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Morphodynamique des systèmes de flèches sableuses : Etude comparative entre les embouchures tidales de l'Archipel de St Pierre et Miquelon et de la côte ouest du Cotentin (Manche)

Abstract : The main objective of this thesis is to understand the formation and the evolution of sandy spits and tombolos using various spatio-temporal scales. In this perspective, two field sites were chosen, the Pointe d’Agon (Normandy) and the tombolo of Miquelon-Langlade (archipelago of St Pierre and Miquelon). The pointe d’Agon is a complex spit that has on its distal part several well-defined hooks. A new mechanism of formation of this type of morphology is proposed on the basis of a relation between the dynamics of a surf bar, migrating on an ebb delta, and the shoreline. The spit elongates in an intermittent way, in parallel of the extension of the sedimentary platform which supports it. The topographic monitoring of one of these bars indicates that it migrates with a mean speed of 35 m / year over several years. However, speed fluctuations appear to a shorter scale because its kinematics is strictly correlated with wave height. A significant height of 0.7 m is necessary to induce bar migration. On the scale of the process, the movement takes place essentially during the surf action. The formation and the geometry of the Miquelon-Langlade tombolo is due to two important factors, the presence of available important sedimentary stock and the existence of different hydro-meteorological conditions between both coasts. The west coast presents generalized erosion in opposition to the accretion of the east coast. This evolution suggests a possible reopening of the tombolo in the short-term.
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Nicolas Robin. Morphodynamique des systèmes de flèches sableuses : Etude comparative entre les embouchures tidales de l'Archipel de St Pierre et Miquelon et de la côte ouest du Cotentin (Manche). Sciences de la Terre. Université de Caen Basse-Normandie, 2007. Français. ⟨NNT : 2007CAEN2059⟩. ⟨tel-01926140⟩

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