Mattmark dam: raising by ten metres under review

16.01.2025 - A total of 15 projects for the expansion of Swiss hydropower have been identified by the government's ‘Round Table on Hydropower’. One of these involves raising the Mattmark dam in the canton of Valais. On behalf of Kraftwerke Mattmark AG, Axpo is currently examining the possibility of raising the dam by 10 metres, which could shift around 60 GWh of electricity production into the winter and make a substantial contribution to security of supply. However, a number of challenges still need to be overcome before the expansion project can be realised. 

Axpo has been commissioned by Kraftwerke Mattmark AG (KWM) to examine the feasibility of two options for the Mattmark project: raising the dam by three or ten metres. A preliminary study has shown that a ten-metre increase is the more advantageous option, as it would enable the greatest possible shift of electricity production into winter. 

60 GWh of additional winter electricity

Raising the dam by ten metres would increase the volume of the Mattmark reservoir by around 18 per cent. This means that the current annual inflow to the lake could be stored in full, and more water would be available for electricity production in winter. Although the total annual production of the KWM would remain unchanged, the shift would enable the production of around 60 GWh of additional electricity during the winter months. The dam would thus be raised to make a substantial contribution to improving the security of supply in winter. The current layout of the KWM plants would be retained, and no new water intakes or supply lines to the reservoir would be created. The necessary investment is currently estimated at around CHF 83 million. The construction period would be around four years.

Axpo is currently working on the technical preliminary project and an environmental impact report on behalf of the KWM, in which possible ecological measures are also evaluated. In addition, support groups are being initiated in which representatives of various stakeholder groups (environment, tourism, population) can voice their concerns.

In addition to improving the security of supply in winter, the region and the municipalities in the Saas Valley could also benefit from a possible increase in the Mattmark dam. A construction phase would strengthen the regional economy and create jobs in the region. The increase in the Mattmark dam could further enhance the region's profile and attractiveness for tourists with corresponding accompanying measures during the construction phase and with additional offers in the long term.

In 2001, the height of the spillway was already increased by 2 metres, creating an additional retention volume of 3.6 million m³. This is available to the Canton of Valais in the event of flooding to protect the Saas Valley and the Visp region. This flood protection will be maintained by raising the Mattmark dam.

Challenges for realisation 

Whether the raising of the Mattmark dam can be realised depends on various factors. The conclusion of a residual value agreement for the investment with the eleven concession municipalities and the Canton of Valais is indispensable. Furthermore, an additional concession is required for the dam raising. Agreement between the environmental organisations, the Canton of Valais and KWM is required for the additional compensatory measures for the protection of biodiversity and the landscape. Furthermore, the economic viability of raising the dam depends on many variables. However, all parties involved are currently endeavouring to work towards a possible realisation of the 10-metre increase in the Mattmark dam.