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| Titel |
A theoretical analysis of river bars stability under changing channel width |
| VerfasserIn |
S. Zen, G. Zolezzi, M. Tubino |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7340
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| Digitales Dokument |
URL |
| Erschienen |
In: Proceedings of river, coastal and estuarine morphodynamics ; Nr. 39 (2014-04-01), S.27-35 |
| Datensatznummer |
250121301
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| Publikation (Nr.) |
 copernicus.org/adgeo-39-27-2014.pdf |
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| Zusammenfassung |
| In this paper we propose a new theoretical model to investigate the influence
of temporal changes in channel width on river bar stability. This is achieved
by performing a nonlinear stability analysis, which includes temporal width
variations as a small-amplitude perturbation of the basic flow. In order to
quantify width variability, channel width is related with the instantaneous
discharge using existing empirical formulae proposed for channels with
cohesionless banks. Therefore, width can vary (increase and/or decrease)
either because it adapts to the temporally varying discharge or, if discharge
is constant, through a relaxation relation describing widening of an
initially overnarrow channel towards the equilibrium width. Unsteadiness
related with changes in channel width is found to directly affect the
instantaneous bar growth rate, depending on the conditions under which the
widening process occurs. The governing mathematical system is solved by means
of a two-parameters (ε, δ) perturbation expansion, where
ε is related to bar amplitude and δ to the temporal width
variability. In general width unsteadiness is predicted to play a
destabilizing role on free bar stability, namely during the peak stage of a
flood event in a laterally unconfined channel and invariably for overnarrow
channels fed with steady discharge. In this latter case, width unsteadiness
tends to shorten the most unstable bar wavelength compared to the case with
constant width, in qualitative agreement with existing experimental
observations. |
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