Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2005
Publication Date: May 15, 2005
Citation: Wren, D.G., Kuhnle, R.A., Wilson, C.G. Velocity and suspended-sediment measurements over mobile sand dunes in a laboratory flume. Environmental and Water Resources Institute World Congress Proceedings. Available: http://ascelibrary.org/2005conferences/ASCECP000173040792 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 in two sets of experiments with similar flow conditions. Physical samples of the water/sediment mixture were collected to aid in identifying patterns of sediment suspension. The results presented here are preliminary and do not represent the full scope of work or analysis planned for this series of experiments.
Technical Abstract: Knowledge of the flow structure over mobile sand dunes is important for modeling flow resistance and sediment transport in fluvial systems. Many previous studies of flow over dunes in laboratory channels have utilized some type of immobile dunes. In the current work, a Laser Doppler Velocimeter (LDV) and an Acoustic Backscatter System (BSS) were maintained at a fixed point relative to a given dune by using a motion control system to track bedforms over a 1.7 meter test section. A second BSS continually traversed the test section to map the bed profile. Under similar hydraulic conditions, isokinetic samples of the water-sediment mixture were collected simultaneously from 4 depths to assess suspended sediment characteristics and to calibrate acoustic backscatter measurements of concentration. Two different flow stages were used: Fr'0.15 and 0.3. Preliminary results from the velocity and suspended-sediment concentration measurements are reported.