HR: 16:20h
AN: H14B-02    [Abstracts]
TI: Turbulent Coherent Flow Structures In Gravel-Bed Rivers: An Approach Combining Flow Visualisation And Velocity Measurements
AU: * Roy, A G
EM: andre.roy@umontreal.ca
AF: Universite de Montreal, Departement de geographie C.P. 6128, Succ. Centre-Ville, Montreal, QC H3C 3J7, Canada
AU: Marquis, G
EM: ge.marquis@gmail.com
AF: Universite de Montreal, Departement de geographie C.P. 6128, Succ. Centre-Ville, Montreal, QC H3C 3J7, Canada
AU: Lacey, J R
EM: jay.lacey@umontreal.ca
AF: Universite de Montreal, Departement de geographie C.P. 6128, Succ. Centre-Ville, Montreal, QC H3C 3J7, Canada
AB: There is compelling evidence showing that flow turbulence in gravel-bed rivers is dominated by large-scale flow structures that are elongated and that occupy the entire depth of the flow. These structures scale with flow depth (Y) and their length is between 2 to 6Y. There are many questions concerning the origin, scales and dynamics of these coherent flow structures. Recent progress in answering these questions has been achieved through a combination of approaches that uses the field as a laboratory. Experimental designs relying on data derived from flow visualisation and from records of various lengths and resolutions of single and multiple point velocity measurements have been used to obtain pictures of the space-time dynamics of turbulent processes in rivers. In this paper, we present results from a range of experiments conducted in situ in gravel-bed rivers and highlight the relative contribution of various techniques and methods to our understanding of turbulence in gravel-bed rivers. Five main results are emphasised: 1. the frequency-magnitude scalings of the turbulent flow structures in the boundary layer which exhibit very robust relations over a range of conditions; 2. the relative role of mean flow velocity and depth on the dynamics of ejections; 3. the imbrication of intermittent sweeps and ejections into self- similar large scale flow pulsations; 4. the very local effects of a pebble cluster on the structure of the turbulent boundary layer and 5. the presence of a double shedding frequency of turbulent structures behind protuberant obstacles into the ambient flow. Even though there are limitations to the approach combining flow visualisation and velocity measurements (e.g. quantifying vorticity), the evidence provided by these methods encompasses a range of scales, bed roughness and forms in an general view of turbulent flows in rivers.
DE: 1856 River channels (0483, 0744)
DE: 1860 Streamflow
DE: 1872 Time series analysis (3270, 4277, 4475)
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting