Bedload transport: the effects of particle shape and an investigation of a wide range of transport rates

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Virginia Polytechnic Institute and State University

The effects of particle shape on bedload transport and a wide range of bedload transport rates using both bed subsurface and surface layer based approaches are investigated using fractional transport analysis with a similarity approach. Bedload transport data from a stream containing flat, low density shale particles indicates that the reference transport critical shear stress for the median surface grain size is approximately 2 to 3 times higher than those for more spherical particles. This conclusion indicates a lower susceptibility of disc-like particles to initial entrainment and lower transport rates for given flow conditions than more rounded particles. Analysis of a wide range of transport rates verifies that the slope of the log-log bedload transport rate - bed shear stress relation decreases with increasing transport rate and becomes constant at very high transport rates. This result implies that the dependence of the transport rate on grain size decreases with increasing transport rate. Comparison of bed subsurface and surface layer based bedload transport approaches indicates that the two approaches produce similar transport - shear relations and reference shear stress values.