What is a working main power plant

April 2014
In 2014, the machine groups of the main power plant and the doping power plant will gradually be put into operation. The Aare runoff is therefore increasingly directed again via the power station canal. Most of the new power plant will be able to operate under the new regime by the end of the year. The test runs and commissioning are accompanied by the UBB with regard to the spread of turbidity in the Aare and level fluctuations. The evaluation of the measuring probes could so far be classified as without hesitation. The VFAB's water officer follows the developments in KW Rüchlig as an accompanying committee member, so the flow of information can be guaranteed.

June 2014
Construction work on the new KW Rüchlig project is in full swing. With the trial operation of machine groups 1 and 2, which is currently in progress, the power plant is already producing its own electricity. On the environmental side, the commissioning of the new fish pass at the doping power plant is on the agenda. Before the actual flooding, the bottom substrate should now be introduced into the fish pass in a final step.

Fabian Müller (VFAB water officer)

The Rüchlig power plant in Aarau is currently being converted by Axpo in accordance with the latest aquatic ecological findings. For the first time in Switzerland, a fish descent is planned and carried out. This project gives hope for our migratory fish.
After the renovation, the expansion water volume should be 380 to 420 m3 / s. The residual water from November to February 30 m3 / s, March, April, September and October 35 m3 / s and May to August 40 m3 / s.

The following article was kindly made available by Axpo Power AG, Hydroenergie.


River power plants represent an obstacle to fish migration, which is why the aspect of fish migration is taken into account when planning new power plants or new concessions. While fish ascent can be guaranteed with the current state of the art, the know-how for the implementation of fish descent systems in hydropower plants on large Central European rivers is not yet sufficiently known, or it is associated with major structural and hydraulic challenges.

As part of the new licensing of the Axpo Rüchlig power plant, the aspect of fish migration was examined in detail and taken into account. In the following, the measures with regard to hiking trails for the fish that were set out in connection with the re-licensing of the Rüchlig power plant are explained. The implementation of the project has been in progress since April 2, 2012. As part of the implementation, the new fish passages will also be built and put into operation by 2015.

Fish ladder

At the main Rüchlig power station (HKW), a new, state-of-the-art vertical slot pass is being built (April 2010). As part of a pilot project, a lure current pump is used for the main entrance to the fish ladder on the land side, with which the amount of lure water that is important for finding the fish ladder is to be significantly improved. Depending on the flow of the Aare, the attraction flow pump generates an attraction flow of up to 3.6 m3 / s (1% of the expansion water volume at the HKW). The entrance to the fish ladder is a few meters below the turbine outlets.

A new vertical slot pass is also being built at the defense-side doping power plant (DKW). Here the attraction flow is generated solely by the water from the fish ladder (1% of the expansion water volume DKW or more). The entrance is a few meters below the end of the suction tube and consists of a slot, similar to the one in the fish passage itself.

In addition, as part of the ecological compensation measures, the Frey Canal will be opened and a connection to the upstream water will be created by means of a vertical slot pass. Because the mouth of the Frey Canal into the Aare is about 1 km downstream of the weir and is difficult to find for fish in terms of targeted migration, no major fish migration is to be expected. The Frey Canal serves primarily as a living space, not as a walking corridor.

With the implementation of the new fish ladders, it can be assumed that the conditions for upward migrating fish in the concession section of the Rüchlig power station will improve significantly. In order to prove the functionality of the new fish ladders, success controls are planned after the implementation.

Fish descent

In Germany, functioning fish migration aids have recently been used for small hydropower plants. Axpo checked these installations by experts and then proposed them for implementation at DKW Rüchlig.

The planned fish descent system is a combined fish and floating debris drain with horizontal rakes (clear rod spacing 20 mm). This type of fish migration system was tested in Germany at two power plants on the Saale and shows good results. The fish follow the horizontal rake or a half-shell bottom guide wall into a bypass that is open to the surface and close to the bottom. Due to hydraulic and static limits, this principle is only suitable for smaller pen power plants up to around 80 m3 / s expansion water volume. The fish mortality when passing through the DKW can be markedly reduced with this measure, or it drops to zero.

At the HKW, however, no fish descent aid can be implemented according to the current state of the art. In the case of large power plants with a frontal flow, fine screens cannot be used for static reasons, which prevent the fish from entering the turbine area or guide the fish to a migration corridor. Furthermore, due to the high flow velocity at the rake, other behavior barriers such as light pulses or electric curtains are not effective according to the relevant literature. However, choosing a fish-friendly, horizontal-axis Kaplan turbine with only 3 rotor blades can significantly reduce mortality. In addition, two pipes dm = 30 cm will be installed between the new flood relief and machine group 4. These pipes remain closed for the time being and are only used when there is scientifically sound knowledge of how the fish can be guided to the pipes with mechanical or behavioral barriers.

With the creation of a fish descent system at DKW and the choice of horizontal-axis, fish-friendly Kaplan turbines at HKW Rüchlig, all currently possible measures for fish descent are implemented according to the current state of the art. Furthermore, the functionality of the fish descent system at the DKW should be checked by means of a success control.

Overall, the implementation of the new fish migration facility as part of the new Rüchlig power plant project will result in an improvement, particularly for the environmental areas of surface waters, fisheries, as well as landscape and nature. In addition, the concession area can be upgraded with the implementation of nine ecological compensation measures and a significant increase in the amount of residual water. General plan [390 KB]

Axpo Power AG, Hydroenergie, March 4, 2013