Presented at the Hydropower and Dams 2025 conference, 22-24 October 2025, Thessaloniki, Greece
Spitallamm Dam: Commissionning new Arch Dam in Switzerland
Managing dam replacement, impounding, and monitoring in a century-old reservoir system
Authors : E. Odermatt, A.Wohnlich, Gruner Stucky Ltd, Switzerland
The 114 m high Spitallamm arch-gravity dam, together with the Seeuferegg gravity dam, form the Grimsel reservoir with a live storage of 94 mio m3 at an altitude between 1’800 and 1’900 masl in the Bernese Alps, Switzerland. The dam was erected from 1926 to 1932. It was at that time one of the highest concrete dams in Europe. The dam is set in a narrow gorge cut mainly in Aare granite and granodiorite, both rocks of high strength and low deformability.
After almost one century of operation, it was necessary to replace the dam following damage at the upstream dam face (concrete ageing). The construction of the new Spitallamm arch dam, 113 m high, was concluded in 2025, after 7 years of construction, including blasting of rock foundation, concrete works and rock foundation drilling and grouting. The new dam is located immediately downstream of the old arch-gravity dam. The dam's first impounding is occurring from spring to fall of 2025. The old arch-gravity dam will remain in place and be flooded in the new reservoir.
The paper addresses several topics regarding the new Spitallamm dam. First, it presents briefly the general geopolitical situation in which such dam substitution takes place, namely the current and future energy situation in Switzerland, also influenced by the European and worldwide geopolitical context. In particular, it is recalled the initiative of the Swiss government to face the challenges of the energy crisis, where a round table was organized in 2021 to develop a common approach among the various energy market stakeholders (national and local authorities, academic technical schools, environmental and landscape protection NGOs, electricity utilities).
Second, the paper explains the background which led to such dam replacement, addressing first the reasons why the old dam had to be decommissioned, and then explaining how it was decided to go for a completely new dam located right downstream of the existing dam.
Third, selected interesting technical topics specific to this configuration are presented. One selected issue is the creation of a new reservoir (so-called "Zwischensee"), between the old and the new dam, and its connection to the main reservoir (Grimselsee) through the decommissioned dam, to ensure that the reservoir level is the same on both sides of the old dam. Another specificity is the selected impounding strategy, dictated only by the dam and not by the reservoir banks, which have been undergoing operation for nearly 100 years. In addition, the paper explains the monitoring approach applied to this impounding phase, with a predictive model based on the principle of influence lines, used throughout the commissioning phase to control the proper behavior of the structure.
Finally, the heightening possibilities and current design phases of the Spitallamm dam and the Grimselsee reservoir are presented as an outlook to the future, as well as allowing a link to the introduction of the paper (energy context in Switzerland).
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