V_Foussard_A_Hubert.mp4

Recording of presentations at the Suricates project closing conference

Title : Management of the Rance estuary sediments: onshore storage and reuse

Authors : Valérie FOUSSARD*1, Auxane HUBERT1 1 Etablissement Public Territorial de Bassin Rance, Frémur, Baie de Beaussais, Rue Gambetta, 22100 Dinan (France) * Corresponding author e-mail: sediments@eptb-rance.fr

Summary :

Following the construction of the tidal power plant located at the mouth of the Rance estuary in 1966, the hydro sedimentary functioning of the estuary has been highly modified. The water levels in the estuary are controlled in order to produce as much electricity as possible at each tide. The modification of the water levels in the estuary enabled the development of various uses: electricity production, sailing and other nautical activities, shore fishing, etc. The presence of the dam along with the upstream Châtelier lock resulted in an increase in muddy sediments deposit in the estuary for decades.

The issue of sedimentation is of great concern to many local stakeholders, who want to reduce silting because of its impact on uses and landscapes. To tackle this issue, an experimental management plan has been put in place from 2018 to 2023 under the supervision of the EPTB Rance Frémur Baie de Beaussais. This plan aims at testing various management solutions in order to develop a permanent management plan. This includes the onshore management of extracted sediments and their reuse within the territory.

In 2014, the La Hisse transit site has been created for the management of marine sediments extracted from the nearby Lyvet sediment trap. This treatment facility, classified as an Installation for the Protection of the Environment (ICPE), can desalinate and dehydrate a maximum volume of 100,000 m3 of sediment. According to the French ICPE regulation, sediments must be reused within a maximum of three years. Historically, sediments are reused locally as soil improvers for agriculture after a two to three years period of storage in the la Hisse decantation basins. This recovery option is considered by regulations to be an addition of soil. It is limited by three main factors: metallic trace element (particularly nickel), salinity (risk of soil contamination) and water content (influence on the texture of sediments).

The work carried out as part of the Interreg NWE Suricates project has made it possible (1) to make recommendations on how to manage the La Hisse site to improve the sediment desalination and dehydration phases in order to facilitate the reuse of sediments (in collaboration with BRGM); (2) to test the use of La Hisse sediments for dike and concrete applications (in collaboration with IMT Nord Europe and IXSANE) and for soil reconstitution; (3) to evaluate the benefits of mixing sediments with other materials (e.g. green waste) before spreading them on fields or for soil reconstitution (collaboration with BRGM, University of Strathclyde); (4) to carry out initial environmental and economic assessments of the solutions tested (in collaboration with the University of Strathclyde and MTU) and to estimate the territory's capacity to receive sediments for future reuses (in collaboration with the University of Lille); (5) to identify promising new recovery methods for the reuse of sediments in the region.

Acknowledgements: The SURICATES project is funded by the European Regional Development Fund (ERDF) as part of the Interreg NWE programme 2014-2020 and by the funders of the Rance estuary sediment management plan: French State, Brittany Region, Dinan Agglomération, Saint-Malo Agglomération, Communauté de communes Cotes d’Emeraude and Electricity of France.