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Evolution morphodynamique d'une plage macrotidale à barres : Omaha beach (Normandie)

Abstract : This work deals with the morphodynamics of Omaha beach, a macrotidal beach on the Normandy coastline. The main objective is to study the morphological evolution of the intertidal bars using hydrodynamic and topographic data collected in the field at two distinct time scales. At the short-term time scale (from tidal cycle to weekly duration), the intertidal morphology is controlled by wave energy and modulated by the tidal cycles. During fair weather conditions, onshore bar migration is generated by sand tranport from the seaward bar flank to the landward side through surf and swash processes. As the wave height increases, the undertow becomes larger and the upper beach bars can be eroded. On the medium-term time scale (months to years duration), the intertidal bars show a sequential morphodynamic behaviour. The accretion stage is produced by a long time duration of fair weather conditions whereas the bars build up and migrate onshore with a 1 m maximal daily rate. In contrast, destruction stages result from storms; their erosional effects are modulated by tidal cycles and pre-existing morphology. The wind climate and shoreline exposure control this specific sequential behaviour. The dynamics of longshore bars and drainage channels are also highlighted. These dynamics tend to destabilize the bars and weaken their resistance against storm-wave effects. Moreover, the presence of bars and their morphological evolution correspond to reorganisation of intertidal sand volume which seems to be quite stable over the medium-term period. The wave conditions controlling bar accretion, migration and erosion are thus identified. The morphodynamic evolution of Omaha beach is presented in a diagram showing different evolutionary stages, and an hypothesis of intertidal bars formation on a macrotidal beach is proposed.
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https://tel.archives-ouvertes.fr/tel-00003997
Contributor : Alexis Stépanian <>
Submitted on : Tuesday, December 16, 2003 - 7:07:58 PM
Last modification on : Monday, April 27, 2020 - 4:26:29 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:51:53 PM

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  • HAL Id : tel-00003997, version 1

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Alexis Stépanian. Evolution morphodynamique d'une plage macrotidale à barres : Omaha beach (Normandie). Océan, Atmosphère. Université de Caen, 2002. Français. ⟨tel-00003997⟩

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