Estimations des capacités de transport et de leur contrôle sur une base moyennée par tronçon le long du Rhône, France

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU [Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUInternational audienceThe Rhône River represents a highly complex fluvial system owing to its basin characteristics and tectonic and climate histories. Superimposed on this natural complexity are intense changes in land use within the basin and management works in the main channel over the past 150 years. The sum of these modifications have drastically altered the delivery of sediments to the main stem and their transfer downstream. We present the results of work in progress that is part of a large-scale multidisciplinary study aimed at understanding how sediment is mobilised and transferred between successive reaches from Lake Geneva to the Mediterranean sea. A main goal of the study is to establish a physically-based classification of reaches based on transport dynamics for targeting restoration projects

Effects of continuous embankments and successive run-of-the-river dams on bedload transport capacities along the Rhône River, France

International audienceThis study was aimed at untangling the relative impacts of successive phases of human modifications on changes in bedload transport along a 430 km-long river reach: the Rhône River from Motz dam to the sea. We used a 1D hydraulic model to solve for water lines across a range of discharges and all along the reach. Next, using grain sizes measured in the channel, we estimate flow competence and mean annual bedload transport capacities using the Recking (2013) bedload transport equation. In addition, we used the Generalized Threshold Model to estimate the relative fine and coarse fractions of the load. Bedload transport estimates were carried out under present-day hydraulic conditions and compared to estimates based on model runs simulating an unimpeded flow regime and using grain sizes measured in bars as a proxy for conditions prior to armouring. Our results show that present-day bedload transport along the Rhône is significantly fragmented by multiple closely spaced dams. Mean annual bedload capacity varies between 2500 and 16,300 m3/year over all the reaches, with an average of 4700 m3/year. Results of the GTM analysis suggest that this load is composed of 89% fines. We find bed sediment mobility to be very low in most reaches, and that potentially mobile sediments are finer than the median grain size in the riverbed even at high flows. Our results suggest that bedload capacities were 25-35 times higher prior to bed armouring and flow modifications; dams had an impact 2-3 times more important on transport capacities than channel embankments, and bed armouring was foremost a response to channel embankments. Based on an analysis of the ratio of sediment yields to transport capacities, we propose a conceptual scheme illustrating how bedload supply, channel morphology, and surface texture coevolved in the Rhône over the past century and half

ZABR-OSR - Livrable action I.1 : Quantification de la charge sableuse

Ce rapport présente les résultats obtenus suite aux campagnes de mesures de 2015 à 2017. Ils incluent des développements méthodologiques et expérimentaux ainsi que les premiers jeux de données sur les sites pilotes de l'OSR : à Chancy-les-Ripes et Bognes autour de la retenue de Génissiat, à Champagneux, et au niveau de la confluence avec l'Isère pour le secteur nord, et enfin en Arles et au niveau du bac de Barcarin pour le secteur sud. Une discussion est proposée sur l'application de courbes de tarage sédimentaire sur ces différents sites. Enfin, un paragraphe est plus particulièrement proposé sur le développement de la mesure des flux de sables en suspension par une méthode acoustique

ZABR-OSR - Livrable action I.1 : Quantification de la charge sableuse

Ce rapport présente les résultats obtenus suite aux campagnes de mesures de 2015 à 2017. Ils incluent des développements méthodologiques et expérimentaux ainsi que les premiers jeux de données sur les sites pilotes de l'OSR : à Chancy-les-Ripes et Bognes autour de la retenue de Génissiat, à Champagneux, et au niveau de la confluence avec l'Isère pour le secteur nord, et enfin en Arles et au niveau du bac de Barcarin pour le secteur sud. Une discussion est proposée sur l'application de courbes de tarage sédimentaire sur ces différents sites. Enfin, un paragraphe est plus particulièrement proposé sur le développement de la mesure des flux de sables en suspension par une méthode acoustique