River-bed armouring as a granular segregation phenomenon

Ferdowsi, Behrooz; Ortiz, C. P.; Houssais, Morgane; Jerolmack, D. J.

doi:10.1038/s41467-017-01681-3

Cited by 113 publications

(80 citation statements)

References 62 publications

(111 reference statements)

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“…Recently, it has been found that such granular creep is very similar to kinetic sieving processes in dry granular flows [14]. The segregation phenomena we observed The last entry in the table was found by linear interpolation yield a similar outcome, but occur at much shorter time scales.…”

Section: Bidisperse Bedsupporting

confidence: 59%

Onset of sediment transport in mono- and bidisperse beds under turbulent shear flow

2017

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In this paper, we present a study on the onset of sediment motion of particles under turbulent shear flow. We use a fully resolved coupled lattice Boltzmann-discrete element solver to study the behavior of monodisperse and bidisperse beds of spheres. For monodisperse beds, we find that the onset of sediment motion is in agreement with the predictions with models from the literature. For bidisperse beds, segregation phenomena at a short timescale are found that lead to increased entrainment of larger particles. This shows that, in addition to long-term segregation phenomena such as riverbed armoring, segregation also occurs at much shorter timescales.

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Section: Bidisperse Bedsupporting

confidence: 59%

Onset of sediment transport in mono- and bidisperse beds under turbulent shear flow

2017

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“…We found that sheetflow thickness increased with steeper bed slopes, unlike sheetflows at lower bed gradients, and particle velocities increased with bed shear velocity, similar to sheetflows on lower bed gradients . This is in contrast to discrete element modeling by Ferdowsi et al (2017), who found that creep motion in granular beds is independent of shear rate for Shields stresses up to five times the critical Shields stress, though they used bimodal sediment sizes and a horizontal flume bed slope. Understanding the conditions under which these highly-concentrated sheetflow layers occur is important, as they might be considered analogous to the body of a debris flow or occur where hyper-concentrated flood flows or debris floods have been observed (Wells, 1984;Sohn et al, 1999;Hungr et al, 2014), such as on alluvial fans (Stock, 2013).…”

Section: Mode Of Transport: Fluvial Versus Mass Flow Behaviorcontrasting

confidence: 40%

Flow resistance, sediment transport, and bedform development in a steep gravel-bedded river flume

et al. 2018

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Highlights: Flow resistance increased with shallow flow, bedforms, and high sediment transport intensity  Downstream and upstream migrating alternate bars developed on bed slopes up to 20%  Transition to upper plane bed coincided with development of concentrated sheetflow Abstract: Quantifying flow resistance and sediment transport rates in steep streams is important for flood and debris flow prediction, habitat restoration, and predicting how mountainous landscapes evolve. However, most studies have focused on low gradient rivers and the application of this work is uncertain for steep mountain streams where surface flows are shallow and rough, subsurface flows are not negligible, and there is form-drag from bed-and channelforms that differs from those in low gradient rivers. To evaluate flow resistance relations and sediment transport rates for steep channel beds, experiments were conducted using a range of water discharges and sediment transport rates in a 12 m long recirculating flume with bed slopes of 10%, 20%, and 30%, and a bed of nearly uniform natural gravel. Flow resistance for planar beds and beds that developed bedforms match empirical models that account for bedloaddependent roughness. Some bedforms were atypical for natural rivers at these bed slopes, such as ACCEPTED MANUSCRIPTA C C E P T E D M A N U S C R I P T 2 stepped alternate bars and upstream migrating alternate bars. Total flow resistance increased with decreasing particle submergence and energetic sediment transport and drag on bedforms. Using linear stress partitioning to calculate bed stresses due to grain resistance alone, sediment flux relations developed for lower gradient rivers perform well overall, but they overestimate fluxes at 20% and 30% gradients. Based on previous theory, mass failure of the bed, which did not occur, was predicted for the highest Shields stresses investigated at 20% and 30% bed slopes; instead a concentrated layer, four to ten particle diameters deep, of highly concentrated granular sheetflow was observed.

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“…In the creeping regime,

μ < μ_{s}

, but flow events are triggered via the bedload transport regime at the top of the bed via spatial correlations in the force network. These creeping events, although slow and intermittent, can lead to segregation effects over long times (

\sim

10–100 hr), where large particles are sorted to the top (Ferdowsi et al, ). Thus, creep and nonlocal rheology may play a crucial role in armoring of gravel‐bedded rivers, as opposed to size sorting in the transported layer.…”

Section: Yield and Flow Of Dense Granular Media In The Context Of Sedmentioning

confidence: 99%

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

Pähtz

Clark

Valyrakis

et al. 2020

Reviews of Geophysics

121

149

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Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering the following questions: Is the flow strong enough to initiate sediment transport, is the flow strong enough to sustain sediment transport once initiated, and how much sediment is transported by the flow in the saturated state (i.e., what is the transport capacity)? In the geomorphological and related literature, the widespread consensus has been that the initiation, cessation, and capacity of fluvial transport, and the initiation of aeolian transport, are controlled by fluid entrainment of bed sediment caused by flow forces overcoming local resisting forces, whereas aeolian transport cessation and capacity are controlled by impact entrainment caused by the impacts of transported particles with the bed. Here the physics of sediment transport initiation, cessation, and capacity is reviewed with emphasis on recent consensus‐challenging developments in sediment transport experiments, two‐phase flow modeling, and the incorporation of granular physics' concepts. Highlighted are the similarities between dense granular flows and sediment transport, such as a superslow granular motion known as creeping (which occurs for arbitrarily weak driving flows) and system‐spanning force networks that resist bed sediment entrainment; the roles of the magnitude and duration of turbulent fluctuation events in fluid entrainment; the traditionally overlooked role of particle‐bed impacts in triggering entrainment events in fluvial transport; and the common physical underpinning of transport thresholds across aeolian and fluvial environments. This sheds a new light on the well‐known Shields diagram, where measurements of fluid entrainment thresholds could actually correspond to entrainment‐independent cessation thresholds.

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River-bed armouring as a granular segregation phenomenon

Cited by 113 publications

References 62 publications

Onset of sediment transport in mono- and bidisperse beds under turbulent shear flow

Onset of sediment transport in mono- and bidisperse beds under turbulent shear flow

Flow resistance, sediment transport, and bedform development in a steep gravel-bedded river flume

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

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