In Vienna, flooding is prevented pretty frequently without a lot of people even noticing it - thanks to the services of general interest

Climate change does not only result in hotter summers, it causes increasingly heavy thunderstorms and heavy rain fronts as well, with potential flooding as a constant threat. Vienna therefore relies on sophisticated protection against flooding: intelligent canal control, huge underground buffer basins and, last but not least, the New Danube. Without those protective measures, the city would have been under water several times in the last decades. Safety is not the only focus of flood protection though; Vienna also takes care to interfere as little as possible with nature, thus maintaining the high quality of life.

"Without the Danube Island, large parts [of the City] would probably already be meters under water." This is what the NEWS magazine Profil wrote during the so called "flood of the century" in 2013, when the relief channel and the New Danube saved the city from disaster for the second time within only 13 years.

However, the New Danube is only a small - albeit extremely effective - part of the flood protection system in Vienna. Thanks to the perfectly coordinated flood protection system, most people usually don't even notice that the large number of heavy rains and thunderstorms might cause regular flooding within Vienna otherwise. Why is that? Because the superb flood protection system of the city can easily "digest" the masses of water.

That is only possible because Vienna has not privatized her services of public interest. This means that the city can use the sewer system for flood protection, therefor a multidimensional approach is used. It is built to absorb and drain heavy rainfalls. If the sewer system is no longer sufficient for the amount of rainfall, a sophisticated safety net directs the water into underground collection tanks. Only once this is no longer sufficient and the Danube floods, does Vienna pull out its joker and opens the floodgates to the relief channel.

DANUBE ISLAND: ONE OF VIENNA’S LANDMARKS WAS ONCE DEEMED CONTROVERSIAL

Building of the Danube Island started in 1973. Before that, floods caused mass flooding of large parts of Vienna every few decades. Nevertheless, the construction of the Danube Island was highly controversial at times. These conflicts subsided after the Danube Island was inaugurated. It didn't take long for the Viennese to fall in love with their new recreational area, and the relief channel was completed in 1988. However, another 14 years were to pass before the relief channel passed its most crucial task until today: in 2002, while a flood only seen very rarely, left a trail of devastation throughout Austria, the New Danube ensured that Vienna was pretty much spared though. Even those, who were once fierce opponents of the project, subsequently conceded: "The Danube Island is a good thing".

NEW DANUBE: WATER CAN CHOOSE ITS OWN PATH

There are three weir systems built within the New Danube, which act as a collective lock. The first of these, located as little bit outside Vienna, separates the relief channel from the Danube river proper. Unless flooding is expected, the weir system remains closed. The New Danube acts as a stagnant body of water and one of the most popular spots to swim in Vienna. Only during floods water from the main stream of the Danube are diverted into the New Danube at Langenzersdorf by the City of Vienna to avoid potential harm of the city and her inhabitants. Both of the two remaining weirs regulate the flow of water in the relief channel and its discharge back into the Danube river downstream of Vienna.

Masses of water, that would flood parts of Vienna otherwise, can thus be diverted into the New Danube. That is the reason why swimming in the Danube is prohibited during flooding – and that is not without any reason: On the one hand, polluted water from the Danube enters the New Danube during flooding. On the other hand though, the New Danube turns into a river with a strong current during flooding.

MULTI-LEVEL FLOOD PROTECTION

In the last 20 years alone, the relief channel has already had to protect Vienna from two historical floods, and the weather extremes are only going to increase. Having learned her lessons, the city has in hindsight started providing protection against the consequences of climate change since the 1970s. This, too, is a provision for the common good: taking preventive measures even if the threats, of which the city needs protection, are only slowly emerging.

And even if the Danube is not affected by flooding: Heavy rainfalls, which used to only occur infrequently, are now business as usual, at least least in the summer months – this is, why the City of Vienna continues to invest in well thought-out flood protection systems.

Vienna has expanded her sewage system so that it offers sufficient reserves to operate: Vienna’s sewage system can absorb and drain very large amounts of heavy rain as a matter of fact. To achieve this, water is intelligently controlled within Vienna's sewage network. If rain fall is particularly heavy in certain parts of Vienna, the employees of Vienna’s sewage system divert water from there to less busy parts of the sewer. The city has already prevented many floods as a result.

INVISIBLE PROTECTION FOR THE CITY

Should the masses of water be so enormous that a municipality’s capacities are not suitable any more, five huge underground storage basins are available as a buffer. Those five underground basins alone can hold up to 210 million litres of water. Where are these reservoirs, one might ask? For example, one of those reservoirs is located 30 metres under Vienna’s innermost district, there is one beneath a meadow orchard in Liesing in the outskirts of Vienna as well as one beneath a sports field in Simmering on Vienna’s outskirts. The masses of water are fed there through huge pipes. In total, Vienna's sewer network can hold half a billion litres of water at a time.

‘IMPROVED FLOOD PROTECTION VIENNA’

The Danube Island, canalization and underground collection tanks - all of these are part of the far-reaching ‘Improved Flood Protection Vienna’-project. Nowadays, more than 50 years after the ground-breaking opening ceremony of the Danube Island, the far-reaching project has been finished. The final piece of the puzzle was the renovation of the Marchfeld protective dam just on the outskirts of Vienna, stretching as far as the Slovakian border. The dam does not only protect Vienna from flooding, but also offers numerous excursion opportunities with 77 kilometres of cycle and gravel paths.

VIENNA PREVENTS FLOODINGS WITHOUT MAKING A BIG FUZZ ABOUT IT

Many Viennese are not aware that Vienna would be frequently at risk of being flooded without the existing flood protection measures. Only in case of extreme flooding the city of Vienna has to resort to more drastic measures, like opening the floodgates to the New Danube in order to protect Vienna from widespread flooding within the city area.