Sponge City Development in China
The nationwide implementation of the sponge city concept in China since 2014 is being followed with worldwide attention. Initially, pilot measures for sponge city development were implemented in 30 cities in all parts of the country, of which the first 16 locations are currently under evaluation. On the basis of the findings soon available, 20% of the built-up urban areas in China are to be developed as sponge cities by 2020 and 80% by 2030.
Thus, the concept of the sponge city has become one of the central planning variables in urban development in China. A new green and blue infrastructure has taken priority on the urban surface to provide a convincing response to urban flash floods caused by heavy rainfall events. Rainwater is not only to be stored, but also used as a new water resource for urban water needs. In this way, there are still issues to be solved, such as how the pollution of precipitation/urban run-off can be removed, Thus, how to deal with plollution of urban run-off with tyre abrasion, fine and often particularly polluted particles as well as pathogens before rainwater is ready to be used in urban contextes.
Project Area: Sponge City Development in Tongzhou Area, Beijing
The climate conditions in Beijing are characterised by hot and rainy summers and cold and dry winters. The climate characteristics can be taken from the following diagram, compiled from national climate data by Zhang (2019).
Figure: Monthly average temperature ranges and rainfall depth in Beijing from 1981 to 2010 ZHANG, 2019 derived from National Climate Data)
Beijing belongs to the second batch of pilot citites nominated in 2016. The Beijing city government is moving into Beijing’s Tongzhou district, which is located south-east of the city centre. This is why, Beijing also pilots the sponge city concept in this area, and - with KEYS – also includes a German contribution. Tongzhou’s sponge city pilot area is about 19 km² large. It includes built-up residential areas (45%), commercial and industrial areas (31%) and areas for new urban development (24%). According to the Chinese partner Beijing Water Sciences and Technology Institute (BWSTI) the core tasks include pollution control of combined sewer overflows, treatment of stormwater from traffic areas, initial stormwater interception and drainage monitroing in different scale. The following figure illustrates some of the sponge city elements implemented in the Zijingyayuan community. Here, the built-up communities are characterised by a building density of approximately 20%, while 20-33% of the area are green spaces.
Figure: Tongzhou disctrict: Sponge city elements in Zijingyayuan community (April 2019) (Pictures: ISAH)
Permeable pavements are the most widely used Low Impact Development element in the analysed communities in Tongzhou. They cover about 14-30% of the community area. Parking lots, pedestrian and bicycle areas are all covered with permeable materials. In most cases the runoff from these resident traffic areas is redirected into infiltration facilities. Furthermore, rooftops are disconnected and the runoff is either stored in rainwater retention tanks or infiltrated. The most widely used infiltration facilities are low eleveation green belts, covering 4-20% of the area, followed by ditches and bioretention cells. Both, permeable pavements and bioretention facilities have an emergency overflow into the sewer system.
In the context of urban transformation, the concept of sponge urban development will have to be proven especially in existing urban neighbourhoods. To do this, an exchange of data and experience should take place on suitable platforms, covering both aspects of the operation and maintenance of the facilities. In order to ensure the long-term functional maintenance of the sponge city infrastructure, a reliable determination of responsibilities as well as the availability of adequate financial resources for the plant operators is required. With a view to the future, numerous further positive impulses for a city worth living in can be expected from the development of Sponge City, as there are many points of contact to other urban trends such as Urban Gardening, Urban Agriculture and Green Facades/Green Architecture.