The Sibila dam will be transformed to restore ecological continuity on the Daronne River, connecting it with the Doux River.
The Sibila ford is a submersible road structure owned by the municipality. The structure comprises 11 nozzles cast in concrete.
This structure poses a problem of sedimentary and ecological continuity, particularly for fish. Every time a large hydrological event occurs, sediment clogs the nozzles. Fish are prevented from migrating upstream by two phenomena:
Located downstream of the Daronne, 100m apart from the confluence with the Doux in Ardèche, this main tributary from the Doux is therefore not connected to the Doux river basin. The SMBVD has drawn up an inventory of ecological continuity in the Doux catchment area. An exhaustive inventory of obstacles was carried out, and a prioritisation of the obstacles has been established. The Sibila bridge appears to be a priority barrier to remove in the catchment strategy, given its location, its characteristics, and the environmental issues.
The Daronne is classified as a 1st category fish river. This corresponds to waters mainly inhabited by Salmonid fish. In the case of the Daronne, two species are primarily affected: the eel and the brown trout.
This structure is identified in the Eel Management Plan for the Rhône Méditerranée basin as a barrier preventing fish migration to the Daronne and hindering population exchanges between the Doux and the Daronne. Eels are present at the Doux/Rhône confluence.
The Daronne is also listed in the SDAGE as a “biological reservoir”. This designation means the river is essential for trout to complete key parts of their life cycle, including reproduction, feeding, and growth. Partitioning this river is therefore harmful to fish life in the Doux.
The structure also prevents the movement of some aquatic fauna (beavers, otters, etc.), which must bypass the structure’s nozzles to cross the road, increasing the risk of collision.
The Sibila ford causes sediment brought in during floods to accumulate upstream of the structure. One effect of this is a modification to the slope of the Daronne riverbed.
The presence of the structure creates a “pond effect” upstream, leading to water heating. This impacts fish populations, as sensitive species (such as trout, minnow, and blageon) cannot survive in warmer water. As a result, the fish population deteriorates, with only less sensitive species able to thrive. Warmer water also increases the risk of eutrophication and the death of aquatic life.
The Sibila Bridge appears to be a priority barrier for removal in the catchment strategy, given its location, characteristics, and the environmental issues it poses (eel and brown trout). To fully restore the minor bed of the Daronne, while maintaining the uses associated with the structure, it is necessary to modify the bridge. The new structure will remain submersible during major floods, minimising the impact on the river while restoring river continuity.
Technical studies have been conducted to assess the structural characteristics, develop the final plans, refine the costs, and request authorisation from the authorities.
The project was completed in January 2026 and received a follow on demolition grant from the programme.
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