Synergistic benefits between stormwater management measures and a new pricing system for stormwater in the City of Hamburg

Hamburg is a growing metropolitan city. The increase in sealed surfaces of about 0.36% per year and the subsequent increased runoff impacts on the city's wastewater infrastructure. Further potential risks to the drainage infrastructure arise also from effects of climate change, e.g. increased intensity and frequency of heavy rainfalls. These challenges were addressed in the Rain InfraStructure Adaption (RISA) project conducted 2009–2015 by HAMBURG WASSER and the State Ministry for Environment and Energy, supported by several municipal stakeholders. RISA addressed intensifying conflicts in the context of urban development and stormwater management at that time. Major results of the project are improvements and recommendations for adequate consideration of stormwater management issues during urban planning as well as new funding mechanisms for stormwater management measures. The latter topic resulted in the introduction of a separated stormwater charge based on the amount of sealed area connected to the sewer system of each property. For both undertakings – the RISA project and the introduction of the separated stormwater charge – a novel, comprehensive, digital database was built. Today, these geographical information system (GIS)-based data offer various scale-independent analysis and information opportunities, which facilitate the day-to-day business of HAMBURG WASSER and stormwater management practice in Hamburg.