Can ‘sponge cities’ solve China’s urban flooding problem?

The following edited article, ‘Can ‘sponge cities’ solve China’s urban flooding problem?’ by Wade Shepard first appeared in Citiscope. For further information on China’s ‘sponge park’ design read our earlier post, ‘Green Sponge’ Stormwater Park which featured Qunli Stormwater Park in Heilongjiang Province, China

China fdlooding 1

Source: An improvised pontoon bridge,Wuhan  PHOTO: WANG HE/GETTY IMAGES

From September to December 2013, the Office of State Flood Control and Drought Relief Headquarters, China conducted research on flood control and countermeasures. According to the results, 641 cities are at danger of flooding in China.  At China’s Central Government Conference on Urbanization in 2013, President Xi Jinping announced that cities should act “like sponges.” This proclamation came with substantial funding to experiment with ways cities can absorb precipitation through permeable pavements, rain gardens and wetlands, or reuse the water locally for irrigation, parks or for drinking.

China is now poised to incorporate sponge-city concepts into its ambitious city building program. By 2015, the Guiding Opinions of the General Office of the State Council on Advancing the Construction of Sponge Cities was published to further facilitate the construction of sponge cities. China’s State Council announced a new set of urbanization guidelines in February as a response to complaints that the country’s cities have grown too large, too fast, and without the proper amount of quality planning. The guidelines state that new urban developments should have sponge city-like water-retention capabilities, essentially making this strategy a new national standard.

China fdlooding stats

China is currently undergoing its worst flooding in 20 years. More than 300 people have died and over half a million have been displaced across dozens of provinces in both the north and south of the country.  Ponds, rivers and wetlands have been replaced with pavement, buildings and sidewalks. More than 40,000 square kilometers (15,000 square miles) were newly urbanized in China over the past 35 years, as the number of cities climbed from 193 to 653.   This rapidly encroaching urbanisation stops rain from being absorbed into the soil below. That increases runoff, which can grow to flood-like proportions as it flows downhill in even moderate storms.

While China’s drainage network of mostly conventional sewer systems grew 20-fold since 1981, it hasn’t kept pace with the expanding development above the surface. In 2013 alone, 230 of these cities were hit by severe flooding, according to the Ministry of Housing and Urban-Rural Development (MoHURD). The situation is only expected to get worse as a changing climate triggers more extreme rain events.

Chongqing

The Chinese government selected an initial batch of 16 cities for pilot testing in 2015. An additional 14 cities are being added. Each city in this program is allocated RMB 400 to 600 million ($US 60 to 90 million). Cities such as Beijing, Chengdu, Chongqing, Shenzhen, Guangzhou, Shanghai and Wuhan all have large scale projects underway.

In Yuelai New City, Chongqing the pavement absorbs the water, sucking it up into the ground beneath. If you were to pour out a bottle of water onto the ground water would immediately soak into the pavement and into the soil below, where it can then permeate down into the shallow aquifer or seep into nearby rivers, ponds or lakes. This porous pavement also feels different on your feet.

Yuelai New City is one of China’s most prominent emerging sponge cities and is one of the original 16 pilot sites and demonstrates creative thinking about water. The landscaping around the edges of the center blur right into the untamed foliage of the surrounding wooded hillside. Permeable parking lots are covered in gardens, with bushes separating each parking space rather than painted lines. Sponge cities are verdant places, focusing on nature based solutions, blending natural features and the city together. They also are wet places, and there will typically be a network of canals, ponds, lakes, and wetland parks, which distribute water throughout the development.

China fdlooding 2

Source: gettyimages

After an initial round of implementation, some of these sponge-city projects were tested by MoHURD. In terms of flood prevention, researchers found that 85 percent of rain runoff could be controlled. In addition, the presence of retained water, well-hydrated soil, and foliage also has the effect of counteracting the urban “heat island” phenomenon. According to Li Zhongwei, the director of D+H Scape landscape architecture firm, these strategies actually cool the air by two or three degrees centigrade.

The sponge-city concept is likely to work best if it can be implemented widely across broad urban areas. It has to be part of a holistic urban plan, not just some permeable concrete here or an extra-absorptive gutter there. That makes blank-canvas “new cities” that are so prevalent in China — like Yuelai New City — prime testing grounds.

“A sponge city is a system, it is not one part. You do a pilot park, you do a pilot neighborhood, it doesn’t help. You have to make sure the whole city is doing that. So it needs huge infrastructure. It’s not a small thing.”

Source: Li Zhongwei, Director, D+H Scape Landscape Architects

On the other hand, for the sponge-city notion to really make a difference, existing cities will need to be gradually retrofitted. That won’t be easy or cheap, with all the hard-wired street grids, pipes, tunnels and other existing infrastructure that Chinese cities have already built. There’s only one way to start, though, and that’s to begin experimenting.

“Most current [sponge city] projects are still very local and in a pilot phase,” says Harry den Hartog, an urban designer and researcher at Tongji University in Shanghai. “The current flooding issues make clear that more action is required urgently, especially in the more poor and vulnerable regions.”

“China’s urban construction was carried out at too fast a pace,” says Jia Haifeng, associate professor with Tsinghua University’s environmental science and engineering department. Officials have tended to focus on visible projects such as roads, bridges and housing, he said. “They emphasized infrastructure above ground, but not so much infrastructure below ground.”

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