Sand dunes as migrating strings

Guignier, Lucie; Niiya, Hirofumi; Nishimori, Hiraku; Lague, Dimitri; Valance, Alexandre

doi:10.1103/physreve.87.052206

Cited by 23 publications

(23 citation statements)

References 16 publications

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“…In such conditions, the dune migrates back and forth laterally. The dune sinuosity is then reminiscent of the transverse instability of dunes (Courrech du Pont, ; Guignier et al, ; Parteli et al, ; Reffet et al, ). This instability does not occur in our numerical setup because the sand source maintains the upstream end of the linear dune which does not migrate laterally except at the tip.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Elongation and Stability of a Linear Dune

Rozier

Narteau

Gadal

et al. 2019

Geophysical Research Letters

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Compared to barchan dunes, the morphodynamics of linear dunes that elongate on a nonerodible bed have barely been investigated by means of laboratory experiments or numerical simulations. Using a cellular automaton model, we study the elongation of a solitary linear dune from a sand source and show that it can reach a steady state. This steady state is analyzed to understand the physical processes at work along the dune. Crest reversals together with avalanche processes control the shape of transverse sections. Dune width and height decrease almost linearly with distance downstream until the minimum size for dune is reached. This is associated with a constant sand loss along the dune, which eventually compensates for the sediment influx and sets the dune length. This sand budget is discussed to distinguish an elongating linear dune from a barchan dune and to explain the complexity of linear dune fields in nature. Plain Language SummaryGiven the seasonal cycle, multidirectional wind regimes are highly prevalent in modern sand seas where linear dunes are the most frequent dune type. They vary in shape and size, but they are all characterized by linear ridges extending over long distances. Here we study the morphodynamics of linear dunes that elongate from a sand source under the action of reversing winds. We show that the sand loss increases with the length of the elongating linear dune which eventually converges to a steady state. We relate the dimensions and the shape of the dune at equilibrium to the sediment influx and the wind properties. The characterization of this elementary dune type is an essential step toward a better understanding of the interplay between winds and complex dune fields in nature. This is important for Earth in a context of climate change, but also for Mars and Titan, Saturn's largest moon, where direct wind measurements are not available to date.

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Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Elongation and Stability of a Linear Dune

Rozier

Narteau

Gadal

et al. 2019

Geophysical Research Letters

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“…Parteli et al [] have shown that a transverse dune is globally unstable because a difference in height accelerates the smallest longitudinal dune slice and is then amplified by lateral flows associated with avalanches. In our case, we show that when there is an input sand flux, the overall dispersive flux may be stronger on the windward face than on the lee face [ Niiya et al , ; Guignier et al , ]. This may be an important stabilizing factor which was not taken into account by Parteli et al [].…”

Section: Discussionmentioning

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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“…Floquet stability analysis supplies the natural modes of the perturbation behavior and hence the general stability properties of the system's equilibrium. According to Floquet theory, the fundamental solution operator associated with (11) is introduced as the matrix (t) which is computed by advancing a 5 × 5 identity matrix over one temporal period (from t = 0 to t = T ) according to (11). Each column of (t) is a linearly independent solution of the system.…”

Section: Modal Analysismentioning

confidence: 99%

“…However, it is worth recalling that transverse dunes can decay into a chain of barchans (crescent-shaped dunes) and display a "sea-wave-like" shape with meandering. The formation of barchan dunes is very common and widely studied in an aeolian environment, as demonstrated by a vast body of literature [9][10][11], but has also been detected in subaqueous conditions both in laboratory experiments [12] and in real rivers [13].…”

Section: Introductionmentioning

confidence: 99%

River bedform inception by flow unsteadiness: A modal and nonmodal analysis

et al. 2016

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River bedforms arise as a result of morphological instabilities of the stream-sediment interface. Dunes and antidunes constitute the most typical patterns, and their occurrence and dynamics are relevant for a number of engineering and environmental applications. Although flow variability is a typical feature of all rivers, the bedform-triggering morphological instabilities have generally been studied under the assumption of a constant flow rate. In order to partially address this shortcoming, we here discuss the influence of (periodic) flow unsteadiness on bedform inception. To this end, our recent one-dimensional validated model coupling Dressler's equations with a refined mechanistic sediment transport formulation is adopted, and both the asymptotic and transient dynamics are investigated by modal and nonmodal analyses.

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Sand dunes as migrating strings

Cited by 23 publications

References 16 publications

Elongation and Stability of a Linear Dune

Elongation and Stability of a Linear Dune

Mean sediment residence time in barchan dunes

River bedform inception by flow unsteadiness: A modal and nonmodal analysis

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