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| Titel |
Morphodynamics of superimposed bedforms in a cellular automaton dune model |
| VerfasserIn |
Deguo Zhang, Clement Narteau, Olivier Rozier |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033985
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| Zusammenfassung |
| In a lattice gas cellular automaton designed to study sediment transport, we analyze the
morphodynamics of bedforms produced under unidirectional flow conditions. In this model,
the same instability is responsible for the formation of dunes on flat sand beds and
the initiation of superimposed bedforms on dune slopes. In transverse dune-fields,
secondary bedforms increase crestline sinuosity and number of defects (end of
crestlines). On the other hand, avalanches and lateral grain motions tend to eliminate
these defects to produce more regular crestlines. Lateral fluxes of sediment are
also essential for stabilizing the shape of isolated barchan dunes. We measure the
propagation speed of superimposed bedforms on steady-state barchan dunes, and show
how they contribute to the formation and detachment of smaller barchans along
horns. The model predicts that barchan dunes are not scale invariant and that their
shape varies with respect to the strength of the flow. In addition, we show that the
increase in bed shear stress between the ground and the crest is proportional to the
dune aspect ratio. Finally, we present a general methodology for estimating the
sediment flux over the brink from dune aspect ratio and flow velocity. Using these
fluxes, we rescale the propagation speed of different generations of bedforms to
verify that dunes and secondary bedforms are dynamically identical. Despite more
fluctuations than in the case of isolated barchan dunes, all these geometric and
dynamical relationships hold for a population of dunes with complex dune-dune
interactions. |
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