We measured the velocity field using particle imaging velocimetry (PIV) and the spatial variations in the sediment transport rates using a high-speed video camera. For a given flow velocity, an increase in cylinder density (by area) augmented the reach-averaged drag, local near-bed turbulence intensities and spatial variability in the shear stress. We incorporated these three effects into a sediment transport equation and tested a number of transport equations using our experimental data. Except for our sediment transport equation, all of the equations predicted sediment fluxes that differed from the measured values by several orders of magnitude. Sediment transport equations that account for vegetation drag but only use the reach-averaged shear stress significantly under-predicted sediment transport. Such equations do not capture the nonlinear variability in sediment flux with spatial variations in boundary shear stress. Thus, the effects of turbulence and spatial variability in the flow must be included in sediment transport predictions through vegetation. We combine our sediment transport equation with a two-dimensional flow model to predict the effects of vegetation on erosion and deposition in natural river channels. Such predictions are used to understand the effects of vegetation on channel morphology and the evolution of channel width.
DE: 1820 Floodplain dynamics
DE: 1825 Geomorphology: fluvial (1625)
DE: 1847 Modeling
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting