  Steep slope streams show large fluctuations of sediment discharge across
several time scales. These fluctuations may be inherent to the internal
dynamics of the sediment transport process. A probabilistic framework thus
seems appropriate to analyze such a process. In this letter, we present an
experimental study of bedload transport over a steep slope flume for small to
moderate Shields numbers. The sampling technique allows the acquisition of
high-resolution time series of the solid discharge. The resolved time scales
range from $10^{-2}$s up to $10^{5}$s. We show that two distinct time scales
can be observed in the probability density function for the waiting time
between moving particles. We make the point that the separation of time scales
is related to collective dynamics. Proper statistics of a Markov process
including collective entrainment are derived. The separation of time scales is
recovered theoretically for low entrainment rates.
