The concept of transport capacity in geomorphology

Wainwright, John; Parsons, Anthony J.; Cooper, James R.; Gao, Peng; Gillies, John A.; Mao, Luca; Orford, Julian D.; Knight, Peter G.

doi:10.1002/2014rg000474

Cited by 65 publications

(52 citation statements)

References 356 publications

(606 reference statements)

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“…In order for the mean turbulent flow to sustain the motion of particles that are already in transport, it needs to compensate, on average, the energy dissipated in particle‐bed rebounds via drag acceleration during the particle trajectories. This mechanism, which is illustrated in detail by means of a thought experiment in section , gives rise to a shear stress threshold of sediment transport (henceforth termed rebound threshold ), as was already noted by Bagnold (, p. 94) for aeolian saltation transport: “Physically [the rebound threshold] marks the critical stage at which the energy supplied to the saltating grains by the wind begins to balance the energy losses due to friction when the grains strike the ground [and rebound].” It also suggests a clear‐cut definition of transport capacity, which is otherwise difficult to define (see review by Wainwright et al, , and references therein), that leads to an experimentally and numerically validated universal scaling of the transport load

M

(i.e., the mass of transported sediment per unit bed area) with the fluid shear stress

τ

(section ). From the appearance of the rebound threshold in this scaling of

M

, one can conclude that at a significant if not predominant portion of the threshold measurements by Shields () and others have been misidentified as measurements of the entrainment threshold (section ).…”

Section: The Role Of Particle Inertia In Nonsuspended Sediment Transportmentioning

confidence: 73%

“…The consensus is, yes, it does make sense when referring to transport capacity (also known as transport saturation in aeolian geomorphology), which loosely defines the maximal amount of sediment a given flow can carry without causing net sediment deposition at the bed. However, a precise definition of transport capacity is very tricky and controversial (see review by Wainwright et al, , and references therein). For example, the fact that equilibrium transport rates may depend on the experimental protocol for a given condition implies that not every equilibrium transport condition is equivalent to transport capacity and that transport capacity is in some way linked to particle inertia.…”

Section: Introductionmentioning

confidence: 99%

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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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M

(i.e., the mass of transported sediment per unit bed area) with the fluid shear stress

τ

(section ). From the appearance of the rebound threshold in this scaling of

M

Section: The Role Of Particle Inertia In Nonsuspended Sediment Transportmentioning

confidence: 73%

Section: Introductionmentioning

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

View full text Add to dashboard Cite

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“…In this context, quantitative estimates of the threshold conditions for particle motion and of gravel bedload at low shear stresses are difficult (Buffington and Montgomery, 1997). Most of these formulae do no take into account aspects such as the grain size distribution (GSD) of bed material, the specific conditions for incipient motion of each grain size fraction (Proffitt and Sutherland, 1983), and the role played by surface bed structures, specifically grain arrangement and orientation (Voepel et al, 2017), and by fine sediments mortaring the gravel on bed mobility (Hodge et al, 2013;Wainwright et al, 2015). Most of these formulae do no take into account aspects such as the grain size distribution (GSD) of bed material, the specific conditions for incipient motion of each grain size fraction (Proffitt and Sutherland, 1983), and the role played by surface bed structures, specifically grain arrangement and orientation (Voepel et al, 2017), and by fine sediments mortaring the gravel on bed mobility (Hodge et al, 2013;Wainwright et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Perret

Berni

Camenen

et al. 2018

Earth Surf Processes Landf

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A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Importantly, the transfer of water and sediment between these compartments over space and time is unequal because different geomorphic factors control water flow and sediment transport over and between these surfaces (Walling, 1983;Bracken and Croke, 2007;Croke et al, 2013a;Bracken et al, 2015;Thompson et al, 2016a). The feedback between entrainment, transport, and depositional processes, along with variability in the time scales over which they operate in different landscape and environmental settings, creates a complex cocktail of possible interactions that dictate how sediment might be contributed from a catchment source to a trunk stream (Webb and Walling, 1982;Walling, 1983;Brierley et al, 2006;de Vente et al, 2006;Wang et al, 2008;Fryirs, 2013;Bracken et al, 2015;Wainwright et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley, SEQ, Australia

Lisenby

Fryirs

2017

Earth Surf Processes Landf

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The nature of catchment-scale sediment (dis)connectivity is the primary influence on sediment delivery to trunk streams and controls the particle size distribution of channel bed sediments. Here, we examine the distribution of major sediment buffers (floodplains, terraces, alluvial fans, trapped tributary fills), barriers (weirs), and effective catchment area (i.e. sediment contributing area) to characterize the potential for coarse sediment (dis)connectivity in 20 tributaries of Lockyer Creek, in the Lockyer Valley, SEQ. We then analyse the distribution of trunk stream sedimentary links to determine how certain tributaries or disconnecting features (buffers and barriers) influence downstream patterns of bed sediment fining along Lockyer Creek. We find that buffering increases downstream in the Lockyer Valley, and that tributary position and shape influence the space available for sediment buffering. Correspondingly, the spatial extent of sediment buffers impacts the distribution of effective catchment area, which influences the sedimentological significance of individual tributaries. Tributary sediment connectivity, the extent of overbank flows (floodwater zones), and weir locations all exert an additional influence on the distribution of sediment links along the trunk stream. These controls are related to the physiographic and climatic setting of the Lockyer Valley, and anthropogenic influences in this system. We conclude that controls on sediment connectivity and bed load sediment characteristics are highly variable between catchments, and that sediment (dis)connectivity merits equal consideration with tributary basin/channel size when determining controls on tributary-trunk stream relationships and channel sediment regime.

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The concept of transport capacity in geomorphology

Abstract: 40The concept of sediment-transport capacity has been engrained in geomorphological literature

Cited by 65 publications

References 356 publications

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

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

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley, SEQ, Australia

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