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Gornerli multi-purpose project – drilling confirms location

As part of the technical pre-design investigations carried out for the Gornerli project, the first boreholes were drilled in the summer of 2023. Drilled in the potential location of the dam wall, these boreholes are a key stage in the progress of this multi-purpose reservoir project. The results look very much in favour of the construction of a dam at this site.

During the summer of 2023, 11 exploratory boreholes were drilled in the Gorner gorge above Zermatt. The drilling formed part of the technical investigations enabling the Gornerli multi-purpose reservoir project to be planned in detail. The boreholes posed a particular challenge, not only because access to the site was difficult, but above all because of the care taken to minimise their impact on the environment.

The Gornerli multi-purpose project is the highest-potential project on the agenda of the federal "Hydropower Round Table". It would have the capacity to meet a third of Switzerland's additional winter hydropower needs. Located at the foot of the Gorner Glacier above Zermatt, the dam will store the glacier's meltwater, which would then be turbined in the Grande Dixence power plants. This would generate 650 GWh of electricity in winter, when Switzerland's consumption needs are greatest. The dam wall will also protect Zermatt and the Matter Valley from major flooding during extreme weather events.

3 questions to ...

Jonathan Fauriel

Head of Civil Engineering and Environment at Alpiq
and Project Manager for Gornerli

Why did you carry out the drilling?

The aim of the drilling carried out this summer was to obtain various core samples from the Gorner gorge in order to determine exactly where and how the wall of the Gornerli dam should be built. The samples give us a better understanding of the geology of the site and help us to determine the best location for the wall. This is a very important technical stage in this type of project.

What were the main difficulties you came across?

This type of project involves a number of challenges. Part of the Gornerli project is located in an area listed in the Federal Inventory of Landscapes and Natural Monuments. So, environmental protection plays a huge part. In particular, we have put in place specific measures to protect flora and fauna and to recover water. We also refilled all the boreholes and left the site as we found it.

Situated at an altitude of over 2000 metres, the site is also difficult to access and is subject to the uncertainties of high-altitude weather, which, thankfully, was very kind to us.

What are the results?

By continuously monitoring the boreholes, we have been able to adapt our planning as we go along. Initial data analysis is encouraging. In particular, the assumptions made during the feasibility and preliminary design phases have been confirmed. To carry out a construction project of this scale, you need solid subsoil, and that's exactly what we've found. It's very promising. The bedrock is of good quality and the amount of alluvium covering it is small.

We still have some lab tests to carry out on specific rock samples, as well as in-depth analyses of the data collected. These elements will provide an excellent basis for the next phases of the project.

The Gornerli multi-purpose project at a glance

The Gornerli multi-purpose reservoir project managed by Grande Dixence and the municipality of Zermatt is Switzerland's highest-potential project for ensuring a reliable source of electricity in winter, while providing vital flood defences for Zermatt.

It involves building a dam wall in the Gorner gorge above Zermatt, to store meltwater from the Gorner Glacier in summer and to generate electricity via the Grande Dixence power plants in winter, when Switzerland needs it most. The dam would also protect Zermatt and the Matter Valley from major flooding and extreme weather events by holding back water during storms. The reservoir could also serve as a source of drinking water for the region, as well as a water reserve for irrigating farmland.