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Conference Papers Year : 2013

Storm deformation of persistent rhythmic bar system on the shoreface of a Mediterranean beach (South France)


Nearshore bars have been widely studied in the last decades, describing bar formation processes, bar states and evolution, but less attention was paid on the rapid evolution inside storm events. The present paper aims at giving a new insight of the morphological deformation of bar patterns with particular energetic conditions and typically irregular wave climate of the Mediterranean coasts. A storm specific dataset of 15 topo-bathymetry was obtained during two winters (8 storm events monitored within the European project MICORE), and more than one year of ARGUS video monitoring on the Lido de Sète à Marseillan (Gulf of Lions, South-France), providing data for 4 additional storms. This unique dataset permits to assess the differentiated response of various types and size of bar morphology observed alongshore on this double barred beach (4 km long). Some very particular changes of rhythmic bar and rip patterns were described during very energetic conditions that seem to be mostly influenced by sensitive modification in wave power and wave direction. However, despite these rapid and important bar deformations, the general bar pattern remains very stable on the long term because of the maintaining of bar irregularities. Even with storms exceeding largely the annual storm return period (Hs > 4.3 m) and 4 active winters. Both monitoring techniques permitted to document various kind of bar deformations. In some cases, a rip channel is able to totally disrupt the bar crest in bay of rhythmic bar and open sensitive connection in between different generation of bars (in the idea of bar shifting) that may influence surrounding and more offshore bar pattern. Tridimensional aspect of bar pattern typically reduces with storm but shoals are able to detach and migrate toward the beach. A longshore trough may also open-up in the direction of longshore current separating a new bar from the beach step. Asymmetric deformations of crescentic bar (becoming skewed) are due to obliquity in rip channel and wave direction. Very fast longshore migration of bar heterogeneity can occur (200 m a day). Consequently wave direction appears to play a major role in bar deformation. After an apparent reset of the bar pattern, some irregularities are still observed where the initial horns were developed, contributing to the reformation of the crescentic pattern. The size of the morphology and the wavelength of crescentic shape clearly increase bar pattern robustness


Earth Sciences
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Dates and versions

hal-00718176 , version 1 (16-07-2012)


  • HAL Id : hal-00718176 , version 1


Mathieu Gervais, Yann Balouin, Jim Tesson, Raphael Certain. Storm deformation of persistent rhythmic bar system on the shoreface of a Mediterranean beach (South France). 12th International Coastal Symposium : ICS2013, Apr 2013, Plymouth, United Kingdom. pp.3276. ⟨hal-00718176⟩
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