PROJECT DESCRIPTION
BACKGROUND
The Danube River and its floodplains retain few of their original ecological characteristics due to river regulation, low-water regulation and the construction of an almost uninterrupted chain of power plants along the main river. Floodplain habitats have also been strongly affected by damming and river regulation.
In the Danube and its floodplains, a key missing habitat type is permanently connected side arms, which provide spawning grounds and nurseries for rheophilic fish species (i.e. preferring swiftly-flowing water) and shelter from ship-induced waves.
The project area, the Tullnerfelder Donau-Auen, contains 42 species protected under the EU Birds Directive and Annex II of the Habitats Directive. The majority of these species are aquatic or prefer wetland habitats, and the bulk of habitat types are either aquatic or depend on hydrological dynamics.
OBJECTIVES
LIFE Network Danube+ aimed to create around 35 ha of these urgently needed permanently connected side arms. A large natural sidearm and several newly created fishways would allow fish to migrate without barriers to one of the last free-flowing sections in the Upper Danube, as well as to several tributaries and floodplain waters. Restoration measures within the floodplains and tributaries would create key habitats such as spawning grounds and nurseries, so enhancing fish production. The project was predominantly targeted at the protected rheophilic fish species of the Danube and its floodplains, but also at the other (semi) aquatic species.
Its specific objectives are listed below.
- Improving habitat conditions by creating new habitats that are no longer abundant in the Danube and its floodplains but necessary for the survival of the majority of the endangered species. These include:
- flowing water habitats such as shallow banks, riffles and steep erosional banks necessary for the rheophilic fauna and the kingfisher (Alcedo atthis);
- shallow floodplain habitats necessary for the typical wetland fauna.
- Improving habitat conditions by interlinking existing or newly created habitats, thus making them accessible, by:
- reconnecting Danube river sections to allow rheophilic fish access to free-flowing stretches;
- reconnecting tributaries with suitable spawning grounds;
- interlinking highly productive floodplain habitats.
- Demonstrating the suitability of a targeted stepwise approach for achieving the goals of the EU Habitats and Birds Directives and the EU Water Framework Directive on a large spatial scale.
- Demonstrating the positive impact of a constructed wetland on the water quality and lifetime of a large floodplain water body.
RESULTS
At the powerplant Altenwörth, a large bypass system of around 12.5 km by 10-25 m was set in function after the creation of two new sections (3 km upstream and 2 km downstream), improvement of one existing water body (7.5 km), and a 39.21 ha increase in functional gravel bars. This large bypass system now enables unhindered migration for all aquatic organisms.
By the newly created bypass, riverine habitats like gravel bars and sand banks, wooden structures and dynamic riverbanks were increased. Natural structures, different depths and the dynamics of discharge will further develop the river in the future.
At the Altenwörth oxbow lake and its different water levels, zones suitable for spawning of cyprinid fish and slow flowing habitats with suitable conditions for freshwater mussels and the European bitterling fish (Rhodeus amarus) were created. The measures also have had a positive impact on the recreational value of the area.
So far, 41 fish species including 8 Habitats Directive Annex II species were detected using the new bypass river as migration route. Additional fish species, including Habitats Directive species, are to be expected in the coming years. The habitat range of the thick shelled river mussel (Unio crassus), the bitterling (Rhodeus amarus) as well as of the kingfisher, were increased.
Near the Greifenstein power plant, 4 vertical slot fishways were implemented. They now allow unhindered fish migration to highly productive floodplain water bodies as well as to several tributaries of the Danube which had not been previously fully accessible.
In total, more than 200 km of river stretches of tributaries and floodplain waters have been connected to each other and to the River Danube giving fish access to new habitats.
