Removal of Two Weirs and Restoration of the Upper Eyrieux River
Removal of the Colonie weir and the Moulin du Pont weir on the Eyrieux River (Rhône watershed), Ardèche, France, 2025
The Project
The Eyrieux valley is a land of contrasts, from its source at an altitude of 1,105 m to its confluence with the Rhône River at 93 m, south of Valence.
The upstream Eyrieux is typical of a good-quality salmon-farming zone, with brown trout being the target species. The white-footed crayfish (Austropotamobius pallipes) has also been invotoried in the vicinity of the project, and the Eyrieux basin is one of the most heavily populated in France to date, with over 100 km of its length occupied. Other heritage species include the yellow-bellied sounder, wetland azure, alpine newt, otter and fine-bodied corduridae.
Two weirs, around 100 m apart, block the upstream Eyrieux in the commune of Saint Agrève. They were created to supply “textile” activities, a mill and a sawmill, but today, these two water intakes are no longer used for any purpose
The work will consist of removing the 2 weirs and recreating the 70 m linear stretch of the Eyrieux in its natural position at the bottom of the valley, on the section that had been diverted. This will contribute to the full restoration of the aquatic environment in this sector of the upstream Eyrieux. In particular, they will enable the renaturation of the river’s morphology, habitats and surroundings (riparian vegetation, open spaces, etc.).
Context and opportunity
The upper reaches of the Eyrieux River are classified as List 1 under Article L.214-17 of the Environmental Code. This section, which remains well-preserved, presents significant challenges for the restoration of whitewater habitats, wetlands, and riparian forests. In the municipality of Saint Agrève, two weirs appart from 140m block the continuity of the Eyrieux River. These structures, which were once used for textile manufacturing, are now disused. The Colonie weir diverts the waters of the Eyrieux into a canal and lacks any mechanism to ensure a minimum flow in the river at all times. The Moulin du Pont weir supplies water to a former mill that has been converted into a residence. The course of the Eyrieux is entirely diverted at this point. The owners of this site, who are experiencing significant water seepage into the building, have approached the local fishing association to find a solution and divert the water away from their mill.
A study conducted in 2020 by the Ardèche Departmental Fishing Federation assessed the restoration options. In 2021, the owners of the weirs approved a plan aimed at restoring the reserved flow, improving ecological continuity, and eliminating water seepage, in exchange for relinquishing their water rights.
The project is led by the Syndicat mixte de l’Eyrieux in Crussol, which has jurisdiction under the GEMA framework. Funding comes from the RMC Water Agency, the Ardèche Department, and the Open Rivers Programme.
The project is part of the 2022–2027 program of measures under the Rhône-Mediterranean SDAGE.
At a glance
- Location : Ardèche (07), France
- River : Eyrieux
- Focal species : Fario trout, White-footed crayfish
Key habitats : riparian forest, ash alder grove, rivers, riverbanks, ash and alder woods, salmonidae areas - Km to be reopened : 33 linear kilometres, all stream
- Km à ouvrir : 33 km de cours d’eau principaux (amont et aval) : Fish continuity will be fully restored along 15 km of the upstream Eyrieux, reconnecting it with 4 of its tributaries (18 km), for a total of 33 km of reopened main watercourses and 12.5 km of secondary streams.
- Project by : SMEC
Download
- Factsheet de ERN (mai 2026), french only
- Open Rivers Programme webpage
- Communiqué de presse du 22 septembre 2024
The Colonie weir, before and after Construction
The steep gradient of the watercourse, the wetland areas, the bridge, and the surrounding homes significantly constrained the post-construction landscaping.
Seuil de la Colonie avant travaux – CR SMEC
Seuil de la Colonie après travaux – CR SMEC
The Moulin du Pont weir before and after the work
The Eyrieux River has been restored to its historic course, and the flow to the Montrond Stream has been reestablished.
Seuil du Moulin du Pont, avant travaux, CR : SMEC
Seuil du Moulin du Pont, après travaux, reconnexion du ruisseau de Montrond, CR : ERN
