Auckland flood update from Auckland emergency management
As Aucklanders clean up after the city’s worst weather event in history, lessons for other cities and towns abound. Jamie Morton looks at three of the biggest.
Our infrastructure isn’t ready for climate change
As sewage-fouled floodwaters washed through Auckland streets on Friday night, it’d perhaps never been more apparent that our infrastructure isn’t ready for the warmer, wilder world we now live in.
While scientists say the deluge would’ve been disastrous even without climate change’s contribution – something that potentially made the rainfall 10 to 20 per cent more intense – it’s nonetheless what our cities and towns can expect more of in coming years and decades.
Even if the world managed to rein in global warming to within the symbolic target of 2C, our atmosphere would still be left carrying about 10 per cent more moisture – adding perhaps 20 to 30 per cent more rainfall to an event like Friday’s.
And much of that extra rain will come in the form of torrential hourly extremes, just like those that put Auckland Airport’s terminal underwater, brought down thousands of slips, and overwhelmed treatment plants and pumping stations.
Despite hundreds of millions of dollars having been poured into Auckland infrastructure upgrades over recent years, experts say storm and wastewater networks were simply found unprepared.
Much of New Zealand’s $20b worth of water networks – including some 24,000km of public wastewater channels, 17,000km of storm systems and more than 3000 pump stations – was never designed for massive volumes it will have to manage with rising seas and dramatic shifts in precipitation.
In many places, where networks were built 60 to 70 years ago, and then built and paved over, carrying capacity had already been exceeded.
It was common for local urban systems to rely on roads as back-up stormwater routes - a clear problem when sewerage overflows contaminated floodwaters, on top of others like saltwater increasingly corroding pipes.
Bringing all of these networks up to scratch is likely to cost an eye-watering amount – perhaps $120b to $180b over the next few decades, and eclipsing the $1.5b councils typically spend each year on water pipes.
Contractors try to clear surface flooding on Porana Road in Glenfield, Auckland, on February 1. Photo / Brett Phibbs
As making more space for water meant larger pipes – and larger costs – strategic funding models would be needed, said Iain White, a professor of environmental planning at Waikato University.
Linking investment to areas of increased intensification was one solution, as was easing the burden on ratepayers through central government support.
With reforms through the Three Waters programme, in which the Government has already invested billions of dollars, it’s projected per-household costs over the next 30 years could be lowered from the $1900-$9000 range to $800-$1640.
Still, wholesale upgrade wouldn’t be enough.
“Even if we were to dig up [current] infrastructure and replace it with newer and larger pipes, it would only be a matter of time before we exceeded that capacity,” said Dr Tim Welch, director of the University of Auckland’s Urban Planning Programme.
“We were under-prepared for the rainfall, but it’s not something we could have prepared for in the weeks or months leading up to the event – it’s something we should have been preparing for decades ago.”
Looking forward, Welch saw two possible avenues to take.
“We can go the path of business as usual and put in bigger new pipes at the cost of tens of billions of dollars - or we can work to supplement the existing system.”
A good way to think about the problem, White said, was to consider how much space a given volume of water needed – and what happened once that space was exceeded.
“Traditionally, we’ve perceived water as a hazard to be removed, so we move it as quickly as possible from the hard surface it lands on, into our drains, and then away out of sight,” he explained.
“And when this approach fails water takes up space that can create serious damage, disruption, as well as loss of life.
“So how can we create space for water beyond the pipes? How do we design cities so that we can slow down water to lower peak flows and give our infrastructure a chance to cope?”
Brown's Bay lies awash with floodwater on the morning after last Friday's disastrous floods in Auckland. Photo / Brett Phibbs
New Zealand urgently needed a national policy solution, he said, that shifted urban design closer to this “safe-to-fail” approach and created more safe storage areas.
This was where concepts like “Sponge Cities” - something proposed by Chinese researchers more than two decades ago - could help shield our urban centres.
“We can preserve wetlands where they still exist, and we can replace impermeable surface, like roads and carparks, with porous cement that helps drain and filter rainwater,” Welch said.
“Planting a lot more native trees will help to mitigate flooding during extreme rain events and help cool our urban centres to reduce ‘heat island’ effects.”
Just how much water could green spaces soak up?
A surprising amount: Large trees could absorb many cubic metres of stormwater over a year.
Canopies alone could intercept half the amount of water before it reached the ground.
In Auckland, however, much of this greenery has been replaced with concrete and other impervious surfaces.
Much of the most recent loss had come through Resource Management Act amendments that stripped away general tree protection.
Auckland hasn't learnt the lessons from Hurricane Harvey in Houston - they removed wetlands & vegetation & increased concrete (impervious surfaces). We can't intensify housing at expense of removing veg/trees - we need to get smarter & have both #flooding#greeninfrastructurepic.twitter.com/C7VziLmII4
University of Auckland ecologist Associate Professor Margaret Stanley thought it “disastrous” that just 15 per cent of trees on the city’s private land had protection, given these made up some 66 per cent of the city’s urban forest.
Last year’s housing intensification amendments also relaxed planning rules to allow more intensification, without adequate protection for Auckland’s green-scape.
“The ‘death by a thousand cuts’ that occurs on individual properties via tree felling cannot be undone by planting a few seedlings or saplings that can take 50 to 100 years to provide those same benefits.”
Meanwhile, as climate impacts increasingly hit home, more cities were realising the critical value of green spaces.
In “megacities” of more than 10 million people, for instance, researchers have estimated the median benefit of trees at over three quarters of a billion dollars each year.
Another recent global analysis found vegetation was sparing cities from about a third of the rainfall in extreme events.
