As the climate warms, some regions suffer crippling drought, while others are hit by deadly floods. Often worst hit are urban areas which suffer catastrophic water damage and loss of life when engineered drainage is breached – New Orleans, Rhineland-Palatinate and  Henan spring to recent mind. But one Chinese architect thinks he has the solution to urban flooding – sponge cities. By Jared Green (courtesy ASLA) and James Teo.

Beijing, November 2021. ​​“More than ever, we have to rethink the way we build our cities, and the way we treat water and nature,” says Yu Kongjian, professor of landscape architecture at Beijing University, and founder of the innovative Turenscape urban design agency, which was selected as one of 2021’s most innovative organisations, worldwide.

“An infrastructure of concrete, steel, pipes and pumps can help solve urgent …(flooding) problems, but it consumes huge amounts of concrete and energy, lacks resilience and often accumulates a higher risk of disaster,” explains Yu. “(All this) breaks the connection between man and nature.”

For the last couple of decades Yu and Turenscape have been working on changing urban design to reconnect that link, and minimise approaches which harm the environment. Drawing on what he saw and learned about the living and during his childhood, he uses what he describes as “ancient wisdom of water and waste management” principles to design environment-friendly urban water solutions.

The need for change is increasing; flooding has become a huge problem in areas like in Zhengzhou which was hit by massive floods in July 2021. In parallel, global water demand has increased nearly eightfold over the last 90 years, and in many places water is running out. As cities grow larger, Yu is convinced the answer is ‘sponge city design’ which uses a combination of city-wide ponds, wetlands, and parks that soak up, reroute and retain stormwater when the rains come.

“Since ancient times, cities with monsoon climates along the Yellow River have used ponds to manage flooding and stormwater. So we know these approaches worked for over 2,000 years – simply because these cities survived.”

The ‘sponge city’ design approach uses the natural properties of the landscape to retain water at its source, slow down flow as the volumes increase during heavy rain, and clean water too as it flows through the system - all as integral parts of the process. The focus is simple – not to “dispose of” but to retain rainwater in urban areas.

This can be done by reducing the number of hard surfaces and increasing the amount of absorbent (green) land, which helps promote significant reductions in the severity and frequency of flooding.

More currently conventional and artificial flood control solutions, such as building walls, culverts and massive water cisterns (like those proposed in New York), are only a short-term fix says Yu. “This approach is unsustainable,” he warns. “The concrete cisterns have to be huge and therefore expensive and high maintenance, and the approach wastes water, which is a living resource.”

Other sponge city approaches include building in more green rooftop spaces, building roads with porous instead of impermeable surface materials, planting water-intensive plants and trees and using water retarding land basins, ponds and lakes to absorb or hold excess water. This when combined with existing plants and washed-down soils and mud creates even more natural resources within a city – a bonus from what would otherwise be a disaster. Even better, efficient, environmentally friendly channelling and water storage systems can also help to mitigate water shortages, which are often issues in large cities.

Like flood waters, the sponge city word is spreading. Today, Chinese cities are required to maintain 30% of their area as green space, with an additional 30% dedicated to community space.

According to Yu’s design approach, this means there is more than enough space to create ponds and water-absorbing parks with the capacity to capture vast amounts of water.

“We can use nature to retain water so it doesn’t drain away. In China, we have a saying — ‘water is precious, don’t let it go.’ And there is plenty of space to be used to retain water,” he adds.  

But sponge city design adherents say there is more to be done to educate about the benefits of sponge cities. “Some of the public still doesn’t understand the concept, and some even think it is a waste of money,” says Yu. “Some civil and hydrological engineers (have attacked) the approach because it takes away their jobs,” he adds.

“The issue (in China) is that some designers and engineers are building parks but not building in the stormwater management capacity needed.” But the increased scrutiny of city flooding has brought a new perception to urban design – with sponge city principles being much more widely accepted.

“Flooding in the era of climate change presents an opportunity for landscape architects,” says Yu. “We have an opportunity to build up our approach. Landscape architects can solve these problems — not with concrete pipes and cisterns — but with nature.”