It used to be that cemented channels and underground piping in cities controlled storm flows so water would run off quickly….but now such ‘gray’ infrastructure is being replaced by the green infrastructure of ‘sponge cities’, accommodating rainfall instead of fighting it. It has been policy in China since 2015 and is becoming more common in cities globally.
The urban designer most responsible for China’s sponge city rollout is Yu Kongjian, dean of Peking University’s college of architecture and landscape. As a child, he nearly died when swept into the flooding creek near his farming commune. Willows and reeds along the bank made it possible for him to climb out. Today, with concrete flood walls, he would have drowned, he told the BBC. It was a powerful lesson about the value of ‘green infrastructure’ in an era of climate change.
A sponge city soaks up rainfall and slows down surface run-off from start to finish. At the source, the city tries to contain water with many ponds, just like a sponge. Then, as the water flows, it avoids straight channels (often with concrete walls) that speed water away. It prefers meandering rivers with vegetation or wetlands that slow the water, creating green spaces, parks and animal habitats and purifying the surface run-off with plants that remove polluting toxins and nutrients. Finally, where the water empties out to a river, lake or sea, flood plains are protected.
Prof. Yu’s design philosophy is based on traditional Chinese concepts. His firm’s name, Turenscape, is derived from the Chinese words “Tu” (meaning “land”) and “Ren” (meaning “people”), combined with the English word “scape”, indicating the harmony between land and people. In 2015, Turenscape won the World Landscape of the Year prize for the 26-hectare Yanweizhou Park, a natural wetland park at the mouth of three rivers in China’s Zhejiang province. It features flood-resistant topography, natural wildlife habitats, and a network of meandering pathways and bridges.
The architects widened the banks of the river, which was channelled in the 1970s as an unsuccessful solution to flooding.
In 2015, the Chinese government announced a multi-million yuan plan and an ambitious goal – by 2030, 80% of China’s municipal areas must have elements of a sponge city and recycle at least 70% of rainfall. The need for such policies was underlined in 2016, when Wuhan, one of China’s first 16 “sponge cities”, experienced a devastating flood whose economic cost was estimated at 2.3bn yuan (£263m). Prof Yu says that done right, a sponge city is much cheaper than conventional solutions. Many of Turenscape’s projects are now aimed at fixing flood infrastructure that cost millions, and he says this money could have been saved if officials followed sponge city principles in the first place. (Some of his projects can be seen here.)
In 2016, Copenhagen adopted ‘sponge city techniques’ as a way to better manage run-off water. The $1.4 billion, 20-year plan included expanding the city’s underground sewer networks, and adopting 300 ‘surface’ solutions to be rolled out across the city at a rate of 15 a year. It is creating reservoirs in a city park—in areas that people can use when it’s not raining—and rain gardens that help soak up water to avoid overloading the sewer system. In other neighborhoods, sunken gardens double as rainwater storage.
“As a society we have to invest a lot of money to climate adapt our cities to handle the new amounts of rainwater, and it is essential that we use the money as intelligently as possible so that we both take care of the rainwater and, at the same time, contribute to making better and more liveable and active cities,” says Anne-Mette Gjeraa, head of projects for Realdania, which has installed four WATER PLUS projects, including one on the outskirts of Copenhagen that has transformed the centre into a multifunctional sports area.
In the Dutch city of Rotterdam, a sunken basketball court can store nearly half a million gallons of water in a storm. In Bangkok, a recently built park was designed with a slope that sends water into large storage tanks underground. New York City has right-of-way bioswales – planted areas in the sidewalk designed to collect and manage stormwater. They consist of a swaled drainage course with gently sloped sides filled with vegetation or compost and are being installed in Brooklyn, the Bronx and Queens. Bioswales help “green” a local area, reducing the heat island effect and absorbing carbon emissions.
Green infrastructure is becoming standard in many new developments, urban designer Geeti Silwal told Fast Company this month. In a Palo Alto project, the firm is working on a design to restore a concreted channel to a natural state, creating both a bigger area for water to soak into the ground and new access to nature for people living nearby. In New York City, permeable pavement and rain gardens kept one apartment building from flooding during extreme weather.
Sources:
The man turning cities into giant sponges to embrace floods. BBC, Nov. 11, 2021
Turenscape. dezeen magazine.
Inside China’s leading ‘sponge city’: Wuhan’s war with water. Guardian, Jan. 23, 2019
Copenhagen unveils first city- wide masterplan for cloudburst. The Source Magazine, Mar. 1, 2019
This new park is designed for a future of flooded cities. Fast Company, Aug. 20 2018
How sponge cities are redesigning themselves for extreme rain. Fast Company, Jan. 10, 2023