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Floods triggered by heavy rainfall are increasing in the city of Vienna. Sloping areas on the edge of the Wienerwald, such as the Nussdorf region, are affected particularly. MA 45, the water department of the city of Vienna, took this as an opportunity to conduct a pilot study. In this study, it has reviewed the sewer drainage capacity of the 19th district. in the 19th district. For this purpose, the department has relied on the expertise of the Viennese engineering company RIOCOM and the simulation and visualization technology viscloud of VRVis. viscloud enables high-resolution 3D simulations of heavy rainfall scenarios and floods.

When it comes to flood protection, the city of Vienna is internationally known as very progressive. The areas of Neue Donau and Donauinsel, now Vienna´s largest recreational area on the waterfront, are the centerpiece of the city´s flood protection for the Danube. The reason for the construction of the Donauinsel and Neue Donau were several floods and high tides that repeatedly submerged parts of the districts Leopoldstadt and Brigittenau. The straightening of the Danube at the end of the 19th century was also one of the major projects realized to make the river flood-proof. Since then, flooding in the city due to rising water levels of the Danube has been absent.

Heavy rain can cause problems in the city

Increasing heavy rainfall is also creating difficulties in the city of Vienna. Extreme weather events are occurring more frequently due to climate change. They are a particular challenge in densely built-up, urban regions, which the MA 45 "Wiener Gewässer" is especially keeping an eye on: Where does the water fall, where does it flow to, and how can it be drained in the best possible way to avoid damage and accidents? For this purpose, the city of Vienna has cooperated with the local water protection experts of RIOCOM. They have set up a high-resolution 3D model of the Viennese regions of Schreiberbach and Nussberg, supported by VRVis. RIOCOM has conducted numerous hydrodynamic simulations of heavy rainfall and flooding for the catchment areas to assess the sewer network and runoff capacities of the 19th district. The runoff capacity of an area is affected by numerous factors, from actual precipitation, to interception of stormwater by vegetation, to soil infiltration, to sewer systems, to the roughness of the surface - all of these aspects affect how and where the rain will flow through the city's streets. Equally, however, the city itself affects the runoff of heavy rainfall: sidewalk edges, buildings, garden walls, fences, or culverts must be considered when modeling a heavy rain event. If all these factors are taken into consideration, the resulting visualization is very close to reality.