The Roman settlement Vindobona was directly built on the main stream of the Danube. By the end of the Middle Ages the river shifted north and the former main stream became the Vienna Arm, the present Danube Canal. The city, however, did not develop on the river – like Paris, for example – but aside of it. The 5 km wide floodplain area definitely limited the urban expansion. The suburbs that developed between the Vienna Arm and the main stream, e.g. the Brigittenau and Leopoldstadt, were repeatedly devastated by floods. Flood protection dams were built and side branches closed to control the flood situation and to protect the lower lying parts of Vienna and the suburbs.
The most severe interference with the natural regime of the Danube was obviously the “Wiener Durchstich” 130 years ago. The floods of 1897 and 1899, however, clearly showed that protection measures were still not sufficient.
Bypass channel in the floodplain
After the flood of 1899 many proposals and projects were developed to improve flood protection. They ranged from the construction of a completely new bed for the main stream in the north of the city to the digging away of the floodplain.
The flood in 1954 again demonstrated the limits of flood protection and especially the bad condition of dams. Extensive studies for improving the flood safety of Vienna elaborated four major variants: The decision favoured a bypass channel in the floodplain area, that would – in a flood with a flow of 14,000 m3/sec. – hold the water level down by about 1 meter below the level that would occur upon draining within the existing dam system. This so-called “Danube Island Project” did not only meet the flood protection requirements, but had also advantages with respect to city planning and water management.
The best solution: the “Danube Island” project
The excavation material of the New Danube – the bypass channel on the left bank of the Danube – was used to bank up a flood-free island, the Danube Island, on the remaining part of the floodplain between Danube and New Danube. The New Danube is only run through in case of floods. Drainage is controlled by weir installations.
The influx building divides the Danube in main stream and New Danube and is operated only in case of floods. In periods without flood, two further weirs guarantee horizontal water levels in the New Danube so that it gets a lake-like character. The New Danube also has a system of secondary dams. The essential elements are the flood protection dam on the left bank of the New Danube, the “Right Danube Dam” on the right bank of the Danube and the confinement dams of the port facilities. In case of a flood, maximally 14,000 m3/sec can be drained off without damage.
Construction works began in 1972 and in 1988 the main parts were completed. The total costs of the project amounted to about ATS 8 billion.
Aspects of city planning and design
The project area of the “Improved Danube flood protection” comprises about 60 km2. “Vienna to the Danube” was the motto of the town planning and design competition “Danube Area Vienna,” which was advertised by the City of Vienna and the Republic of Austria. As a result, an international jury drew up principles for the design and use that were accepted by the Municipal Council of Vienna and have been valid since. Among them were the nature-close design of the Northern and Southern Danube Island and the New Danube, the establishment of traffic-free zone and the connection to public transport. After a period of two years the final report was available and included a utilisation plan and a principal proposal for area planning.
The Danube Island offers many recreational possibilities
Meanwhile the Danube Island and the New Danube have become a unique recreational and resting place with regard to size and accessibility from the city centre. The city administration plans to keep this area accessible for the population without restrictions (as far as possible) and for free.
The central zone of the Danube Island between the Floridsdorfer Brücke and the Reichsbrücke has developed into a place for events and eating out in the past few years. For example the “Festplast” downstream of the Foridsdorfer Brücke can hold 80,000 visitors. Close to the Reichsbrücke a number of pubs, bars, restaurants and discotheques have settled down. The area is know as the “Copa Cagrana” and has also become an international place of attraction. The annual highlight and fixed point of the event calendar is the “Danube Island Festival”. It has taken place for 16 years now and attracted 2.5 million visitors to the Danube Island last year.
The construction of the barrage weir Vienna-Freudenau can be regarded as the temporary completion of redesigning the Vienna Danube region by hydraulic engineering. Due to the completion of the improved flood protection measures on the Danube, no backlog dam had to be built for the construction of the dam installations. The dammed-up Danube will also secure enough water for the recreational area of the Danube Island. The characteristic feature of the dammed up region is the basic difference between the left bank, i.e. the side of the Danube Island, and the right bank, the side of the Handelskai. The design of the left bank is marked by ecological compensatory measures (parallel drains, islands, inlets, flat water areas) to replace free flowing stretches, while the right bank is characterised by town planning measures (quay walls, park-like design).
The water management measures on two banks differ, too. A sophisticated groundwater management system replaces the former direct communication on the right bank between Danube and groundwater body. On the left bank, the New Danube serves as a buffer against the groundwater body. Even if many visions that have been discussed in the past few years are still far from being realised or are already discarded, we can conclude that the new trend in hydraulic engineering not only has an ecological aspect but also an aspect of town planning. The construction of the Danube Island and of the Right Danube Dam, and finally the damming-up of the Danube have initiated a development in town planning that is marked by a merging of the left-bank and right-bank side of the city. With the International Centre as crystallisation point, a new district is developing that reaches down to the New Danube with its apartment houses, offices and schools. On the right bank, too, the city was able to move up closer to the Danube, since the Right Danube Dam offers adequate protection. Vienna is now actually situated on the Danube.
(Source: aqua print 06/99)
Dipl. Ing. Franz Michlmayr
Information & Contact:
Municipal Department 45 - Water Engineering
Dipl. Ing. Franz Michlmayr
Tel. +43 1 488 29-96 541
Fax +43 1 488 29-99-96 515
