Fish passage Egglfing-Obernberg

A LIFE Riverscape Lower Inn initiative to boost biodiversity

VERBUND is constructing a 5.8 km-long bypass channel at the Egglfing-Obernberg power station on the River Inn, to be completed by 2027. Preparations began as early as autumn 2024. In future, fish will be able to pass the power station, and new habitats for endangered species will be created.

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Aquatic Habitat Technology and Data

A near-natural aquatic habitat

Building on the positive experiences at the Ering-Frauenstein power station on the River Inn, VERBUND has developed a similar concept for fish migration assistance at the Braunau-Simbach power station on the River Inn.

To enable fish to swim past the power station, a bypass channel with near-natural flow dynamics was constructed. It extends from the upstream section to the downstream section of the river, downstream of the power station.

The fish migration aid is more than just a migration corridor: with fords, gravel banks shaped by the current, shallow water zones, deadwood and coves, a structurally rich watercourse has been created that offers an attractive habitat for numerous Inn fish and other aquatic organisms.

Shallow gravel banks serve as spawning grounds and habitats for young fish, whilst deeper areas provide space for river-dwelling fish such as the nase and the huchen. Alongside the bypass channel, new habitats are being created for gravel-nesting bird species, amphibians, reptiles, insects and typical floodplain vegetation. The bypass channel also ensures a better water supply to the adjacent floodplain and enhances its ecological value.

The fish migration aid will allow 2 to 6 cubic metres of water to flow per second. From spring to summer, during the spawning season for most Inn fish, more water flows; in autumn and winter, less. The water is diverted from the River Inn into the fish migration aid at the so-called diversion structure; a controlled supplementary flow enables the seasonal increase in discharge. Over a length of 3.1 kilometres, the water flows through structurally rich sections and empties into the River Inn between the power station and the Inn Bridge. Here, stone structures on the banks of the Inn have been removed and near-natural gravel banks created. These areas provide important resting, breeding and spawning grounds for birds, amphibians and other riparian species.

Fish migration and the ecological development of the bypass channel and its surroundings are documented through a monitoring programme, and the results are published.

A comparable project at the Ering-Frauenstein Inn power station provides clear evidence that natural, dynamic and large-scale bypass channels are well received by fish. It came into operation in 2019, and by the end of 2020 a total of around 40,000 fish had swum past the power station. They belonged to 36 different fish species. The largest fish was a catfish measuring 1.2 metres in length. One of the highlights was also the detection of several specimens of the stone loach, a fish species previously thought to be extinct in the Lower Inn.

In the Lower Inn European Reserve, the LIFE project contributes to the implementation of the Fauna-Flora-Habitat Directive and the Birds Directive, as well as the European Union’s Water Framework Directive. The project is co-financed by the European Union through funds from the LIFE Programme.

Umgehungsgewässer und Uferrenaturierung
Technik und Daten

Verantwortlichkeit

Innwerk AG

Genehmigungsverfahren

Dezember 2019 bis Dezember 2025

Baudurchführung

März 2026 bis Ende 2027
Inbetriebnahme und Restarbeiten 2028

Die Bauarbeiten werden so umwelt- und klimaschonend wie möglich umgesetzt: Aushubmaterial wird für neue Kieslebensräume direkt vor Ort wiederverwendet - so werden Transportwege und Fahrzeugemissionen auf ein Minimum reduziert. Es wird mit Materialumlagerungen von etwa 530.000 m3 gerechnet.

Lage des Umgehungsgewässers: am linken (bayerischen) Innufer zwischen Inn-km 40,6 und 34,8, vollständig im FFH-Gebiet „Salzach und Unterer Inn“, in Teilen im Vogelschutzgebiet (SPA Gebiet) „Salzach und Inn“. Der Inn ist Teil des RAMSAR Gebiets „Unterer Inn, Haiming-Neuhaus“.

Länge

5,8 km (abgewickelt)

Breite der Wasserfläche

7-10 m

Höhendifferenz

10,6 m bei W30

Gefälle

0,05 bis 3,6 %

Dotation

Mindestens 4 m³/s bis 10 m³/s (abhängig von der Jahreszeit)

4 m³/s (Mitte November bis Mitte Februar)
sonst zwischen 4 und 10 m³/s (Maximum Mai)

Anpassungen nach fischökologischem Monitoring möglich

Lage der Uferrenaturierung

1,65 km am linken (bayerischen) Innufer
zwischen Inn-km 34,45 und 32,80