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Tour Stop #7: Experimental Studies of Gravel Transport
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R. A Kuhnle
.

S. J. Bennett
.

V. D'Agostno
University of Padua, Italy

          Movement and deposition of sand and gravel by flowing water reduces the capability of rivers and streams to carry flood water, reduces water storage in lakes and reservoirs, pollutes surface waters, and can cause or increase bank erosion. Despite these problems it is difficult to predict the size and amount of sediment that a given flow of water will move. These problems are compounded when the material on the stream bottom consists of a mixture of sand and gravel.

          The experiments conducted in this flume have concentrated on measuring the rate of transport of sand and gravel for given flow conditions with different mixtures of sand and gravel. In the most recent series of experiments, the sediment transport rate for flows with large non-moving clasts was compared to experiments with comparable flows in which all of the bed material was in transport.

          Experimental results have indicated that the relative amounts of sand and gravel on the stream bottom affect the magnitude of the water flow that will move them. Sand sizes were all entrained over a narrow range of bed shear stress while entrainment of gravel sizes was still a function of grain size. The size of sediment in transport for low flow strengths is nearly all sand, while for high flow strengths the size distribution of the transported sediment equals that of the bed material. Experiments with large non-moving clasts have significantly lower transport rates than for comparable flows in which all of the bed material is in motion.

Key Words:
fsGravel transport, Incipient motion, Bimodal size distributions

Publications:
Kuhnle, R. A. Fractional Transport Rates of Bed Load on Goodwin Creek. In P. Billi, R.D. Hey, C.R. Thorne, and P. Tacconi (eds) Dynamics of Gravel Bed Rivers, J. Wiley and Sons Ltd., Chichester, UK., p. 141-155,1992.

Kuhnle, R. A., Incipient Motion of Sand-Gravel Sediment Mixtures. Journal of Hydraulic Engineering, 11 9(12):1400-1415, 1993.

Kuhnle, R. A., Closure to Incipient Motion of Sand-Gravel Sediment Mixtures. Journal of Hydraulic Engineering, 121(5):448450,1995.