Fish Passage Braunau-Simbach

A LIFE Riverscape Lower Inn initiative to improve habitat connectivity

Between 2023 and 2024, VERBUND constructed a 3.1 km-long, near-natural bypass channel at the Braunau-Simbach power station on the River Inn. In future, fish will be able to pass the power station, and endangered animal and plant species will find new habitats.

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Aquatic habitat Technical Details 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.

Bypass watercourses and riverbank restoration
Technical details and data

Responsibility

Österreichisch Bayerische Kraftwerke AG

Approval process

January 2020 to December 2022

Construction

July 2023 to September 2024

The construction work was carried out in as environmentally and climate-friendly a manner as possible: excavated material was reused on site to create new gravel habitats – thereby minimising transport distances and vehicle emissions.

Location of the bypass watercourse: on the left (Bavarian) bank of the Inn between Inn km 63.0 and 60.6, entirely within the ‘Salzach and Lower Inn’ Habitats Directive (FFH) site, and partly within the ‘Salzach and Inn’ Special Protection Area (SPA). The Inn is part of the RAMSAR site ‘Lower Inn, Haiming-Neuhaus’.

Length

3.1 km (unrolled)

Width of the water surface

4-10 m at a flow rate of 4m³/s

Height difference

12,73 m at W30

Average gradient

0,4 %

Flow rate

At least 2 m³/s to 6 m³/s (depending on the season)

2 m³/s (January/February/November/December)
4 m³/s (March/September/October)
6 m³/s (April/May/June/July/August)

Adjustments possible following monitoring