Nifty way of keeping water at bay
Flooding is one of the most serious waterrelated issues in Chinese cities due to rapid urbanization, land-use changes and the disappearance of natural wetlands.
To cope with such problems, five years ago the country turned to the concept of building what are dubbed sponge cities.
In 2015 the State Council launched the Sponge City pilot project, in which 30 cities are taking part.
The aim is for about 80% of urban areas to absorb and reuse at least 70% of rainwater by 2030, according to a paper issued by the State Council in October 2015.
Qu Jiuhui, an academician at the Chinese Academy of Engineering, said: “It refers to the management of rainwater runoff so that this water can be stored, used and channelled like a sponge.
“It can solve the problem of too much rainwater flow
ing into the drainage system, and through eco-engineering, plants can also absorb pollutants and purify the water, as in nature.”
Eco-engineering refers to the application of ecological principles to shape and manage the environment, in tandem with the design and use of technology that minimizes damage to the environment, or which helps to protect or sustain it.
A multi-layered array of artificial holes and pores at the entrance to the Shanghai Lingang Sponge City Exhibition Center showcases the sponge city concept.
Sitting beside the Dishuihu, a 2.2-square-mile artificial lake, the center’s role is to explain the complicated concept of eco-engineering and urban planning to deal with flooding in big cities.
Lingang New City, on the coast in Shanghai and which covers about 38.6 sq mi, was selected as a pilot sponge city in 2016. Of the 30 pilot cities nationwide it is the largest.
The exhibition center, opened last year, has set out to demonstrate how the sponge city concept has been translated into tangible infrastructure in the new city.
In the past three years grass ditches, water-absorbent footpaths, garden rooftops and artificial wetlands and water pools have been created to store rainwater.
About 22 miles of roads have been renovated and concrete footpaths replaced with water-absorbent bricks to reduce waterpooling during heavy rain. Instead of going directly to drainage, the bulk of the rainwater is absorbed by the soil in grass ditches alongside the roads.
Retrofits have been completed in Lingang at 26 residential neighborhoods covering 494 acres.
This work included placing small water storage units under the earth, adding small stretches of grass in carparks and building underground water pools in existing gardens.
The southwestern metropolis of Chongqing has been building sponge city infrastructure as it looks for ways to solve water problems in urban areas.
By the end of last year a sponge city covering a little more than 16 sq mi had been built in Liangjiang New Area, Wanzhou and Bishan districts and Xiushan county, according to the municipal Commission of Housing and Rural and Urban Construction.
Chongqing has annual rainfall of more than 3.3 feet, the bulk of which falls in summer and autumn. Because of the city’s complex landscape it faces challenging issues such as flood control and drainage.
The quality of water flowing through Chongqing, situated on the upper reaches of the Yangtze River, is not only important to the city itself but also to many other parts of the country.
The Yangtze River, the world’s third-longest, flows 3,915 miles from the glaciers of the Qinghai-Tibet Plateau east through Chongqing, Wuhan, Hubei province, and Nanjing, Jiangsu, before reaching the East China Sea in Shanghai.
More than 400 million people obtain their drinking water from the river, and water security has become a major national development issue.
Yuelai New City, situated in Chongqing Liangjiang New Area, and which covers 7.21 sq mi, was one of 16 sponge cities on a national pilot list of climate-resilient urban designs published in 2016.
The city has established a model sponge system in mountainous areas through a number of demonstration ventures. These include the Yuelai International Expo
Center Sponge Reconstruction Project and the Yuelai Convention Center Park Reconstruction Project, which have significantly reduced the amount of pollutants discharged into the Yangtze River.
Yang Ping, deputy general manager of Chongqing Yuelai Investment Group, said: “During heavy rainfall the water is absorbed by porous bricks and by plants to prevent flooding. We collect and store most of it, then use the water for irrigation or cleaning.
“The roof of a huge exhibition hall features a special rainwater collection path. Before the water flows into a pipe we use a special device to purify it for the first time before directly discharging it into wetland through the pipe.”
Surplus water is purified again and discharged into six reservoirs. The company has been able to save 600,000 yuan ($89,000) in water charges every year, Yang said.
In 2016 approval was given for Zhuanghe, a countylevel city in Dalian, Liaoning province, to be included in the second group of pilot cities receiving financing for sponge city construction.
The Zhuanghe pilot area, covering 8.42 sq mi, lies in the south of the city on the lower reaches of a three-river estuary.
Zhu Qinghui, director of the Zhuanghe Sponge City Construction Office, said 143 demonstration projects involving investment of about 3.35 billion yuan have been completed in pilot areas.
“The construction of a sponge city has brought real benefits, with the rivers becoming cleaner and the environment improving,” Zhu said.