Two- and three-dimensional double-sandbar system behaviour under intense wave forcing and a meso–macro tidal range

Five weeks of hourly, 10-min time-exposure video images were used to analyze the meso–macro-tidal double-barred Truc Vert Beach, SW France, under intense wave forcing. The four storms experienced, one of which with an offshore significant wave height over 8 m, induced dramatic changes in the double...

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Bibliographic Details
Published in:Continental shelf research 2010-04, Vol.30 (7), p.781-792
Main Authors: Almar, R., Castelle, B., Ruessink, B.G., Sénéchal, N., Bonneton, P., Marieu, V.
Format: Article
Language:English
Subjects:
Continental shelves
Double-sandbar system
Dynamic tests
Dynamics
Marine
Meso–macro tidal environment
Nearshore
Offshore
Offshore engineering
Offshore structures
Short-term morphodynamics
Storm impact
Storms
Truc Vert Beach
Video imaging
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Summary:Five weeks of hourly, 10-min time-exposure video images were used to analyze the meso–macro-tidal double-barred Truc Vert Beach, SW France, under intense wave forcing. The four storms experienced, one of which with an offshore significant wave height over 8 m, induced dramatic changes in the double sandbar system. The subtidal outer bar migrated offshore rapidly (up to 30–50 m/day) and its pre-existing crescentic pattern was wiped out. The seaward-protruding parts of the outer bar barely migrated offshore during the most intense storm, whereas a landward-protruding part was shed off. Over the entire study period, the outer-bar dynamics was dominated by alongshore-averaged changes rather than alongshore non-uniform changes, while the opposite was observed for the inner bar. In addition, the outer-bar dynamics was predominantly controlled by the time-varying offshore wave conditions, whereas the inner-bar dynamics was influenced largely by the tide-range variations. Our observations put forward the key role of morphological settings (the presence of a subtidal bar and its shape) and tidal range in governing inner-bar behaviour within a double sandbar dynamics, and provide strong support for previous suggestions that sandbars cannot be studied in isolation.
ISSN:0278-4343
1873-6955
DOI:10.1016/j.csr.2010.02.001