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United States Department of Agriculture

Agricultural Research Service

Title: Coherent Eddy Structures and Suspended Sediment Transport over Fixed Two_dimensional Dunes.

Authors
item Venditti, J - UNIV OF BRITISH COLUMBIA
item Bennett, Sean
item Bauer, B - UNIV OF SO CALIFORNIA LA

Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 1997
Publication Date: N/A

Technical Abstract: Dunes are the most common bed configuration in sand-bedded rivers and are known to play an important role in governing sediment transport rates. The wake developed in the lee of dunes is characterized by highly-turbulent, coherent eddy structures such as 'bursts' or 'ejections', thus transport and diffusion of suspended sediment should be linked to the frequency and size of these structures. This paper reports on a laboratory experiment undertaken to examine these turbulent eddy structures and their effect on suspended sediment transport. Fixed, two-dimensional dunes, 0.6 m long and 0.4 m high with a slip face of 30 degrees, were installed in a 1-m wide flume, and a quasi-equilibrium flow with a mean depth of 0.17 m and a mean velocity of 0.46 m/s was established. Fluid turbulence and suspended sediment concentration were concomitantly monitored using acoustic Doppler and electromagnetic current meters and optical backscatter probes. A dense sampling grid allowed the construction of contour maps of the spatial turbulence structure and sediment transport field. In the turbulent wake, spectral analysis reveals eddy recurrence intervals of 1 to 2 seconds, and the spatial distribution of time-averaged suspended sediment concentration appears to be well-correlated to these macroturbulent events. Although highly variable, time and length scales of the coherent turbulent flow structures are grossly related to height above the bed. The integral scales of the sediment concentration records will be compared to the recurrence periods of eddy structures, thus defining the link between fluid turbulence and suspended sediment flux.

Last Modified: 7/23/2014
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