Hervé Piégay, Fanny Arnaud, Laurent Schmitt, Anne Clutier, Valentin Chardon, Laboratoire Image, Ville, Environnement (LIVE), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), Environnement, Ville, Société (EVS), École normale supérieure de Lyon (ENS de Lyon)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université Lumière - Lyon 2 (UL2)-Université Jean Moulin - Lyon 3 (UJML), Université de Lyon-Université de Lyon-Institut National des Sciences Appliquées de Lyon (INSA Lyon), Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Jean Monnet - Saint-Étienne (UJM)-École Nationale des Travaux Publics de l'État (ENTPE)-École nationale supérieure d'architecture de Lyon (ENSAL)-Centre National de la Recherche Scientifique (CNRS), EDF (EDF), ANR-17-EURE-0018,H2O'LYON,School of Integrated Watershed Sciences(2017), Environnement Ville Société (EVS), École normale supérieure - Lyon (ENS Lyon)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut National des Sciences Appliquées (INSA)-Université de Lyon-Institut National des Sciences Appliquées (INSA)-Université Jean Monnet [Saint-Étienne] (UJM)-École Nationale des Travaux Publics de l'État (ENTPE)-École nationale supérieure d'architecture de Lyon (ENSAL)-Centre National de la Recherche Scientifique (CNRS), Institut National des Sciences Appliquées de Lyon (INSA Lyon), Université de Lyon-Institut National des Sciences Appliquées (INSA)-Université de Lyon-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-École nationale supérieure d'architecture de Lyon (ENSAL)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-École Nationale des Travaux Publics de l'État (ENTPE)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Jean Moulin - Lyon 3 (UJML), and Université de Lyon-Université Lumière - Lyon 2 (UL2)-École normale supérieure - Lyon (ENS Lyon)
International audience; Over the last two centuries, rivers have been strongly regulated, inducing notable sediment starvation and flow reduction. This regulation has altered aquatic habitats, biocenosis and ecosystem services. Gravel augmentation (GA) is increasingly promoted to restore bedload transport, rejuvenate bed sediments and diversify aquatic and riverine habitats. However, practical questions remain in terms of efficiency and sustainability. The objective of this study is to provide unprecedented feedback from three GA experiments conducted along the Rhine River downstream of the Kembs dam (France/Germany). The restored sites were monitored over periods of 1 to 7 years and the stockpile deposits (SDs) and channel responses were compared to highlight the strengths and limitations of such experiments. The monitoring was based on topo-bathymetry, bedload tracking and grain size surveys. Two-dimensional hydraulic modelling was also performed to link the SD erosion patterns to the critical flow conditions. We show that (i) SD erosion is dependent on the grain size of the introduced sediments and the local flow velocities, (ii) sediment dispersion occurred mostly along the thalweg and increased over time, with a progressive decrease in the virtual velocities, (iii) bathymetric simplification and bed grain size fining were observed when downstream sediment diffusion began, (iv) in the mid-term (~5 years), local channel diversification occurred due to the fragmentation of sediment waves, with deposition occurring preferentially on riffles, and (v) new sediment starvation conditions appeared when the sediment waves travelled downstream in the absence of an upstream sediment supply. These results allow us to propose operational recommendations and management scenarios to improve both the efficiency and the sustainability of GAs conducted in large regulated rivers.