Side arm re-connection ‘Spittelauer Arm’

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At the Danube section Petronell to Hainburg (Lower Austria), several important renaturation projects have already been implemented in recent years and low water level regulations have been adjusted. With the renaturation measures at ‘Thurnhaufen’ almost 3 km of natural riverbanks were created. The project was implemented in cooperation with Donau-Auen National Park and has also been awarded by the EU as the best LIFE project in 2007/2008. Another 1.4 km of riverbank were restored between 2012 and 2014. During this time the so called ‘Johler Arm’ – a former side arm - was reconnected to the main stream of the Danube. Professionals from all over the world are still visiting this lighthouse project.
For the time being, the last significant step towards the renaturation of the section was the reconnection of the Spittelauer side arm system, which is situated on the opposite side of the city of Hainburg on the left bank of the Danube (Stream-km 1886-1882, left bank).

Description of measures

The existing inflow opening was lowered to ensure that water can flow into the side arms almost all year long. The existing traverses made from stone blocks were removed. The big traverse at the mouth of the side arm was removed so that water and sediments can flow back into the Danube unhindered. The connection created a tributary about 4,34 km long, which is flowed through almost all year round. In addition, the 550 m long fishermen's ditch was strengthened in the estuary area. The area of ‘Thurnhaufen’ opposite of the city of Hainburg has become an island that serves as a retreat for alluvial forest residents. In the system, existing bank protections were removed over a total length of 710 meters.

Map of the realised measures at Spittelauer Arm — Realised measures at Spittelauer Arm, source: viadonau

Ongoing activities & Outlook

In December 2019, the necessary clearing was carried out as essential preparatory measures. The hydraulic engineering work to connect the Spittelauer Arm started in January 2020 and lasted until summer 2021. The breakthrough took place on September 10, 2020. Since then, Danube water has been able to flow through the tributary again. The dismantled stones (riprap) were collected on the Danube banks and gradually transported away for reuse in other projects. The new sidearm has already transformed into a dynamic lifeline for the Danube floodplains.

The renatured branch will be expanded at the outflow opening through a follow-up MERLIN project and will be structurally completed by mid-2024. Post-monitoring will run until 2026.