‘Sponge cities’ offer answers for NZ after devastating floods

A general view of a damaged house after a storm battered Titirangi, a suburb of New Zealand's West Auckland area, on February 13, 2023. (PHOTO / AFP)

Will China’s ‘sponge cities’ be the answer to alleviate future urban flooding in New Zealand?

It is a question analysts are asking as New Zealand starts the long process of rebuilding following the worst flooding in the country’s history.

Auckland, the biggest city in New Zealand, saw four months’ worth of rain dumped in a 24-hour period in late January. While Auckland had a good record for flood mitigation it was not enough to hold back the water that turned streets into rivers and caused widespread flooding throughout the city of nearly two million people.

Chinese landscape architect Kongjian Yu, one of the leading proponents of the sponge city concept, believed cities should incorporate nature’s “ability to absorb, store and filter water”

As urban centers keep expanding around the world, ever more land is being taken up for buildings and roads. The more concrete covering the ground means the less water that can be absorbed.

Amid this problem, experts say New Zealand should take a closer look at the so-called sponge cities solution, a concept that has China has implemented successfully in major cities to collect stormwater and prevent flooding.   

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In 2015, China launched the “sponge cities” program in 16 cities to reduce the intensity of rainwater runoff.

The idea was simple. Restore parks and grasslands, keep creeks and lakes, and incorporate major drainage projects to allow water to be collected and stored or piped away from urban areas.

Chinese landscape architect Kongjian Yu, one of the leading proponents of the sponge city concept, believed cities should incorporate nature’s “ability to absorb, store and filter water”.

He has said that if urban planning involves more concrete, buildings and roads, it reduces the potential for water to be absorbed into the ground.

Timothy Welch, senior lecturer in urban planning at the University of Auckland, said: “The sponge city concept, and ideas about letting nature handle stormwater, don’t have to be extravagant or expensive. They can be as simple as planting more trees and greenery, using less pavement for driveways or more porous cement for car parks.”

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In an interview with China Daily, Bharat Dahiya, an international expert on urban development, said: “Whether they are well-established cities like Auckland, or new ones such as Nusantara —Indonesia’s upcoming new capital city — they will be affected by the imminent impacts of global climate change.” 

Dahiya, director of the Research Center for Sustainable Development and Innovation at the School of Global Studies at Thammasat University, Bangkok, said: “These impacts include the increasing frequency and intensity of hydro-meteorological hazards, and related higher precipitation and catastrophic flooding.”

For climate adaptation in cities and towns, one way to move forward, he said, is to come up with hybrid solutions combining what he calls “gray and green infrastructures”.

In this Feb 1, 2023 photo, residents wade through a flooded street after torrential rain at the suburb of Langholm in Auckland. (PHOTO / REUTERS)

Gray infrastructure includes pipes, pumps, concrete drainage systems, and green infrastructure or nature-based solutions –– which are also called “sponge city” approaches. Green infrastructure includes public green spaces, parks, lakes, and wetlands. 

Dahiya said that none of this will come cheaply, and that it calls for “strong political will” and significant investment in grey and green infrastructure.

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“How cities, including their communities and leaders, will be able to bring these multiple approaches together will go a long way in effectively tackling the evolving challenges posed by climate change,” he said.

Tom Logan, senior lecturer in risk and civil systems analysis at the University of Canterbury in New Zealand, however, said creating sponge cities will only go so far.

“Auckland communities affected by flooding are going to have to make some hard choices,” he said.

“When you get that much water, it's going to overwhelm your systems. We don't design our systems for the worst possible event because it'd be so expensive.”

In a commentary for the academic website The Conversation in January, Welch said, “In a way, we should do less building and let nature do what it was meant to do.” 

Auckland’s flooding was, to a large extent, “of our own making”, he said. “We’ve built a supercity covered in impervious surfaces, expanded the built environment across sensitive (and flood-prone) areas, and created massive greenhouse gas emissions destabilising the climate.”

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Logan said building flood walls or barriers is an option, but these can actually make flooding worse, citing New Orleans’ experience in 2005 following Hurricane Katrina.

“We have to decide our risk tolerance and how regularly we are willing to accept some amount of damage,” Logan said.

Some of the hard choices, he said, could include giving Auckland Council the power to stop building in flood prone areas and relocating communities.

“This constant cycle of insurance, rebuilding, another hazard, rebuilding, isn't sustainable. Insurance companies are going to move out and make us unprotected,” Logan said.