In summer 2017, numerous interested people visited the Greifenstein fish migration aid. They gathered directly in front of the drop height.

Summer break at the
Greifenstein fish migration aid

01 August 2017

The Greifenstein Danube power plant was an ecological showcase project when it opened in 1985. The company management and scientists proudly presented the "watering channel" to which the Greifenstein power plant owes its Natura2000 protected area. A system of artificial reservoirs in the floodplain saved the landscape from drying out and repaired the consequences of flood protection and meadow drainage. (The fact that the power station was nevertheless unable to dispel all concerns about the construction of Hainburg as a shining example is another page in Austrian industrial history).

But science does not stand still and 30 years later it is no longer (just) about renaturation, but about connecting habitats on the Danube, which is sometimes heavily obstructed. In the "LIFE+ Netzwerk Donau" project, VERBUND has set itself the goal of connecting existing ecological stepping stones along the Danube and making the Danube power plants passable for fish. The project is supported by six funding partners: the EU as part of the LIFE+ program, the Ministry of Agriculture, Environment and Water Management, the provincial governments of Upper and Lower Austria and the provincial fishing associations of Upper and Lower Austria.

David Oberlerchner is in charge of the package of measures. He himself is in charge of the detailed project management for the Greifenstein fish migration aid project. That's why he knows all the amazing details.

Slaloming through the landscape

The lush Gießgang nature reserve is located in the immediate vicinity of the construction site for the fish migration aid. The quality of the landscape forced a few loops and detours. "We actually wanted to cross an old soccer pitch near the power station - but valuable orchid colonies have formed there that we didn't want to destroy," says David Oberlerchner. We also didn't want to plow a path right through the riparian forest. The result was a pretty, meandering course of 4 kilometers. "The fish will be happy if they can hide in small bays and bends," says David Oberlerchner sympathetically. On top of this, "predatory trees" were deliberately anchored in the course of the fish migration aid. They simulate an old floodplain landscape with deadwood. A retreat for young fish as well as a hunting ground for kingfishers.

The map shows a rudimentary section around the fish migration aid at the Greifenstein power station.

Summer break in August

Summer 2017 is half-time for construction. Work will be suspended for the rest of August, after which the excavators will continue to work their way down from the top. The "exit", i.e. the mouth of the fish migration aid, has already been completed. Two small barriers regulate the water level here. In the event of a flood, the water level in the vicinity of the power station drops sharply (we explain this paradox better in a video). To ensure that the fish migration aid does not run dry even in such an exceptional case, there is an "emergency water supply", i.e. a pipe system for irrigation.

At the lower end of the fish migration aid, even the uninitiated can immediately see the problem: there is a height difference of 10 meters at the Greifenstein power station. The turbines use this to generate electricity, but for the fish it is an insurmountable barrier. The first excavations illustrate these 10 meters. Curves and bends are needed for this and, of course, small pools where the fish can catch their breath on their long journey around the power station.

Project manager David Oberlerchner visits the Danube Network project area with squeaky duck Doris to get an overview of the situation.

This brings us to our favorite question for project manager Oberlerchner: Why wasn't the existing casting channel in Greifenstein modified to be suitable as a fish migration aid? The casting channel is even lower than the power plant dam, so there would be even more height to overcome between the Danube and the fish migration aid. In addition, it would first have to be comprehensively investigated whether and how more water in the casting channel would affect the groundwater, a highly sensitive issue, especially in the Tullnerfeld. "Years of research would be needed to establish certainty. The fish can't wait that long," says Oberlerchner, explaining the pragmatic approach to solving the problem.

A total of 330,000 cubic meters of gravel will be dredged from the floodplain. The closer they can be used, the more environmentally friendly the transportation. The material is used to build wildlife rescue mounds (for floods in the floodplain) and, if possible, to supply construction sites in the neighborhood. There is therefore no unnecessary haste in the project. "We are making the power plant ecologically fit for the next 30 years and hope that the new habitat will also be appreciated by the fish." Project manager Oberlerchner is convinced that the biodiversity promoted in this way will also benefit the Danube. "We hope that future generations will recognize our achievements just as much as we do those of the power plant builders in Greifenstein, who have set the environmentally friendly bar high with the casting channel."

Foto: Lorem ipsum / VERBUND

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