River Engineering on the Danube

The regulation of the Danube in the 19th century has significantly changed the river landscape and stands in the way of a natural development of the wetland ecosystem. One of the main objectives of the hydraulic engineering measures of the National Park is therefore the withdrawal of "hard" hydraulic engineering structures. The landscape-forming processes are to be reactivated and brought into as natural a balance as possible.

New Projects

Viadonau, the partner organisation of Donau-Auen National Park in ecological river management, focuses on a combination of conservation measures and projects, based on lessons learned. The three main goals are: 1) stabilization of water levels 2) improvement of the Danube floodplain habitat and 3) optimization of the waterway infrastructure.

Extended bedload management is now in place to stabilize the river bed. The gravel dredged for the maintenance of navigation conditions is already transported upstream and dumped there in areas where the riverbed is deep. This approach has been expanded. The gravel is now dumped as far upstream as possible, so it can remain longer within the National Park and help stabilize water levels. The bedload transfer will be combined with additional coarse grain in the future. In order to ensure navigability also during low water periods and to reduce the running costs of the waterway infrastructure, low-water regulation (groynes, training structures) in critical ford areas (shallow points) are optimised. Furthermore, side-arm reconnection as well as riverbank restoration will be enhanced. One of the target areas for future measures is the “Regelsbrunner Au”.

Evaluations show that the deepening of the Danube riverbed has already decreased due to the successful implementation of pilot projects and the disposal of dredging material at deep locations. Scientific monitoring of restoration projects also showed positive ecological effects. For example, the abundance of juvenile fish along the restored shores increased significantly.
For the development of future projects a new partnership-model capitalizes on the successful stakeholder forum from the “Bad Deutsch-Altenburg” pilot project. The constituent meeting took place in mid-2017.

Linking of the Spittelau Arm and the Haslau-Regelsbrunn river systems

In the course of viadonau's catalogue of measures for the Danube east of Vienna, several tributary systems are to be reconnected to the main river. The reconnection of the two tributary systems Haslau-Regelsbrunn and Spittelauer Arm is given priority.

The implementation of these river links is being carried out within the framework of the LIFE project "Dynamic Life Lines Danube". The focus is on improving the river dynamics and, as a consequence, the condition of the succession stages of the Weiche Au, which forms in the transition areas between the river and the forest. The implementation of the Spittelauer Arm watercourse network began in winter 2019/20 and was completed in autumn 2020. The Haslau-Regelsbrunn watercourse network is currently in the planning phase.

Further information and current project status on the viadonau website.

Connecting the Waters

Reconnecting side channels of the Danube requires the development of dynamic bodies of water. Habitats dependent on such dynamic conditions (bluffs, pioneer areas, sediment banks etc.) and specialised species (kingfisher, other water fowl such as the Common Sandpiper which nest on gravel surfaces, river fish species, pioneer plants, and species thriving in currents) will again receive much-needed support. Similar successful projects in water connectivity have already been carried out in several locations in the Donau-Auen National Park.

Gewässervernetzung Regelsbrunn - Maria Ellend

An diesem Standort wurden als Pilotprojekt die ersten Maßnahmen gesetzt. Durch die Absenkung des Ufers um 1,5 m auf 32 m Länge, den Bau eines Durchlasses sowie die Öffnung von Traversen konnte wieder Wasser in die Regelsbrunner Au gelangen. Die Erfahrungen führten zu weiter reichenden Maßnahmen bei den Folgeprojekten.

Water Connectivity in Orth

Upstream from Orth on the Danube, three Danube inflow areas into the Little Binn and Big Binn were re-established by removing the solid embankments along the river
A traverse structure was removed completely from the side channels and another was equipped with a massive bridge passage. In addition, old rip-raps were removed from the stream and an extensive amount of documentation was obtained from the site.
Since then, significant changes in the water flow of both have been observed. Deposits which have accumulated in the past 100 years have been washed away, at least in part. On a smaller scale, the effect of these changes may also be seen in the composition of the communities of species.

Connecting the Waters in Schönau

In Schönau, two lowerings of revetments along the river were carried out. As well, the traverses dividing the stream of water were partially opened and equipped with a novel, 20-meter wide bridge passage.
In the upper reaches of the project area, the measures undertaken have effectively prevented or significantly slowed the long-term accumulation of build-up. And the maintenance of a dynamic, fluctuating environment in the middle reaches is now assured.

In the lower reaches, increased and more frequent inflow has improved water quality and reduced the entry of contaminants via the reverse flow.

Restoration of Crossings on Forest Roads

In the Orth area of the wetlands (shore-based and upstream from the dam), road crossings of ditches and watercourses which were no longer needed were removed as part of the second LIFE project in 2005. This was done to reduce the inherent ecological disadvantages created by such barriers: they interrupt the flow of water and prevent animals and plants from utilising the waters as corridors for expansion.
Removing these barriers leads to sustainable improvements in a variety of other areas as well. For the convenience of visitors, especially important crossings points were maintained by erecting boardwalks. In some instances, navigable depressions were created.

