Acoustic observations of near‐bed sediment concentration and flux statistics above migrating sand dunes

Wilson, Gregory; Hay, Alex E.

doi:10.1002/2016gl069579

Cited by 10 publications

(11 citation statements)

References 47 publications

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“…It is difficult to quantitatively interpret the spectra shape given the relatively sparse data on near bed particle concentration spectra in the literature. However, it is interesting to note that this f À1 dependence has also been reported as an empirical result in the recent work of Wilson and Hay (2016). As in the present study, Wilson and Hay (2016) made measurements using a bistatic high-resolution coherent Doppler velocity profiler, under steady flow conditions, but not in the sheet-flow regime (Shields parameter~0.2).…”

Section: 1029/2017jf004560supporting

confidence: 84%

“…However, it is interesting to note that this f À1 dependence has also been reported as an empirical result in the recent work of Wilson and Hay (2016). As in the present study, Wilson and Hay (2016) made measurements using a bistatic high-resolution coherent Doppler velocity profiler, under steady flow conditions, but not in the sheet-flow regime (Shields parameter~0.2). The f À1 spectra shape seems to be applicable to both flow regimes.…”

Section: 1029/2017jf004560supporting

confidence: 84%

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On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

et al. 2018

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Intense sediment transport experiments were performed in a gravity‐driven open‐channel flow with two sizes of uniformly distributed nonspherical acrylic particles having median diameters of 1.0 and 3.0 mm and a maximum packing volumetric concentration (ϕ) of 0.55. The flow conditions were adapted to each particle size to ensure similar sediment transport flow regimes as sheet flow corresponding to Shields numbers slightly above unity and a suspension number, ratio of settling velocity to friction velocity, near unity for the two experiments. An acoustic scattering‐based system (Acoustic Concentration and Velocity Profiler) and conductivity probes (Conductivity Concentration Profiler [CCP]) with two different vertical resolutions, 1 mm (CCP1mm) and 2 mm (CCP2mm) were used to measure instantaneous concentration profiles across the bedload and suspension layers. Measured concentration profiles, bed interface position, and sheet flow layer thicknesses are compared between the two techniques. The capabilities and limitations of both technologies are outlined. Average volumetric sediment concentration profiles were overestimated by 10% with the Acoustic Concentration and Velocity Profiler in the dense sheet layer when ⟨ϕ(z)⟩≳ 0.35, and by 100% with the CCP in the more diluted region when ⟨ϕ(z)⟩≲ 0.015 and ⟨ϕ(z)⟩≲ 0.20 for CCP1mm and CCP2mm, respectively. Good agreement is found between the three systems in terms of average and time‐resolved bed level position and sheet layer thickness, validating the different bed interface detection methods on data from the two sensors.

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Section: 1029/2017jf004560supporting

confidence: 84%

Section: 1029/2017jf004560supporting

confidence: 84%

On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

et al. 2018

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“…Today, the most obvious explanation would seem to be the very nature of bedload transport, which involves the random motion of particles carried by the turbulent water stream (Einstein, 1950). Although the macroscopic consequences of particle agitation at the microscale have been studied theoretically and experimentally (Ancey et al, 2008;Ancey & Heyman, 2014;Ballio et al, 2014;Campagnol et al, 2012;Furbish et al, 2012;Martin et al, 2012;Radice et al, 2009;Redolfi et al, 2018;Roseberry et al, 2012;Singh et al, 2009;Wilson & Hay, 2016), to the best of our knowledge, no clear connection between particle agitation and pulses has been demonstrated. While particle agitation is usually considered to be noise and inhibit structure formation, there are instances in which nonlinear instability mechanisms induced by noise generate coherent structures.…”

Section: Introductionmentioning

confidence: 99%

Are Bedload Transport Pulses in Gravel Bed Rivers Created by Bar Migration or Sediment Waves?

Dhont

Ancey

2018

Geophysical Research Letters

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Bedload transport exhibits considerable spatial and temporal variability, as reflected by large fluctuations of transport rates. Among the various mechanisms proposed for explaining this variability, bedform migration is often cited as the main cause. We took a closer look at this issue by running long‐duration experiments in a gravel bed flume using constant water discharge and sediment feed rates. We monitored bed evolution and measured bedload transport rates at the flume outlet using high‐resolution techniques. The bed was initially flat, but within a few hours bedforms consisting of alternate bars and pools had developed. The bars exhibited a stick‐slip motion: they were stable for long periods but moved episodically (every 10 hr on average). Their downstream migration produced 36% of the sediment volume transported, mostly in the form of intense pulses. Much of the transport was caused by the displacement of sediment waves from pool to pool.

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“…In two-dimensional flows, e.g., flows around alternate bars, sediment transport does not occur necessarily in the same direction as the water stream [23]. Vortices can also cause the particles to move against the stream [27]. This makes the coupling between flow and particles much more complicated.…”

Section: Discussionmentioning

confidence: 99%

Stochastic bedload transport in mountain streams

Ancey

Bohorquez

2018

E3S Web Conf.

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Describing bedload transport as a stochastic process is an idea that emerged in the 1930s with the pioneering work of Einstein. For a long time, the stochastic approach attracted marginal attention, but the situation has radically changed over the last decade with the recent advances in the theory of bedload transport. In parallel, the implementation of bedload monitoring techniques at high temporal resolution has produced a wealth of interesting results showing, among other things, that classic empirical bedload transport equations do not capture neither the mean behavior of sediment transport rates qs nor its order of magnitude, especially at low sediment transport rates (a case that is most frequent in mountain streams). We have developed a stochastic model, which takes inspiration from population dynamics and provides a stochastic partial differential equation for the number of moving particles. Taking the ensemble average leads to a fairly simple advection diffusion equation for particle activity (i.e., the number of moving particles per unit streambed area). The model has a number of unique features. For instance, it yields the probability distribution of the bedload transport rate and predicts bedform formation for a wide range of Froude numbers.

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Acoustic observations of near‐bed sediment concentration and flux statistics above migrating sand dunes

Cited by 10 publications

References 47 publications

On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

On Bedload and Suspended Load Measurement Performances in Sheet Flows Using Acoustic and Conductivity Profilers

Are Bedload Transport Pulses in Gravel Bed Rivers Created by Bar Migration or Sediment Waves?

Stochastic bedload transport in mountain streams

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