Fourteen years before, in the wake of intense debates between power station planners and the federal government, ecologists had managed to block the construction of the Danube hydropower plant at Hainburg (east of Vienna) and thus to preserve the unique marshlands extending between the Vienna city suburbs (Lobau) and the Slovakian border. Today, this 48-km-long section of the Danube River forms the internationally reputed Donau-Auen National Park, a recreational area for the Viennese population and a major attraction for nature lovers from all over the region.

The defeat of the Hainburg project, however, also brought to light a phenomenon that more or less affects all large European rivers: the deepening of the riverbed due to erosion. The original cause lay in a number of river development projects, such as the large-scale Danube restoration project back in the 19th century, which unleashed the force of water and increased the transport of bedload sediment.

What has further aggravated this trend is a series of hydropower plants built alongside the upstream section of the Danube, their reservoirs trapping most of the sediment loads washed in from the Danube’s tributaries. In Vienna’s east, this has caused the riverbed to deepen by 2 – 3.5 cm annually. The Danube riverbed is now one metre below the level it had fifty years ago! This naturally reduces the water flow in the lateral river branches and side arms and also lowers the groundwater table. All these factors pose a massive threat to the existence of the Donau-Auen National Park.

The Danube, representing Corridor VII of the Trans-European Networks (TEN), is also an important international shipping route linking the east with the west. According to the Austrian Federal Ministry of Transport, Innovation and Technology (bmvit) and the European Commission, this role shall be even further promoted in the future. To make Danube navigation more competitive compared to road and rail transportation, several bottlenecks along the river hampering the shipping of goods have to be eliminated.

Complaints about the navigability of the Danube in Austria mostly relate to the river section east of Vienna where low-flow conditions may produce insufficient navigation depth, hence limiting the ships’ load capacity to currently 60 percent.

The only thing ecologists and navigation advocates have agreed upon over the years is that there are problems in the Danube section east of Vienna. This comes as no surprise, considering that environmental experts favour low waterway depths, through which they hope to keep the extent of dredging and technical installations to a minimum. For navigation advocates, however, there is never enough “under keel clearance” (the minimum navigation depth demanded in 1997 still was 320 cm). Ecologists and navigators also hold different views regarding the water waves produced by ships.

Together with the Freudenau power plant and its impact on the National Park (e.g. hydraulic transport of fine sediment matter), the whole controversy has become a modern Gordian knot which was long thought impossible to solve.

The first attempts to counteract the degradation of the Danube riverbed to save the National Park ecosystem date back to 1984. The Ecology Commission then reviewed the possibility of adding an extreme amount of coarse sediment; however, this would have resulted in a total riverbed seal-off. In 1997 experts devised a holistic river restoration concept which also took navigation interests into account. It became clear that some of the dynamics of the riverbed had to be preserved.

In collaboration with experts from an interdisciplinary steering committee, the project operator via donau – Österreichische Wasserstraßen Gesellschaft m. b. H. evaluated additional options and in 2002 finally chose a holistic river restoration project for the Danube stretches east of Vienna (“Flussbauliches Gesamtprojekt für die Donau östlich von Wien” – FGP).

Acccording to via donau project manager Christian Schramm, this project seeks to achieve the following goals:

• sustainable riverbed stabilisation to achieve increased stability of the riverbed while preserving some of the river dynamics,
• improvement of shipping conditions in low water flow,
• sustainable improvement of the Danube ecosystem between Vienna and the national border.

Novelty: granulometric riverbed stabilisation

Riverbed stabilisation is achieved through a method called “granulometric riverbed improvement” (Donau Consult, Zottl & Erber, 1997). Roland Schmalfuß from DonauConsult, the company in charge of river planning and environmental impact assessment coordination, explains the technique: “This method consists in applying a 25-cm-thick layer of coarse gravel across the Danube riverbed. The material added has a grain diameter of 40 – 70 mm (average: 50 mm), which is coarser than the bulk of the Danube’s natural bedload (average: 26 mm), but finer than the maximum natural grain size.

The material chosen has the proper grain size to avoid absolute riverbed stability. We rather expect that in case of a heavier flow the coarse gravel and the underlying riverbed sediment get mixed up. By applying this first load (total amount: 2 million m3) an upper layer is created which is much coarser than the current sediment and cannot be carried off as easily by the force of the water (10 – 15 % of current value).”

The selected grain size used for riverbed stabilisation is also the most important aspect by which this technique differs from the supply of sediment over the 11-km-long conservation stretch downstream of the Vienna-Freudenau power plant. In the course of this project, the plant operator VERBUND-Austrian Hydro Power AG (AHP) has committed itself to continuously feed natural sediment (approx. 190,000 m3/a) into the river.

Yet this only serves to stabilise the riverbed in the predefined conservation stretch. Granulometric riverbed improvement, in comparison, effects the entire 41-km-long river stretch and in addition helps to reduce the amount of sediment supply to 40,000 m3 annually. And this, Schmalfuß says, cuts down costs considerably. A study conducted by the Geological Survey of Austria in Vienna reveals that there are sufficient supplies of suitable coarse gravel in the Vienna Basin.

The concept of graulometric riverbed improvement was evaluated in the framework of a physical model experiment conducted at the Institute for Hydraulic and Water Resources Engineering of the Vienna University of Technology in collaboration with the Institute of Water Engineering and Hydrometric Survey.

“Adopting the above-mentioned measures and improving the groynes will not only help to raise the water level of the Danube for the benefit of the National Park, but also provide cargo ships with about 30 cm more under keel clearance (UKC) in low flow conditions,” says Christian Schramm. Depending on ship type and combination, this may allow adding several hundred tonnes of extra load.

