Autor: |
Ferdowsi, Behrooz, Ortiz, Carlos P., Houssais, Morgane, Jerolmack, Douglas J. |
Rok vydání: |
2016 |
Předmět: |
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Zdroj: |
Nature Communications, 8 (1363), 2017 |
Druh dokumentu: |
Working Paper |
DOI: |
10.1038/s41467-017-01681-3 |
Popis: |
Gravel-river beds typically have an "armored" layer of coarse grains on the surface, which acts to protect finer particles underneath from erosion. River bed-load transport is a kind of dense granular flow, and such flows are known to vertically segregate grains. The contribution of granular physics to river-bed armoring, however, has not been investigated. Here we examine these connections in a laboratory river with bimodal sediment size, by tracking the motion of particles from the surface to deep inside the bed, and find that armor develops by two distinct mechanisms. Bed-load transport in the near-surface layer drives rapid segregation, with a vertical advection rate proportional to the granular shear rate. Creeping grains beneath the bed-load layer give rise to slow but persistent segregation, which is diffusion dominated and insensitive to shear rate. We verify these findings with a continuum phenomenological model and discrete element method simulations. Our results suggest that river beds armor by granular segregation from below --- rather than fluid-driven sorting from above --- while also providing new insights on the mechanics of segregation that are relevant to a wide range of granular flows. |
Databáze: |
arXiv |
Externí odkaz: |
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