Author(s): Alliau Damien, Sebastien Roux

Linked Author(s): Sébastien Roux

Keywords: Sandy bed-load; Loire River; Distorted physical model; Similitude laws; Dunes;

Abstract: Human activities seriously affected the Loire River morphology during the past decades: incision of the bed and disconnection between the main stream and the river sides branches. In the frame of the plan Loire IV (2014-2020) funded by the European Union, and managed by the French Waterways Administration (VNF), the design and implementation of a sediments settlement structure has been proposed in the vicinity of Nantes, with the goal of generating a solid backwater. For the morph-dynamics studies, the Compagnie Nationale du Rhône proposed implementing a hybrid model based on a 1/100 physical scale model with geometrical and sediments density distortions. This scale model with movable bed is designed to fulfill both Froude and Shields similitudes. Such a complex model required numerous preliminary investigation and model tests in order to confirm that experimental conditions were matching theoretical design rules: from granular behavior of sediment to macro phenomena dynamics (dunes). In addition, 341 dunes formed in the laboratory during more than 50 tests, were analyzed according to 2 axis: the first one concerns the determination of the geometrical sizes (height, wavelength) with the availability of Digital Elevation Model captured by photogrammetry in “wet” condition, the second focuses on the dynamic measurement of dunes migration using Large Scale Particles Image Velocimetry method (LS-PIV). Relevant similitude for the geometry and the dunes dynamics opens interesting perspectives on the understanding of observed phenomena during the tests: for understanding the dynamic effect of the dunes on the mass recordings and for estimating bed-load discharge in the area of the physical model.

DOI: https://doi.org/10.3850/38WC092019-1557

Year: 2019