Feasibility study for the removal of two unused weirs, Eyrieux Basin, France

Conducting the necessary pre-demolition works to restore a 70-meter stretch of river to its natural position, fostering comprehensive ecological restoration, and ensuring fluvial continuity along 33 km of main watercourses.

Introduction

The Eyrieux Valley presents diverse landscapes, spanning from its mountainous upper basin, characterized by beech and fir forests, to its lower valley, exhibiting Mediterranean features. Stretching 80 km and encompassing 853 km², it is the second-largest watershed in Ardèche, featuring an intricate river system with 11 tributaries. The Eyrieux and its tributaries, characterized by Cevennes-type rivers, experience varying flow patterns, impacting the ecosystem that supports brown trout, white-footed crayfish, and various other heritage species across its extensive length.

At a glance

CountryFrance
RiverEyrieux
Km to be opened33
Focal speciesFario trout, white-footed crayfish
Project typeDam removal (pre-demolition)
TimelineStudy phase until January 2024, and work phase in September 2024
Websiteern.org/en/openrivers/
Project statusLive

Project context and opportunity

The rugged terrain of the Eyrieux River network bears the legacy of past human activities, notably mills, agricultural water intakes, and hydroelectric structures. In the commune of Saint Agrève, two weirs, spaced approximately 100 m apart, obstruct the upstream Eyrieux. Initially serving textile activities, a mill, and a sawmill, these water intakes are now obsolete. One of the weirs lacks a mechanism for maintaining a minimum flow in the river throughout all periods, while the other diverts water toward an old mill-turned-residence, causing significant water infiltration.

Prompted by the weir owners seeking a solution for water diversion, the Ardèche Departmental Fishing Federation initiated a project in 2020 to explore ecological continuity restoration in this area. In the final report by December 2021, the owners endorsed one of the proposed scenarios, addressing reserved flow compliance and revitalizing Eyrieux’s ecological continuity. This undertaking, entailing the relinquishment of water rights, will be executed collaboratively with the Syndicat Mixte Eyrieux Clair, tasked with aquatic environment management.

With support from ERN and the Open Rivers Programme, the initial project phase involves conducting studies and preparing the regulatory file adhering to water law, with the second phase of work slated for the latter half of 2024. This operation aligns with the 2022-2027 program of measures outlined in the Rhône Méditerranée Masterplan for Water Development and Management (SDAGE).

Project aims

The project involves studies to determine the feasibility of removing the two weirs and re-establishing a 70 m linear stretch of the Eyrieux in its natural position at the bottom of the valley, reinstating the diverted section. This endeavour aims to comprehensively restore the aquatic environment in the upstream Eyrieux sector, contributing significantly to the renaturation of the river’s morphology, habitats, and surroundings, including riparian vegetation and open spaces.

Furthermore, the restoration efforts will ensure the complete reinstatement of fish continuity along 15 km of the upstream Eyrieux, facilitating reconnection with four tributaries spanning 18 km. In total, this initiative will reopen 33 km of main watercourses and 12.5 km of secondary streams.