Multi-scale fluctuations of bed load transport rate over steep slope.

The bedload transport rate is of large fluctuation across several time scales. Understanding bedload transport fluctuation would be helpful for modeling the transport process. In this talk, we first report a multi-scale phenomenon of fluctuation of bedload transport rate by an experimental study. Analysis of the experimental results shows that the fluctuations of bedload transport rates decay with the sampling time scales. A clear three-stage scale-dependent decaying process can be found. Then, an expression for the dependence of the fluctuation of bedload transport rates on the sampling time scales is derived from a stochastic theory (Ancey et al., 2008). The expression is consistent with experimental observations demonstrating that the bedload transport rates behave as a homogeneous Piosson process at the small time scales, which is consistent with Einstein’s theory. However, at the media and large time scales, the internal memory of the stochastic sediment dynamics would induce more fluctuations. It is closely related to the collective entrainment mechanism of bedload transport which was newly introduced by Ancey’s theory. Together with the very recent finding by Heyman et al. (2012), our theoretical expressions can calibrate all the necessary parameters in Ancey’s theory by the experimental observation of bedload transport rates.


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