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Title:
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Generation and nonlinear evolution of shore-oblique/transverse sand bars
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Author:
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Garnier, R.; Calvete, D.; Falqués, Albert; Caballeria, Miquel
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Other authors:
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Universitat de Vic. Escola Politècnica Superior; Universitat de Vic. Grup de Recerca de Medi Ambient |
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Notes:
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The coupling between topography, waves and currents in the surf zone may selforganize
to produce the formation of shore-transverse or shore-oblique sand bars on
an otherwise alongshore uniform beach. In the absence of shore-parallel bars, this has
been shown by previous studies of linear stability analysis, but is now extended to the
finite-amplitude regime. To this end, a nonlinear model coupling wave transformation
and breaking, a shallow-water equations solver, sediment transport and bed updating
is developed. The sediment flux consists of a stirring factor multiplied by the depthaveraged
current plus a downslope correction. It is found that the cross-shore profile
of the ratio of stirring factor to water depth together with the wave incidence angle
primarily determine the shape and the type of bars, either transverse or oblique to
the shore. In the latter case, they can open an acute angle against the current (upcurrent
oriented) or with the current (down-current oriented). At the initial stages of
development, both the intensity of the instability which is responsible for the formation
of the bars and the damping due to downslope transport grow at a similar rate with
bar amplitude, the former being somewhat stronger. As bars keep on growing, their
finite-amplitude shape either enhances downslope transport or weakens the instability
mechanism so that an equilibrium between both opposing tendencies occurs, leading
to a final saturated amplitude. The overall shape of the saturated bars in plan view
is similar to that of the small-amplitude ones. However, the final spacings may be
up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller
or larger. In the case of alongshore migrating bars, the asymmetry of the longshore
sections, the lee being steeper than the stoss, is well reproduced. Complex dynamics
with merging and splitting of individual bars sometimes occur. Finally, in the case of
shore-normal incidence the rip currents in the troughs between the bars are jet-like
while the onshore return flow is wider and weaker as is observed in nature. |
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Subject(s):
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-Hidràulica
-Mecànica de fluïds |
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Rights:
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(c) Cambridge University Press. The published version of the article:GARNIER, R. i altres . "Generation and nonlinear evolution of shore-oblique/transverse sand bars". A: Journal of Fluid Mechanics, 2006, vol. 567, pàg. 327-360. DOI: 10.1017/S0022112006002126 , is available at http://journals.cambridge.org
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Document type:
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Article
Article - Published version |
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Published by:
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Cambridge University Press
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