Tuesday 1st of july – 14:00
14:00
Morpho-ecological restoration strategy for the Dordogne’s river alluvial area to hydro-sedimentary alterations – LIFE-Nature Dordogne river
AUTHORS
POTET Baptiste, GUERRI Olivier, MOINOT Frédéric, HUGHE Ghislain, DEBIAIS Nicolas
France
Short Abstract: The physical evolution of the Dordogne riverbed results from several anthropogenic factors: the advent of large dams starting in the 1930s, extractions from the riverbed until 1984 and riverbed modifications between 1970 and 2000. These interventions caused a loss of fluvial dynamics, incision of the riverbed and simplification of fluvial forms, thus reducing the diversity of biological habitats. To restore the ecosystem, the LIFE-Nature Dordogne River program (2020-2026) proposes 30 morphological-ecological restoration projects over 280 km of river. The actions include the removal of bank stabilization works, reconnection of floodplain annexes, sediment reinjection to promote migratory fish reproduction, and land acquisitions to preserve natural habitats. The project relies on the expertise of BIOTEC to reclaim alluvial environments through natural regeneration of plant communities. These operations focus on specific sites with high restoration potential, such as the Gaule oxbow (7 ha) and the Maison-Neuve terrace (22 ha), two former gravel pits where extraction works have homogenized the forms and simplified the vegetation. The interventions aim to reconnect the river to its margins and annexes to revitalize the floodplain. Thus, the LIFE program seeks to restore a sustainable ecological balance, considering flood dynamics and the natural regeneration of habitats.
14:20
A participatory experiment to co-construct ecologically and socially robust river restoration projects
AUTHORS
GRAMAGLIA Christelle, ALP Maria, MAURINES Béatrice, MORARDET Sylvie, NAVRATIL Oldrich, GHESQUIÈRE Anaelle
France
Short Abstract: River restoration projects often give rise to controversy. In some cases, this can even prevent them from being implemented. Our hypothesis was that opening up a space for discussion very early on in the development process could make it possible to use these inevitable moments of controversy as moments for collective exploration. We therefore defined a methodology of interdisciplinary participatory workshops to promote the co-construction of desired future states for rivers such as the Auzon (Vaucluse) and Rize (Rhône) – in the Rhône catchment, in France. We created the conditions for a sufficiently symmetrical debate to hope to see the emergence of a shared hybrid culture of watercourses that is at once expert, sensitive and riparian. We then designed models to guide project owners in the design of concrete restoration proposals, discussed and validated with local residents. After three years of experimentation, we are in a position to offer feedback that shows that, despite the difficulties, participation can make it possible to co-construct restoration projects that are robust and ambitious in ecological and social terms. We explain the conditions for this.
14:40
Restoring fish continuity in the Lower Durance : a long-awaited and ambitious project
AUTHORS
NOROTTE Thomas, JACOPIN Bertrand, DUVERGER Eric, GARRIGOU Johan, MERCIER Fabienne
France
Short Abstract: The SMAVD is the contracting authority for an ambitious project to restore fish continuity at weirs 68, 67 and 66 in the Lower Durance, which are obstacles to the circulation of many species. This long-awaited priority project will enable migratory fish such as shad (opening up 40km of river to their migration) and eels (facilitating their migration over more than 100km) to move upstream. The project involves the construction of fishways, namely: the partial lowering of weirs 68 and 67 by means of notches, coupled with the installation of block ramps with large roughness; the rehabilitation of a bypass channel on weir 66. The optimal layout for these structures has been identified following an extensive cycle of multidisciplinary studies, including modelling the impact of weirs’ lowering work on groundwater, or anticipating hydromorphological changes in this stretch of river. The Durance’s flow regime and the ecological issues require that this major work has to be concentrated on the summer months, and thus that it has to be phased over 2 successive summers (2024 and 2025). The first phase of these works was successfully completed in September 2024, and the assessment of the actual impact of works on groundwater has been carried out. The entire project represents a budget of 7.3 million € excl. VAT, including works, studies and monitoring costs. The scientific monitoring involve checking that the fishways built are functional and used by the fish population, hydro-morphological monitoring of the river stretch, ecological monitoring of the site, monitoring changes in groundwater and its effects on water uses.
15:00
Rhinaissance – Ecological Restauration of the Old Rhine and its French and German alluvial areas in the Upper Rhine Section
AUTHORS
LUTZWILLER Nadja, Volker SPÄTH, Bettina SAIER
France
Short Abstract: The Rhinaissance feasibility study is a Franco-German INTERREG project being carried out between 2020 and 2022 by the Regierungspräsidium Freiburg (Germany), supported by the Grand Est Region (France). Its overall aim is to restore the ecology of the Old Rhine in the Rhinau section and its Franco-German alluvial zones in a context of climate change. To achieve this, a series of modular measures were studied. The study area is located on the Upper Rhine about 25 km upstream of Strasbourg and covers an area of 16 km2 over an 11 km stretch of the Rhine. The solutions studied by the Ingérop – ILN (Institut für Landschaftsökologie und Naturschutz) consortium include the creation of new habitats, the lowering of towpaths to encourage overflow, the modification of hydraulic structures to improve the connectivity of the aquatic network, and the integration of structures to guide floods and revitalise the river within the established major flood section. The ultimate aim is to re-establish a sustainable balance in the watercourse that is dynamic, connected and beneficial to local ecosystems, while taking account of human uses. In 2025 and 2026, as part of a new INTERREG project, the next phase will be carried out. It will include a detailed design, 2D hydraulic modelling, a hydromorphological study, fauna and flora investigations and a study of the ecological benefits of potential habitats.
15:20
Move back the Petit Rhône levees : an opportunity to retore alluvial environments
AUTHORS
Marion Cesari, Thibaut Mallet, Laura Marre-Cast, Manu Pivasset, Tao Manicacci
France
Short Abstract: The Rhône, France’s most powerful river, splits into two branches, the Petit Rhône and the Grand Rhône, before flowing down to the Mediterranean Sea. The Petit Rhône runs for more than 60 km, capturing 11 to 13% of the Rhône’s flow. There are levees almost all along its entire course, protecting some 30,000 inhabitants from the risk of flooding. These levees, built under Napoleon III, date from the second half of the 19th century. They are very old, with numerous flaws such as badger burrows and very heterogeneous layers, allowing water to flow through them when the Rhône is swollen. This water infiltration can cause major erosion and lead to a breach in the levee, i.e. total destruction of the structure, causing massive water releases and devastating floods to population and goods. The natural environments bordering the river and levees are essentially composed by riparian vegetation and wetlands. These environments have very little place to develop due to the presence of the levees, which are often located very close to the river. Choosing to reinforce the existing levees as the same place would have led to the destruction of these environments. This is why the SYMADREM has chosen to rebuild levees set back from the river in areas where the stakes are lower, thus avoiding the risk of bank scouring. Moving back the levees offers an interesting opportunity to restore alluvial environments in the space freed for the river. An ecological restoration program has been designed to return the river to a more natural state.