More renewable energy from hydropower: Refurbishment work at an altitude of 1,700 metres
10 July 2026
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- Doubling the storage capacity makes the region’s energy supply more flexible
- Efficient implementation of the energy infrastructure project through work on existing infrastructure
STRABAG is refurbishing the Wurtenspeicher reservoir in Austria for energy provider Kelag. The project will almost double the reservoir’s capacity, increasing its volume from 2.7 million to 5 million cubic metres – roughly equivalent to 2,000 Olympic-sized swimming pools.
By storing water when electricity is plentiful and generating power when demand rises, reservoirs like the Wurtenspeicher help to balance the grid and strengthen the supply of renewable energy in southern Austria.
Work on existing infrastructure
The circumstances for the development projects in the Alps are demanding for the STRABAG groups, in terms of organisation and because of challenging terrain. Some of the heavy construction equipment had to be transported along a narrow road with a gradient of over 10 per cent.
In total, STRABAG produced and installed 246 large-diameter bored piles in record time. The piles are positioned close together and extend up to 25 metres into the ground, requiring the team to work with centimetre-level precision. An additional protective plank seals the dam securely against scouring. Using the existing energy infrastructure enables faster expansion of the existing infrastructure.
Adaptations to the new water level
A total of 230,000 m³ of material was excavated from the quarry at the base of the dam and used to build up the Wurtenspeicher. Numerous structures must be adapted to the new water level of the Wurten reservoir as a result of the dam raise. STRABAG is also refurbishing the valve chamber, which controls the water supply, and the spillway funnel.
In order to carry out the expansion work, the Wurten reservoir had to be completely emptied twice: once last year and again at the beginning of this year. The reservoir had to be refilled before winter set in to prevent damage to the dam. Thanks to close collaboration between STRABAG Civil Engineering and ZÜBLIN Specialised Civil Engineering, the first phase of the works was completed in December 2025. To ensure completion on schedule, the team worked additional shifts, including nights.
The Wurtenspeicher reservoir forms part of Kelag’s Fragant hydropower scheme in the Möll Valley. This scheme comprises 15 reservoirs and headwater channels totalling around 79 km in length, as well as 10 power stations. Together, these facilities generate around 800 million kilowatt-hours of electricity each year, which is equivalent to the annual consumption of around 225,000 households.
STRABAG Group
STRABAG AG Austria & ZÜBLIN Specialised Civil Engineering
Client
Kelag
Location
Fragant Power Station Complex, Innerfragant/Mölltal
Start of construction
Spring 2025, completion of the main works in 2026
Storage capacity
2.7 millionm³ to date; 5 millionm³ in future
Raising the reservoir’s maximum water level
8.5 m
Bulk material
230,000m³
Workers on the building site
Around 70 people
