Introduction
Over the past centuries Vienna was often severely hit by floods of the Danube River. During the years 1870 and 1975 the first major river training took place, but the catastrophic floods in the years 1897 and 1899 gave rise to doubts concerning the designing criteria. The 1954 flood clearly illustrated that the amount of protection provided was limited.
The length of the New Danube and the Danube Island is 21.1 km, with a channel width of about 150 m and a varying width of the Island of 70 to 210 m. Approximately 390 ha of its surface area are unaffected by floods and used mostly for recreation.This project is the first truly multipurpose fully sustainable flood protection scheme, considering aspects of flood control, water resources, power generation, recreational activities, ecological restoration, city development and many other aspects important to the development and well-being of the inhabitants of a city. Furthermore, the realization of the project was the impetus for new developments on the left bank of the Danube River.
Flood Control on the Danube in Vienna, Austria - The Danube Island Project
Reason to Be Selected
From a number of studies on improving flood protection, the city decided on a project, which proposed the constructing of an approximately 21 km long flood bypass canal - the “New Danube” - using the material excavated from the New Danube to create a flood-free island -the “Danube Island” - between the new waterway and the existing river bed; and directing water through the New Danube during flood-periods only. The discharge would be regulated by means of weirs: the inlet structure at the upstream end of the New Danube and two weirs to maintain the water level in the New Danube. Outside the high-water periods, i.e., most of the year, the water in the New Danube is kept constant by weirs 1 and 2, resulting in two calm recreational lakes. Legal authorization was issued in 1970, and construction began in 1972.
Highlights:
The idea behind the Danube Island was to provide easily accessible facilities for both sports and leisure activities. In addition areas with flat beaches for swimming, the island can also boast of an extensive network of paths for strollers, joggers, bike-riders and roller-skaters; grills and picnic areas; meadows; playing fields with markings; hard courts; separate courts for beach volleyball; and much more. A number of businesses have opened here, thereby expanding the range of leisure time activities which are available. Various gastronomic facilities and other commercial enterprises, including a bike rental shop; a wind-surfing school; a water slide; a water-ski lift; a diving school; paddle-boat, rowboat and electric boat rental shops; etc. have been established.
Details
Vienna was over many centuries subject to severe flooding. Only the very oldest parts of town, where the roman fort was once established were flood free. The Danube flowed through a wide belt of marshy meadows severely hampering the crossing by trade routes towards Bohemia and Moravia but also the expansion of the city. Therefore it became clear already in a very early stage that the river should be trained. The main goal was to provide flood protection, but also suitable navigation, a secure port close to the city and the construction of permanent crossings were important issues. In 1869, the decision was made to regulate the Danube in the Vienna area. This first regulation project entailed a cut-off through the meandering arms, thereby unifying and straightening the river bed. The Danube's new bed measured 280
meters in width and was adjoined by a 450 m floodplain on the left bank and a dike to protect the flat, low-lying surrounding areas. Work on the cut-off lasted from 1870 to 1875. Some of the machinery had previously been used to dig the Suez Canal.
However, shortly after the first Danube regulation was finished, the catastrophic floods in the years 1897 and 1899 gave rise to doubts concerning the estimates used for designing the height of the embankments. Furthermore, the 1954 flood clearly illustrated that the amount of protection provided by the embankments was limited.Extensive scientific studies were performed to determine the maximum flood level upon which Vienna's flood protection system should be based. The result was a generally accepted figure of 14.000 m³/s (reconstructions have shown that this amount of water probably was the peak-flow of the 1501 flood). A number of studies on improving flood protection for Vienna focused on increasing the discharge capacity for the section of the river within the city limits. The various proposals called for raising and reinforcing the existing dikes, removing parts of the floodplain, widening the river bed and constructing bypass canals within and in addition to the existing protection facilities.
The city council decided against strong political opposition on a project, which proposed the construction of a new flood bypass canal - “New Danube” – and the construction of a flood-free island - “Danube Island” - using the excavated material. and the existing river bed; and directing water through the New Danube during high-water periods only. The discharge in the flood relief canal New Danube is regulated by means of weirs: the inlet structure at the upstream end of the New Danube is used to regulate the flow into the New Danube and further downstream two weirs are used to maintain the water level in the New Danube during non-flood periods. Shipping traffic remains unaffected by taking the main river course as before. Outside the high-water periods, i.e., most of the year, the water in the New Danube is kept constant by the two weirs, resulting in a calm, lake-like surface. The first decision to implement the new flood control system on the Danube was made by the City of Vienna in 1957. Due to proper planning and incorporating most people affected by flooding the project finally received a very high level of acceptance which is expressed today by up to 300.000 recreation seekers during a sunny weekend.
Conclusions
The impact of the project was even more positive than envisioned during the decision and design period. After the completion of the project the development on the left banks of the Danube took place more rapidly. Of course other factors, such as a new subway line, also increased the attractiveness of the area, but proper flood protection made sure that the investments in property was secure. The once neglected districts on 'the other side' of the Danube became the major development areas for services and industry as well as for new housing projects. Since implementation of the project the population in these two districts approximately doubled.
Although recreational aspects were already included during the design period, it was not foreseen that the 21 km long island will become such a major attraction for all Viennese . Not only the people who live in the vicinity use the Island but also people from other districts take the effort and reach the New Danube either by public transport or private car. The peak usage occurs during sunny weekends, where up to 300.000 recreation seekers can be counted.
Overall the project by far outperforms its original multi-purpose design criteria.
FULL STORY:
Flood Control on the Danube in Vienna, Austria - The Danube Island Project
TOPICS |
Vienna | EcoCity | Civilian
