Temporal variability of contaminated sediments in a strongly regulated reservoir of the upper Rhine River

Water Qualit

Restauration morpho-dynamique et redynamisation de la section court-circuitée du Rhin en aval du barrage de Kembs (projet INTERREG / EDF)

National audienceThe Upper Rhine River has been heavily impacted by channelization for flood protection and navigation, and then by damming for hydropower generation. In normal non flooding conditions, most of the flows are diverted in a canalized section whereas the regulated “old Rhine” bypassed reach runs a minimum flow. Between Huningue and Neuf-Brisach, engineering works induced simplification and stabilization of the channel pattern from a formerly braiding sector to a single incised channel, hydrological modifications, bottom armouring due to bedload decrease, and thus ecological alterations. Two complementary and interdisciplinary projects have been initiated to restore alluvial morphodynamics: i) the international “INTERREG IV - Redynamisation of the old Rhine” project (2009-2012) coordinated by the Alsace region, France; ii) the left bank “controlled erosion” project launched by Electricité de France (EDF) within Kembs hydroelectric station relicensing process since 2003-2004. The purpose of these projects is to evaluate the feasibility of an important hydro-morphological and ecological restoration plan on a 45 km long reach, through both field testing of bank erosion techniques at favourable locations, and artificial sediments input from right bank excavations. This will help define possible long term prospective scenarios, in order to restore sustainable sediment transport, morphodynamics variability and associated ecological functions. The study will involve historical analysis, hydro-morphological / hydraulic physical and numerical modelling, physical and ecological monitoring, and sociological aspectsLe Rhin alsacien-allemand a enregistré de profondes modifications morphologiques et hydrologiques à la suite de sa correction et de sa régularisation pour la protection contre les crues et la navigation, puis après la construction de barrages hydro-électriques. Les aménagements réalisés entre Huningue et Neuf-Brisach ont engendré une simplification et une stabilisation du style fluvial. Un fleuve en tresses a cédé la place à un chenal unique incisé. Le fond de chenal est devenu pavé à cause d’une diminution des apports de charge de fond et des altérations écologiques ont été observées (simplification des habitats aquatiques et riverains). Deux projets complémentaires et interdisciplinaires ont été engagés afin de restaurer une dynamique des formes alluviales : i) le projet international INTERREG IV – Redynamisation du Vieux Rhin (2009-2012) sous l’impulsion de la région Alsace ; ii) le projet d’érosion maitrisée des berges de la rive gauche conduit par Electricité de France (EDF) dans le cadre du renouvellement de la concession de l’aménagement de Kembs. L’objectif des deux projets est de définir un plan de restauration hydro-morphologique et écologique conduisant à la redynamisation d’un tronçon de 45 km. L’étude repose sur une analyse historique, l’exploitation de modèles à la fois physiques et numériques, et les suivis morphologiques in situ d’une recharge artificielle en sédiments et d’érosions de berge contrôlées. Ces études de faisabilité sont complétées par des analyses écologique et sociologique pour apprécier l’impact socio-environnemental de ces projets

Hybrid local and teleseismic P-wave tomography in North Tanzania: role of inherited structures and magmatism on continental rifting

International audienceWhile local earthquake tomography is typically used to image the crust, this technique has restricted depth penetration due to. Regional tomography however aims to short receiver-source distances image the upper mantle from teleseismic events but suffers from poor resolution from 0 down to 40 km depth. We present here a hybrid method that combines the two approaches taking advantage of the short-wavelength resolution within the crust to better constrain the ray path at depth, and thus to improve the lithospheric imaging. Using this new method enhances the continuity or disruption of mantle anomalies towards the surface. Such hybrid tomographic images of crust-to-upper mantle structures are then critical to understand the relation and interplay between the thermal and mechanical lithospheric processes and the role in the localisation of the deformation at the surface. We apply our approach to the North Tanzanian Divergence (NTD), where those processes interact with a cold cratonic lithosphere. Our new tomographic images clearly demonstrate the impact of deep-seated processes on surface features. First, strong lateral velocity anomalies and clustered seismicity in the crust are consistent with the surface geology of the NTD (rifted basins, volcanoes and border faults). Then, at a lithospheric scale, the velocity distribution highlights the major role of inherited structures in guiding the rift opening. In particular, our study suggests a strong influence of the Masai cratonic block, south of the NTD, in the rift evolution. The transition from the North-South axial valley into three diverging rift arms (Eyasi, Natron-Manyara and Pangani) is likely due to the change in rheology and to the presence of magma along inherited sutures between the craton and the mobile belts

