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Title: Sediment-generated noise (SGN): Comparison with physical bedload measurements in a small semi-arid watershed

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

Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/19/2015
Publication Date: 4/19/2015
Citation: Rigby Jr, J.R., Wren, D.G., Kuhnle, R.A., Nichols, M.H., Goodwiller, B.T., Carpenter, W.O., Chambers, J.P. 2015. Sediment-generated noise (SGN): Comparison with physical bedload measurements in a small semi-arid watershed. In: Proceedings of the Federal Interagency Sedimentation Conference. April 19-23, Reno, Nevada. pp. 400-407.

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 gravel-sized particles that are in frequent contact with the stream bed, may be dominated by a few significant storms each year. Measurement of the amount of coarse sediment moving along these streams is difficulty, expensive and often of unknown accuracy. The use of underwater microphones to record and quantify the sound generated by particle impacts along the bed shows great potential for providing a relatively low-cost method of measuring transport in these streams. While the method shows promise 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 small watershed in southeastern Arizona in which the entire sediment load generated during a storm could be captured and measured to compare with underwater sound recorded during the event. The results will be used to calibrate the use of sound equipment for the measurement of stream bedload.

Technical Abstract: Passive acoustic techniques for the measurement of Sediment-Generated Noise (SGN) in gravel-bed rivers present a promising alternative to traditional bedload measurement techniques. Where traditional methods are often prohibitively costly, particularly in labor requirements, and produce point-scale measurements in time and space under highly heterogeneous conditions, acoustic techniques offer the potential to inexpensively monitor gravel movement quasi-continuously over larger spatial scales. While acoustic methods show great potential, significant work is required to provide a general relationship between acoustic signals and physical bedload sampling under field conditions. We addressed this problem by deploying hydrophones for monitoring SGN in the Lucky Hills subwatershed of the USDA-ARS Walnut Gulch Experimental Watershed for the 2014 runoff season (July-September). Bedload was collected using a pit sampler attached to a supercritical Santa Rita-style measuring flume at the catchment outlet. Results of the comparison of physical measurements with SGN monitoring are shown for three runoff events. The field results are compared with expectations derived from theory and laboratory experiments to suggest improvements and new directions for future SGN investigations.