In a little under a year and a half, right in the urban setting of the nation's capital, a special kind of fish bypass was created in Vienna's 20th district. It is not only unusually large, but also actually tunnels under the historic Schemerlbrücke Bridge from 1898. Thanks to extensive special civil engineering works, the waterway construction fits into the limited space of the Otto Wagner ensemble at the Brigittenauer Sporn. Today the fish ladder was ceremoniously opened by Jörg Leichtfried, Minister of Infrastructure; Dorith Breindl, Deputy Head of Department of BMLFUW; the Board of VERBUND AG; and the Management of DHK and viadonau.
For more than 10 years, the small power plant at Nussdorf has been supplying energy for Vienna's population. However, many river organisms need a range of different habitats for their natural life cycle. And power plant barrages often present an insurmountable hurdle for them. "With the new fish bypass in Nussdorf," Minister Leichtfried commented at the opening, "we are removing the barrier between the Danube and the Danube canal, and ensuring that this habitat is once again connected. So make way for our domestic fish population: they are now once again able to migrate upstream to spawn. We are returning a piece of nature to them and assuring their survival in the future as well." The genetic exchange is likewise supported by fish bypasses. This of course also affects the fish populations in individual river sections. In addition, it increases their chances of finding the living conditions in the river that they need for their respective stage of development. In this way, fish passes or fish ladders play an important role both in species protection and in the renaturation of formerly built-up river sections when this provides suitable habitats.
Unusual waterway structure
On their route over the Nussdorf fish ladder, fish will overcome an altitude difference of around 3.6 metres. A total of 37 migration basins ("vertical slots") were constructed over a distance of approximately 320 metres. Just as noteworthy: Tunnelling under the Schemerlbrücke Bridge, which was completed in the year 1898, is a hitherto unique solution as far as fish ladders are concerned. "In an urban environment it is especially important to leave room for nature, or when possible to return areas to nature. With the modern fish ladder in Nussdorf, the power plant is no longer the ‘last stop’ for migratory river fauna, but rather a new opportunity to preserve their population on a sustained basis – an important step for sustainable species protection," as Ulli Sima, City Councillor for the Environment, was pleased to note upon completion of the water construction.
The restoration of connectivity for fish took place in accordance with the specifications of the EU Water Framework Directive and the national Water Management Plan. Planning was oriented towards the guidelines for fish ladder construction for the Danube's dominant fish species, the wels catfish. Dorith Breindl, Deputy Head of the Water Sector in the Federal Ministry of Agriculture, Forestry, Environment and Water Management, emphasised on the occasion of the opening: "In order to improve the ecological conditions, we are not merely taking measures for water pollution control, but also to improve the physical river structure. Fish ladders are being constructed, water habitats interconnected and barriers in the water removed or adapted. For this reason the Federal Ministry of Agriculture, Forestry, Environment and Water Management is supporting the Nussdorf fish ladder project, and with approximately 2.5 million euros made a significant contribution towards making this measure possible."
"As the largest hydropower electricity producer in Austria, we know what we owe to water bodies. The project in Nussdorf is a perfect example of good cooperation among all concerned, for the goal of a healthy, biodiverse aquatic landscape," says Günther Rabensteiner, Member of the Board of VERBUND AG.
The City of Vienna, Specialist Department MA 45 - Wiener Gewässer (Viennese water bodies) submitted the project in 2008 as a measure in the First National Water Management Plan (NGP). The first stages of planning and basic agreements with partners, and on to the first water management submission, were done by the experts of the specialist department. Following this, final planning and the constructional implementation were handed over to viadonau. The City of Vienna is involved in the project with a share of about one sixth of the total costs.
The constructional implementation was initiated by DHK - Donau Hochwasserschutz Konkurrenz in close cooperation with VERBUND Hydro Power GmbH. The successful construction was ensured by financing from the three shareholders in Kraftwerk Nussdorf GmbH, namely VERBUND Hydro Power, evn naturkraft and Wien Energie, with support from the Federal Ministry of Agriculture, Forestry, Environment and Water Management, the Federal Ministry for Transport, Innovation and Technology, the City of Vienna, the Vienna Fisheries Committee (Fischereiausschuss) and the Lower Austrian Fisheries Association.