Sponge city

A sponge city is a new urban construction model for flood management, strengthening ecological infrastructure and drainage systems. It can alleviate the city's waterlogging, water resources shortage, and urban heat island effect and improve the ecological environment and biodiversity by absorb and capture rain water and utilize it to reduce floods. Rain water harvested can be repurposed for irrigation and for home use. It is a form of a sustainable drainage system on an urban scale.

China has been noted for its effort in adopting the Sponge City initiative. In 2015, China was reported to have initiated a pilot initiative in 16 districts.[1][2][3] This initiative presents an alternative to solve Asia's flood problems. China seeks to curb its flood with the initiative. The country plans for 80 percent of its urban cities to harvest and reuse 70 percent of rainwater. Building sponge cities requires huge investments, but has a lot of benefits. Funding sponge cities has been a challenge.[4][5]

Background
People biking through a waterlogged pavement in Foshan

City infrastructure construction accelerates alongside the urbanization process, but excessive utilization and water resources development lead to water shortages, pollution, and overall degradation of water ecosystem services. Unscientific architectural planning will also create a large number of buildings, thereby limiting cities' green space, drainage, and rainwater collection. Consequently, rain discharge cannot meet modern cities' requirements, bringing cities lots of problems regarding water ecology and aquatic environments.[6]

Meanwhile, high-intensity artificial constructions, such as buildings, roads, and squares, lead to the lower pad's excessive hardening, changing the original natural foundation and hydrological characteristics. Because of this, surface flow increases from 10% to 60%, while infiltration is drastically reduced, even to zero.[7] According to a waterlogging investigation that the Ministry of Housing and Urban‑Rural Development conducted in 2010, 62% of 351 cities across the country faced waterlogging between 2008 and 2010; 137 cities suffered waterlogging more than three times during this time period. This frequent urban waterlogging makes more and more people recognize the importance of water ecosystems and urban ecological infrastructure. The simple concept of fast discharge, a traditional gray water management model, is no longer helpful in addressing the rainwater dilemma during rapid urbanization. To cope with such prominent urban water issues, China is increasingly attaching importance to urban flood management and water ecological-system services and vigorously promoting the idea of Sponge City.

Policy

In terms of policy and management, on December 12, 2013, Present Xi Jinping put forward in his speech at the Urbanization Work Conference, 'When upgrading the urban drainage system, priority should be given to retaining limited rainwater and using the power of nature to drain water. Build a sponge city with natural accumulation, natural penetration, and natural purification.' [8]

To this end, in October 2014, the Ministry of Housing and Urban-Rural Development issued 'Technical Guidelines for Sponge City Construction,' emphasizing the importance of the top-level design of urban rainwater management, as well as planning to guide urban construction with ecological priority as the basic principle.

In August 2015, the 'Sponge City Construction Performance Evaluation Method' clarified requirements for the use of central fiscal funds and provided guidelines for the construction effectiveness of pilot demonstration cities. According to the guidelines and related standards and specifications, the China Building Standard Design and Research Institute has initially established a 'sponge city construction standard design system,' including newly built, expanded, and rebuilt sponge buildings and communities, roads and squares, parks, green spaces, and urban water systems.

The General Office of the State Council Guideline to promote building sponge cities (Guobanfa [2015] No. 75) pointed out that the construction of sponge cities occurs through strengthening the management of urban planning and construction, giving full play to the impact of buildings, roads, green spaces, and water systems on rainwater. Under the guideline, cities in China will collect and utilize 70 percent of the rainwater, with 20 percent of urban areas meeting the target by 2020, and the proportion will increase to 80 percent by 2030.[9]

In 2015 and 2016, pilot projects for sponge cities were organized with the support of national policies. Sixteen cities, including Zhenjiang, Jiaxing, and Xiamen, were selected as the first batch of pilot cities, and 14 cities, including Shenzhen, Shanghai, Tianjin, and Beijing, were selected as the second batch of pilot cities to carry out the construction of sponge cities in an orderly manner. In addition, the Central Ministry of Finance has introduced a public-private partnership (PPP) model to increase financial policy support.