The Weir at Gänshaufen Traverse

In 2001, the Gänshaufen Traverse on the Kühwörther waters was renovated and modernised by the National Park Society and the City of Vienna Municipal Department 45 (Water Engineering). The adjustable weir was expanded to nine meters; it can be both automatically and manually controlled. For much of the year, the new weir facility restores the water continuum and supports a more natural alternation of water surface levels and groundwater levels. Opened during receding water levels in the case of floods, the weir enables the more efficient removal of suspended sentiment present during floods.
The observation platform which was erected on the roof of the weir's control centre has been greeted with enthusiasm by visitors. The view across the largest backwater of the National Park is not only impressive thanks to its scenic beauty; it also allows for the non-intrusive observation of rare water fowl species.

Revitalization of the Fadenbach Creek

The Fadenbach Creek near Orth/Eckartsau is one of the few known natural habitats of the mudminnow (Umbra krameri) in Austria. For decades, this species was thought to be extinct until specimens were discovered in the Fadenbach Creek in the 1990s. Within the framework of the first LIFE project, a series of measures were enacted to ensure the survival of this species and to improve the ecological situation of this former Danube side arm.
Watercourses were deepened and "survival ponds" were dug and/or connected with other bodies of water. These allow the mudminnow to utilise this habitat for most of the year and re-established the area's function as a natural expansion corridor. At the initiative of the municipality of Orth's Fadenbach task force, funds were made available from the Fadenbach Water Association with which additional sections between Orth and Mannsdorf were deepened. Further activities are planned.

Hainburg River Restoration

This project involved the removal of all artificial elements strengthening the banks of a river section on the Danube's left bank across from the city Hainburg. In the entire lower section of the project area, all stone and boulder supports were removed from a length of around 2.1 km. Because the upper section exhibited a nascent overhanging bank character, it was necessary to safeguard the embankment at the height of the regulated low water level, heeding however navigational requirements.
In the long term, the new riverbank should

  • allow a natural and structurally multi-facetted riverbank landscape to develop

  • bring about a continuous lateral shift of the bank edge and thus cultivate the associated erosion, siltation, and fluctuation zones and keep these in dynamic interplay in the long run

  • work to counteract the formation of riverbank formations

  • intensify the extent to which high water can replenish the riparian woods, inflow channels and bodies of water

  • improve the groundwater connection between main stem and wetlands and keep it open in the years to come.

Indeed, shortly after construction had ended, the restoration potential of the landscape became clear: the flowing water had caused the river bank line to recede. After only a few months, the first signs of riverine habitat rejuvenation were observed in the flat sections of the inside bends. In particular the pioneer sites, the early succession stages and the wetland meadows were aided. Thus the highly-endangered species which find their home in these wetland habitats will be able to utilise them for a long time to come.

Witzelsdorf Pilot Project: Rebuilding of Groynes and Riverbank Restoration

Another milestone in revitalization was the completion of construction of a riverbank restoration project at Witzelsdorf in the Donau-Auen National Park. The Witzelsdorf section of the river had been one of the most heavily built-up along the entire Danube. Thus ideal conditions prevailed here for a restoration aiming to improve the overall ecological situation: to encourage the momentum and formative power of the Danube and to initiate the natural development of the shore. Project measures included:

  • Removal of eight old groynes and field experiments involving novel, ecologically-optimized groyne structures

  • Lowering of existing retaining walls to 0.5 meters above the low navigable water level (LNWL)

  • Riverbank restoration on a stretch nearly two kilometres long between river kilometres 1891.7 and 1893.4 with preservation of bank revetments to just over LNWL in areas of strong currents.

Approximately 30,000 m3 stone material was removed from the banks and transported away by ship. The National Park provided professional support for this project in collaboration with the project team. The Witzelsdorf restoration project was co-financed by the Federal Ministry of Transport, Innovation and Technology (BMVIT) and the trans-European networks of the European Union.
Meanwhile, the Danube has been busy forming her newly-won natural banks. The second riverbank restoration project in the Donau-Auen National Park is thus a veritable success story.

The Bad Deutsch-Altenburg Field Experiment

A real-life test of water engineering activities has been carried out in the form of the Bad Deutsch-Altenburg Field Experiment. Application of additional granulometric material, behaviour of underlying riverbed material, restoration of groynes, new types of groynes and upstream river restoration were tested on an island upstream. An ecologically comprehensive research programme accompanied the experiment and charted the effects of these measures on flora and fauna. The creation and planning of this nature project was coordinated by the steering committee with input from the National Park; implementation was carried out by viadonau.