News originally published on the GrowGreen website. Republished with permission from GrowGreen.
Wuhan, the capital city of Hubei Province, is well-known as the “city of one hundred lakes” located in central China. Abundant water resources and extensive water systems shape beautiful landscapes and make the city liveable. The water systems in Wuhan, consisting of rivers, lakes, water channels aSponge City Programme in Wuhan Chinand reservoirs, cover 25% of the entire municipal area.
However, water management and prevention of waterlogging in Wuhan are challenging. Wuhan has suffered from waterlogging for years mainly due to the low-lying built-up area and the uneven distribution of precipitation, with 70% of the rain falling in April to September. Rapid urbanisation has reshaped the urban landscape, changed the natural hydrological process and exacerbated waterlogging[i]. The size of natural lakes has shrunk by nearly 70% from the 1950s to 2013[ii],[iii], resulting in the reduction of regulation and storage capacity of the lakes. On top of waterlogging, water pollution deteriorates the water management system. Sewage pipes and stormwater pipes are mixed and misconnected and the sewage water is discharged into urban water channels, forming black and malodorous water bodies. The overexploitation of groundwater and the heat island effect make the situation even worse. Therefore, it is urgently needed to develop an effective system for water management and waterlogging prevention.
“Sponge City” – a new solution for urban water management
In 2013, Chinese President Xi pointed out that cities should “act like sponges” to retain rainwater and make use of natural forces to accumulate, infiltrate and purify rainwater[iv]. Since then, the concept of the “sponge city” has gradually entered the public view. To start the sponge city initiative, 16 pilot cities were chosen as the sponge pilot cities in 2015 and Wuhan was among them.
The sponge city concept refers to a way of urban management that allows cities to resolve urban waterlogging, improve water storage and discharge capacity, enhance water quality, and alleviate heat island effects through a mix of nature-based solutions and grey solutions. Sponge cities also prioritise the protection and restoration of original ecosystems in the urban area, such as rivers, lakes and wetlands, and emphasise natural forces by applying the concept’s six technical measures – “infiltration, retention, storage, purification, utilization and discharge”[v]. The use of natural processes became a new solution to rebuild a harmonious relationship among people, water and city. Thus, with the purpose of addressing waterlogging problems, the Sponge City Programme became the primary means used in Wuhan.
Wuhan Sponge City Programme
As suggested by the national sponge guidelines[v], the target of the Wuhan Sponge City Programme is that 20% and 80% of the urban area should achieve the sponge city requirements by 2020 and 2030 respectively. Based on its local conditions, Wuhan has also set up goals for its sponge projects. The sponge projects must absorb 60%-85% (17.6-35.2mm/d) of the annual rainfall, achieve a capacity to resist 50-year storm effectively (303mm/d), and eliminate black and malodorous water bodies[vi].
To achieve the targets, Wuhan designed sponge infrastructures under the guidance of the national technical guide for sponge cities. The sponge infrastructure applied in Wuhan includes nature-based solutions, such as rain gardens, green roofs, grass swales and bio-retention facilities, and grey infrastructure, such as permeable pavements, pervious concrete pavements, infiltration trenches, and rainwater storage modules.
In 2015, Wuhan started to implement the sponge city demonstration project, which consists of two demonstration areas and 288 pilot projects within the two areas. The pilot projects work with roads, green space and residential quarters. The construction of demonstration projects lasted for three years and attracted CNY 11 billion (EUR 1.4 billion) of investment from both government funds and social investments. Hundreds of sponge projects across the city have been in construction to date.
So far, the Wuhan Sponge City Programme has achieved great success and showcased the great ability of flood control and waterlogging prevention[vi]. In the summer of 2020, Wuhan experienced multiple rounds of intense, record-breaking precipitation during the long-lasting rainy season. In some areas of Wuhan, the daily precipitation even reached 472.3mm, but no serious floods and waterlogging occurred. Compared to the storm event in 2016, the number and size of waterlogging points reduced significantly. The impact of waterlogging on traffic and the public was greatly alleviated, which demonstrated huge potential and capability of the sponge projects. A cost analysis[vii] showed that the use of sponge measures with a focus on nature-based solutions in the city’s demonstration areas have saved around CNY 4 billion (EUR 509 million) compared to the conventional approach to upgrade the drainage system, which reveals the great potential of nature-based solutions.
What leads to the success of the Wuhan Sponge City Programme?
1 Applying whole-process management in waterlogging prevention
A multi-level management system has been established from the overall concept of the Wuhan Sponge City Programme – the systematic and whole-process controlled water management[vi]. The system consists of non-engineering measures for regular maintenance and disaster response, and engineering measures, which include blue and green infrastructure to absorb rainwater at source, grey infrastructure to reduce excessive rainfall and prevent waterlogging, and lakes to regulate and store water at the end of the process.
