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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #340017
Title: Measurement of gravel bed load using impact plates

Author
item Kuhnle, Roger
item Wren, Daniel
item HILLDALE, ROBERT - Us Bureau Of Reclamation
item GOODWILLER, BRADLEY - University Of Mississippi
item CARPENTER, WAYNE - University Of Mississippi

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2017
Publication Date: 7/8/2017
Citation: Kuhnle, R.A., Wren, D.G., Hilldale, R.C., Goodwiller, B.T., Carpenter, W.O. 2017. Measurement of gravel bed load using impact plates. In Proceedings of Hydraulic Measurements & Experimental Methods Conference, Durham, New Hampshire, July 9-12, 2017. 5 pp.

Interpretive Summary: Knowledge of the rate of sediment being moved in streams and rivers by flowing water is necessary because the sediment may fill reservoirs and reduce their capacity, may fill channels and cause flooding, may degrade water quality, and may cause instability of the channel banks which can cause the destruction of valuable agricultural and other lands. A special case of sediment movement occurs in rivers downstream of dams that have recently been removed. Dams are often removed because of obsolecence of the dam and/or to restore the natural functioning of the stream and allow anadromous fish to migrate upstream of the dam site. Two dams on the Elwha River in the state of Washington were recently removed and the study of the sediment released after removal of the dams by the U. S. Bureau of Reclamation has involved the use of 72 impact plates. In this study a series of experiments were conducted in a model stream channel in the laboratory which had two full scale replicas of the Elwha River impact plates mounted near the downstream end of the channel. The goal of this study was to develop a calibration relation for the impact plates. The existing equipment in the flume allowed the sediment to be measured independently from the impact plates and for calibration relations to be developed. It was found that each sediment grain greater than 5.7 mm in diameter could be accurately recorded and identified as it was transported over the impact plates. The results of this study indicate that accurate quantitative measurement of sediment in rivers in the field using impact plates is reasonable for many streams and rivers.

Technical Abstract: Accurate determinations of the rate of bed load transport are difficult to make but important for determining the fate of sediment released after the removal of a dam. Two dams were removed from the Elwha River in the state of Washington beginning in 2011, and 72 impact plates were installed downstream of the dams to monitor the movement of gravel bed load that had been stored during the nearly 100 years that the dams existed. This study will consider the 25 plates of the 72 which were equipped with accelerometers. Two copies of the Elwha River impact plates were installed in a laboratory flume channel with bed sediment that ranged in diameter from 0.062 to 76 mm. Calibration experiments were conducted over a wide range of flows during which signals from the impact plates were recorded at 50 kHz and all grains were trapped. The mass of the sediment grains was found to be related to the peak amplitude of the signals generated by each grain as it contacted the impact plates. Power functions were found to predict total masses and size distribution for gravel greater than 5.66 mm to within 25% for one plate and to within 14% for the other during the calibration experiments.