Vienna strengthens flood defences for once-in-5,000-year floods

Vienna has upgraded the flood-control system at Auhof on the city’s outskirts to withstand a flood statistically expected once every 5,000 years, ORF reported Thursday. The work follows the 2024 floods, which were estimated to occur once every 1,000 years.

The renovation raised the facility’s weir walls by up to one metre. Its retention basins can now hold a total of 1.2 million cubic metres of water, the city said.

In September 2024, the Vienna River reached the limits of the system for the first time, with flows of up to 440,000 litres per second. Mayor Michael Ludwig and city councillor Ulli Sima inspected the upgraded defences.

Ludwig said the city had managed the heavy rainfall two years ago well, but argued that further improvements were warranted because climate-related extreme weather can be difficult to predict and unusually severe.

The flood-control system was built in the late 19th century and was designed to handle ten times the level of protection now standard for floods expected once every 100 years. Several streams from the Vienna Woods flow into the Vienna River.

The work also included a new flood wall on Ludwiggasse and reinforcement of the flood wall beside the Danube Canal, on the side facing the underground railway. Renovations to historic parts of the Vienna River system followed heritage-protection requirements.