2 Integrating sponge projects in Wuhan Comprehensive Planning with collaboration of different city departments
The Wuhan Sponge City Programme is not a construction project that exists separately from other urban plans but is interdependent with them, especially aligning with the Wuhan ecological planning framework[viii]. It also entails the cooperation of different departments, such as water affairs, landscape and road traffic, for sponge projects to be planned and implemented. All responsibilities are clearly defined to effectively collaborate among different departments and implement the sponge projects.
3 Developing localized strategies and technical standards
As one Chinese idiom said “applying appropriate medicine according to the symptom”, it is essential to adopt localised strategies. Wuhan has established a sponge index system[ix] as the standard reference for the design and assessment of sponge infrastructures. The design of zoning for sponge subregions follows the target values of key indicators as well. The existing built-up area in Wuhan focuses on problem-solving and the new development area highlights the high standard of control and construction. Moreover, Wuhan has finished the compilation of local technical standards in 2019 throughout the entire project process from planning, design and implementation to maintenance of sponge projects.
4 Establishing a fund-raising mechanism and attracting social participation for risk- and benefit- sharing
The cost of sponge city construction is tremendous, thus, fund-raising is crucially important. Wuhan, as one of the sponge pilot cities, received CNY 500 million (EUR 64 million) of national funds each year from 2015 to 2017. District governments, namely the main responsible bodies for project implementation, and the Wuhan Municipal Government are both responsible for establishing their own investment funds for sponge projects. The municipal government also encourages the participation of social capital (refers to capital from private enterprises and state-owned companies) and the application of the public-private partnership (PPP) to allow the market to play a role in resource allocation and to share risks and benefits.
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[i] United Nations Development Programme China. (2017). Research Report on Urban Flood Risk Management Capacity: https://www.cn.undp.org/content/china/en/home/library/crisis_prevention_and_recovery/environmental-risk-identification-and-obviation-in-post-earthqua1.html
[ii] WANG Fang. (2005). Research on Evolution of Urban Lakes in Wuhan Based on RS/GIS (Master’s thesis). Wuhan University. (In Chinese)
[iii] The Beijing News. (2016). The History of Lake Filling Behind the Waterlogging Siege in Wuhan: https://www.bjnews.com.cn/detail/155150665214239.html (In Chinese)
[iv] People.cn. (2019). Why China Builds Sponge Cities? http://politics.people.com.cn/n1/2019/1020/c429373-31409450.html (In Chinese)
[v] The State Council of China. (2015). Guideline on Promoting the Construction of Sponge Cities: http://www.gov.cn/zhengce/content/2015-10/16/content_10228.htm (In Chinese) & http://english.www.gov.cn/policies/latest_releases/2015/10/16/content_281475212984264.htm
[vi] KANG Dan, Wuhan Urban and Rural Construction Bureau. (2020). Wuhan-Manchester Webinar: “How to deepen further cooperation around Sponge City & GrowGreen project”. (Internal presentation, in Chinese)
[vii] Oates, L., Dai, L., Sudmant, A. and Gouldson, A. (2020). Building Climate Resilience and Water Security in Cities: Lessons from the sponge city of Wuhan, China. Coalition for Urban Transitions. London, UK, and Washington, DC: https://urbantransitions.global/wp-content/uploads/2020/03/Building-climate-resilience-and-water-security-in-cities-lessons-from-the-Sponge-City-of-Wuhan-China-final.pdf
[viii] Wuhan Planning and Design Institute. (2015). The Guideline for Wuhan Sponge City Planning and Design (trial): http://www.whxtgs.com/xwzx/hyxw/201607/P020160719361229436403.pdf (In Chinese)
[ix] Wuhan Planning and Design Institute. (2016). Wuhan Sponge City Specialized Plan: http://www.wpdi.cn/project-3-i_11332.htm (In Chinese) & http://zrzyhgh.wuhan.gov.cn/UploadFileNew/20161021001753506.doc (In Chinese)
East Lake, Wuhan, China (Stephen Fang / Unsplash)
Waterlogging in Wuhan (KANG Dan, Wuhan Urban and Rural Construction Bureau)
Rain garden in Huazhong University of Science and Technology, Wuhan (KANG Dan, Wuhan Urban and Rural Construction Bureau)
The timeline of Wuhan Sponge City Programme (produced by Yunyue Peng)
Before and after sponge construction in Qingshan demonstration area (KANG Dan, Wuhan Urban and Rural Construction Bureau)