Riverbank restoration MERLIN completed

FGP, viadonau, environment

On 11 March 2025, the joint project team from BOKU and viadonau carried out a site inspection to mark the completion of the construction works for the bank restoration in the Hainburger floodplain.

Construction works on the riverbank, photo: © viadonau

Project team in front of the bank restoration - immediately after completion, photo © BOKU/IHG

The riverbank restoration is part of the EU-funded MERLIN research-project to restore Europe's freshwater ecosystems. The measure on the Danube is intended to demonstrate the possibilities of the restoration of inland waterways. This makes a further contribution to enhancing the habitat and preserving biodiversity in the Donau-Auen National Park.

Work carried out

The stone bank protection was completely removed over a total length of 920 metres. Around 8,000 m³ of riprap were removed from the national park. Around 40,000 m³ of fine sediment, which covered the bank protection, had to be relocated for the work.

Alice Kaufmann was responsible for construction management at viadonau: “Right at the start of the construction work, we found another bank stabilisation that was previously unknown to us. In order to achieve the goal of complete restoration, we decided to extend the construction project. The planned 800 metres ultimately became 920 metres, along which the hard stone cover of the riverbank could be completely removed. Another challenge were the high water levels of the Danube in 2024, which significantly delayed the completion of construction. All the better to have now reached this important milestone.”
Of the two traverses that separated two natural ditch systems from the Danube in the project area, one was removed and another was significantly lowered, allowing the restoration to work deeper into the floodplain at higher water levels.

The Danube takes over the finishing touches

Immediately after the construction machinery has left and when the water level is very low, the bank looks very ‘tidy’, but it won't stay that way. From now on, the Danube will take over the finishing touches. Higher water levels will remove the loosened fine sediment and expose the underlying gravel. Shallow gravel zones and steep walls will form in the finer sediment layers. To support this process, an initial trench has been created along the reclaimed bank.

Silke-Silvia Michelitsch is coordinating the scientific aspects of the project: “The river can now shape the bank itself. We will monitor further developments and we also plan to carry out investigations along the new bank. The experience gained here can be used to learn for future hydraulic engineering projects.”

Restoration of the Danube waterway

The bank restoration is part of the river engineering Catalogue of Measures for the Danube east of Vienna. With its completion, two major existing restoration projects will be significantly expanded once again: the Thurnhaufen riverbank restoration opposite the town of Hainburg and the reconnection of the Spittelauer tributary system as part of the Dynamic LIFE Lines Danube project, which was completed in 2021. The restoration work took place directly downstream of the outflow opening of the tributary, meaning that there is now great potential for an even wilder river landscape. These extensive restoration measures are possible without affecting navigation on the international Danube waterway. This is one of the key messages arising from this case study.

The MERLIN project enters its final phase

MERLIN is a Europe-wide research project co-funded by the EU's HORIZON 2020 programme. 47 partner organisations are working together to create the basis for even more effective restoration of freshwater ecosystems. Research is also being carried out in particular on the basis of the implementation of 17 case study projects along streams and rivers, in lakes and moors. The Austrian case study involves the waterway company viadonau as ‘implementation partner’ and the Institute of Hydrobiology and Water Management IHG at BOKU as ‘science partner’. The results of the MERLIN project should be available by March 2026.