ABSTRACT: Channel stability and sediment transport patterns in steep armored streams: A case of stochastic non-linear behavior.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Flume experiments were conducted to examine the stability of steep streams. A particular interest was the jamming ratio (channel width/grain size) and its effect on bed stability. Small jamming ratios are apt to increase the stability of the bed as the large stones are likely to more readily structure across the channel. The bed stability limit, indexed using the reference Shields number, was indeed found to be related to the jamming ratio. The relationship was however more variable than expected, especially for identical replicate experiments. The scatter was due to the stochastic non-linear behavior of the bed. During critical flow conditions the bed forming grains could remain stable for some time, but once an instability formed, a large amount of sediment transport frequently occurred due to headward migrating instabilities. When these instabilities occurred, the bed did not consistently adjust to a new critically stable state that was at the limit of stability, but rather was observed to adjust to a range of states, varying from critically stable to being able to withstand a flow increase of 20 percent or more without failing. This behavior is akin to what has been observed during sand-pile (or rice-pile) experiments and makes the prediction of bedload transport in such streams difficult. The stochastic nature of the instabilities is likely responsible for much of the variability observed in the jamming ratio/reference Shields number plots.

Bibliography of Canadian Geomorphology