'Sponge Cities' Combat Floods By Replacing Cement With Wetlands

"Sponge Cities" are a new initiative designed to contend with climate change and rising water in cities built to reject rain water, rather than absorb or use it.


May 28 2019, Updated 11:18 a.m. ET

Climate change is forcing huge shifts in how city planners deal with rising waters. A district in Shanghai known as Lingang was renamed Nanhui New City as architects and government agencies work to change the area into a space that could absorb water in times of flooding. 

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The Guardian reports that such locations are known as "sponge cities," and they're becoming a more popular alternative to other more traditional forms of flooding protecting, and becoming far more positive for the environment than ever before.

Coastal areas and drainage spots in China have been hampered by quickly developing cities that pave the ground in concrete, which blocks the flow of water. Nanhui is being built up with wetlands and green infrastructure that gives somewhere for the water to naturally go and be absorbed. 

Permeable pavement allows the ground soil to soak it up and the central Dishui Lake, which is man made, helps control its flow. Raised walkways make the city navigable during times of heavy rain or water flow.

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Wen Mei Dubbelaar, director of water management China at Arcadis, told the Guardian that one of the biggest issues with flooding is that cities are not built to absorb water or let it reach the ground.

“In the natural environment, most precipitation infiltrates the ground or is received by surface water, but this is disrupted when there are large-scale hard pavements,” explained Dubbelaar. “Now, only about 20-30% of rainwater infiltrates the ground in urban areas, so it breaks the natural water circulation and causes waterlogging and surface water pollution.”

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Nanhui was in part inspired by the dangerous flooding in Beijing in 2012. In 2015, the Sponge City initiative was officially launched, beginning with 16 locations. There are now 30 Sponge Cities in development.

Hui Li, a professor at Tongji University, says that facilitating a city's transformation is about recognizing the natural waterways of the land and supporting them instead of covering them up.

“The first thing is to try and preserve or restore natural waterways, because that is the natural way to reduce the flooding risk,” said Li. “In Wuhan, for example, the main problem is that a lot of small rivers were filled in during building. That is a benefit the Lingang area has, as there is still a lot of agricultural land and a manmade lake which has capacity to hold more water during heavy rain."

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Lingang's change into Nanhui is also a way for humans to consider their responsibility to the Earth, Li added, saying, "In the past, humans have taken the land away from the water; now we need to give the land back."

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This is a project with a number of challenges. Older, more historic areas in Lingang are more difficult to retrofit. Even older parks are often built above sea level, making them green areas where water will run off instead of absorb into. But the Shanghai government is both optimistic and ambitious. 

By 2020, they want 20 percent of every pilot's area newly built facilities to have sponge capabilities, which would equate to 70 percent of all runoff from rain water being absorbed or reused. There is also an issue with money—central government will only provide one fifth of what cities need and the rest must be raised by local government or private companies, who have been reluctant to invest.

Also, designs for sponge cities have been distributed somewhat universally, and China's coastal areas are vast and often unique from one another. What works in one place may not work in another. There is a lot of learning that needs to happen before these innovations make the shift necessary for the project's success. 

It's pretty radical to change a city into a green space wonderland that absorbs flood water, but it is also the sort of experiment needed in a radically changing environment.

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