‘Sponge cities’ making gains while it rains
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In years gone by, Binhu Square in Nanning, capital of south China’s Guangxi Zhuang Autonomous Region, would become flooded during the rainy season, causing chaos in the bustling city.
However, a recent project has changed all that, turning the once-burdensome floodwater into a boon for the local community.
“By replacing the square’s granite surface with a permeable, sandy material, it now absorbs, purifies and collects water, which can then be used to irrigate local fields,” said Gan Linyi, a local management official.
The project, which was completed earlier this year, is part of the “Sponge City” campaign, which aims to make better use of Nanning’s rainwater by upgrading its sewer system, and developing ponds, filtration pools, wetlands and permeable public spaces.
The Ministry of Housing and Urban-Rural Development said similar schemes have been mapped out for 130 cities.
By 2020, 20 percent of China’s cities should have modern sewer systems and infrastructure that allows for the efficient absorption of rainwater, it said.
The program was launched in response to the growing need for better water management infrastructure in China, which has the twin problems of urban flooding and water scarcity.
According to the Beijing-based Tsinghua Holdings Human Settlements Environment Institute, about 66 percent of Chinese cities are short of water.
A study of 351 cities by the Ministry of Housing and Urban-Rural Development found that 62 percent witnessed urban flooding between 2008 and 2010.
Li Chuanming, an official with the drainage department of Hefei, capital of east China’s Anhui Province, said that in an ideal situation, 80 percent of rainwater should be absorbed and the rest drained through sewers.
The ratio is the reverse in most Chinese cities, he said.
Over the past two years, Beijing has been renovating streets with permeable materials, constructing storage ponds, filtration pools and “bioswale” — gullies filled with drought-resistant plants, throughout parks and communities. City authorities said that 28 million cubic meters of rainwater were collected last year.
Lin Binzhang from the Nanjing University of Information Science and Technology said that among the 200 big and middle-sized Chinese cities, about two-thirds are facing both waterlogging and water scarcity.
Each must take a different approach to the sponge concept, basing their efforts on each of their individual circumstances, he said.
An engineer surnamed Wang from the water conservation bureau in Anqing, Anhui, said that since the lay-out and structure of cities are already formed, improving sewer systems, increasing green areas and creating permeable road surfaces would be costly.
The housing ministry said it would cost up to 180 million yuan (US$28.3 million) per square kilometer.
“It is important for governments to find effective ways to attract private capital to the project,” Wang said.
Cities should also integrate the sponge city program into urban planning and make sure new development projects do not get in the way of sponge facilities, he said.
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