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Morphodynamique des bancs alternés d'une rivière de montagne aménagée

Abstract : The current research investigates the morphodynamics of gravel alternate bars in an engineered mountainous river. The experimental site corresponds to an 8 km long reach of the Arc River, in the French Alps. An analysis of historical maps and recent aerial photographs and topographic campaigns shows that the original braided river bed has evolved to a straight bed with alternate bar system constrained within two embankments following two centuries of man-made engineering projects. In the mid 1990s the river bed was flattened to fit a trapezoidal cross-sectional design. However, alternate bars re-appeared in less than ten years. An analysis of the controlling factors of bar formation and evolution is provided. Field observation and 1D numerical analysis suggest that the alternate-bar pattern represents a quasi-equilibrium state of the river bed. A single gravel bar within the reach was monitored 18 times from 2006 to 2012. A methodology of DTM construction based on breaklines is proposed for river beds and an error estimation is presented. DTM differencing technique was used to detect morphologic changes of the gravel bar. Therefore, the gravel bar and main channel dynamics were analyzed relative to main controlling processes such as extreme hydrologic events, sediment supply, hydrograph shape, bed shear stress distribution and river energy. Sediment supply and hydrograph shape appeared to be the main factors influencing the study site sediment budget. Moreover, 2D numerical modelling of water flow and sediment transport was performed. Sensitivity analysis was conducted to yield results in agreement with observations. Simulations revealed the relevance of the interaction between fine sediments and gravels on the bar dynamics.
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  • HAL Id : tel-02599442, version 1
  • IRSTEA : PUB00040326

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M. Jaballah. Morphodynamique des bancs alternés d'une rivière de montagne aménagée. Sciences de l'environnement. Doctorat Mécanique des Fluides, Université Lyon I, 2013. Français. ⟨tel-02599442⟩

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