Bifurcation Analysis of the Transition of Dune Shapes under a Unidirectional Wind

Niiya, Hirofumi; Awazu, Akinori; Nishimori, Hiraku

doi:10.1103/physrevlett.108.158001

Cited by 13 publications

(15 citation statements)

References 16 publications

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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: 62%

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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Section: Discussionmentioning

confidence: 62%

Mean sediment residence time in barchan dunes

Zhang

Yang

Rozier

et al. 2014

J. Geophys. Res. Earth Surf.

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“…The simulations of the genesis of barchan fields were discussed in detail in previous works (Durán et al, 2010;Luna et al, 2011Luna et al, , 2012. As shown in these works, the small transverse bedforms emerging from the instabilities which develop on the flat hill upwind give place to small barchans after reaching the bedrock -due to the cross-wind instability inherent to transverse dunes (Reffet et al, 2010;Parteli et al, 2011;Melo et al, 2012;Niiya et al, 2012). The barchan dunes, which are subjected to a strong influx, grow in size during their migration, thereby experiencing multiple collisions with their counterparts and producing complex, asymmetric dune shapes.…”

Section: Dune Collisionsmentioning

confidence: 97%

Origins of barchan dune asymmetry: Insights from numerical simulations

et al. 2014

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Barchan dunes -crescent-shaped dunes that form in areas of unidirectional winds and low sand availability -commonly display an asymmetric shape, with one limb extended downwind. Several factors have been identified as potential causes for barchan dune asymmetry on Earth and Mars: asymmetric bimodal wind regime, topography, influx asymmetry and dune collision. However, the dynamics and potential range of barchan morphologies emerging under each specific scenario that leads to dune asymmetry are far from being understood. In the present work, we use dune modeling in order to investigate the formation and evolution of asymmetric barchans. We find that a bimodal wind regime causes limb extension when the divergence angle between primary and secondary winds is larger than 90• , whereas the extended limb evolves into a seif dune if the ratio between secondary and primary transport rates is larger than 25%. Calculations of dune formation on an inclined surface under constant wind direction also lead to barchan asymmetry, however no seif dune is obtained from surface tilting alone. Asymmetric barchans migrating along a tilted surface move laterally, with transverse migration velocity proportional to the slope of the terrain. Limb elongation induced by topography can occur when a barchan crosses a topographic rise. Furthermore, transient asymmetric barchan shapes with extended limb also emerge during collisions between dunes or due to an asymmetric influx. Our findings can be useful for making quantitative inference on local wind regimes or spatial heterogeneities in transport conditions of planetary dune fields hosting asymmetric barchans.

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“…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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Bifurcation Analysis of the Transition of Dune Shapes under a Unidirectional Wind

Cited by 13 publications

References 16 publications

Mean sediment residence time in barchan dunes

Mean sediment residence time in barchan dunes

Origins of barchan dune asymmetry: Insights from numerical simulations

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

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