15.06.2022 | Hydropower on the Vorderrhein - and the matter of dam raises

Winter reserves behind high walls

In the side valleys between the Oberalp Pass and the Lukmanier Pass, the Curnera, Nalps and Santa Maria reservoirs collect water all year round for electricity production in winter. With a power shortage expected in the coming years, a proposal to heighten the walls of these dams aims to reduce risks and contribute to power supply security in the future. The project is one of the proposals of the ‘Hydropower Round Table’ led by Federal Councillor Simonetta Sommaruga. Feasibility and funding studies are currently being carried out.  

A few bends after the Oberalp Pass in the direction of Sedrun (GR) you’ll find an inconspicuous gravel path which turns off in the direction of the SAC ‘Maighelshütte’ (an alpine hut). If you’re not deterred by the bumpy path, behind the first alpine building you will discover a turn-off to a well-kept road with a gate. The access road to Lai da Curnera, closed to the public, meanders along the mountainside and, after a tight bend, reveals a view of the Curnera valley with its 153-metre-high dam. 

"Turquoise blue water": The Lai da Curnera with the 153-metre-high dam wall

At the damn crest reached via serpentine curves, the railing of the dam wall shakes in a gusty southerly wind – the fabled ‘Föhn’. The lake – turquoise water flanked by pale gravel slopes – lies far below the dam wall. ‘The water level only reaches the maximum volume in September,’ explains Peter Lustenberger. As the former Head of Asset Management Hydro he knows Axpo hydropower inside and out.

The Curnera reservoir has a surface area of 82 hectares and a total of 41 million cubic metres of water. Within the rock, a sophisticated tunnel system leads to two other reservoirs. The Lai da Nalps is in the next valley over while the Lai da Santa Maria runs along the Lukmanier Pass road, two valleys away. The two lakes are located more than 1900 m above sea level and are owned by Kraftwerke Vorderrhein AG (Axpo stake: 81.5%). The two power plant facilities produce electricity on a large scale: Sedrun (151 MW) and Tavanasa (180 MW). Axpo also recently started using the gradient of a transfer line to generate electricity. The average annual production is around 840 million kilowatt hours of electricity, equivalent to 840 gigawatt hours (GWh).

Almost precisely 1400 metres deeper underground, below the Curnera dam, you might feel a draught; passenger trains travel at 200 km/h in the two tubes of the 57-kilometre Gotthard Base Tunnel – faster than anywhere else in Switzerland. Peter Lustenberger recalls: ‘When they were building the Gotthard Base Tunnel the huge tunnel boring machines caused us some concern. To detect vibrations and any possible impact on the dams, we attached probes to the three dam walls as a precaution.’

Winter electricity shortage

It is quite possible that the electricity for this rapid tunnel transit comes from hydropower – in winter, at least. That’s when water becomes a valuable commodity which Axpo hoards carefully. While run-of-river and nuclear power plants meet a large part of Switzerland’s daily electricity requirements, the reservoirs play an important role at peak consumption times, especially in winter. ‘Electricity consumption increases in winter,’ says Peter Lustenberger. ‘But water becomes rarer. Because as soon as precipitation settles as snow on the Swiss mountains, it only liquefies again in spring.’ 

Similar yet different: the Lai da Nalps

The three reservoirs of Curnera, Nalps and Santa Maria use the eastern Gotthard Massif as their catchment area, totalling 315.8 km2. It is significant that the Alps of all places – the epitome of Switzerland’s defence capability – secures part of Switzerland’s power supply from renewable energies in winter. Most Swiss reservoirs lie on the Alpine divide, with the rest in pre-Alpine areas.

No power without winter reserves

The situation is both simple and complex. If Switzerland manages to store more water in the future, it will be better able to use its own resources to counteract winter power shortages which could begin in 2025. As is often the case, however, pragmatic solutions are faced with special interests, environmental concerns and economic obstacles.

