Why do we still build
There are already 55,000 houses in flood zones in Auckland. Many of them were inundated in the recent deluge, including some that were just a few years old. So why are we continuing to build in these areas – and can we prevent it? investigates.
Diane Tieni wasn’t bothered when the rain first came. ‘‘It started out on the road and we thought nothing of it. Roads got swamped, that’s fine.’’
A little later, one of her children said, ‘‘Mum, look outside.’’
Things were no longer fine. Tieni saw cars floating in the street. Her neighbours across the road were already up to their waists in water. And the floodwater was lapping at Tieni’s door. She watched it creep inside the house, across the plush new carpets, soaking into her furniture as the family rushed to lift everything they could to safety.
By the time the rain finally stopped around midnight, the basement was flooded out and the entire ground floor was awash in a foot of water.
Many, many families in Auckland have a similar story to tell of the January 27 flood: frantic attempts to shift possessions out of harm’s way, wading to safety through chest-high floodwaters, evacuations through top-storey windows.
What sets Tieni and her neighbours in Ventura St apart from many others, though, is that these weren’t older houses, built in flood zones before anyone had heard of climate change. Diane’s house is just over three years old.
She, four of her children and two of her grandchildren, were among the first to move into dozens of brand-new Kā inga Ora townhouses in a mixed-housing development known as Mā ngere West, in South Auckland. An upbeat brochure from late 2019 shows a beaming Tieni holding up the keys to her new home.
Hundreds more houses, including KiwiBuild and open-market homes, will eventually replace older state housing.
Mā ngere is among the lowest-lying land in Auckland and Te Ararata stream flows down the middle of the development. Together, these factors mean that the development lies almost entirely in a flood zone.
Tieni did not know this when she and her family moved here from the cold, older-style state house they’d been living in. ‘‘The excitement was, we were getting new-build homes – warm, safer for us,’’ she says. ‘‘We were just happy with what we got offered, and I think that’s a very common mentality with us low-income families. We don’t question these things. We don’t question where it’s built.’’
Since the beginning of 2016, Auckland Council has granted resource consent for 9220 new dwellings in flood plains (areas where runoff from waterways will flow) and 4295 dwellings in flood prone areas (natural and human-made features like depressions, dips and gullies where rainwater can collect).
There isn’t data for the number of dwellings consented on land where there are also ‘‘overland flow paths’’ – the routes taken by stormwater when the normal stormwater system is overwhelmed.
Sunday News has analysed Auckland Council data of the flood risk areas the council predicts would be inundated in a one-in-100-year rainfall event, together with Land Information (LINZ) data of building locations. This reveals just over 55,000 existing buildings in these areas, most of them residential.
Many of the newest houses will not be included, as they do not yet appear on LINZ maps.
Zoomed-in sections of the map reveal how flood-risk areas are pepper-potted throughout the Auckland region. Take the suburbs surrounding Eden Park in central Auckland, where half of some streets are designated at-risk, while their neighbours remain beyond the danger zone.
The rain on January 27, which was an all-time record, exceeded the one-in100-year risk. Niwa estimates it was a one-in-200-year event. But observations from residents and others on the ground are that the flooded areas still matched the flood risk maps very closely.
The map on this page shows the footprint of the Mā ngere West development, and the existing buildings in the area (many of which are meant to be demolished and replaced).
Mā ngere resident and Monte Cecilia Housing Trust chief executive Vicki Sykes was, until recently, part of the Mā ngere Community Housing Reference Group that raised concerns with Kā inga Ora – which led the development – about the flood risk in the early days of the development.
Kā inga Ora was ‘‘very aware’’ that the physical stormwater and other infrastructure was outdated and needed work, Sykes says. But many other groups were involved, including the council and developers. ‘‘Everyone wanted to fix the issue but everything was siloed and nobody had the budget on their own.’’
Kā inga Ora deputy chief executive Caroline Butterworth said Mā ngere was ‘‘well known in the construction sector as an area of Auckland where ground stabilisation is required prior to the construction of new homes’’.
‘‘Specific to the Mā ngere West catchment area we completed a Storm Water Management Plan and implemented flood mitigation measures including the installation of storm water basins in Ventura Street, the upgrade of storm water pipes, installation of new and upgrade of existing outfalls.’’
Butterworth also points out that the rainfall ‘‘exceeded the one-in-100-year event that infrastructure is designed to withstand in urban development’’.
But Sykes still believes that whatever was done was not enough. ‘‘There’s anger at how on earth can we collectively allow this kind of mistake to happen. And just huge sadness for the families that’ve been affected by this, many of whom won’t have contents insurance.’’
The biggest mistake was building on a floodplain at all, she says. ‘‘It was a disaster waiting to happen.’’
The one-in-100-year event that councils, developers and engineers are all meant to plan for is a slightly misleading turn of phrase. What it actually means is that, in any given year, there is a 1% chance of the event occurring (known as a 1% annual exceedance probability).
Belinda Storey, a senior research fellow at Victoria University’s Climate Change Research Institute, says the problem with that, is that the risk has been calculated at a fixed point in time. ‘‘If you’re currently in a 1% AEP, that is only going to go up with climate change from 1% to 2% to 4%.
‘‘When I first started the research I’m doing, I assumed that the change in the probabilities for rainfall would happen decades later. [But] those probabilities are changing quicker than I or anyone predicted.’’
Her solution is the same as Vicki
Sykes’ solution.
‘‘We need to stop building in flood plains. I recognise that there’s a significant housing shortage, so we need to be building mid-rises in those parts of Auckland that are on higher ground.’’
Some newer developments on floodplains did withstand the January rain. Among them was the huge, masterplanned Northcote development on the North Shore, which encompasses state housing, KiwiBuild homes and openmarket houses.
In Takanini, on the southern outskirts of the city, thousands of homes have been built on flood plains since a special housing area was created there in 2014.
Andre´ s Roa, the director of engineering consultancy AR & Associates, worked on the stormwater and flood mitigation design for one section of the Takanini development. It was a ‘‘real technical challenge’’, which involved rearranging and lifting the entire site to redirect the flow of water