Experiments on dispersion of tracer stones under lower‐regime plane‐bed equilibrium bed load transport

Wong, M.; Parker, Gary; DeVries, Paul; Brown, Timothy M.; Burges, Stephen J.

doi:10.1029/2006wr005172

Cited by 128 publications

(215 citation statements)

References 67 publications

(127 reference statements)

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“…Einstein (1950), suggested, based on a simple flume-like configuration, thatr/D c takes a value on the order of 100-1000, so that a step length is about 100-1000 grain sizes. This order of magnitude has been confirmed by the experiments of Nakagawa and Tsujimoto (1980), Wong et al (2007) and Hill et al (2010).…”

Section: A Pelosi and G Parker: Morphodynamics Of River Bed Variationsupporting

confidence: 71%

Morphodynamics of river bed variation with variable bedload step length

Pelosi

Parker

2014

Earth Surf. Dynam.

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Abstract. Here we consider the 1-D morphodynamics of an erodible bed subject to bedload transport. Fluvial bed elevation variation is typically modeled by the Exner equation, which, in its classical form, expresses mass conservation in terms of the divergence of the bedload sediment flux. An entrainment form of the Exner equation can be written as an alternative description of the same bedload processes, by introducing the notions of an entrainment rate into bedload and of a particle step length, and assuming a certain probability distribution for the step length. This entrainment form implies some degree of nonlocality, which is absent from the standard flux form, so that these two expressions, which are different ways to look at same conservation principle (i.e., sediment continuity), may no longer become equivalent in cases when channel complexity and flow conditions allow for long particle saltation steps (including, but not limited to the case where particle step length has a heavy tailed distribution) or when the domain of interest is not long compared to the step length (e.g., laboratory scales, or saltation over relatively smooth surfaces). We perform a systematic analysis of the effects of the nonlocality in the entrainment form of the Exner equation on transient aggradational/degradational bed profiles by using the flux form as a benchmark. As expected, the two forms converge to the same results as the step length converges to zero, in which case nonlocality is negligible. As step length increases relative to domain length, the mode of aggradation changes from an upward-concave form to a rotational, and then eventually a downward-concave form. Corresponding behavior is found for the case of degradation. These results may explain anomalously flat, aggradational, long profiles that have been observed in some short laboratory flume experiments.

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Section: A Pelosi and G Parker: Morphodynamics Of River Bed Variationsupporting

confidence: 71%

Morphodynamics of river bed variation with variable bedload step length

Pelosi

Parker

2014

Earth Surf. Dynam.

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“…The thickness of the active layer is characterized as L a ¼ n a D s90 , where n a ¼ an order-one dimensionless constant often assumed to be unity (Parker 2004). In principle, n a should vary with flow conditions (Wong et al 2007), but here it is assumed to be a constant. In stratigrafia, n a is a user-specified parameter.…”

Section: Formulation Of Sediment Mass Conservationmentioning

confidence: 99%

River morphodynamics with creation/consumption of grain size stratigraphy 2: numerical model

Viparelli

Sequeiros

Cantelli

et al. 2010

Journal of Hydraulic Research

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104

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As a river-carrying sediment mixture aggrade, it creates a stratigraphic signature that records this evolution. This stratigraphy is characterized by the vertical/horizontal variation of substrate grain size distribution. If a river degrades, it mines this stratigraphy, and transfers the sediment so accessed farther downstream. Although several numerical models tracking the creation/consumption of stratigraphy are available, none has been tested against experiments under plane bed regime conditions. Here nine physical experiments modelling the creation/consumption of stratigraphy are described. These are compared with nine corresponding numerical experiments using a model that tracks stratigraphy. The results justify the numerical model, and in particular the scheme to track stratigraphy. This scheme can be used at field scale to characterize e.g. the response of a river to an increased/ decreased sediment supply. The numerical model shows a discrepancy with the experiments, however, whenever a distinct delta front forms, because the model does not describe sediment sorting across an avalanche face.

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“…The motion of particles in bed load transport is comprised of sliding, rolling, or short hops called saltations (Drake et al, 1988), where the travel time is generally much shorter than the rest duration (Lajeunesse et al, 2010;Martin et al, 2012;Furbish et al, 2012b, a;Roseberry et al, 2012). For near-threshold bed load transport, in which only bed surface particles are mobile, bed load flux may be described as the product of the particle velocity and surface density (particles/area) of moving grains (Bridge and Dominic, 1984;Wiberg and Smith, 1989;Parker et al, 2003;Lajeunesse et al, 2010;Furbish et al, 2012b), or similarly the product of the particle entrainment rate and the average particle step length (Einstein, 1950;Wilcock, 1997a;Wong et al, 2007;Ganti et al, 2010;Furbish et al, 2012b). The combination of particle velocity, number of mobile surface particles, depth of the mobile layer, and a threshold stress typically result in a nonlinear relationship between bed load flux and the fluid shear stress (MeyerPetter and Muller, 1948;Fernandez Luque and Van Beek, 1976;Wong and Parker, 2006;Furbish et al, 2012b).…”

Section: Sediment Transport At the Particle Scalementioning

confidence: 99%

Dynamics and mechanics of bed-load tracer particles

Phillips

Jerolmack

2014

Earth Surf. Dynam.

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Abstract. Understanding the mechanics of bed load at the flood scale is necessary to link hydrology to landscape evolution. Here we report on observations of the transport of coarse sediment tracer particles in a cobblebedded alluvial river and a step-pool bedrock tributary, at the individual flood and multi-annual timescales. Tracer particle data for each survey are composed of measured displacement lengths for individual particles, and the number of tagged particles mobilized. For single floods we find that measured tracer particle displacement lengths are exponentially distributed; the number of mobile particles increases linearly with peak flood Shields stress, indicating partial bed load transport for all observed floods; and modal displacement distances scale linearly with excess shear velocity. These findings provide quantitative field support for a recently proposed modeling framework based on momentum conservation at the grain scale. Tracer displacement is weakly negatively correlated with particle size at the individual flood scale; however cumulative travel distance begins to show a stronger inverse relation to grain size when measured over many transport events. The observed spatial sorting of tracers approaches that of the river bed, and is consistent with size-selective deposition models and laboratory experiments. Tracer displacement data for the bedrock and alluvial channels collapse onto a single curve -despite more than an order of magnitude difference in channel slope -when variations of critical Shields stress and flow resistance between the two are accounted for. Results show how bed load dynamics may be predicted from a record of river stage, providing a direct link between climate and sediment transport.

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Experiments on dispersion of tracer stones under lower‐regime plane‐bed equilibrium bed load transport

Cited by 128 publications

References 67 publications

Morphodynamics of river bed variation with variable bedload step length

Morphodynamics of river bed variation with variable bedload step length

River morphodynamics with creation/consumption of grain size stratigraphy 2: numerical model

Dynamics and mechanics of bed-load tracer particles

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