Can we still build dams in Switzerland?

More than 90% of the hydropower potential in Switzerland is already being used. It is therefore unlikely that new large storage dams will be built. This is not only due to the lack of suitable sites, but also because of their environmental impact. Only a few large run-of-river structures could still be built. The remaining potential lies mainly in the expansion of the capacity of existing structures, as well as in small-scale hydropower.

Hydropower plants generate electricity using the force of moving water. The production capacity of a hydraulic power plant therefore depends directly on the amount of water available (the flow rate) and its drop height (the higher the water falls, the more force it has to drive turbines). Everyone is familiar with the large, often spectacular dams built at the bottom of alpine valleys. These so-called “storage dams” store water in artificial lakes at high altitudes. When the gates of the dam open, the water flows through penstocks to the plains, where turbines convert the enormous energy acquired during the 1000-1500m drop into electricity.

Switzerland has about 80 large-scale hydroelectric storage power plants, the majority of which are located in Valais, Grisons, Ticino and the canton of Bern. The highest dam in Switzerland, the Grande Dixence in Valais, is 285 m high. The oldest, Rütiweiher, in the canton of St. Gallen, is nearly 170 years old.

There is hardly any possibility of building new large-scale storage dams in Switzerland. On the other hand, it is possible to raise or extend existing structures [→ Q76] where the environmental impact is limited, as in the case of the Muttsee dam (Glarus), whose 1 km wall will make it the longest dam in Switzerland, and the Vieux Emosson dam (Valais), whose construction was completed in 2016. New potential could also arise as glaciers melt, which in some cases could leave room for glacial lakes with potentially attractive storage capacities. Although some projects are currently under study, this potential is still very difficult to estimate [→ Q14].

The potential of hydropower is far from limited to storage dams. In fact, storage dams account for only about 50% of our current hydroelectric production. The other half comes mainly from so-called “run-of-river” power plants built on lowland on rivers with large flows. They produce electricity simply by pumping flowing water through turbines, and thus have virtually no production flexibility. Switzerland has 559 run-of-river facilities, including 136 on the Rhine, 126 on the Rhone, 65 on the Reuss, 103 on the Aar and 72 on the Limmat.

Unlike storage dams, run-of-river structures still offer some untapped potential. Some 15 large-scale run-of-river power plants could be created in Switzerland, adding 1.4 TWh a year to our hydroelectric production. Run-of-river power plants currently produce an average of 15 to 17 TWh of electricity, compared with 19 to 22 TWh of electricity from storage power plants. The development potential of hydroelectric facilities has been reassessed several times, and in 2012 it was estimated at approximately 1,500-3,000 GWh per year, resulting in an expected generation of 37-38.5 TWh/year. These forecasts were revised downwards in a more recent study, due to the new Law on the Protection of Watercourses. The maximum potential was estimated at only 1,560 GWh per year, for production between 36 and 37.5 TWh/year. However, this figure does not include the potential of small hydropower, which is included in new renewable energies [→ Q57]. Moreover, the new requirements of the Water Protection Act will result in a decline in estimated annual production of 1.5 TWh by 2050 in order to increase minimum flows into rivers.