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Theses

Morphodynamique des rivières: Sélection de la largeur, rides et dunes.

Abstract : The river morphology results from the interplay between the turbulent flow over an erodible bed and the sediment transport dynamics. This PhD thesis investigates two river related problems, shedding some light on both aspects. We have investigated experimentally the river width selection problem, comparing measurements performed in the field and on laboratory micro-rivers. We have show, that the power-law relating width and water discharge results form the local river dynamics, and not from the self-organization of river basins. We have analyzed the mean velocity fields and shown that transverse diffusion of momentum should be taken into account to reproduce experimental measurements. In order to investigate the formation of ripples and dunes on a river bed, we have performed the linear stability analysis of a sand bed sheared by a turbulent flow. We have computed the turbulent flow over a relief and characterized the effect of the various dynamical mechanisms (inertia, hydrodynamic roughness, turbulent fluctuations, free surface). We have shown that ripples form by a primary linear instability and that their initial wavelength is governed by the sediment transport relaxation length. On the contrary, dunes form by progressive merging of bedforms. This non-linear pattern coarsening is limited by the stabilizing effect of the free surface. Moreover, the same general framework has allowed to address the formation of Aeolian giant dunes.
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Submitted on : Monday, December 7, 2009 - 8:00:00 AM
Last modification on : Saturday, September 26, 2020 - 11:44:03 PM
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Antoine Fourrière. Morphodynamique des rivières: Sélection de la largeur, rides et dunes.. Sciences de l'ingénieur [physics]. Université Paris-Diderot - Paris VII, 2009. Français. ⟨pastel-00005562⟩

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