Explainer: Why NZ’s cities need to get ‘spongier’ – and fast

8 min read

The collaborative Te Ara Awataha project has been opening up a new “greenway” in Northcote – while helping make the Auckland suburb “spongier” in extreme weather events like January 27. Photo / Kainga Ora

Following a summer of disastrous deluges, a major new report concludes our cities will need to be “spongier” to meet increasingly extreme weather. Jamie Morton reports.

When the rain came hard on January 27, Northcote residents might’ve guessed what was next.

Floods have been such a headache in the Auckland suburb – sitting smack in the middle of an overland flow path – that locals have sometimes taken to kayaks to negotiate streets awash with stormwater.

Auckland Anniversary Weekend’s, of course, wasn’t a typical rainstorm.


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In what Niwa described as a one-in-200-year event, shin-high water gushed through Auckland Airport’s main terminals, holiday traffic sat stuck on flooded motorways and fire crews were swiftly slammed with an avalanche of callouts.

But over in Northcote, this time, things turned out differently.

Homes that would’ve been swamped in much lighter deluges were spared heavy damage, as a freshly-re-developed Greenslade Reserve, replete with a new urban wetland and detention basin, took on an incredible 12 million litres of water.

Northcote's recently redeveloped Greenslade Reserve has been soaking up vast amounts of water in this year's big floods. Photo / supplied
Northcote’s recently redeveloped Greenslade Reserve has been soaking up vast amounts of water in this year’s big floods. Photo / supplied

Its transformation had come in step with the surfacing, or “daylighting”, of the Awataha Stream, easing pressure on ageing pipelines that’d been much to blame for the suburb’s past woes.


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And it so happened that these two parts of the Te Ara Awataha greenway project – a years-long collaboration between Eke Panuku, Auckland Council’s Healthy Waters team, Kāinga Ora Homes and Communities, Kaipātiki Local Board and mana whenua – had only been completed just weeks before the giant storm hit.

To see what might have been viewed as just another expensive park makeover work exactly as it was designed to on January 27, Eke Panuku’s Sara Zwart said, was “incredibly exciting”.

“We’ve had so much interest in it since – along with a huge amount of pride from locals.”

It stood as a powerful case study of groups working together to deliver infrastructure making way for nature and water, even in the face of growing intensification.

It also demonstrated a concept engineers and ecologists alike have been calling for after our extreme summer: the “sponge city”.

Cities as sponges

While new to many of us, the idea of sponge cities goes back decades, to when Chinese landscape architect Dr Yu Kongjian came to realise that building more pipes and drains wasn’t a sustainable solution to the increasing floods he was seeing in cities.

Inspired by rice paddy farmers, he proposed less “grey” infrastructure and more “green” and “blue” – like parkland, rivers, wetlands and trees – to work with water, rather than treating it as a hazard to be channelled away.

China has now invested billions of dollars in 30 pilot sponge cities, while further south in Singapore, a growing network of urban ponds, streams and greenspace has taken shape amid its concrete jungle.

 Singapore's Gardens by the Bay nature park.
Singapore’s Gardens by the Bay nature park.

“We’ve been hearing more and more about sponge cities globally over the past few years as the climate warms and floods become more frequent and intense,” Kali Mercier, deputy director of the Helen Clark Foundation, and lead author of a major report just launched by the public policy think-tank, in conjunction with WSP in New Zealand.

“People can now see the evidence before their eyes that we have to be ready to adapt to a new reality.”


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Studies are now revealing the impact our climate crisis is having on weather disasters: the storm that put Westport underwater was likely made about 10 per cent worse by a warming world.

Even if the world meets the Paris Agreement’s ultimate target and holds the line of global warming at 2C, the extra moisture loaded into the atmosphere at that point would mean perhaps 20 to 30 per cent more rain falling in big storms.

Much of that would come in torrential hourly extremes, just like those that wreaked such havoc on January 27.

When the skies unloaded more than 200mm in some parts of the city over a few hours, storm and wastewater networks were rapidly overwhelmed, despite the hundreds of millions of dollars spent on recent upgrades.

