Deluge raises doubts about building houses on West Auckland floodplain

Some Kumeu locals believe last month’s deluge proves the rush for new housing is putting old and new homes at risk of more flooding. Tom Dillane reports.

On the last day of August, farmers from across Taupaki stopped to gaze at 109 underwater hectares of green paddock bought by Fletcher Building last year.

It was a source of amusement for many and contempt for some.

This was land slated as Auckland’s next “urban village” which Fletcher has potential plans to build thousands of homes on by 2045.

The construction giant had bought the land along Waitakere Rd for a price above the Auckland Council valuation of $6.4 million from veteran dairy farmer of three decades, Len Kay.

Greg Jonkers, a multi-generational farmer of the region and neighbour to Kay, said that while Fletchers may not have control of the land yet, he believed either arrogance or ignorance led to the purchase.

“This particular farm is very low-lying and it’s disappointing for all the locals but hey you’ve got to move with the times,” Jonkers said.

“They’re all laughing too, going: ‘why would they want to build on such a low-lying area?'”

The dairy farm was, admittedly, flooded in a storm that broke all Auckland Council’s flood metrics for the West Auckland/Kumeu area since they went on record in the late 1970s.

On August 30 and 31, the Kumeu River was at its highest level ever recorded.

On August 30, Kumeu in West Auckland received 201mm of rain in just 14 hours – and a staggering 149 per cent of the August monthly normal rainfall fell in a single day.

That was the suburb’s second wettest day on record. Around 50-60 homes needed to be evacuated and the clean-up continues still. The body of a 54-year-old man, who was known to be a rough sleeper, was also pulled from a creek in Henderson Valley Park.

“Huapai pub was out of order [from flooding] and it’s been there for 150 years,” Jonkers says.

“In the old days we used to build on the high points. Look at the photographs [of the August flood] – the only thing that’s above the water line is the railway line. Whoever engineered the railway line, engineered the whole of Kumeu.”

The land where Fletchers has a “vision of creating a residential community” borders Kumeu to the south and got its own lashing at the end of August.

It’s not surprising to see some of it underwater, given it sits right within floodplains as determined by Auckland Council’s hazard mapping ArcGIS website.

A Fletchers spokesperson assured the Herald “fortunately there was no notable damage on the land we own” in Tuapaki from the August 30 floods.

“We sympathise with residents and the surrounding rural communities whose properties were damaged as a result of recent significant flooding in the area. Our plans for the land are still at an early stage. As we progress them we will obviously be working within the relevant regulations regarding flood control and we will engage with the local community to reassure them of this.”

Flood plain risk

Fletcher’s Taupaki site is a microcosm of the dilemma many newer residents to the housing boom around the Kumeu area are continually grappling with, and veteran farmers are lamenting.

New developments need flood mitigation – in floodplains that means raised land and building platforms – but there are also questions about what effect this artificially raised land has on older properties bordering it.

Auckland Council’s Healthy Waters department is currently investigating what flooding effects the new raised housing developments in and around the Kumeu region have had on properties built before the 2016 Auckland Unitary Plan.

Directly north of Tuapaki, Sandra Wallace owns a house in Nobilo Quarter within the new ​​Huapai Triangle Estate. Wallace says she only realised in the days after the August 30 floods that their property was built on a floodplain.

Houses are still being built in the development, which is located on the corner of Station Rd and Nobilo Rd, Huapai. It may eventually house up to 2500 people.

Wallace claims the magnitude of this development has escalated since the initial residents bought in. The block her Huapai Triangle house is situated was originally only supposed to have 10 properties in total.

“Auckland Council changed this to 21 houses and didn’t even notify us as a directly affected party,” Wallace claims.

“Not only that, this extra development has resulted in our yard being flooded several times since the earthworks and laying of stormwater pipes began.

“It is still a greenfield site but is in a flood-prone area, which raises major concerns. Once the 21 houses get built the rapid water flow may cause the stormwater system to overflow and the existing houses to all become flooded as we are below road level. That in itself is another cause for concern.”

Housing pressure

Head of Auckland Council’s Healthy Waters department, Andrew Chin, says they would prefer development not to occur on floodplains, but the demand and pressure from Auckland’s housing market makes that unfeasible.

“Our clear preference is that development proceeds outside of floodplains, however you know with land being in such short supply in Auckland there’s a lot of pressure to be able to modify floodplains and to create more housing,” Chin said.

Raising building platforms and artificially raising land about the floodplain level can mitigate this. But this has problems of its own.

“What concerns us then is where does the floodwater go? Does that create a problem somewhere else for neighbouring property and the like?” Chin said.

“So that’s a lot of the technical work that has to get done around property development. If you are modifying the floodplain, will that have adverse effects on a property surrounding the development? So by far the lowest risk thing is not to tinker with the floodplain but that’s not really realistic in Auckland when we’ve got such a housing crisis and the demand in the market forces driving development is so strong.”

Chin says all new housing developments the council gives consent to must have floor levels above what’s called the 1 per cent annual exceedance probability (AEP) event.

A 1 per cent AEP is a flood threshold that only has a 1 per cent chance of being broken in a given year.

Commercial property has a less strict flooding threshold than 1 per cent, but all new residential developments in Auckland should have their floors above this 1 per cent AEP level.

Chin says whether that’s the case will form a key part of an investigation into the August 30 Kumeu floods.

“That was the highest level we’ve ever recorded the Kumeu River at. So since the gauges have gone in on the river they’ve never been measured higher,” he says.

“When you think about the pipes network in the urban areas, it’s not designed to take that kind of flow. It’s totally normal in an event that size for the pipe capacity to be exceeded and then all of the remaining flows go via overland flow paths.

