Author(s): V. Bacchi; A. Recking; P. Frey; M. Naaim

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Keywords: Bedload fluctuations; Grain sorting; Bedload sheets; Image analysis

Abstract: Field observations and flume experiments have demonstrated that bedload is not a one to one response to shear stress but largely fluctuate with time, even under constant feeding conditions. This phenomenon was previously investigated by authors (Iseya and Ikeda, 1987; Kuhnle and Southard, 1988; Recking et al., 2008a) through flume experiments. The slope and the bedload fluctuations were observed and interpreted as the consequence of grain sorting. More precisely, bedload sheet produced at the flume entrance and propagating downstream were observed to control the fluctuating process. However, available results were obtained essentially for very steep slope experiments (ranging from 5 to 12%) and with bimodal mixture. This is why new experiments were performed under constant feeding rate conditions and for long duration in a 6 m long and 0.1 m wide flume on slope 3%, using a bimodal sand gravel mixture. Bed slope variations were observed at different locations of the channel and associated with solid discharge fluctuations measured with image analysis (Frey et al., 2003) at the flume outlet. Fluctuations are periodical and correspond to different bed states (from paving to bed fining). Experiments are presented and a model proposed by (Recking, 2006) for the bed slope fluctuation is tested on these new results.

DOI:

Year: 2009