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Submitted to: Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 3/17/2016 Publication Date: 7/13/2016 Citation: Kuhnle, R.A., Langendoen, E.J., Wren, D.G. 2016. Prediction of sand transport over immobile gravel from supply limited to capacity conditions. Proceedings of the 8th International Conference on Fluvial Hydraulics. River Flow 2016. July 12-15, 2016 St. Louis, MO. pp. 340-341. 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 is in streams downstream of dams or other impoundments which block nearly all of the sediment moving on the bottom of the stream from upstream. This usually causes the bottom of the stream to become depleted in finer sediment sizes and prevents motion of the accumulated coarser sediment except in all but the largest flows. A stream in which the bottom is made up coarse gravel sediment which seldom moves is said to be armored. Finer sediments, such as sands are introduced to armored streams by tributary streams downstream of the dam or by sand bypassing the dam. The characteristics of the flow and the movement of sand sediment in armored streams has been successfully predicted in previous studies at the National Sedimentation Laboratory. A series of experiments were conducted in a model stream channel in the laboratory to measure and characterize the movement of sand with an immobile gravel bed from supply limited sand to capacity conditions in which the gravel bed was buried with sand. It was found that the movement of the sand from sediment starved to capacity conditions was well predicted by using a modified form of a published sand prediction relation. This relation also provided accurate predictions of previous measurements of sand transport over gravel in other studies. The modified sand transport relation developed in this study will be useful for watershed managers to predict sand movement in streams which have similar characteristics to those used in the experiments. Information of this type is critical for improving sediment prediction and sampling techniques and will lead to advances which will allow agricultural and other watersheds to be managed in a more informed and environmentally sensitive manner. Technical Abstract: Prediction of the transport of sand in channels armored with gravel downstream of dams is difficult but necessary for the range of bed conditions from supply limited to capacity transport. Previous work has shown that information on the mean elevation of the sand relative to the gravel and on the shear stress at the elevation of the sand is needed for a successful prediction of sand transport. Experiments were conducted in a laboratory flume channel with increasing sand elevations to document the transition of sand transport over gravel to a capacity sand bed system. A technique was developed which uses a modified form of a sand transport relation to predict the transport of sand in channels with sand coverage ranging from gravel dominated through sand dominated channels. |
