Analyse multi-échelle de la morphodynamique d'une plage artificielle, Avant-port Ouest de Dunkerque (Nord de la France).

Abstract : Summary The Clipon beach is a13 km long artificial beach, created in the 1960s, following the extension of Dunkirk harbour. This study is based on a multiscale approach: a temporal scale extending from half a century to the tidal period, and a spatial scale going from the analysis of the morphological dynamics of the whole beach (104 m) to the examination of the morphosedimentary processes of elementary landforms like intertidal bars (101 - 102 m). The large-scale analysis concerns (1) coastline evolution during the successive stages of harbour extension, and afterward, using a series of vertical aerials photographs, (2) nearshore and foreshore bathymetry during and after the harbour development, as well as (3) modelling of wave propagation over different historical bathymetries, which allowed to assess the variability of wave impact along the shore with changing seabed morphology. In order to increase our understanding of the beach morphodynamics, a series of field surveys were conducted from 2003 until 2007 during which hydrodynamic and topographic measurements, as well as sediment sampling, were carried out. The wave and current data obtained on the beach and shoreface were used in conjunction with meteorological data to analyze the hydrodynamics of the coastal system. This analysis showed the dominance of eastward-directed flood currents, but also the existence of a counter current associated with the presence of the eastern pier of the outer harbour. The results of the morphometric analysis of the beach showed a large spatial variability of the general shape and width of the intertidal zone. At the annual time scale, the nearshore zone is characterized by significant erosion, which can reach 0.3 meter per year. Monthly beach profile measurements revealed that the various morphological zones of the beach experienced distinct morphodynamic behaviours in response to the forcing conditions that occurred during the surveys: flattening of the beach during the periods of high wave energy and development and onshore migration of intertidal bars during fair-weather conditions. The analysis of potential sediment transport shows that a weak eastward transport takes place during low energy conditions. The most important transport occurs during high energy conditions during which wind can strongly reinforce tidal and wave-induced. During conditions of strong winds from the north, a seaward-directed undertow develops over the whole beach, inducing offshore sediment transport to the lower beach and nearshore. All these results suggest that the Clipon beach is a semi-closed sediment cell showing a trend towards a negative sediment budget.
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Submitted on : Thursday, March 11, 2010 - 1:48:04 PM
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Jimmy Bertier. Analyse multi-échelle de la morphodynamique d'une plage artificielle, Avant-port Ouest de Dunkerque (Nord de la France).. Géomorphologie. Université du Littoral Côte d'Opale, 2009. Français. ⟨tel-00463152⟩

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