Author
|
Submitted to: Journal of Hydro-environment Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/17/2013 Publication Date: 6/1/2014 Citation: Wren, D.G., Langendoen, E.J., Kuhnle, R.A. 2014. A note on acoustic measurements of turbulence, suspended sediment, and bed forms in mobile bed experiments. Journal of Hydro-environment Research. 8:(2)164-173. Interpretive Summary: Observations of rivers and streams have led to many advances in the field of fluvial hydraulics. Studying real systems can reduce issues with scaling and oversimplification, but there are many drawbacks to making hydraulic measurements under field conditions. Unsteady flows, harsh environmental conditions, potential damage to expensive instrumentation, difficulty in mounting instruments, lack of access to electricity, and uncertainty in instrument position are just a few of the reasons why so many in-depth investigations into flow and sediment transport are performed in hydraulic laboratories. An additional difficulty in using field observations for research is in formulating general conclusions based on channel reaches, which may have unique characteristics that make comparison with other locations challenging. A major difficulty in hydraulic experimentation is designing experiments that are complex enough to capture physical processes while keeping the experiment simple enough for useful, accurate measurements. The complex nature of water flow and sediment transport makes detailed measurements of small-scale processes necessary to advance the knowledge of these systems. When the environmental uncertainties of working in field conditions are added to the unsteady, non-uniform conditions often present in channels, the necessity of laboratory channel-based experiments becomes evident. Three important types of data needed for mobile-bed hydraulic experiments are turbulence, sediment transport, and bed topography. Collecting these data in mobile-bed experiments presents unique challenges. Successful strategies for each of the three areas are discussed, based on the authors’ experience and the literature. Technical Abstract: One of the challenges of hydraulic experimentation is designing experiments that are complex enough to capture relevant processes while retaining the simplicity necessary for useful, accurate measurements. The intricacy of the interactions between turbulent flows and mobile beds in rivers and streams makes the task of identifying governing mechanisms challenging. Detailed measurements of small-scale processes are necessary to advance the science of fluvial hydraulics. When the environmental uncertainties of working in field conditions are added to the unsteady, non-uniform conditions often present in channels, the necessity of laboratory channel-based experiments becomes evident. Three important types of data needed for mobile-bed hydraulic experiments are turbulence, sediment transport, and bed topography. Collecting these data in mobile-bed experiments presents unique challenges. Successful strategies for each of the three areas are discussed, based on the authors’ experience and the literature. Examples of processed acoustic backscatter and acoustic Doppler velocimeter data are shown. In the bed topography section, semivariogram analysis is applied to synthetic data and to sand elevation data collected in a flume at the National Sedimentaton Laboratory or four bed configurations: dunes at Fr=0.34, dunes at Fr=0.48, ripples, and upper stage plane bed. |