Deep phlogopite-olivine melilitite and melt-rock interaction in subcontinental lithospheric mantle (Tanzanian Craton)

International audienceThe North Tanzanian Divergence (NTD) corresponds to early stage rifting of the eastern branch of the East African Rift. In the southern part, quaternary volcanoes of the Manyara-Balangida rift have erupted primary melilitites (34.9–42.1 wt% SiO2 and Mg# = 79–65) with deep mantle xenoliths. Melilitites are olivine-rich and contain up to 4 vol% magmatic phlogopite as a liquidus phase suggesting that primary melts were K2O-rich and contain H2O (4.63–5.48wt% H2O, 66-117 ppm Cl in phlogopite, from SIMS measurements). Lavas have high incompatible element contents, LREE/HREE fractionation, high Rb/Sr ratio and negative anomaly in K and Zr-Hf. Geochemical modelling indicates that the melilitite magmas resulted from deep and low partial melting of a carbonate-rich (0.3–0.5%) garnet peridotite containing ~2 vol% phlogopite. The depth of partial melting is estimated close to or below the lithosphereasthenosphere boundary (>130 km).Mantle xenoliths include phlogopite-bearing peridotite and phlogopitite (100% phlogopite + rare spinel). Mantle phlogopites have high Al2O3 and MgO content (12.7-15 wt.% Al2O3, Mg#=83-93) and high water and Cl content (2.6-5.3 wt% H2O, 100-200 ppm Cl) with major element composition close to magmatic phlogopites. They have very low incompatible element contents compared to phlogopite in melilitite and differs significantly from phlogopite in phlogopite-rich PIC and MARID xenoliths as deep-seated segregations from melts genetically linked to kimberlitic magmas. Percolation of deep asthenospheric CO2-H2O alkaline magmas during their ascent may have produced the strong heterogeneities in the thick sub-continental lithospheric mantle beaneath the East part of the Tanzanian craton by inducing metasomatism and phlogopite crystallization in spinel lherzolite and phlogopitite lithologie

Méthodes d'estimation de la granulométrie de tronçons restaurés de grands fleuves : potentialités et limites

International audienc

Geomorphic effects of gravel augmentation and bank re-erosion on the Old Rhine River downstream from the Kembs dam (France, Germany)

International audienceThe Old Rhine is a 50 km bypassed reach downstream from the Kembs diversion dam in the Alsacian plain (France/Germany). It has been impacted by engineering works since the 19 th century. This reach exhibits poor ecological functionalities due to severe geomorphological alterations (e.g., channel bed stabilization, narrowing, degradation and armoring, sediment deficit). In the frame of the Kembs power plant relicensing (2010), Électricité de France has undertaken two gravel augmentations (18 000 and 30 000 m 3) and three controlled bank erosions following riprap protection removal over ~300 m bank length to enhance bedload transport and habitat diversification. A first pilot gravel augmentation was also implemented in 2010 (23 000 m 3). A geomorphological monitoring based on bedload tracking, grain size analyses and topo-bathymetric surveys has been performed on the 3 gravel augmentation reaches and one of the controlled bank erosion sites to assess the efficiency and sustainability of these actions (2010-2017). Results show that augmented gravels are entrained for a Q2 flood. Gravels moved several hundred meters for moderate floods and up to one kilometer for more intense floods (Q15), while sediment deposition mainly diffused within the channel. Morphological and grain size diversification, including sediment refinement, are still relatively limited following gravel augmentation. Furthermore, sediment armoring reestablished once the sediment wave moved more downstream, after only four to six years, due to the stability and the narrowness of the channel but also by the absence of upstream bedload supply. Habitat diversification was higher on the controlled bank erosion site thanks to the presence of two artificial groynes, even though eroded sediment volumes were lower than expected (less than 1500m 3 for a Q10 flood). This monitoring demonstrates gravel augmentations are not sufficient to really diversify geomorphological conditions of the Old Rhine. Channel enlargements by controlled bank erosion and other actions should be carried out downstream from gravel augmentations to create channel geometry conditions promoting bar development and habitat diversification

Impacts d’actions de restauration géomorphologique du Vieux Rhin à l’aval de Bâle (France, Allemagne)

