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Title: Sediment-generated noise (SGN): Laboratory determination of measurement volume

item Wren, Daniel
item GOODWILLER, BRADLEY - University Of Mississippi
item Rigby Jr, James
item CARPENTER, WAYNE - University Of Mississippi
item Kuhnle, Roger
item CHAMBERS, JAMES - University Of Mississippi

Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: 4/19/2015
Publication Date: 4/19/2015
Citation: Wren, D.G., Goodwiller, B., Rigby Jr, J.R., Carpenter, W.O., Kuhnle, R.A., Chambers, J.P. 2015. Sediment-generated noise (SGN): Laboratory determination of measurement volume. Joint Federal Interagency Sedimentation and Hydrologic Modeling Proceedings, april 19-23, Reno Nevada. pp. 408-413.

Interpretive Summary: Sediment measurements are important for many areas of stream and river management, such as detecting changes in watershed erosion and evaluating the effects of mitigation efforts. In many streams, bed load transport, which is comprised of coarse particles that are in frequent contact with the stream bed, may be dominated by a few significant storms each year. These flood events are hard to predict and frequently occur at night, making it difficult and expensive to collect physical sediment samples. Instrumentation can alleviate the need to have personnel at field sites during dangerous conditions and at inconvenient times. Using hydrophones to record the sound made when rocks in the stream contact one another and the stream bed has the potential to provide a low cost method for monitoring coarse bed load in streams; however, there is still a need to further develop our understanding of the acoustic properties of stream channels so that a general calibration methodology can be found. This extended abstract briefly describes a series of measurements that were taken in a laboratory for the purpose of determining how the magnitude of sound decreases with increasing distance from the source of the sound. The results will be used to find out the size of the area that a hydrophone can receive sound from.

Technical Abstract: Passive acoustic technology has the potential to allow continuous measurement of bedload moving through streams by recording Sediment-Generated Noise (SGN) from interactions between coarse bedload particles. The technology is relatively economical and is amenable to automated operation. While the magnitude of recorded sound has been shown to be well-correlated with bedload transport, substantial work is still needed before the technique is ready for wide-spread deployment. A key need for its advancement is a quantitative understanding of the measurement volume from which sounds are received so that field sites may be properly instrumented and data properly analyzed to estimate bed material flux. The propagation of sound in an acoustic waveguide, limited propagation of lower frequencies in shallow streams, and the effect of bed roughness on sound propagation are examples of specific areas that require new laboratory data to address. Towards this end, a series of experiments was initiated, in collaboration with the University of Mississippi National Center for Physical Acoustics, in a flume at the National Sedimentation Laboratory in Oxford, Mississippi. The results of sound propagation testing in an empty tank, over a gravel bed, and over a cobble will be presented, along with a relationship for determining transmission loss over the different bed types.