Submitted to: Proceedings of Sediment Monitoring Instrument and Analysis Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: 2/11/2004
Publication Date: 5/1/2005
Citation: Wren, D.G., Kuhnle, R.A., Chambers, J.P. 2005. Measurement of suspended-sediment concentration and particle-size in laboratory flumes. In: Gray, J.R. (Ed.), Proceedings of the Federal Interagency Sediment Monitoring Instrument and Analysis Research Workshop, September 9-11, 2003, Flagstaff, AZ, U.S. Geological Survey Circular 1276, Appendix 4. Interpretive Summary: Knowledge of the amount of sediment moved by streams is poorly known. Yet this information is necessary to determine the net erosion of the land surface upstream from the measurement point. Excessive erosion of the land surface can cause the destruction of valuable agricultural and other lands. Much of the sediment carried by streams is located in the water column above the bottom of the stream. Because of large variations in the amount of sediment in the water column, accurate measurement of sediment movement rates are very difficult and expensive to make. One technique to measure the amount of sediment being moved in the water column consists of recording the echos of sound waves (acoustic backscattering) that are propagated through the water. This research focused on determining the effect of the size of the sediment on the level of echo return. The use of acoustic backscattering to determine the amount of sediment in the water column has the potential to improve the coverage of sediment movement information and reduce the costs of obtaining it. Improved information on sediment movement is required to allow land managers to effectively manage agricultural and other watersheds for sustained production in an environmentally responsible manner.
Technical Abstract: Acoustic techniques have been used successfully to measure suspended sediments in marine environments, but more research is needed for effective acoustic measurements in fluvial environments. The high concentrations and wide size distributions of suspended-sediment in fluvial systems present difficult challenges. Multi-frequency particle sizing is necessary before a reliable instrument with no particle size bias can be fielded. Experiments have been under way with the goal of improved hardware and software for acoustic sediment measurement and particle sizing. Time series of backscatter data 1.8 hours long were collected from a fixed position. Cross-sectional suspended-sediment concentration variation was measured acoustically by repeatedly traversing a transducer across a laboratory flume, producing cross-sectional data at discrete time intervals. Multi-frequency acoustic techniques were used to size suspended -sand particles in a specialized jet tank.