Sponge Cities: China’s solution to flooding and drought

What is a Sponge City?

The traditional idea of managing surface water runoff in an urban environment is to funnel that water away from cities as fast as possible. Recently, however, city planners and governments are realising that this design concept is flawed as it means that they are, to all intents and purposes, throwing away a highly valuable resource: water.

The new mode of thinking is to design a city in such a way that it retains all the surface water runoff that occurs within the confines of the city and that it can be reused at a later date, thereby creating an urban environment that absorbs the water then releases that water when required—in a similar manner to a sponge.

Why has this concept been adopted? What has driven it?

The concept is already established in many urban areas around the world on various scales through sustainable urban drainage systems (SuDS) and low impact development (LID). China has embraced the Sponge City concept because, combined with the facts of rapidly growing urban populations, poor water management and climate change, half of China’s 657 cities are reported to be water scarce. Of these cities 230 were affected by flooding in 2013 alone.

In 2013 Chinese President Xi Jinping called for the development of Sponge Cities and early in 2015 the Chinese Central Government pledged billions of dollars over the next three years to help 16 cities—including Wuhan, Chongqing and Shenzhen—to become Sponge Cities.

How will Sponge Cities benefit the populations of those cities? What will the impact be of taking this approach?

The main benefit to the population is a better urban environment in terms of aesthetics and quality of life. Sponge City design allows the inhabitants to better enjoy where they live and work—and of course in addition the city has the ability to use their water resources far more effectively.

What could be the impact if we don’t take this approach?

More flooding, with rivers and lakes becoming even more polluted to the point that these water bodies become dead; there are numerous examples around the world of engineers having continued with traditional water management solutions only for the problems of flooding and water pollution to get worse.

At the same time, however, we see examples of engineers employing good, water-sustainable urban design where as a result the quality of the urban environment is dramatically improved and the incidence of flooding is reduced.

Are Sponge Cities difficult to develop? Are they costly?

In the sense of getting governments and authorities to recognise the need to move away from the traditional paradigm of water management to that of waster sustainable urban design, yes.

Once that mind shift happens and there is a will to change, however, then Sponge Cities will become relatively easy to develop.

How do you see Sponge Cities developing over the coming years? What trends have you seen?

In China alone the idea of Sponge Cities will grow far beyond the first 16 cities for which the Chinese Central Government has allocated development funds, and the idea is relevant to city planners all over the world—more and more governments are recognising the need to manage their water resources more effectively.

Increased urbanisation, population growth and climate change will continue to drive the need globally for better, smarter and more sustainable water management solutions.

What do city planners need to be most aware of when developing a Sponge City?

Make sure that any solution is sustainable, that any product supplier can stand by their performance claims, and preferably work with companies that have experience in providing the technologies and can provide design and installation support locally.

Are there any popular misconceptions about Sponge Cities?

The primary misconception seems to be that there is only one solution, when the reality is that there is no “silver bullet”. The best sustainable designs are those that use a combination of engineered products and natural features.

The other misconception is that the solution is expensive; relatively speaking this is incorrect, and the truism is that prevention is less expensive than the cure. Water is a hugely valuable resource that has no replacement and it is incumbent on today’s society to look after such a precious commodity.

Is Hydro International involved with any Sponge Cities already? If so, how?

In Anhui province we have supplied a Storm King® as part of a solution to protect the water quality of a lake. The challenge for engineers in the city is that the drainage system is a combined sewage system, and during rain events the drainage network cannot cope with the additional flows and as such diverts these excess flows directly into the nearby lake—thus heavily polluting the lake not only with sewage but also with the pollutants associated with surface water runoff. The Storm King® provides a level of treatment to the flows before they enter the lake, and then redirects the removed pollutants to the wastewater treatment plant where they may be safely treated.

We are also currently in discussions with a number of Chinese design institutes to incorporate a range of Hydro International products into Sponge City designs. The interest in Hydro International products from these engineers is based on our experience in supplying products for storm water management and combined sewage systems. Further, the fact that the products require no external power and have no moving parts makes our product proposition even more appealing to both designers and city authorities.