Opening the Rollerdamm

MAGYARUL

EN FRANÇAIS

On 30 May 1875, in the presence of His Majesty Franz Joseph I, Emperor of Austria and King of Hungary, the Danube in Vienna was inaugurated with a ceremony in its new, straight, canalised riverbed. On 15 April, a month and a half before the inauguration ceremony, they opened the Rollerdamm and the Danube entered into its new channel just under the Nordwestbahnbrücke. Three days later, the first steamship was already crossing the new stretch. The below history of the Rollerdamm is reconstructed on the basis of the writings of the book Wasser | Stadt | Wien.

The Rollerdamm in Vienna on April 10. 1875. (Original image)

In Vienna, the Danube was already a relatively regulated river before the start of the Great Regulation Works in 1870, despite its remaining natural meanders. Almost the entire banks of the main riverbed had been stabilised by 1869 on the basis of some local or central plannning. However, the main bed, stabilised with groynes, stone boulders and piles, was still too wide, creating the potential for further gravel bar formation, such as in the Gänsehaufen near the port of Kaisermühlen. At that time, regulation works were still primarily for the benefit of navigation, flood protection being only a secondary concern. When an icy flood in 1862 inundated the lower suburbs of Vienna, the Monarchy's government set up a Danube regulation commission, which could only begin its work after the lost war with Prussia in 1867. Members of the committee (engineers, administrators and shipping, railways experts) soon began to group around two widely divergent positions. The Pasetti group was in favour of a straightening of the existing main riverbed, while the other group argued for a new, single, channelised riverbed. There was a long stalemate on the issue, which was finally settled by Pasetti's withdrawal in favour of the supporters of the chanellized version. This plan was mainly supported by trade and transport advocates.

The French company "Castor, Couvreux et Hersent", which has already proved its worth in the Suez Canal, was awarded the contract. The route of the new, curved canal, which was laid out in 1868, had three fixed points: the outcropping near Nußdorf, the recently erected pillar of the Ostbahnbrücke near Stadlau and the section of the already completed dyke at Lobau. This plan required two major cuts under and above the Ostbahnbrücke. The upper cut was 6640 m long, the lower one 2550 m long, and a barren 475 m wide inundation area (Inundationsgebiet) was planned to be created on the left bank to drain off the excess flood water.

The position of the Rollerdamm (source)

The lower section of the new Danube near Freudenau at Weidenhaufen was done by the construction of a 114-170 metre wide ditch, which was then widened further by the Danube, washing out most of the sediment towards the Marchfeld. The upper section had been fully excavated, but when the new riverbed was dredged near Nußdorf, the workers were in for a nasty surprise: the riverbed was littered with the remains of river engineering works from previous centuries. For years, steam dredgers had struggled to dredge them out, but the machines used at the time were too weak to remove the massive defences. In all, thousands of wooden piles from different centuries and 18 and a half kilometres of various wooden structures were dredged out.

To build the canal, the steam dredgers and transporters were used for the first time on a mass scale had to move an incredible amount of sediment for the time. Most of the 16.4 million cubic metres of sediments, gravel and sand excavated were used to fill the suburban areas of Brigittenau and Leopoldstadt, contributing greatly to the increase in the urban area of Vienna. The new Danube riverbed in Vienna included the construction of flood protection embankments on both sides, the deepening of the Danube canal and the construction of five new bridges over the Danube.

During the dredging of the new riverbed, a narrow earth dike called the "Rollerdamm" was left in the northernmost part of the riverbed, maintaining the flow direction towards the Alte Donau until the very last moment. It was not originally perpendicular to the new riverbed, but followed the flow line of the Alte Donau from the left bank of the present-day Florisdorf bridges to the Handelskai on the right. It also had an industrial railway on top, one of its terminal was at today's Friedrich-Engels-Platz. On 15 April 1875, one and a half months before the official opening ceremony, the Rollerdamm was opened under the direction of geologist Eduard Suess, the small gap being rapidly widened by the Danube until the dam was completely washed away along the width of the new riverbed.

At first, the Danube was reluctant to occupy the new riverbed. After the spring floods receded, the technical closure of the Alte Donau began, but in the narrowing bed the river still exerted considerable force, displacing stone-laden boats sunk into the bed, destroying the embankment under construction and carving deep pits in the loose sediment. Finally, wooden structures filled with boulders were wired together and lowered into place on railway tracks, permanently closing the old riverbed. Relatively soon afterwards, in February 1876, the first "stress test" of the new Vienna water system was carried out.  In the still unregulated Danube section of Vienna, under the Ostbahnbrücke in Stadlau, the ice was piled up and the raising water, pushed back by the ice dam, found its outlet in the Alte Donau oxbow. Both the lower and upper embankment broke and the thirty-three ships of the company "Castor, Couvreux et Hersent" were washed out of the old branch and put ashore, damaging them, in a riverine meadow near Fischamend. On 25 February 1876, the London Times also reported on the alleged total failure of the regulation works in Vienna, and published the fake news that the new central cemetery in Vienna was so flooded that dead bodies had been washed from their graves. 

The opening of the Rollerdamm on 15 April 1875.
Beyond is the Nordwestbahnbrücke, constructed in 1872. (source)

After closing the Alte Donau, large stretches of gravel fields were left dry. The area was soon swarmed by bathers from Vienna. In their favor authorities dredged the oxbow to improve water quality, which ultimately led to the survival of this urban wetland. As a result of the Danube regulation in Vienna, the groundwater level has sunk by an average of 1.3 metres, so that the real estate value of the Danube floodplain has increased greatly in parallel with the landfills. The loss of natural meander development, the formation of islands and gravel bars and the cessation of their migration ultimately led to the rapid urban development of river banks and, in parallel, to the rapid degradation and disappearance of natural habitats.