Auckland's southwestern motorway flooded amid the January 27 deluge. Photo / Dean Purcell
Auckland’s southwestern motorway flooded amid the January 27 deluge. Photo / Dean Purcell

It was a dramatic warning shot to the rest of New Zealand, whose $20b worth of water networks were never designed for the massive volumes they’ll soon have to manage.

In many places, where storm and sewer pipes were built and paved over more than half a century ago, carrying capacity had already been exceeded.


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While councils have commonly relied on roads as back-up stormwater routes, that became a clear problem when floodwater was fouled with overflowing sewage, and the host of nasty pathogens within it.

The ultimate cost of just bringing our tired infrastructure up to scratch could stretch to as much as $180b, compared with the $1.5b that councils currently spend each year on water pipes.

As replaced pipes would need to be larger – and more expensive – experts have suggested strategic new funding models, like linking investment directly to areas of increased intensification.

But just as Kongjian foresaw, city planners likely wouldn’t be able to solve the problem without turning to more nature-based solutions.

Globally, cities are increasingly realising the benefits of more vegetation, now estimated to be sparing them a whopping third of the rainfall that extreme events dump on them.

Studies have told us how large trees can soak up many cubic metres of stormwater over a year – and their canopies alone can intercept half of what falls before meeting the ground.


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In Auckland, however, ecologists have been dismayed the city has only been losing its greenery, often to be replaced with concrete and other impervious surfaces.

Resource Management Act (RMA) amendments have stripped away general tree protection, leaving just 15 per cent of trees on Auckland’s private land safe-guarded.

Last year’s housing intensification amendments also relaxed planning rules to allow more intensification, without enough protection for green areas estimated to cover just half the city a decade ago.

Along with sponging up rainfall, urban greenery offered myriad other benefits, Mercier said.

“They link blue and green spaces across the city, providing habitats and corridors for wildlife,” she said.

“They also make cities cooler, reduce carbon dioxide, and provide lovely spaces to live, work and play: what’s not to love?”


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The case for change

Mercier pointed to the other big facet of sponge cities: giving water space to flow and rise, meaning overland flow paths weren’t blocked, streams were kept clear, and that vulnerable homes be moved if needed.

But putting these principles into practice wasn’t straight forward, and Mercier’s report highlighted the maze of poorly co-ordinated laws, regulations and policies governing management of our city spaces.

In Auckland particularly, there was limited space for developing blue-green networks, while commercial and public service needs – be they development yields or affordable housing and transport – often outweighed the considerations and benefits of sponge-city approaches.

“The full life-cycle value of water-sensitive design is not fully embedded in our decision-making processes yet, challenging our ability to adequately incentivise these approaches in the urban environment,” Auckland Council’s natural environment strategy senior analyst, Olivia Blanchette, told the Herald.

But there was hope for progress in the council’s 30-year Future Development Strategy, which encouraged nature-based infrastructure, while trying to avoid flood-prone urban development.

“Feedback indicates significant support for this approach.”


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The concept had also been built into Auckland Council’s water-sensitive design guide, whose principles have been showcased in recent projects like the waterfront Wynyard Quarter.

Auckland's Wynyard Quarter.
Auckland’s Wynyard Quarter.

More initiatives were underway with the six-year Making Space for Water programme.

This effort, part of the Resilient Auckland initiative, aimed to expand the city’s network of waterways and parks, adding to the likes of Mt Albert’s Oakley Creek, Mt Roskill’s Freeland Reserve, Taiaotea Creek in Browns Bay and Takanini’s Awakeri wetlands.

At a national level, the report pointed to some promising moves in the regulatory space.

By October next year, for instance, councils now require consent to release stormwater into freshwater spaces – as dictated by Te Mana o te Wai – while the RMA’s replacement with the built environment and spatial planning bills also offered hope of bringing nature closer to planning.

Local Government NZ’s director of policy and advocacy, Grace Hall, told the Herald councils were “always” looking for innovative ways to build their communities’ resilience.


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Again, there were common challenges.

“The Future for Local Government Review demonstrates that a broader range of funding and financing tools, aligned central-local agencies, and targeted place-based investments can boost local climate change efforts,” Hall said.

Mercier’s report offered a raft of its own recommendations – starting with “retrofitting” cities and towns to include more greenery in public spaces like roads and streets, along daylighting streams and creating and enhancing parks.

