SUEZ, Arup: The Firms Helping Cities Become 'Sponges'

Urban areas are particularly vulnerable to flash floods.

Concrete and tarmac do not let water through easily, preventing it from being absorbed into the ground. 

When drainage systems cannot handle the amount of water from a storm it can lead to flash floods.

These floods caused billions of dollars of damage in 2023 alone and pose a serious threat to life.

Dr. Tedros Adhanom Ghebreyesus, Director General at the World Health Organisation, says: “There is no question that the climate crisis is a health crisis.

“Heatwaves, storms, floods and food insecurity driven by climate change are jeopardising the well-being of individuals and health systems across the globe.

“I call on world leaders, who will join us at COP28, to commit to protect the health of all people!”

What is a sponge city?

A sponge city uses green infrastructure to absorb and store rainwater, making urban areas more resilient to climate change.

Parks, wetlands, ponds and rivers can lower the amount of excess water entering the sewage system. 

The water can then be stored in underground storage systems for use, conserving water whilst preventing floods.

Adding green spaces to cities also allows for increased biodiversity. 

Berlin Wasserbetriebe 

Berlin Wasserbetriebe (BWB), also known as Berlin Water Company, is Europe’s largest integrated water utility,

It is responsible for the drinking water supply and wastewater disposal for the 3.7 million residents of Berlin. 

It has been responsible for sanitation and water supply in Berlin for 150 years.

The company’s Future Strategy 2030 (Zukunftsstrategie 2030) aims to make the city more sustainable and resilient to climate change. 

Prof. Dr. Christoph Donner, Chairman of BWB, says: “Every drop of water counts and a sponge city is synonymous with the blue-green infrastructure transformation that we, and other regions in Germany, are developing and implementing for the next generation.”

How Berlin is becoming a sponge city

By 2025 Berlin will contain around 300,000 cubic metres of underground storage space for water as per a 1998 agreement.

The project is the result of a €140m (US$155m) investment, 60% from local government and 40% from BWB.

As of 2024, the company has already built 253,000 cubic metres of storage across more than 80 construction projects.

Astrid Hackenesch-Rump, a spokesperson for BWB, told DW: “The driving force behind this programme was not only resource conservation and drought, but also preventing combined sewer overflows.

“These sewage overflows regularly lead to fish being killed and oxygen depletion in the waters.”

Berlin has combined sewers that collect wastewater and rainwater and transport this to sewage treatment plants. 

Microorganisms are used to clean the water, and this process cannot be sped up, so only a certain amount of water can be sent to treatment plants at a time. 

When treatment plants reach the limit on water they can take, wastewater is discharged into waterways to prevent flooding. 

BWB says the sponge city developments should half the amount of discharges.

Sponge cities around the world

Around the world, cities are seeing the benefits of becoming ‘spongier’. 

Wuhan, China has implemented nearly 400 projects across 38.5 square kilometres as part of its sponge city initiatives. 

These projects include urban gardens, parks and green spaces and have saved the city US$600m compared to upgrading traditional infrastructure. 

Rotterdam in the Netherlands has built water collection ponds, now known as the ‘water square’.

When dry, the square can be used for sports or as an amphitheatre. 

Companies supporting the sponge city transition

Arup, a design and engineering consultancy, used satellite imagery to determine the 'spongiest' cities.

Auckland, New Zealand had the best urban centre in its survey, with 35% spongy land. Nairobi, Kenya came in close second with 34%, a city full of green-blue areas.

Arup has successfully applied a 'Sponge City Master Plan' in Baotou, a city in Inner Mongolia. 

French-based waste and water management company SUEZ has implemented its AQUADVANCED urban drainage system in Chongquing, China to assess the city's sponge facilities.

The system provides local authorities with a real-time view of the entire sanitation network from sensors to analyse and forecast the operating status of drainage systems. 

China State Construction Company (CSCEC) combined engineering with biological measures to conserve soil and water in Quingyang, China as part of an initiative to make the city more water resilient.

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