Sponge city—a principle of sustainable urban development
Have you ever heard of the “Skybrudsplan”? What sounds so imaginative in Danish is also justified in German. After all, the “skyburst plan” stands for a new concept of urban development, the sponge city, or to put it more simply: the principle of the sponge city.
What is a sponge city?
The challenges of climate change and increasing urbanisation require innovative solutions for dealing with extreme weather events and the sustainable use of resources. One such solution is the sponge city concept, which is characterised by efficient rainwater management and the integration of natural systems into urban environments.
The term “sponge city” is derived from the ability of natural sponges to absorb, store and slowly release large quantities of water. This principle is being applied to urban areas by designing urban landscapes to absorb, store and release water as needed to mitigate the negative effects of heavy rainfall events.
This is achieved through the following mechanisms, among others:
- unsealing the infrastructure or permeable surfaces for roads, pavements and squares
- Green roofs and façade greening that can absorb water and release it again with a delay
- Retention ponds and biotopes that can allow water to seep away and later release it again as evaporative cooling
- Underground infiltration systems that channel water into the ground and store it there for dry periods
Copenhagen as a role model
This is where the “Skybrudsplan” from Copenhagen comes back into play. The plan was developed in response to the severe storms in July 2011, which caused considerable damage and highlighted the need for better rainwater management. A central element of the plan is the creation and utilisation of green spaces and parks that serve as natural retention and infiltration areas. These areas can absorb large quantities of rainwater and slowly release it again, relieving the burden on the city's sewerage system. What serves as a planting bed, hockey field or architectural seating element on sunny days can hold back enormous amounts of water during heavy rainfall until the sewerage system can absorb it. In addition, canals, waterways, ponds and underground basins can be created to collect and drain water, further reducing the risk of flooding. The redesign of streets and squares also plays an important role. By using water-permeable surfaces and integrating rainwater collection systems, water can seep away directly on site instead of being quickly drained away. Modernising infrastructure and creating new green and blue recreational spaces not only enriches the cityscape and increases the quality of life for residents and visitors, but also promotes long-term sustainability.
What is the next logical step?
The principle of the sponge city can be applied as a sponge region to entire urban agglomerations and rural areas. A sponge region integrates urban and rural water systems, utilises regional water reservoirs and wetlands, and promotes coordinated planning and management at the regional level. This integrated management improves water supply, reduces flood risks and strengthens adaptation to climate change. At the same time, the Circular Water City concept emphasises the circular economy by recycling and reusing water within the city. Measures such as grey water recycling, decentralised water systems and natural wastewater treatment plants minimise waste and maximise efficiency. Education and awareness-raising play a key role in successful implementation.