Transport capacity and saturation mechanism in a real-space cellular automaton dune model

Gao, Xin; Zhang, Deguo; Rozier, Olivier; Narteau, C.

doi:10.5194/adgeo-37-47-2014

Cited by 9 publications

(11 citation statements)

References 27 publications

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“…By definition, ( τ s − τ 1 ) is the excess shear stress. To compute the saturated sand flux on a flat sand bed for different τ 1 values, we use the relation suggested by Gao et al [],

Q_{sat} (τ_{1}) = \frac{Λ_{t}}{Λ_{c}} \int_{- \infty}^{\infty} Λ_{e} (τ_{s}; τ_{1}) f (τ_{s}) normald τ_{s},

…”

Section: Two Grain Sizes In a Real‐space Cellular Automaton Dune Modelmentioning

confidence: 99%

Controls on and effects of armoring and vertical sorting in aeolian dune fields: A numerical simulation study

Gao

Narteau

Rozier

2016

Geophysical Research Letters

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Unlike ripples, there are only few numerical studies on grain size segregation at the scale of dunes in aeolian environments. Here we use a cellular automaton model to analyze vertical sorting in granular mixtures under steady unidirectional flow conditions. We investigate the feedbacks between dune growth and the segregation mechanisms by varying the size of coarse grains and their proportion within the bed. We systematically observe the development of a horizontal layer of coarse grains at the top of which sorted bed forms may grow by amalgamation. The formation of such an armor layer controls the overall sediment transport and availability. The emergence of dunes and the transition from barchan to transverse dune fields depend only on the grain size distribution of the initial sediment layer. As confirmed by observation, this result indicates that armor layers should be present in most arid deserts, where they are likely to control dune morphodynamics.

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“…By definition, ( τ s − τ 1 ) is the excess shear stress. To compute the saturated sand flux on a flat sand bed for different τ 1 values, we use the relation suggested by Gao et al [],

Q_{sat} (τ_{1}) = \frac{Λ_{t}}{Λ_{c}} \int_{- \infty}^{\infty} Λ_{e} (τ_{s}; τ_{1}) f (τ_{s}) normald τ_{s},

…”

Section: Two Grain Sizes In a Real‐space Cellular Automaton Dune Modelmentioning

confidence: 99%

Controls on and effects of armoring and vertical sorting in aeolian dune fields: A numerical simulation study

Gao

Narteau

Rozier

2016

Geophysical Research Letters

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“…(c) Dune aspect ratio with respect to the saturated flux over a flat sand bed. To estimate this flux, we use the analytical expression suggested by Gao et al []:

Q_{sat} = (Λ_{t} / Λ_{d}) \int_{0}^{\infty} f (τ_{s}) Λ_{e} (τ_{s}) normald τ_{s}

, where f ( τ s ) is the distribution of the bed shear stress over a flat sand bed. Dashed line shows a linear fit to the data.…”

Section: Effect Of Flow Depth and Flow Strength On The Steady State Omentioning

confidence: 99%

“…However, ejected dunes may also in turn affect the stability of the downstream train of dunes (i.e., see throughpassing bed forms in section 3.2 and (c) Dune aspect ratio with respect to the saturated flux over a flat sand bed. To estimate this flux, we use the analytical expression suggested by Gao et al [2014]:…”

Section: Effect Of Flow Depth and Flow Strength On The Steady State Omentioning

confidence: 99%

Development and steady states of transverse dunes: A numerical analysis of dune pattern coarsening and giant dunes

2015

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We investigate the development and steady states of transverse dunes for ranges of flow depths and velocities using a cellular automaton dune model. Subsequent to the initial bed instability, dune pattern coarsening is driven by bed form interactions. Collisions lead to two types of coalescence associated with upstream or downstream dominant dunes. In addition, a single collision‐ejection mechanism enhances the exchange of mass between two adjacent bed forms (throughpassing dunes). The power law increases in wavelength and amplitude exhibit the same exponents, which are independent of flow properties. Contrary to the wavelength, dune height is limited not only by flow depth but also by the strength of the flow. Superimposed bed forms may propagate and continuously destabilize the largest dunes. We identify three classes of steady state transverse dune fields according to the periodicity in crest‐to‐crest spacing and the mechanism of size limitation. In all cases, the steady state is reached and maintained through the dynamic equilibrium between flow strength and dune aspect ratio. In the limit of low flow strength, where it becomes the primary factor of size limitation, the bed shear stress in the dune trough regions is close to its critical value for motion inception. Comparisons with natural dune fields suggest that many of them may have reached a steady state. Finally, we infer that the sedimentary patterns in the model may be used to bring new constraints on the development of modern and ancient dune fields.

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“…where Q crest is the sand flux at the crest which is known to be proportional to Q sat [Elbelrhiti et al, 2005;Gao et al, 2013]. Thus, smaller barchans are faster than bigger ones and, within dune fields, collisions are frequent and may result in the formation of larger structures or secondary bed forms.…”

Section: 1002/2013jf002833mentioning

confidence: 99%

“…In all cases, the same relationships can be found between their characteristic dimensions and propagation speed, suggesting that whatever the physical environments, they are driven by similar underlying mechanisms [ Claudin and Andreotti , ]. For example, assuming that all the sediment that passes the crest is captured in a well‐established recirculation zone, the equation of conservation of mass can be used to estimate the migration speed c of barchans with respect to their height H ∞

c \propto \frac{Q_{crest}}{H_{\infty}}

where Q crest is the sand flux at the crest which is known to be proportional to Q sat [ Elbelrhiti et al , ; Gao et al , ]. Thus, smaller barchans are faster than bigger ones and, within dune fields, collisions are frequent and may result in the formation of larger structures or secondary bed forms.…”

Section: Introductionmentioning

confidence: 99%

Mean sediment residence time in barchan dunes

Zhang

Yang

Rozier

et al. 2014

J. Geophys. Res. Earth Surf.

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When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3‐D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.

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Transport capacity and saturation mechanism in a real-space cellular automaton dune model

Cited by 9 publications

References 27 publications

Controls on and effects of armoring and vertical sorting in aeolian dune fields: A numerical simulation study

Controls on and effects of armoring and vertical sorting in aeolian dune fields: A numerical simulation study

Development and steady states of transverse dunes: A numerical analysis of dune pattern coarsening and giant dunes

Mean sediment residence time in barchan dunes

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