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  • VIEWPOINT OF PARTNERS

    -Xavier Ursat \ EDF
    "The renovation of the Poutès dam, proposed by EDF and confirmed by the Ecology ministry, will enable passage of fish and sediment transport, while maintaining a maximum of hydroelectric production. The innovative solution was the product of the partnership between the Onema ecohydraulic research centre and EDF..."

    -Roberto Epplé \ SOS - Loire Vivante
    "The idea to replace the Poutès dam with a moveable weir and innovative fish passes is a win-win compromise born of our collective intelligence..."

An innovative solution for the Poutès dam

On 6 October 2011, the Ecology ministry officially announced the partial razing of the Poutès hydroelectric dam on the Allier river. This solution, which puts an end to over 20 years of disputes on the need to remove the dam, will enable the passage of salmon while maintaining 90% of the hydroelectric production. The new system was designed by the EDF centre for hydraulic engineering in conjunction with the engineers at the Onema Ecohydraulic centre in Toulouse.

Commissioned in 1941 in the Allier gorges (Haute-Loire department), the Poutès-Monistrol hydroelectric plant is still in operation. The Poutès dam supplies the EDF Monistrol hydroelectric plant and produces 83 GWh, which corresponds to the annual consumption of the entire Puyen- Velay area (34 000 inhabitants).

Impact on salmon migration

The dam, 17 metres high and 70 long, is a major obstacle to salmon migration and their access to the 60% of the total spawning grounds that lie upstream. In spite of efforts by EDF to equip the dam with effective fish passes, it causes delays in migration and remains a barrier for some of the adult salmon. The dam also impacts downstream migration. The juveniles, which must reach the ocean as quickly as possible, tend to lose their way in the 3.5 km long reservoir behind the dam. This delay in their migration may be fatal, particularly given the enhanced risk of predation, notably by trout and cormorants. Almost 90% of the young salmon reaching the dam pass safe and sound through the downstream-migration bypass. The 10% going through the turbines suffer 50% losses.

An innovative solution

The dam will be replaced by a new dam only 4 metres high and equipped with a central gate that can be completely lowered to allow sediment transport and the passage of fish if need be. The dam will also be equipped for salmon upstream migration via a pool and weir pass enabling passage of over 90% of fish and for downstream migration via a surface bypass. The reservoir will be only 100 metres in length, thus avoiding any risk of stagnation and fish becoming delayed in their downstream migration. Water intakes will be equipped with fine screens to block the entry of juveniles into the turbines.

The minimum flow rate of the river will be doubled to 5 cubic metres per second on average, i.e. 30% of the normal mean flow rate, which is much higher than the mandatory legal 10% rate.

This solution, financed 100% by EDF, will maintain hydroelectric production at 90% of the current level.

Contact : phillipe.baran@onema.fr