International audienceLe Vieux Rhin est un chenal court-circuité de 50 kilomètres à l’aval du barrage de dérivation de Kembs. Il a été fortement impacté par divers aménagements depuis le XIXè siècle visant la protection contre les crues, le développement de la navigation et la production d’hydro-électricité. Une part importante du débit (jusqu’à 1 400 m3/s) est dérivée dans le Grand Canal d’Alsace, équipé de quatre centrales hydro-électriques. Ce chenal présente des fonctionnalités écologiques qui ont été affectées par les ajustements hydro-géomorphologiques résultant de ces aménagements (rétraction, incision et fixation du lit, formation d’un pavage, simplification des formes fluviales…). Dans le cadre de la nouvelle concession de l’usine hydro-électrique de Kembs (2010), Électricité de France a augmenté le débit réservé de 20-30m3/s à 52-150m3/s. En complément, cinq actions de restauration géomorphologique ont été entreprises afin d’améliorer la dynamique morpho-sédimentaire du Vieux Rhin et diversifier les habitats : deux injections sédimentaires artificielles (18 000 m3 et 30 000 m3) et trois actions d’érosion maîtrisée de berge par déroctage (linéaire de 300 m chacun). Un suivi géomorphologique est effectué pour évaluer les effets des restaurations en termes d’efficacité et de durabilité grâce à des indicateurs morpho-sédimentaires (un suivi hydro-écologique est mené en parallèle). Il repose notamment sur le suivi de la charge de fond, les évolutions granulométriques et topo-bathymétriques. Les premiers résultats, qui portent sur les deux recharges sédimentaires et une érosion maîtrisée de berge, montrent que : (1) la mobilisation des sédiments injectés peut se produire dès une crue biennale, mais qu’elle est aussi fonction des conditions locales de mise en place des cordons sédimentaires, (2) les vagues sédimentaires transitent majoritairement au centre du chenal, sur des distances de plusieurs centaines de mètres selon l’intensité et la durée des crues, (3) la diversification granulométrique et morphologique est relativement limitée à l’aval des injections sédimentaires, contrairement au site d’érosion maîtrisée, mais dans ce dernier cas l’hétérogénéité est accentuée par la présence d’épis transversaux, (4) les volumes sédimentaires injectés dans le chenal par érosion maîtrisée de berge sont relativement faibles en raison notamment de la présence en berge de blocs d’enrochement enfouis hérités d’aménagements anciens. L’ensemble des résultats apporte d’ores et déjà au gestionnaire un précieux retour d’expérience qui permet d’améliorer l’efficacité et la durabilité de futures actions de restauration géomorphologique. Ce retour d’expérience, dont certains éléments peuvent être transposés à d’autres cours d’eau court-circuités, sera enrichi par la poursuite à moyen terme du suivi géomorphologique. Mots clés : Restauration physique, recharge sédimentaire, érosion maîtrisée de berge, suivi géomorphologique, traçage sédimentaire, analyse granulométrique, LiDAR aéroporté et terrestre

Geomorphic impacts of restoration actions of the Old Rhine River downstream Basel and insight of ecological benefits

International audienc

Geomorphic impacts of restoration actions of the Old Rhine River downstream Basel and insight of ecological benefits

International audienc

Mapping Sustainable Fashion Opportunities for SMES

This report maps many current initiatives and key organisations operating in sustainable fashion and textiles across Europe and provides an overview of the opportunities for and challenges hindering the adoption of environmentally and economically sustainable business models in the fashion sector. It also identifies key enablers that will assist in the transformation towards a circular economy. With a special focus on designers, start-ups and SMEs, the report provides 12 case studies drawn from 9 member states as exemplars of best practice, to encourage sustainability throughout all stages of the fashion value chain from design and production, to services and end-of-life solutions. These include: new fibre development and materials recycling (Orange Fiber, Ecoalf, re:newcell); design and manufacture of fashion products and accessories using a range of sustainable, recycled and upcycled materials (Elvis & Kresse, VEJA, REDU, Rif\uf2, MUD Jeans, Stanley/Stella); retail customer services including repair and take back (MUD Jeans, Elvis & Kresse), new clothes sharing and reselling business models (The Nu Wardrobe), software systems for on-demand fashion production (Unmade), plus a consumer and industry facing campaign for positive action and education for a more transparent and sustainable fashion system (Fashion Revolution). Within each case study comparator businesses have also been identified, working around particular business models, sub-sectors or practices that may use a different assortment of sustainable or circular activities