NOAH

New concept to prevent and control urban floods

NOAH helped towns around the Baltic Sea mitigate the risks of floods and enhance climate resilience of their urban areas. By bringing together methods of stormwater management, spatial planning and real-time control of urban drainage systems in a holistic concept, the partners proposed steps for local municipality governments and water utilities on how to prevent and control urban floods. The concept included both passive measures targeted at modelling and monitoring, and active measures such as the modernisation of the existing infrastructure or the implementation of smart urban drainage. During the project, hundreds of experts from local city governments, water utilities and consultancy companies learned how to control floods and reduce the inflow of pollutants into the Baltic Sea.

Testing the concept in real urban environment across the Baltic Sea region

The partners tested the concept in eight pilot sites selected on the basis of their location near a natural water body (sea, river, channel) that was connected directly to the Baltic Sea. These were:  Haapsalu and Rakvere in Estonia, Slupsk in Poland, Jurmala, Liepaja, and Ogre in Latvia, Söderhamn in Sweden, and Pori in Finland. After the analyses of flood risks in the selected urban areas, a few active measures were implemented across the partner towns. Automated hydrological stations installed in Jurmala, Liepaja, Ogre and Slupsk enabled to monitor the status of the stormwater system and make data driven decisions to reduce flood risks and related wash-off of toxins and hazardous substances to the Baltic Sea. Smart weirwall systems were installed in Rakvere and Haapsalu that made the urban drainage systems smarter and ensured flood risk reduction in the pilot areas. In Haapsalu the system automatically prevents water inflow from the sea to the drainage system in case of high sea levels. In Rakvere the smart weirwall restricts the water inflow to the town's main urban drainage system collector in case of heavy rainfalls and buffers the excess water at the upstream pond until the end of the rain event.

The partners also developed a new passive measure as part of their concept: they introduced an extreme weather layer in the city’s GIS.  This helps planning specialists to consider and analyse the impact of various land use and soil types in the urban environment to simulate the response of the stormwater system and catchments to different rainfall events. As a result, the partner towns embedded the flood risk maps under different climate scenarios to the municipality’s urban planning procedures. Some towns implemented solutions to counteract these flood risks, using other funds than the Programme funding.  For example, Söderhamn invested in a raingarden, and Slupsk started the investment into climate proofing the city.

The partners concluded that the average costs of the active and passive measures carried out in the project were about hundreds of thousand euros per pilot compared to millions that would have had to be invested in pipelines and tanks to increase the system’s capacity in a traditional way.