Steep slope streams show large fluctuations of sediment discharge acrossseveral time scales. These fluctuations may be inherent to the internaldynamics of the sediment transport process. A probabilistic framework thusseems appropriate to analyze such a process. In this letter, we present anexperimental study of bedload transport over a steep slope flume for small tomoderate Shields numbers. The sampling technique allows the acquisition ofhigh-resolution time series of the solid discharge. The resolved time scalesrange from $10^{-2}$s up to $10^{5}$s. We show that two distinct time scalescan be observed in the probability density function for the waiting timebetween moving particles. We make the point that the separation of time scalesis related to collective dynamics. Proper statistics of a Markov processincluding collective entrainment are derived. The separation of time scales isrecovered theoretically for low entrainment rates.
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