FRANCE - Moingt River - Loire department
The Moingt is a tributary of the Vizézy (Lignon du Forez watershed, Loire department, France). This river flows through a Natura 2000 site which is home to numerous protected species, including the white-clawed crayfish, which is rare and protected worldwide ! The European otter is developing in this sector, and could soon settle on the Moingt. The Moingt river is a nursery for fario trout, protected in France, which needs to reach the upstream parts of the basin to spawn.
The River Moingt is classified in List 1 and List 2 and as a biological reservoir according to the Article L214-17. Moreover, it flows through a wild valley. The Moingt river has a strong potential for biodiversity conservation! However, its downstream section is partitioned by several barriers, preventing the free movement of species and sediments. Fish cannot access the refuge and spawning areas located upstream. The entire river does not present a good status according to the WFD, and the barriers are identified as risk factors.
The Moingt has low flows in summer, impacting on wildlife and water quality. With climate change, the decrease in flows will become more and more pronounced. Actions need to be taken now to increase the resilience of the Moingt! Otherwise, in the coming decades, the high potential of the river could be lost.
The old weir of Montbrison was built on the Moingt riverbed, in the commune of Ecotay-l'Olme, to ensure the supply of drinking water to Montbrisson. This weir have been abandoned since 1980 and causes problems for ecological continuity. The quality of the landscape is also impacted, as it constitutes a concrete structure in the middle of the natural environment where the river flows in a mixed zone between forests and pastures. The federation for fishing and for aquatic environments protection of the Loire department, in cooperation with the owners of the weir, have launched this project of weir removal which is in line with their strategy for sustainable development. Indeed, the federation the federation invests a part of the income from fishing in the restoration and monitoring of the environment, to ensure the maintenance of fish populations while developing the fishing activity!
The removal of the barrier is planned in 2021 or 2022 at the latest, and will allow the reopening of a 4.5 km of river for all species, notably the protected trout and crayfish.
The weir is entirely made of concrete and metal reinforcement. It is made up of a footbridge and a large concrete ramp which had been the subject of rustic fish pass arrangements (now obsolete and inefficient).
The federation have experience in barrier removal, since they have already removed 7 weirs!
More precisions about the works :
Just before the beginning of the works, a rescue fishery will be carried out to recover and relocate the fish present on the work site.
During the works, the suspension of sediments can have a strong impact on the fauna present downstream. To limit the impact as much as possible, filtration will be carried out using straw and if necessary geotextiles.
The entire structure will be removed, including the attached walls and walkway. The materials will be transported to a waste disposal centre or specialised recycling centre.
Cuttings of local species (willow, alder) will be planted. The banks will be protected by plant techniques.