The restoration of the Aufhausener Lacke

As an example of the renaturalisation of reservoirs on the Lower Inn

The LIFE project Riverscape Lower Inn comprises a large number of measures to improve the situation of still waters. The example of the Aufhausener Lacke is a good illustration of the ecologically negative development of the silting up of standing waters in the side areas of the Inn reservoirs.

The Aufhausener Lacke was a standing water body on the left bank of the Inn between river kilometres 44 and 42. It has been dry all year round since 2022 due to siltation and reeds are beginning to overgrow the area. Decades of sand input during Inn floods caused it to dry up, and now the Aufhausener Lacke is completely silted up. As the residual dynamics in the floodplain on the water side of the dams are not sufficient to flush out the sediments again, structural measures must be taken here.

For this purpose, over 70,000 m³ of sediment will be removed from the Aufhausener Lacke and relocated to the river bank. The sediments are transported further when the water flow of the Inn is higher, although this does not significantly increase the natural suspended matter load of the Inn.

There are numerous other areas along the Inn that have undergone a similar development. As the floodplain waters are very important habitats for a large number of rare animal and plant species, the LIFE project aims to renaturalise them and thus enhance the habitat.

Once completed, the still waters should remain in existence for decades and serve as a valuable habitat for fish, water birds, amphibians and insects in the Inn floodplains. Shallow water zones and deep areas will be created. By connecting the deep zone to the Inn, fish will once again be able to use the Aufhausener Lacke as a habitat. The shallow water areas will be re-covered by water-bound vegetation and thus offer a perfect environment for fish larvae and juvenile fish as well as for waterfowl.

The connection to the Inn will be limited to its downstream end in order to avoid rapid resedimentation due to the entry of suspended matter. Experience from other projects has shown that floodplain waters that are only connected to the river at their downstream end last the longest.

The restoration of the Aufhausener Lacke will therefore improve habitat diversity in the European nature reserve, thereby contributing to the implementation of the EU Water Framework Directive.

Further measures

A natural water area surrounded by trees and reeds.

Floodplains

Lost river structures should be recreated around a total of three power plants in the project area. The floodplains play a special role in this – as habitats for typical flora and fauna.

Floodplains
Purple blooms of a wild flower surrounded by green grass and foliage in sunlight.

Flourishing Embankments

Embankments in the area of the power plants are not just side effects of hydropower. They are also habitats of special quality – assuming appropriate care is taken. The opportunity to develop species-rich meadows and drygrass areas of European importance should be taken at a total of four power plants.

Embankments in Bloom
Aerial view of a power plant on a river with backed-up water, adjacent wooded area, and hiking trails in clear weather.

Continuity and habitat

Power plants represents barriers to the migration of aquatic lifeforms. The aim at two power plants is to create not only continuity but also habitat.

Habitat
Foto: Lorem ipsum / VERBUND

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