Designing for Sponge Cities

The theory of Sponge City emphasizes the basic principles of 'focusing on nature,' 'source control,' 'local adaption,' protecting nature, learning from nature, preserving urban ecological space as much as possible, restoring biodiversity, and creating a beautiful landscape environment. All of this can be realized by achieving natural accumulation, natural infiltration, and natural purification. The infiltration effects of the natural ecological background (such as topography and landforms), the purification effect of vegetation and wetlands on water quality, and the combination of natural and artificial means allow the city to absorb and release rainwater. Urban green spaces and urban water bodies—constructed wetlands, rain gardens, roof greening, recessed green spaces, grass ditches, and ecological parks—are the central "sponge bodies."[10]

There are three main facets to developing such systems: protecting the original urban ecosystem, ecological restoration, and low-impact development.

  • Protection focuses on the city's original ecologically sensitive areas, such as rivers, lakes, and ditches. Natural vegetation, soil, and microorganisms are used to gradually treat the aquatic environment and restore the damaged urban ecosystem.
  • Restoration measures include identifying ecological patches, constructing ecological corridors, strengthening the connections between the patches, forming a network, and delineating the blue and green lines to restore the aquatic ecological environment.
  • Mandatory measures apply to urban roads, urban green spaces, urban water systems, residential areas, and specific buildings to protect ecological patches, maintain their storage capacity, strengthen source control, and form ecological sponges of different scales.[11]

These processes are implemented in the sponge city design and to the transformation of urban planning areas at different levels, including urban master planning, special planning, and detailed regulatory planning.

Advantages
  • Improves overall water quality
  • Rainwater is captured and can be reused
  • Reduces chance of flooding
  • Reduces the railway problems
  • Reduces urban heat island intensity.[12]

See also

References
  1. Harris, Mark (2015-10-01). "China's sponge cities: soaking up water to reduce flood risks". The Guardian. ISSN 0261-3077. Retrieved 2019-08-24.
  2. "What is a Sponge City?". Simplicable. Retrieved 2019-08-24.
  3. Biswas, Asit K.; Hartley, Kris. "China's 'sponge cities' aim to re-use 70% of rainwater – here's how". The Conversation. Retrieved 2019-08-24.
  4. Harris, Mark (2015-10-01). "China's sponge cities: soaking up water to reduce flood risks". The Guardian. ISSN 0261-3077. Retrieved 2019-08-25.
  5. simoncox (2016-05-31). "Sponge Cities". Hydro International. Retrieved 2019-08-25.
  6. "Yu, K. J., Li, D. H., Yuan, H., Fu, W., Qiao, Q., Wang, S. S., "Sponge City": Theory and practice, City Planning Review, 2015, 39(6): 26–36". www.chinadoi.cn. doi:10.11819/cpr20150605a. Retrieved 2020-12-15.
  7. Wu, Ye Gang (2016). Sponge City Design: Concept, Technology & Case Study. Jiangsu: Phoenix Science Press.
  8. "中国为什么要建设"海绵城市"？--时政--人民网". politics.people.com.cn. Retrieved 2020-12-15.
  9. "Guideline to promote building sponge cities". english.www.gov.cn. Retrieved 2020-12-15.
  10. "面向"海绵城市"建设的特大城市总体规划编制内容响应 - 期刊". ie.cnki.net. Retrieved 2020-12-15.
  11. 仇, 保兴 (2015). "海绵城市(LID)的内涵、途径与展望". 中国勘察设计 (07): 30–41. ISSN 1006-9607.
  12. "He, B. J., Zhu, J., Zhao, D. X., Gou, Z. H., Qi, J. D., & Wang, J. (2019). Co-benefits approach: Opportunities for implementing sponge city and urban heat island mitigation. Land use policy, 86, 147-157".
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