Pradapunt hydropower plant - new construction project protects flora and fauna

With the new Pradapunt construction project, a consortium comprising the three partners Axpo, Arosa Energie and IBC Energie Wasser Chur is demonstrating how environmental measures and electricity production can go hand in hand. The future hydropower plant will rehabilitate the surge of the Litzirüti power plant located upstream, thereby protecting the floodplain landscapes in the course of the Plessur river. The hydropower plant, which will be underground, is expected to produce invisible CO₂-free electricity for around 10,000 four-person households from 2031.

Legend has it that 365 bends wind their way from Chur to Arosa. In reality, there are 240 of them, which lead through the bulky Schanfigger Tal valley to the famous ski resort. This impressive number was calculated by the local tourist office and has opened up an interesting source of income through curve sponsorships. Arosa Energie produces electricity in an inconspicuous building just a few metres away from bend 202. Mostly at peak times. This means that the Litzirüti power station uses the water from the Isel reservoir when people are watching television in the evening, firing up the coffee machine in the morning and frying eggs.

Rethinking the remediation of hydropeaking  

When the power plant starts up its machinery, the Plessur swells considerably below the power plant and sinks again just as suddenly when no more electricity is produced. This so-called surge and sink is a well-known phenomenon around storage hydroelectric power plants and can have a negative impact on flora and fauna.

Effectively remediating hydropeaking with reasonable financial resources is a challenge for many hydropower plants. In addition, the Federal Water Protection Act obliges the owners of hydropower plants to take suitable measures to eliminate hydropeaking by 2030. One option is to divert the immediately swelling water into an equalisation basin and release it into the river in doses. However, some hydropower plants do not have space for a basin. "We chose a different approach for the hydropeaking and hydropeaking remediation of the Litzirüti power plant," says overall project manager Peter Oberholzer, looking at the Plessur from bend 202.

"In future, we will no longer channel the irregular surge water back into the Plessur, but from here directly into an underground tunnel and use it generate electricity at Pradapunt." Peter Oberholzer emphasises: "This is close to the "Füüfer und Weggli". With this solution, we can keep the discharge below the Litzirüti power plant constant and supply 10,000 four-person households with electricity at the same time." The installed capacity of the new power plant is 10 megawatts (MW), which corresponds to a medium-sized run-of-river power plant similar to the Rüchlig power plant in Aarau. 

Like all large hydropower plants, the Pradapunt power plant is subject to an environmental impact assessment. The investigations carried out under the direction of Axpo not only prove the environmental compatibility of the project, but also show that the special design of the new power plant as a pure hydropeaking power plant can completely eliminate the negative influences in the section between Litzirüti and Pradapunt. The Plessur can thus be significantly upgraded ecologically in this section in order to establish a self-sustaining biocoenosis that is suitable for the site in the long term.

"By applying protection and utilisation planning, we will also place the section of the river between Litzirüti and Pradapunt with its floodplains of regional and national importance under additional protection," explains the overall project manager. "This means that we are ruling out any further utilisation of the water for electricity production in this section of the river. The other tributaries will remain undiminished in the river in future and cannot be captured by the Pradapunt power plant or third parties." The consortium has decided not to build a new water intake in Litzirüti and thus not to utilise the existing potential of around 7 GWh of electricity.

15 metres of tunnelling per day

Meanwhile, Peter Oberholzer crosses the main road and points to a meadow adjacent to bend 203, where the installation site for the underground construction site will be built in 2028. "It will be worth seeing when specialists prepare the mighty tunnel boring machine here, which we will transport up through the valley in individual parts."

The colossus with a diameter of 3.7 metres will mill its way through the mountain towards Pradapunt at a rate of around 15 metres per day. The project manager estimates that it will take around a year to build the tunnel. The excavated material will find a new home in the meadow near the installation site. "The site will be raised by a few metres, that's all."

Second licence granted

Back in 2008, Axpo, together with representatives from Arosa Energie and IBC Energie Wasser Chur, began planning to close the last gap in the power plant cascade on the Plessur. Peter Oberholzer: "However, the licence granted by the municipality of Arosa in 2016 coincided with a period of low electricity prices, which made a new construction uneconomical." The project was suspended.

The price of electricity and thus the attitude of the Swiss population towards domestic electricity production did not change until 2022 due to the war in Ukraine and the lack of gas from Russia, which made electricity a scarce commodity in Western Europe. 

Due to the systemic importance of Swiss hydropower and in order to secure Switzerland's electricity supply, various hydropower projects have since been relaunched, including the new Pradapunt construction project. "We were able to adopt individual points from the existing plans, but we completely redesigned a lot of things" explains the ETH civil engineer.

Underground - invisible - environmentally friendly

From 2031, the surge water from the Litzirüti power plant will take its very own underground, invisible route to Pradapunt. From the Litzirüti control centre, it will flow into a tunnel running parallel to the Plessur river and, after around 360 metres, will be channelled into a 4.5-kilometre-long pressure tunnel at the Sand portal. Via a pressure pipe from the surge chamber, the water finally drives a 10 megawatt Pelton turbine in Pradapunt.

The new power plant will be able to feed around 42 gigawatt hours of electricity into the grid each year. This corresponds to the needs of the city of Chur with its 40,000 inhabitants. However, neighbouring residents will not feel the effects of the electricity production. With the exception of the central building in Pradapunt, most of the facilities are located underground.

Supported by the project consortium and subsidised by the federal government, the estimated costs of around 81 million Swiss francs are considered an environmentally friendly investment in the future. "I am proud of this concession project," says Peter Oberholzer. "The consistent design of the new power plant to divert surges results in a win-win solution for the environment, the power plant operators and the population, who benefit from safe and clean electricity."

The licence for the Pradapunt power plant is to run for 80 years from the planned commissioning in 2031. The municipality of Arosa will decide on the granting of the concession in the referendum on Sunday, 9 February 2025. The two-stage approval process with the licence approval and building application process will take several years, meaning that the consortium partners will not be able to make an investment and construction decision until 2027 at the earliest.