This is where winter electricity is made: Sedrun power station

The ‘Hydropower Round Table’ encompasses representatives of the cantons, business, administration and associations, and met for the first time in autumn 2021 at the invitation of Federal Councillor Simonetta Sommaruga. Through this forum, Switzerland is striving not only for a mutual basic understanding, but also for constructive, concrete solutions for higher winter electricity production from hydropower. At least 2,000 gigawatt hours of additional winter electricity are required.

‘In the first phase we are focusing primarily on raising the dam walls at existing power plants,’ says Peter Lustenberger. As a member of the Round Table advisory group, he is exploring Axpo’s expansion options. ‘As well as the Mattmark power plant in Valais, we see the largest potential for additional production from the three reservoirs of Curnera, Nalps and Santa Maria.’

20 + 7 + 7 metres = 99 gigawatt hours (GWh) = 218,000 four-person households

The Curnera dam is to be raised by up to 20 metres, with the Nalps and Santa Maria reservoirs increasing by seven metres. ‘Twenty metres is a lot,’ stresses Peter Lustenberger. ‘It’s roughly the size of a seven-storey apartment building.’ This increase would translate to 45 gigawatt hours of electricity. Engineers are studying the robustness of the damn crest and the resilience of the bottom outlet. Geologists are checking the impermeability of the rock and the stability of the mountain flanks, and economists are calculating the costs for structural adjustments to the spillway and the water catchment. ‘We are working with hydrologists to determine how much water we can actually collect from the eastern Gotthard Massif.’

The three Kraftwerke Vorderrhein reservoirs were created between 1962 and 1968 and were earmarked from the outset for winter energy and peak consumption. While the Curnera and Nalps dams were built in uninhabited side valleys, the Lukmanier Pass road and the hospice along with its chapel had to be relocated when the Lai da Santa Maria was dammed. 

Still turquoise blue: Tavanasa balancing basin and power plant

The infrastructure of the Lukmanier Pass still limits the height of the dam wall to seven metres. That has a direct impact on the Nalps dam. ‘The two lakes are connected by free-flow tunnels and balance each other’s water levels.’ But a lake seven metres higher would enable additional production of 27 gigawatt hours per reservoir. This means Kraftwerke Vorderrhein could bring up to 99 gigawatt hours of additional domestic winter electricity to the ‘Hydropower Round Table’. That’s more electricity than the whole city of Geneva consumes. However, the feasibility of this investment for Axpo also depends on framework conditions.

Because every kilowatt hour will count…

It’s not just higher dam walls that contribute to security of supply. Because every kilowatt hour will count in the future, Kraftwerke Vorderrhein is now also using water from a transfer line between the Curnera and Nalps reservoirs to produce electricity. ‘We had long considered the idea of using the gradient of this line,’ as Peter Lustenberger recalls. In 2014 the team began the actual planning and found a 2.5 MW turbine that could squeeze into the extremely tight space inside the mountain. The small new hydropower plant went into operation in early 2022, and is expected to produce up to 10 million kilowatt hours of electricity per year, which is enough to supply around 2,200 households – a town the size of Sedrun, for instance. A drop in the bucket, perhaps, but a further contribution to a secure power supply through domestic hydropower.

Facts & Figures

Curnera reservoir (1956 m above sea level)

Dual-curve arch dam: 153 m

Damn crest: 350 m

Lake volume: 40.8 million m3

Nalps reservoir (1908 m above sea level)

Dual-curve arch dam: 127 m

Damn crest: 480 m

Lake volume: 44.5 million m3

Santa Maria reservoir (1908 m above sea level)

Dual-curve arch dam: 117 m

Damn crest: 560 m

Lake volume: 67 million m3

Sedrun facility: 3 x 50 MW Pelton turbines

Tavanasa facility: 4 x 45 MW Pelton turbines

Curnera small hydropower plant: 1 x 2.5 MW Francis turbine

Median annual production: 840 million kWh (840 GWh)

Free group tours are available on booking (minimum eight visitors) every Thursday. Call +41 (0)81 920 40 30 (Sedrun Disentis Tourist Office) to book

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