The Trient: balancing flood protection and biodiversity

The environmental restoration and flood management work on the Trient involves partially dismantling the existing dam and building a new one in order to enlarge the river bed. The 300-metre extension is located in the “D’Amont des Clous” zone at Vernayaz and corresponds to the space provided for waters. It will enable the Trient to stay in its course in the event of high water, which will reduce the risk of flooding while also supporting the development of wetland habitats for local flora and fauna. This project is a tangible example of the commitment to environmental conservation within the municipality of Vernayaz. The municipality has established nature and landscape conservation areas in the Bois du Trient (Trient forest) and on agricultural land adjacent to the watercourse. The project will also establish a biological corridor connecting the Rhône and the two slopes of the Trient valley. Xavière Schröder, Environmental Project Manager at Alpiq, is heading up this Nant de Drance environmental compensation project, which was launched in 2023. She emphasises the importance of the work, “which marks the start of the Trient flood management programme and helps create an environment that supports biodiversity.”

The cost of the project, which is being funded entirely by Nant de Drance SA, is estimated at 3.6 million Swiss francs. Work is scheduled to be completed by June 2025, provided the weather conditions are favourable. The complexity of the work, which will take place in a watercourse surrounded by high-voltage power lines, roads and residential areas, must also be taken into account.

An urgent project after the 2023 floods

The floods in November 2023, which affected several regions in the canton of Valais, highlighted the importance of improving the resilience of watercourses against flooding. Watercourses like the Trient caused considerable damage when they reached critical levels. This project is the first in a series of improvements aimed at avoiding these risks over the long term. Grégory Borgeat, municipal councillor for Vernayaz, welcomes the initiative: “This work is an essential first step in protecting our citizens against flooding. The flood protection dam will act as a pilot for the wider Trient flood management project led by the Vernayaz and Martigny municipalities.” 

Second phase of the flood safety project in Martigny and Vernayaz to launch at the end of 2025

The second phase of the flood safety project is scheduled to begin at the end of 2025 or start of 2026, and will cover a larger area downstream of the Trient. It will be led jointly by the municipalities of Martigny and Vernayaz, which are separated by the Trient watercourse. It is hoped to keep the time between the two phases as short as possible, in order to ensure a continuous construction period for the local population and for the technical and transitional liaison arrangements between the two projects. It is currently estimated that this second intervention will cost 16 million francs. It will be funded by the canton of Valais and Swiss Confederation, and is particularly crucial because Valais, with its exposure to climate change and heavy rainfall, must make its infrastructure safe to prevent further disasters. The planned measures will enable more effective flood management and protect inhabited areas near the watercourse. 

Status of the Trient, summer 2023 (source: Olivier Duckert)
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Visualisation of the future status of the Trient in the “D’Amont des Clous” zone (source: Olivier Duckert)
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