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https://doi.org/10.5194/esurf-2020-30
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2020-30
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 May 2020

Submitted as: research article | 04 May 2020

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This preprint is currently under review for the journal ESurf.

On how sediment supply affects step formation, evolution and stability in steep streams: an experimental study

Matteo Saletti and Marwan A. Hassan Matteo Saletti and Marwan A. Hassan
  • Department of Geography, The University of British Columbia, 1984 West Mall, Vancouver, BC, V6T1Z2, Canada

Abstract. We present results from an experimental campaign run in a steep flume subject to longitudinal width variations and different sediment feed rates. The experiments were designed to study how sediment supply influences step formation, step location, and step stability. Our results show that steps are more likely to form in narrowing areas (i.e., where the channel width is getting smaller moving downstream) because of particle jamming, and these steps are also more stable. Sediment supply increases particle activity generating a more dynamic channel morphology with more steps forming and collapsing. However, sediment supply does not inhibit step formation, since more steps are generated in experiments with sediment feed than without it. Time-series of step formation, evolution, and destruction show that the maximum number of steps is achieved for average values of sediment supply. We summarize this outcome in a conceptual model where the dependence of step frequency on sediment supply is expressed by a bell curve. Sediment yield measured at the channel outlet followed the sediment feed at the inlet closely, even when we fed 50 % more and 50 % less than the transport capacity. This outcome challenges the applicability of the concept of transport capacity to steep channels and highlights the key role played by sediment supply for channel stability and sediment transport. Finally, we detected a positive correlation between sediment concentration and step destruction, which highlights the key role played by granular jamming for step formation and stability.

Matteo Saletti and Marwan A. Hassan

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Matteo Saletti and Marwan A. Hassan

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Flume experiments on the effects of sediment feed rates on step formation, evolution and stability M. Saletti and M. Hassan https://doi.org/10.5281/zenodo.3754767

Matteo Saletti and Marwan A. Hassan

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Latest update: 02 Jul 2020
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Short summary
Mountain streams often display a stepped morphology but the conditions under which these steps form, remain stable, and eventually collapse are still not entirely clear. We run flume experiments to study how (a) the amount of sediment input and (b) channel width variations affect steps dynamic in steep channels. Steps form preferentially in areas of flow convergence (channel narrowing) and their frequency is higher when sediment supply is larger than zero but smaller than the transport capacity.
Mountain streams often display a stepped morphology but the conditions under which these steps...
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