20.05.2026, 09:15
| Security of supply
Sion – The new Gornerli multi-purpose reservoir project above Zermatt has reached another important milestone. Extensive hydrological and climate studies of the entire Grande Dixence system now allow for the definitive sizing of the storage volume. The construction project and the studies on natural hazards are close to completion, while the logistics concept is also at an advanced stage. In parallel with the ongoing project development, the dialogue with stakeholders on a range of environmental and landscape issues will be pursued over the coming months. The study findings confirm Gornerli’s key role in the future winter supply of renewable electricity in Switzerland, for various regional objectives such as flood protection, long-term water supply, and a strategic energy concept for Zermatt.
Launched in 2019, the Gornerli project is one of the Swiss government’s 16 priority projects resulting from the Hydropower Round Table. Following its inclusion in the cantonal master plan and submission of the preliminary investigation report to the Canton of Valais in early 2024, the construction project is well under way. This includes not only the dam itself, but also the underground pumping station, as well as the logistics concept and the studies on natural hazards. The project builds on a detailed technical basis, incorporating the latest understanding of hydrology, glaciology and geology. As a long-term issue, climate change is an important factor to consider. “The definitive sizing of the storage volume, in the context of the construction project, is part of a normal maturing process for a project of this size. It reflects our desire to base decisions on sound and up-to-date scientific data, while ensuring a dimensioning consistent with the site’s long-term potential,” explains Beat Imboden, Director of Grande Dixence. “Building on this solid foundation, a further major effort is now required, not only from Grande Dixence, but also from environmental organisations, local interest groups, the concession-granting municipalities and the cantonal authorities, to ensure the successful realisation of the project”.
The Gornerli project © Grande Dixence SA / Uzufly
A mature and optimised project
The design of the dam is adapted to the latest topographical and geological findings, resulting in a dam height of 100 m. When the facility is commissioned, the glacier will still partially occupy the valley, temporarily limiting the capacity of the lake. By 2040, storage for winter energy will be at 435 GWh, before reaching its full potential with the complete retreat of the glacier, which is expected between 2045 and 2060 depending on climate scenarios.
Upon completion of the detailed design phase, the Gornerli project is budgeted at around CHF 510 million. The increase in construction costs is primarily due to new and more detailed insights into geology, topography and construction logistics. Considered a project of national interest within the context of the Swiss Confederation’s Hydropower Round Table, it could benefit from federal support of up to maximal 60% of the construction coasts, subject to formal decisions following the submission of the building permit.
The total winter storage capacity of 650 GWh in the entire Grande Dixence network is achieved with the additional project named Dix+. This plan to raise the Grande Dixence dam by about five metres will make it possible to store an additional 20 million cubic metres, equivalent to around 100 GWh, within the Grande Dixence hydraulic system. The project’s technical and operational feasibility has been demonstrated. However, a few regulatory issues still need to be clarified with the federal authorities.
The Gornerli project will not only generate renewable energy — it will also play a vital role in flood protection in Zermatt and across the Mattertal. © Grande Dixence SA / Uzufly
Scientific studies for long-term planning
In order to adapt the structure to make the most of the hydrological potential, Grande Dixence commissioned ETH Zurich and an additional specialist consultancy to analyse the expected water inflows up to the end of the century. These studies take into account the most recent climate scenarios and cover not only the Gornera basin, but the entire Grande Dixence hydrological network. Analyses confirm that Grande Dixence has an additional water storage potential of up to 140 million cubic metres per year by the end of the century.
The current state of knowledge regarding the hydrology of the entire Grande Dixence catchment area leads to the Gornerli storage reservoir being designed with a capacity of 120 million cubic metres, corresponding to an additional winter storage capacity of 550 GWh. The first feasibility studies carried out as early as 2021 indicated a reservoir volume of approximately 150 million cubic metres, corresponding to a maximum winter storage capacity of 650 GWh. In the interest of a long-term sustainable solution, the project design now provides for an adjustment. Gornerli with 550 GWh remains by a considerable margin the largest winter storage project among the 16 proposals that emerged from the Hydropower Round Table. In addition to producing energy, the dam plays an important role in future flood protection for Zermatt and the Mattertal valley. It also provides the municipalities with a long term reliable reserve of water useful for agriculture, tourism or the supply of drinking water. Furthermore, Grande Dixence, under the leadership of the Municipality of Zermatt and in close coordination with EW Zermatt and Zermatt Bergbahnen, is working on an energy concept in which Gornerli plays a key role.
Decisive procedures
As part of Dialog Gornerli, Grande Dixence discusses issues such as various environmental and landscape issues with various environmental associations, Zermatt Mountain Guides Association, SAC Monte Rosa, representatives of the fishing sector, the Municipality of Zermatt and the Canton. In addition, this involves carrying out an analysis of possible alternative project variants requested by stakeholders. Depending on its outcome, the study may influence the project variant currently envisaged by Grande Dixence.
Determining the additional compensatory measures from the Hydropower Round Table is essential to start the project approval process. The scope must be defined jointly by Grande Dixence, the stakeholders and the Canton, with the Canton playing an overarching coordinating role. Grande Dixence will only be able to finalise the application dossier once the dialogue process with stakeholders, the concession-related aspects with the granting authorities, and the compensatory measures with the Canton have been resolved. Construction of the Gornerli project depends on these negotiations, the preliminary consultation process with the Canton, the decision of the primary assemblies of the granting authorities, the decision of the Grand Council of the Canton of Valais and the subsequent cantonal authorisation procedure. Once the final building permit is obtained, there will be around six years of work. Grande Dixence currently envisages commissioning in 2035.
With the detailed engineering design, Grande Dixence has laid a key foundation for the realisation of the Gornerli project. The Gornerli project primarily focuses on security of electricity supply at both national and municipal levels, regional protection against natural hazards and flooding, as well as long-term, supra-regional water security. The project harnesses climate change in a positive way by enabling additional storage and production of renewable energy.