“One of the things that we will be looking at is, particularly in those new development areas that you mentioned, were the actual habitable floors of the houses flooded?”

However, many West Auckland locals say they have been raising the risk of overdevelopment on floodplains before the amalgamation of Auckland Council and its Healthy Waters team in 2010.

Official evidence of this can be found in a 2009 Rodney District Council public submissions document for rezoning the area known as Huapai North for residential development.

The properties along Matua Rd, Huapai, which backs on to Kumeu River were among the worst-hit residential areas in the August 30 floods.

Many of the submitters whose concerns littered a 25-page 2009 Rodney District Council document would not be surprised by this flooding in 2021.

Here is a sample:

– “Submitter 34 operates a commercial flower growing business at 78 Matua Road and has done so for 23 years. This submitter has some concerns with regards to the proposed housing for the land bordering the flood zone, in particular the close proximity of housing to his family business.”

– “Two submitters raised concerns about flooding and the need to ensure that further flooding is not encouraged. It is considered that watercourses as a feature will not encourage flooding, as they are existing and will be enhanced. One of the two submitters specifically noted that there was significant flooding in the area, both in the field behind the submitter’s house … and coming across from the land on the other side.”

In a summary of the “issues” for rezoning Huapai North for more intense residential development, the Rodney District Council stated: “There was significant support for the larger site sizes around the edges of the Huapai North area and a number of people raised concerns over the potential for flooding.”

Auckland Council’s current general manager plans and places, John Duguid, told the Herald the final zoning approved for Huapai North in 2012 ensured no residential zoning was within the 1-in-100-year floodplain.

“The 2009 document provided is a summary of feedback given to preliminary proposals for development in the area now known as Huapai North,” Duguid said.

Duguid said modelling in a Catchment Management Plan informed where the residential zoning would be located, specifically taking into account the location of the 1-in-100-year floodplain.

'Soggy Weet-Bix'

However, a new resident on Vintry Dr, Huapai – who wished not to be named due to fear his developer would not fix his faulty drainage – says his retaining wall drainage left his pebbled backyard like “soggy Weet-Bix” following the August 30 downpour.

“I think it’s time to shed light on developers and the council that ‘hand out’ consents when these new builds have inadequate drainage in these areas,” the Huapai resident said.

“​​After the downpour, my whole surrounding land was like soggy Weet-Bix. [The] Retaining wall drainage is inadequate and has water seeping through into the cesspit where it should actually be connected and drained properly through a stormwater pipe.

The Vintry Dr resident added that the neighbours on either side of him “have the same soggy Weet-Bix soil”.

However, Healthy Waters’ Andrew Chin said the extreme rain on August 30 to 31 was “far in excess” of what stormwater pipes are designed to accommodate.

“Once rainfall exceeds pipe capacity, flow travels overland,” Chin said.

Another request residents raised in the 2009 Rodney Council Document was for the council to undertake sufficiently regular clearing of the Kumeu River,to remove trees and foliage that create an extra flood risk.

Chin admits this has not been undertaken in the subsequent decade.

“No there hasn’t been. Depending on how wide a river is, it’s actually the responsibility of adjoining landowners to maintain the waterways and the riverbeds,” Chin said.

There has, however, been some herbicide spraying of an invasive aquatic weed that chokes the river much further downstream, further out from the Kumeu/Huapai area.

The Rodney Local Board region includes the Kumeu, Taupaki and Huapai area and chairman Phelan Pirrie says all the newer housing developments built after the 2016 Auckland Unitary Plan should have significant stormwater collection areas to prevent flooding.

Pirrie says new housing developments out west in the last 10 years should all be raised around two meters if they’re on floodplains, and there will be ponds landscaped into the developments designed to flood in the case of major rain events and drain gradually.

“Anything done post-Unitary Plan has been built to that standard and I’m not aware of it flooding,” Pirrie said.

“I mean, that said, I know talking to people from Healthy Waters that it is possible that depending on the scale of the event that there’s going to be flooding.

“Primarily, when you look where the flooding was with those properties, the properties that were affected are in what are now clearly marked as flood areas, and those people are aware of it as well.”

Pirrie admits it would be “quite disruptive” for the property owners along the main strip of Kumeu, which was majorly flooded during the late August storms, to have their floors raised the necessary amount.

What Pirrie does identify as a real issue is the extent to which raised new housing developments are compounding flooding in older residential blocks around the Kumeu area.

He says Andrew Chin’s Healthy Water’s investigation will be necessary to determine if theoretical flood prevention measures in new housing developments actually worked in an extreme event like the late August storm.

“When all this stuff is done through and RMA consenting process people do desktop exercises, and they go ‘oh well this isn’t going to have an effect and this will deal with all the issues’, and you don’t know until they’re tested,” Pirrie says.

“So there may be a problem, I don’t know.”

But what is a problem in Pirrie’s mind is the haste with which property developers choose to build on previously undeveloped “greenfield” land, rather than building within existing “brownfield” urban residential areas.

“The big problem has been, and it comes back to the planning from central government regardless of who’s been in power, there’s been a real push to do housing developments, but not a lot of thought has been given to the effects,” Pirrie says.

“Doing more brownfield development means that existing areas can have that infrastructure boosted up, and there are known quantities in terms of flooding and all the rest of it.

“This is the problem in Auckland, that there is a constant push from developers to do greenfield-type development. People, on one hand, want development and greenfields are seen as a cheap, quick way of doing housing. But the long-term effects we have to grapple with in local government.

“I’ve seen Andrew’s [Healthy Waters] team frequently raise issues over various developments and it just gets ignored because the RMA [Resource Management Act] says the ball’s in the developer’s court. It’s all about getting housing done.”

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