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Title: Measurements of the relationship between turbulence and sediment in suspension over mobile sand dunes in a laboratory flume

item Wren, Daniel
item Kuhnle, Roger

Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2007
Publication Date: 7/28/2007
Citation: Wren, D.G., Kuhnle, R.A., Wilson, C. 2007. Measurements of the relationship between turbulence and sediment in suspension over mobile sand dunes in a laboratory flume. Journal of Geophysical Research. 112:F03009, doi:10.1029/2006JF000683.

Interpretive Summary: Mobile bed features exert a strong influence on the both the flow and sediment transport characteristics of streams and rivers with sand bottoms. In order to accurately model these processes, small scale turbulent events and their connection with sediment particle movement must be more clearly understood. In the current work, a laboratory flume has been utilized to investigate the details of flow and sediment transport over mobile sand dunes. Laser Doppler Velocimetry, a very fast non-intrusive method for measuring water velocity, along with acoustic backscatter techniques, were used to collect data over moving sand dunes.

Technical Abstract: Improved understanding of the relationship between flow and suspended-sediment over dunes is essential for improving the accuracy of sediment transport predictions. In the current work, fluid turbulence data from a Laser Doppler Velocimeter (LDV) and suspended-sediment data from an Acoustic Backscatter System (BSS) were collected from the same sampling volume at a constant position relative to passing sand dunes in a laboratory channel by using a motion control system to track the bedforms over a 1.7 meter test section. A second BSS continually traversed the test section to map the bed profile. This data was correlated in order to link turbulence data with variations in suspended-sediment concentration and position on bedforms. Relative sediment backscatter data was used because of the difficulties associated with the accurate conversion of acoustic backscatter data into absolute suspended-sediment concentration. It was found that Reynolds stress values were not strongly affected by dune size over the scales covered in the experiments. Quadrant 4 events were the most numerous, but there wore more strong quadrant 2 events. Quadrant 2 events were best correlated with changes in suspended-sediment concentration and with cumulative sediment suspension.