“The bigger the tree, the more water it can intercept,” Stanley said, “and having these trees onsite adds incredibly valuable assets that mitigate flooding, air pollution and have a raft of other benefits”.
Welch cited Singapore – which regularly receives 200mm of rainfall in a 24-hour period – as an exemplar sponge city.
Frequently flooded in the 1960s and 1970s, its cityscape had been transformed to incorporate more urban ponds, streams and greenspace – and flooding was now much less common.
Tamaki Makaurau itself once happened to have been a vast natural sponge – a complex network of streams, rivers, wetlands and bays - before decades of development and population growth transformed it into a concrete jungle.
Wetlands absorb water & reduce flow/energy of rivers - but we've drained most of our wetlands in NZ. We need to prioritise #NatureBasedSolutions. Some great swales at Stonefields - feeding into the wetland. Boardwalks underwater but did it's job at the weekend. #floodingpic.twitter.com/diAwhaY0By
“A key example of this is Opoutukeha, the stream and wetland that would become Grey Lynn Park and the Cox’s Bay Reserve,” said Matthew Bradbury, an associate professor with Te Pūkenga’s landscape architecture programme, and author of the book Water City: Practical Strategies for Climate Change.
“The Opoutukeha returned with a vengeance on Friday, as Grey Lynn Park flooded and Dryden St became a raging torrent, barreling towards the Waitematā.”
Amid Auckland’s wider biodiversity loss, Bradbury said there’d been several positive examples of streams being restored – notably Māngere’s Tararata Stream and the Te Auaunga around the Walmsley and Underwood Reserve - along with efforts at wetlands, like the Waiatarua in Remuera.
“There are many challenges to overcome, but we can see how by starting to plan to build resilience to future flooding, we can also make a green network of restored streams and wetlands over the entire city.”
We need to stop building in risky areas
Bradbury said that, while new legislation to allow for six-storey housing was welcome, there was also perhaps potential to allow for more greenery.
And, in any case, it was clear that new housing development should no longer be built on overland flow paths, on top of old wetlands, or anywhere else vulnerable to flooding.
Considering one estimate of the current rateable value of exposed residential property, $17 billion worth of homes could already be at risk.
Add together all private and public properties and assets lying in coastal floodplain areas, and that sum stood at a whopping $150b.
According to a 2020 landmark national risk assessment, more than 72,000 people currently live in areas currently considered a once-a-century risk, while some 675,500 of us reside in areas known to be prone to flooding.
Buildings, too, were at extreme risk – nearly 50,000 of them were currently exposed to coastal flooding, and at the highest range of warming scenarios, that could rise to nearly 120,000 this century.
Large slips scar the cliffs of Judges Bay on Auckland's waterfront, following Friday's flooding. Photo / Alex Burton
Yet we now know those figures are almost certainly under-estimates, given what scientists have since told us about the true risk New Zealand faces.
Sobering sea level rise projections revealed last year, and accounting for the effect of sinking and rising land, show that main centres like Auckland, Wellington, Napier, Marlborough and Nelson may be facing more than half a metre of rise by mid-century.
With just 30cm of rise enough to make 100-year coastal storm surge and flooding an annual occurrence, fast-sinking parts of our coastal cities could cross that threshold by 2040.
That carries startling implications for insurers, which are likely to pay out close to $1b in claims from the past week’s events alone.
It was likely that home-owners in seaside areas already at risk of one-in-100-year floods could lose insurance cover within their lifetimes – perhaps even this decade,
The worsening crisis was also a colossal headache for lenders, too: More than 60 per cent of the four largest banks’ loan portfolios are made up of housing loans.
That meant just a relatively small proportion of stranded assets – which houses could become if the once-a-century risk turned annual – posed a threat to financial stability.
Even in the face of these threats, development in risky areas hasn’t stopped – and more than $2b of now-vulnerable homes have been built within roughly the past decade.
In the absence of tougher laws and regulations, the general focus has been on trying to mitigate risks through measures like raising houses or building hard barriers.
Many commentators fear these steps will prove merely temporary, and shunt costs onto future generations as the problem worsened.
At the other extreme, we’ve been hearing increasingly more about managed retreat: Shifting homes, or sometimes whole communities, out of the firing line.
Unlike other countries, New Zealand has little experience with this measure – and the near two decades and $17m it took for one council to buy and relocate 16 exposed homes in the Bay of Plenty town of Matatā offered a taste of the enormous cost and effort that would be involved in repeating that at scale.
The Eastern Bay of Plenty town of Matata, where 16 homes were bought by council at the expense of $17m in a near-two decade process, may prove the first of many instances of managed coastal retreat in New Zealand. Photo / NZME
How to meet the climate threat, broadly, has increasingly proven a headache for local councils, given thorny issues around legal powers, resourcing, funding and the risk of litigation that come with it.
The Government’s response has come through its recently-launched National Adaptation Plan, packed with more than 120 actions - all to be carried out over the next six years – and reflecting more than 40 “priority risks”.
As well, a new Climate Change Adaptation Act emerging out of the RMA reforms was expected to give councils a critically-needed backstop.
In the meantime, experts have urged council planners to make better use of regional and district rules, avoid consenting risky developments and shift away from stop-gap mitigation measures.
For Welch, Auckland’s disaster ultimately highlighted – if it indeed still needed to be – that our current infrastructure was built for an era that “may no longer be the norm”.
“The future will likely be a wetter, more intense climate,” he said.
“To cope with that we can no longer rely on a single solution. We’ll need to use as many tools as possible to adapt our cities the coming climate.”
