Sponge City is an urban construction model capable of tackling weather conditions such as monsoons, swelling, flooding or other water events, through drainage systems or areas that prevent the accumulation of water.
Many cities have expanded rapidly with a focus on concrete and impermeable surfaces, leading to significant challenges with stormwater management and increased flood risks. Therefore, sponge cities offer a solution by integrating natural and engineered systems to manage rainwater sustainably, even in urban areas that have been developed.
For cities with less concrete coverage or more natural landscapes, there is a valuable opportunity to integrate sponge city principles into their urban planning. By preserving and enhancing the permeability of city surfaces through green infrastructure, effective stormwater management, and the maintenance of natural areas, these cities can improve their resilience to floods and enhance overall environmental quality. This approach not only benefits cities with extensive concrete structures but also offers a framework for sustainable development in less urbanised areas, promoting environmental resilience and sustainability from the outset.
China has one of the highest numbers of sponge cities, with the objective of having 80% of its urban areas absorbing 70% of water by 2030. As the country deals with extreme weather conditions, it has long sought to make its highly populated cities less vulnerable to flooding and drought. The sponge city initiative was designed to make greater use of low-impact, nature-based solutions to better distribute water and improve drainage and storage.
How does a sponge city work?
A Sponge City integrates natural and engineered systems to manage rainwater sustainably, mimicking the natural water cycle within the urban environment. This approach reduces flood risks, improves water quality, and enhances urban resilience. It addresses these issues by incorporating green infrastructure that allows water to be absorbed into the subsoil, alongside permeable surfaces made of soil and other materials.
This involves two key mechanisms: storm tanks at ground level for water storage and green areas that facilitate downward water infiltration.
Shenzhen
Shenzhen, a city in China, exemplifies this initiative. Shenzhen Talent Park features floodable greenways around a coastal lake, acting as a sink for canals diverting runoff from the ultra-dense Houhai neighbourhood. The walking pavements in Shenzhen Bay Park’s wide shoreline path, the Coastal Leisure Belt, allows water to infiltrate slowly through a deep bed of gravel underneath, further slowing the water flow. When the water reaches an impermeable liner at the bottom, gravity directs it down a slight slope into pipes which flow back to the ocean, enhancing the city’s water management capabilities.
Photo: Hope Design Co., Ltd
Shenzhen Bay Park, near the mangrove reserve, is a prime example of sponge city techniques. Its 13-kilometre coastline is kept free of large infrastructure, with major highways, buildings, and residential areas located further inland, away from flood zones. By planting mangrove trees and other wetland vegetation along the coastline and limiting new construction to areas further from the shore, Shenzhen’s sponge city programme helps protect its population of over 12 million from storm surges and rising sea levels.
Wuhan
Wuhan is one of the pioneering cities in China to implement the sponge city initiative. The Wuhan Sponge City Programme aims to reduce waterlogging and improve water quality through the ecological remediation of existing urban water systems and the development of blue and green infrastructure to collect and store rainwater.
The project has gained momentum, with a total of 228 initiatives in the pilot districts of Qingshan and Sixin retrofitting public spaces, schools, and residential areas with sponge features. Nanganqu Park, located in the east near a major iron and steel company, transformed from a dirty drainage ditch in the 1980s into a park in the 1990s, and was eventually upgraded into a “sponge site” with permeable pavements, rain gardens, grass swales, artificial ponds, and wetlands.
Photo: Sino/ Getty
These features are designed to absorb excessive rainfall through soil infiltration and retain it in underground tunnels and storage tanks, only discharging it into the river when water levels are low. As a result, the park’s air quality has improved, and temperatures have dropped by two to three degrees due to the lush vegetation.
Photo: Metro Spring
The Wuhan Optics Valley Modern Tram system incorporates green track technology, which helps to reduce surface runoff and provides several other environmental benefits. The green track is designed with permeable materials that allow rainwater to infiltrate through the track bed, which helps manage stormwater and reduces the risk of flooding. This design also minimises the urban heat island effect by cooling the surrounding area through enhanced evaporation. Additionally, the green track helps to mitigate air pollution by acting as a natural filter and contributes to the overall environmental health of the city.
Shanghai
Shanghai has its largest “sponge park,” the Starry Sky Park, which integrates a sustainable drainage system with amusement facilities and a “go green” concept.
Located in Lingang New City, adjacent to the Shanghai Astronomy Museum, the park spans 54 hectares, including 16 hectares of water area. Its curved design features eight buildings with “astronomical” elements.
Photo: Brasil de Fato
The park includes standard sponge city facilities such as permeable pavements and lush gardens, which assist with rainwater purification, storage, and ecological replenishment. It also boasts specialised sponge system features like landscaped ecological corridors, wetlands, urban rainwater storage and purification systems, and a smart water platform.
To prevent waterlogging and ensure effective drainage, the park also facilitates rainwater reuse and ecological protection, releasing stored water as needed. Additionally, a 30-centimetre thick gravel layer is installed beneath the soil to filter salt from the groundwater, addressing issues associated with flooding from typhoons and rainstorms typical in the coastal Lingang area.
These case studies of cities in China implementing blue-green infrastructure showcase the transformative impact of integrating natural and engineered systems into urban planning. These approaches effectively address critical challenges such as flooding, water quality, and urban heat, while also enhancing the overall quality of urban life. The innovative solutions demonstrated offer valuable lessons for urban areas globally.
– Nerissa Ng, Communications Team
References:
Shanghai’s largest ‘sponge park’ opens to the public
Wuhan opens Optics Valley Light Rail network
Inside China’s leading ‘sponge city’: Wuhan’s war with water