The expert explains the two types of ships and their advantages: “In the case of self-propelled motor cargo ships, where the screw propeller submerges under water along with the loaded body of the vessel, the safety distance from the current natural gravel bottom is about 30 cm. After adding the coarse gravel to the waterway sections requiring stabilisation, the safety distance between propeller and bottom has to be increased to 60 cm.

As these ships already have a draught loaded (depth which can be effectively used by a ship) of 220 cm, nothing will change. But even these ships will draw a benefit from a safer and more reliable navigation channel resulting after riverbed stabilisation. The type that definitely benefits more is the push-tow formation. These ships have a propeller which is located at the pusher tug, whilst the pusher barges have no propulsion at all.

The equation for nongranulometric waterway sections therefore is: 270 cm minus 30 cm safety distance results in a draught loaded of 240 cm!” As mentioned before, the average load capacity of ships navigating the Danube is currently about 60 percent. Schramm expects that if the problems occurring under low-flow conditions can be successfully solved, the existing ship types will soon achieve load capacities similar to the ships navigating the Rhine (85 – 90 percent!). And this will make shipping much more competitive compared to road and rail transport.

The € 200 million project to be implemented by 2015 forms an essential part of the National Action Plan Danube Navigation (NAP) and as such is primarily funded by bmvit. 10 – 20 percent of the cost shall be covered by EU funds (TEN-T MIP) earmarked for expanding the Trans-European Networks.

The Danube is an international waterway which cargo ships can navigate without paying a fee. Yet Manfred Seitz, CEO of via donau, believes the project has also great advantages for taxpayers: “In Austria, the promotion of Danube navigation as envisaged in the NAP is a vital measure to curb the heavy increase in truck transits between west and east.

Austria’s transport strategy is to use the NAP to step up the shipping of goods on the Danube in Austria from currently 12 to at least 25 million tonnes annually by 2015. Apart from reducing the road traffic burden, this would also vitally contribute to the protection of the climate by saving about 400,000 tonnes of CO2.

The third objective of the river restoration project is to sustainably enhance the ecological quality of the Danube between Vienna and the national border. There are plans to remove the stone rip-raps from slopes (leading to natural river bank formations) and to improve water connectivity including the reconnection of isolated water bodies.

When considering the planned measures for groundwater table preservation, Carl Manzano (Director of the Donau- Auen National Park) basically takes a positive stance on river restoration. Yet he still views wave performance, ship emissions and ship accidents and their likely implications as problems waiting to be solved.

When asked about the National Park administration’s involvement in individual revitalisation measures, Manzano draws attention to its party status and also calls to mind that environmental protection is much more than merely carbon dioxide reduction.

“I view the revitalisation project, which serves to sustainably restore the Danube riverbed, also as a guarantee for a free-flowing river section and a final Hainburg power plant call-off long hoped for by ecologists,” Carl Manzano concludes. Ecologist Friedrich Schiemer, too, views the project as a sound compromise that reconciles the interests of navigation and environmental protection.

As a member of the aforementioned steering committee, he once more underscores the importance of an adaptive approach. With respect to waterway depth, he is strictly against urging for project implementation in other Danube stretches or riparian states. For him, this adaptive approach means learning from individual implementation steps; on the other hand, Schiemer believes that the project operators must also be open for national and international developments and thereby touches upon a weak spot of the project, namely the lack of coordination with other European countries.

Progress in this area will undoubtedly be spurred by an initiative of the International Commission for the Protection of the Danube River (ICPDR). The one-year debate shall help to achieve a basic consensus between inland navigation and ecology in the entire Danube region and develop relevant guidelines. Workshops will also address the conflict of interests between the provisions of the EU Water Framework Directive and inland navigation, which is also supported by the EU.

The participants in the kick-off meeting held in Orth a. d. Donau at the end of April were state secretaries from several Danube countries, representatives from water and transport ministeries, the Danube Commission and the Save Commission, and NGOs. Research input came from several members of the steering committee. The initiative is of a purely informative nature, does not replace an environmental impact assessment (EIA) and has no master plan as a target.

The years to come will show whether this river restoration project, currently in the phase of EIA, can tackle all conflicting interests. But the very fact that Austria spends so much know-how and money on trying to reconcile economic and ecological interests makes this ambitious project a role model of conflict management for the entire Danube region.
(Source: aqua press Int. 2/2007, Mag. Christof Hahn)

via donau
Mag. Christian Schramm
Tel.: +43/050/4321-2610
@: christian.schramm@via-donau.org
Internet: www.via-donau.org

DonauConsult Zottl & Erber ZT-GmbH
DI Dr. Roland Schmalfuß
Tel.: +43/1/480 80 10-12
E-Mail: r.schmalfuss@donauconsult.at
Internet: www.donauconsult.at

Nationalpark Donau-Auen GmbH
Dir. Mag. Carl Manzano
Tel.: +43/2212/3450
E-Mail: nationalpark@donauauen.at
Internet: www.donauauen.at

Universität Wien, Dept. für Limnologie
o. Univ.-Prof. Dr. Friedrich Schiemer
Tel.: +43/1/4277-54340
E-Mail: friedrich.schiemer@univie.ac.at

Int. Kommission zum Schutz der Donau
GF Mag. Philip Weller
Tel.: +43/1/260 60-5738
E-Mail: icpdr@unvienna.org
Internet: www.icpdr.org