Consultation on a new gallery to optimise hydropower generation

Today, Forces Motrices de la Gougra SA submitted a construction permit application to the canton of Valais to build a new pressure headrace gallery between Vissoie and Niouc, in the Val d’Anniviers. This gallery would replace the existing one connecting the Vissoie compensation reservoir to the pressure line that feeds the Navizence power plant in the Rhône plain.

This non-pressure gallery is currently a bottleneck in the drop between Moiry and the Rhône. Built in 1908 and renovated in 1950, it is sized for a flow rate of 10.8 m³/s. The other Forces Motrices de la Gougra facilities, which connect the Lac de Moiry, via the Mottec power plant, to the Vissoie power station, all have a design flow of 15 m³/s. The Navizence power plant, located downstream in the Rhône plain, was fully renovated in 2013 and was also designed for a maximum flow rate of 15 m³/s. The new pressure gallery will therefore also have a flow rate of 15 m³/s. It will reduce overflow at Vissoie and increase the capacity of the Navizence power plant from 50 MW to 70 MW and the electricity generated each year by 20 GWh, which equates to the annual consumption of almost 4,500 households. This will take the system’s total annual production to around 660 GWh.

Important steps in the process
The new pressure gallery will be located to the east of the current gallery. Excavated using a tunnel boring machine, it will measure 8,200 metres in length. The project costs will amount to around CHF 100 million. Under the provisions of the Federal Energy Act, the project is eligible for an investment contribution from the Swiss Confederation for major renovations of existing hydropower facilities.

The current shareholders of Forces Motrices de la Gougra SA – Alpiq (54%), Rhonewerke (27.5%), the municipalities of Anniviers (7.71%), Sierre (7.5%), Chippis (1.79%) and Chalais (0.5%), and Oiken (1.0%) – will decide whether to proceed with the project based on the granting of investment aid and a profitability assessment. Provided they decide in favour and approval procedures are successful, work is likely to start in 2027 and last around five years. The project involves the “lower” level of the facilities operated by Forces Motrices de la Gougra, which has a licence to use water for the purposes of hydropower generation until 2084.

Environmental compensation measures have already been agreed. Forces Motrices de la Gougra will support a project to revitalise the forest clearings between Pramin and Soussillon. These are located in the Bois de Finges, which is listed in the Federal Inventory of Landscapes and Natural Monuments of National Importance. This project has already been approved by the Federal Office for the Environment and the cantonal authorities.

Comprehensive renovations
The Vissoie – Niouc gallery project is part of a comprehensive round of improvement works on the Forces Motrices de la Gougra facilities. The main facilities, which were built in the 1950s, have been renovated in order to ensure they can reliably produce renewable, local energy for decades to come. The Navizence power plant, which represents the lower level, was fully renovated in 2013. A project to modernise the Mottec power plant was completed last year and work is underway to replace the machinery in the Vissoie plant.

Apart from this modernisation work, the project studies for the raising of the Moiry dam, which is one of the projects of the Swiss Confederation’s Hydropower Round Table, will continue throughout 2025.
 

For more information about Forces Motrices de la Gougra SA, visit www.gougra.ch.