“There are so many approaches that can help – for example, densely populated urban areas can build ‘pocket parks’, ‘tiny forests’, and green roofs on buildings.”

This needed to be urgently backed by consistent, strategic, long-term planning at every level, she said – and with the funding needed.

“This will cost, unfortunately. However, the alternative – failing to prepare – will be significantly more expensive in the long run,” Mercier said.


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“The Global Commission on Adaptation found an overall rate of return on investment for improved resilience in cities can show a cost-benefit ratio of as much as 10:1 within 10 years.”

As at the last assessment more than a decade ago, green spaces comprised only about half of Auckland's urban area. Photo / Doug Sherring
As at the last assessment more than a decade ago, green spaces comprised only about half of Auckland’s urban area. Photo / Doug Sherring

A New Zealand approach could also draw on the holistic principles of Mātauranga Māori, she said.

“In the stormwater management space, that means seeing rainwater as something we would want to work with and value as part of the natural world, rather than something that has to be controlled, or that we need to insulate ourselves from.”

Meanwhile, there was much that individual homeowners could do themselves, like removing downpipes and draining rainwater through gardens or grassy swales, to help take the load off stormwater drains.

“Replacing driveways and compacted lawns with trees and shrubs can also make a huge impact on how much water is running off into drains,” Mercier said.

“Making sure overland flow paths on private properties are clear is also really important – if the water has nowhere to go, it is more likely to run into houses.”


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Looking back to Auckland, she said the super-city was now having to lead the charge toward resilience in many ways.

“The city has a lot of rebuilding to do, and people are calling for that – which makes it the ideal time to make changes that will ensure we don’t have any repeats of what we saw there earlier this year,” she said.

“Auckland is also lucky enough to have a lot of resources compared to many places, in terms of a bigger rates-base and lots of experts working in this space, both for the council and in the private sector.”

It now fell to other cities to follow suit.

“What would be great is for all cities and towns to use this wake-up call to prepare themselves now for more intense and frequent rainfall in the near future,” she said.

“Building back better after a disaster is better than nothing, but it’s far cheaper – and causes much less heartbreak – to prepare before the worst happens.”


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Auckland’s latest ‘living roof’ takes root

Could greening more of our rooftops help cities adapt to climate change?

Now seen from Copenhagen to Chicago, green or living roofs can help manage stormwater runoff, improve air quality, help combat rising temperatures and offer enclaves for wildlife.

But researchers say there’s much to learn about how these should be designed in New Zealand – and they’re transforming the top of the University of Auckland’s Faculty of Engineering building to find out what works best in our climate.

In the new project, a collaboration between the university and Auckland Council, Associate Professor Asaad Shamseldin and colleagues are working with seven small-scale experimental rooftop plots.

The University of Auckland's Associate Professor Asaad Shamseldin and colleagues are running new trials exploring the potential for climate-resilient "living roofs". Photo / University of Auckland
The University of Auckland’s Associate Professor Asaad Shamseldin and colleagues are running new trials exploring the potential for climate-resilient “living roofs”. Photo / University of Auckland

“The extreme weather we’ve seen this year has highlighted the urgent need to accelerate climate change mitigation work,” said the new project’s lead researcher, Associate Professor Asaad Shamseldin.

“Increasing green spaces and making our cities spongier is essential to reducing the impact of weather events like Cyclone Gabrielle and the floods we saw in January.”


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The project aimed to create replica test beds of Auckland’s Central City Library living roof, which was created in partnership with Ngāti Whātua Ōrākei and boasts more than 2,000 low-maintenance native plants.

Its system was now estimated to store between five to 10 litres of water per square metre, with excess rainfall either taken up by the plants or slowly released to the stormwater network.

“Living infrastructure is not the answer to all stormwater challenges, but a part of the suite of tools we can use to reduce the level of impact,” said Auckland Council’s Healthy Waters Project lead, Rachel Devine.

Shamseldin added that the latest effort – which has involved a range of groups and companies, including Ngāti Whātua Ōrākei, Natural Habitats, Daltons, Manaaki Whenua Landcare Research, The Urbanist and Tektus – had another interesting goal.

“One of the long-term grand aims of the project is to investigate the concept of productive landscapes and whether we can use this living roof as a way of producing food.”

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