Raising the intake structure at the Gigerwald reservoir

An alpine structure of significance

The Gigerwald dam towers in the heart of the St. Gallen Alps – a symbol of power and harmony between engineering skills and nature. Since its completion in 1976, it contributes to the energy and water security of the Sarganserland region and stabilizes the power grid in northeastern Switzerland.

The renovations carried out in 2024 and 2025 strengthened its central elements to ensure the efficiency of the Mapragg hydro power plant for future generations. Lombardi was in charge of design and technical management of the project that combines precision, innovation, and respect for the alpine environment.

Why renovation became necessary

Extensive measures hat already been implemented since the 2000s to reduce sediment load, such as raising the minimum water level and stopping the water supply when turbidity levels were high. Nevertheless, the sediment layer continued to grow. By 2014, the distance to the orifice had dropped to only about two and a half meters. A study of various options ultimately concluded that the most robust and effective long-term solution was to completely raise and hydraulically separate the inlet structures.

Innovation in alpine terrain: constructing with precision

To meet the extremely tight construction deadline, the project team opted for a solution that is rarely used on this scale: 73 prefabricated concrete elements, produced with millimeter precision, digitally scanned, and virtually pre-assembled. This allowed the new structures to be installed quickly and precisely – a decisive advantage given the avalanche season and the tight time frame.

The hood of the power intake was particularly challenging: 39 prefabricated elements had to be positioned so that they formed a single unit hydraulically and statically. The low tolerance and complex geometry required a precisely coordinated assembly.

New intake structures – higher, safer, separate

The new structures were built 18 meters (bottom outlet) and 24 meters (power intake) higher and hydraulically separated from each other. This will enable more flexible operation in the future and make the plant resistant to further sediment increases. The hydraulic performance remains virtually unchanged.

Teamwork under most demanding conditions

The work took a total of seven months and, thanks to careful design and resilient logistics, was completed ahead of schedule – before the snow started to melt. The team comprising Lombardi, Axpo, and Kraftwerke Sarganserland mastered unexpected challenges such as high turbidity levels, blocked trashracks, additional excavation, and sudden weather changes.

Our contribution:

• Study of alternatives & project development
• Overall project planning (general planner role)
• Hydraulic design & modeling
• Design & engineering of the new structures
• Concept and implementation of the precast system
• Site & logistics planning in alpine winter conditions
• Site supervision & site engineering
• Safety & natural hazard concept
• Cooperation with operators & authorities

Ready for the coming decades

With the new intake structures, the Gigerwald reservoir has been restored to safety and efficiency – and remains a key component of the regional energy supply. The project demonstrates how modern engineering, a deep understanding of the alpine environment, and interdisciplinary collaboration can work together to create a structure for generations.