Author(s): No S.

Linked Author(s):

Keywords: Gravel Bed River; Grain Sorting; Bed Load; Experiments

Abstract: The purpose of this research was to investigate the effects of grain sorting on bed load. Flume experiments were performed over graded sediment, for long durations, and a Wide range of flow conditions. No equilibrium slope was obtained Whatever the run and the experiment duration (up to more than 60 hours). Instead a periodic pattern fluctuation was observed, affecting the bed slope, the bed state (varying from armor to fined bed) and the bedload discharge. Two kinds of fluctuations were observed: short (length and time) fluctuations associated with the passage of bedload sheet (local bed slope changes) and large fluctuations associated with overall changes in bed morphology. Bedload sheet appeared to be the keystone for explaining the short fluctuation periods, but also the long-term periodic changes in bed morphology. We hypothesized, from steep slope observations, that bedload sheet would be produced by a local and efficient upstream grain sorting mechanism operating over a finite length Ls and producing sediment pulses which propagate downstream. A conceptual compartment model, based on this concept, was proposed to simulate slope fluctuations observed in long-term flume experiments. Even though presented in a rough form, it provides an illustration of a possible endogenous factor responsible for time scales affecting bedload.

DOI:

Year: 2007