Sponge City
Sponge City concepts for sustainable urban planning
Many cities are already densely populated, with much of the land covered by buildings and pavement.
As a result, heavy rainfall can quickly overwhelm drainage systems, increasing the risk of flooding. To address these challenges – both during periods of heavy rain and drought – cities need to rethink how they manage rainwater and treat it as a valuable resource.
Sponge City concept
A Sponge City (also called “Water-sensitive urban design” or “Low-impact development”) is an innovative urban development model that focuses on precipitation management by strengthening green infrastructure in a city.
The concept originated in China, where it became known as "Sponge City" by researchers in the early 2000s and aimed to design areas that could absorb large amounts of rainwater and release it again with a time delay (see also: bgmr landscape architects).
A Sponge City is therefore a holistic concept that combines a number of technical solutions that have already been used for rainwater management for some time.
The key difference is the underlying shift in perspective: rainwater is no longer seen as a burden on cities and municipalities that needs to be collected and removed quickly, but as a valuable resource that should be preserved locally at the building, street and neighborhood level.
There are numerous solutions for making optimal use of precipitation – from simple ones like rain barrels or cisterns – to complex ones like retention with irrigation systems, infiltration, constructed wetlands with greywater use, or the improvement of agricultural land.
The advantage: In some of these solutions, rainwater is essentially purified by the soil, ultimately replenishing the groundwater. Further measures include green spaces with diverse plants and trees, as well as additional areas surrounding traffic and streets. In this way, rainwater is used efficiently in a sponge city to make the area more resilient to precipitation and flooding, while simultaneously creating a green and livable environment.
The advantages of Sponge City
Sponge city concepts address the challenges of heavy rainfall while simultaneously increasing the quality of life through improved rainwater management.
Below are some advantages of the Sponge City concept:
Improved flood protection: By absorbing heavy rain and storing rainwater, the risk of flooding can be reduced.
Sustainable water management: The collected rainwater can be used for irrigating green areas or returned to the water cycle.
Promoting biodiversity: Green spaces and bodies of water promote local flora and fauna and offer residents green oases in the heart of the city.
Optimal planting of fallow land: Optimal planting of unpaved areas prevents high compaction and, at the same time, severe drying of the soil.
This measure allows rainwater to be efficiently absorbed from unpaved areas during extreme rainfall events. This prevents the rainwater from running off uncontrollably and allows it to seep into the ground on site.
The first Sponge Cities in Germany as successful concepts against heavy rain and water scarcity
Successful examples of a state-of-the-art sponge city concept can be found in Berlin with Rummelsburg Bay, as well as at various past Federal Garden Shows. Other major German cities such as Hamburg and Cologne are already planning similar concepts.
Copenhagen is a prime example of a sponge city in other European countries. It features numerous specially designed streets that either drain water above ground or temporarily retain it as a protective measure.
Public squares also serve as retention basins, and greened and unsealed areas serve as areas for infiltration.
AFRY as a strong partner for Sponge City concepts
At AFRY, we are proud to counteract climate change through our sustainable and holistic solutions. Whether for municipalities or large cities, with our comprehensive service portfolio, we contribute to problem-solving and sensible overall measures for heavy rainfall and the responsible use of precipitation.
- Heavy Rain Risk Analysis
- Hydrological reports
- General measures for rainwater management
- Determination of runoff-effective areas and preparation for sewer network calculation
- Hydrodynamic canal network calculation
- Design and optimization of retention basins and combined sewer overflow structures
- Planning and dimensioning of retention basins and soil filter systems
- Rainwater infiltration
- Discharge verification, pollution load and mixture calculations
- General drainage plans
Sponge City FAQs
- What is a Sponge City?
- What are the arguments in favor of the Sponge City principle?
- What measures are there to implement the Sponge City concept?
- When should a municipality or city invest in a Sponge City project?
- What is the optimal approach for Sponge City projects?
- What should be considered when implementing Sponge City projects?
- When do Sponge City projects become worthwhile?
