The so-called sponge city means that the city is like a sponge, absorbing the rain when it meets it, storing and controlling it, and releasing the stored water for use when needed. Like nature, it carries out natural accumulation, infiltration and purification of the rain. During the two sessions in 2017, Premier Li Keqiang proposed to promote the construction of sponge cities in the government work report, redrawing the development blueprint of using "sponge" to fill the "inside" of cities.      

Sponge city construction press the fast forward key to leverage trillions of capital to follow up

In recent years, the city "see the sea" news every flood season will be frequently seen in the newspaper, "every rain will flood, after the rain that drought" has become a common problem in many cities. "Sponge cities" have been high hopes ever since. Thanks to the "geili" support from the central finance, the construction of sponge cities in China has been promoted rapidly and spread out on a large scale in a short time. At the recent two sessions, "Promoting the construction of sponge cities, making cities both 'face' and 'inside'" was also written into the government Work Report.

According to incomplete statistics, 79 cities have experienced waterlogging in 2016 alone. Industry analysis points out that the rainwater that has no place to rest has to rush into rivers, and the reversed hydrological characteristics have led to a wider deterioration of urban ecology, which is forcing innovation in the concepts and methods of urban planning, construction and management. In this context, the concept of "sponge city", which can maximize the accumulation, penetration and purification of rainwater in urban areas, promote the utilization of rainwater resources and ecological environment protection, is gradually emerging.

In fact, compared with the original "gray idea" that mainly relies on urban drainage system and pays attention to horizontal direction diversion, the construction of sponge city with natural accumulation, natural penetration and natural purification is to restore the function of the sponge body of the city, so that it can absorb water and water like a sponge, so as to play the role of rainfall peak cutting, peak shifting and peak stagnation, and effectively alleviate waterlogging. One of the key goals is to retain more rainwater and make it a resource.

China officially launched the construction of a nationwide sponge city in 2015. In the same year, the Guiding Opinions on Promoting the Construction of Sponge City issued by The General Office of the State Council proposed the construction target of absorbing and utilizing 70% of rainfall locally through the construction of "sponge city". The timetable set around this target is that by 2020, more than 20% of the built-up area of the city will meet the target requirements. By 2030, more than 80 percent of the area will meet the target.

In the following year, sponge city construction ushered in a period of intensive policy release. In April 2016, 14 cities including Fuzhou, Zhuhai, Ningbo, Yuxi, Dalian, Shenzhen, Shanghai, Qingyang, Xining, Sanya, Qingdao, Guyuan, Tianjin and Beijing were selected as the second batch of pilot cities for sponge city construction, the Economic Daily reported. On the other hand, Jiangxi, Gansu, Jiangsu, Anhui, Sichuan, Shandong, Jilin and other provinces have also published implementation opinions and related working rules on promoting sponge city construction. In the view of industry experts, from the local planning scheme delimited the timetable, most cities will complete the target in 3-5 years, most of the current layout stage.

It is widely believed in the industry that sponge city construction is a huge project with trillions of yuan of investment space, which is first reflected in the central financial grant of 100 million yuan special subsidies to pilot cities. In addition, the larger scale of social capital investment it leverages cannot be underestimated. According to Dongxing Securities estimates, by the end of the 13th Five-Year Plan, the total investment in sponge city construction will exceed one trillion yuan. According to estimates, the investment of sponge pilot cities is 100 million to 150 million yuan per square kilometer, and the total investment of a city is between several billion and tens of billions of yuan.

Specifically, the total investment scale will reach 1.18 trillion yuan to 1.77 trillion yuan by 2020, and 6.4 trillion yuan to 9.6 trillion yuan by 2030. At the same time, in order to support the construction of sponge cities, the central government has also spent "real money". For cities selected for the pilot program, the central government's special subsidy standard is: 600 million yuan per year for municipalities, 500 million yuan for provincial capitals and 400 million yuan for other cities.

However, public opinion has pointed out that it is not easy to grab the "sponge" this trillion cake. Under the new economic normal, how to further promote the construction of sponge city has become the focus of the industry. In the recently held 2017 sponge city planning and construction forum, the industry generally believes that in the specific application link application level, sponge city construction should also emphasize the change of method, in the past for rain concept is quick drain, each downstairs has rain grate, each hardened ground also has rain grate. The idea of quick discharge should be transformed into a "six-word maxim" : seepage stagnation storage and net use of discharge.

He was joined by Wang Hao, a member of the Chinese Academy of Engineering. According to the People's Daily Online, Wang Hao, an academician of the Chinese Academy of Engineering, said at the forum that the scientific connotation of sponge cities is summed up in three aspects: "peak reduction in water volume, pollution reduction in water quality and utilization of rainwater resources". For the problems existing in sponge cities, Wang Hao proposed that the fundamental solution is to achieve three coupling equilibria at area scale and city scale, namely, the balance between water discharge and dispersed stagnant flow (waterlogging balance), the balance between pollution generation and reduction (sewage balance), and the balance between rainwater control and utilization (water balance).

In other words, urban flood control and drainage planning should be done well one by one, and flood control and drainage standards should be gradually improved through the construction of underground integrated pipeline corridors, so as to realize "planning a map, building a game of chess and managing a network". However, the construction of sponge city can not be accomplished overnight. It not only involves making up the previous shortcomings, but also requires overall planning and reasonable arrangement. "We should adhere to the problem-oriented approach and put solving problems in the first place, so as to truly build a 'green' sponge."