HR: 11:20h
AN: H52B-05    [Abstracts]
TI: Hydrodynamic Dispersion in Turbulent Open-Channel Flow Over an Irregular Bed
AU: * Stefan, D
EM: daniela.stefan@vanderbilt.edu
AF: Vanderbilt University, Department of Earth and Environmental Sciences , Nashville, TN 37240, United States
AU: Iobst, B R
EM: benjamin.r.iobst@vanderbilt.edu
AF: Vanderbilt University, Department of Earth and Environmental Sciences , Nashville, TN 37240, United States
AU: Furbish, D J
EM: david.j.furbish@vanderbilt.edu
AF: Vanderbilt University, Department of Earth and Environmental Sciences , Nashville, TN 37240, United States
AB: Characterizing hydrodynamic dispersion in open-channel flow is a key element in environmental studies aimed at modeling the transport and cycling of nutrients and pollutants. We use a simple flow model together with a particle-tracking algorithm to explore first-order influences of bed topography on the hydrodynamic dispersion. The model is based on linearized versions of the shallow-water equations for flow over an irregular bed topography composed of alternate bars. Theoretical dispersion curves were generated by simultaneously releasing tracer particles across the channel at a fixed location and keeping track of their positions for various intervals of time and different channel geometries. Particles were subject to fluctuating motions mimicking effects of turbulence. The shape and length of the tail of the dispersion curve appears to depend primarily on the time elapsed since the particles were released. For short time intervals, the curve is characterized by a steep leading edge which later transforms into a peak with a less steeply sloping front. This transition occurs more rapidly with increasing bar amplitude, and also with increasing number of alternate bars in the section traveled - thus with shorter bar wavelengths. Rhodamine WT was used in a field dye test conducted on a 150 m straight reach of Panther Creek, KY. This section of the creek has an average channel width of 6.3m, and exhibits a loose alternate bar structure with wavelength of ~55 m and amplitude of ~0.1 m. The bed of the channel has an average slope of 0.01 and consists of coarse gravel with a D85 of 6 cm. Consistent with the modeling results, the tracer test revealed a relative steep leading front and slowing decaying tail. In both the simulated and field case, this tail is similar to the behavior predicted by "dead zone" models of dispersion, and is attributable mostly to spatial variations in the local flow (with superimposed fluctuating motions) associated with vertical velocity structure combined with shoaling and deepening over the bed topography.
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
DE: 1847 Modeling
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: 2007 Joint Assembly