- Hilfreiche Links:
A Sponge City is characterized by the fact that rainwater is not drained away – as is usually the case – but is retained on site and allowed to seep into the ground or be used.
The Sponge City principle can solve several current challenges:
- The risk of flooding is reduced or completely prevented.
- Drought-prone areas are avoided. This allows the soil to absorb precipitation more effectively, which also helps prevent flooding.
- The groundwater is replenished locally with every rainfall.
- The microclimate improves, thus increasing the quality of life and promoting biodiversity.
- Air quality improves because the plants bind CO2 and dust particles and release oxygen.
- The budgets of cities and municipalities are relieved because there is no flood damage to repair, less fresh water is needed for irrigation, and no new plantings are required due to drought damage.
Numerous measures are available, many of which can be combined. Among the most important are:
- Unsealing of surfaces, e.g. by lawn, grass pavers, eco-paving or permeable paving or water-permeable asphalt (drainage asphalt) or drainage concrete
- Infiltration through swales, trenches or swale-trench combinations
- Rainwater retention, e.g. through rainwater retention basins
- Green roofs and facades
- Collection and storage of rainwater in cisterns
Municipalities and cities located in areas with prolonged drought or extreme weather conditions should consider whether they could better protect one or more open spaces or neighborhoods against such extreme weather events using sponge city measures.
When planning stormwater drainage measures, whether for disposal or diversion, it is advisable to include considerations for better and more sustainable use of the precipitation resource. This applies not only to rainwater, but also to snow and hail.
The most sensible starting point is "projects that are going to happen anyway": All projects that require intervention in the landscape or cityscape – whether through new construction or renovation – can be used for the implementation of sponge city measures. This can include the redesign or construction of a community or playground or parking lots, a new neighborhood or commercial area, as well as infrastructure projects such as the construction or redesign of roads or railway lines, pedestrian or cycle paths, or the sewer network.
Furthermore, the sponge city principle is recommended when the hydraulic capacity of the sewer system is no longer sufficient during normal to heavy rainfall events, as well as in the case of more frequent flooding and when the groundwater level drops.
Several levels and aspects should always be considered. It is often advisable to look not only at the project itself, but also at the immediate surroundings, the neighborhood, district or industrial area, the entire city or municipality, or even several cities and municipalities, an entire region or county.
Ideally, sponge city projects are implemented as teamwork with the participation of the city or municipal administration, citizens, and project developers. This approach results in sponge city projects with the greatest benefits for housing, work and mobility, the economy, health, education, and climate protection.
Cities and municipalities can reduce their costs through Sponge City measures: They require fewer or no flood protection measures, and less damage is caused by flooding. Drought damage is avoided, eliminating the need for replanting. Costs for fresh water, such as for irrigating plants and green spaces, as well as for flushing toilets in public buildings, also decrease.
Private individuals can save on the costs of discharging rainwater into the sewer system and rainwater fees.
Besides the financial aspect, the aforementioned advantages of improved flood protection, climate adaptation and the preservation of flora and fauna should also be considered.
Furthermore, it is increasingly becoming mandatory to store rainwater locally in accordance with the sponge city concept and then evaporate, infiltrate or use it.
Regenwasseragentur Berlin - Die Regenwasseragentur des Schwammstadt-Vorreiters Berlin mit nützlichen Hintergrundinfos, Beispielen und praktischen Hilfen, z. B. zu Förderungen, Planung und rechtlichen Grundlagen.
AMAREX (für „Anpassung des Managements von Regenwasser an Extremereignisse") informiert über den aktuellen Stand der Untersuchungen zu Möglichkeiten der Anpassung des Regenwassermanagements an die Extrembelastungen Starkregen und Trockenheit.
KOSTRA-DWD: „Koordinierte Starkniederschlagsregionalisierung und -auswertung des DWD“
Umweltbundesamt - Infos des Umweltbundesamt mit weiteren hilfreichen Links
Sponge-City - Infoplattform Schwammstadt des VSA Verband Schweizer Abwasser- und Gewässerschutzfachleute
