The case for unearthing Auckland's streams in response to climate change

Thursday, 22 September 2022

A concept drawing by Neil Coleman showing Western Park in Ponsonby with a restored Tunamau stream and wetland.

Auckland is built on a network of streams that have, over 150 years, been forced into pipes and pushed underground. In a three-part series, Stuff examines what it would take – and what it would mean – for those streams to be brought back into the light.

As extreme rain events brought on by climate change increasingly flood Auckland, a landscape engineer says it's time to unearth the city’s hidden waterways.

Central Aucklanders wouldn’t know it, but the ground they walk on is teeming with subterranean tributaries and streams – piped, paved over and forgotten by 150 years of an expanding metropolis.

Boffa Miskell landscape engineer Mark Lewis has been on a decade-long mission to promote restoring Auckland’s watercourses into habitats for wildlife and people.

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He said as pipes wore out and struggled to meet the water volumes caused by climate and increased intensification, digging up the streams was a viable solution.

A stream by its nature had a higher and more variable capacity than a pipe, he said.

“Building newer bigger pipes is trying to fix engineering issues with more engineering.

“Nature-based solutions will be key to our success in responding to climate change.”

A perfect candidate was Western Park on Ponsonby Rd which was home to the Tunamau stream, Lewis said.

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It once flowed from Ponsonby, through Freemans Bay and across tidal mudflats out to where Wynyard Quarter is now.

Māori named it Tunamau, meaning “trapping of eels”.

However, after European settlement, the area around the mouth of the stream was renamed Waipiro or “stinking water”, in mockery of drunken residents emerging from what is now The Birdcage Tavern.

Despite now being contained within an underground pipe, during periods of high rainfall Tunamau stream reemerges above ground, flooding Western Park.

There should be a stream here, but instead there’s a manhole leading to an underground pipe.

Lewis’ vision is for the stream to be exhumed and restored and for the bottom of the park to be turned into a wetland which would be integrated into the playground there.

He said the daylighted stream would also run through former council estates, improving their amenity, and through Freemans Bay School, providing education opportunities.

It would then run through to Victoria Park and meet up with Wynyard Quarter.

Buried pipe or not, the shape of the valley means that water is going to flow through the park.

Lewis first prepared a report for the former Auckland Regional Council on stream daylighting in 2008. Then-mayor Len Brown green-lit a pilot project de-piping 200 metres of stream in La Rosa Park in Green Bay.

“That project caught people’s attention and suddenly every local board in Auckland wanted one.”

However, progress had been slow, most likely because of the cost, Lewis said.

He estimated that simply digging up a stream would cost at least $2000 a metre, while a well-formed stream with paths, boardwalks and aesthetic rocks could cost $10,000 a metre.

Daylighting also often required treating water sources due to contamination from road runoff, he said.

“There was an example in Michigan where the stream ended up with dead fish floating in it.”

Despite this, Boffa Miskell successfully daylighted seven pipes at Oakley Creek in Waterview. That project was done to protect a development of 200 houses from being flooded.

When it came to future project sites, Lewis said “choosing a stream is like choosing between children”.

But areas with impending large-scale new developments where there was ageing water infrastructure as well as hills and valleys provided the best opportunity for daylighting in 2022, he said.

“At one point it was fanciful, but now daylighting is a practical solution for a number of problems.

“Climate change will exacerbate things in an unpredictable way. There’s every opportunity to look at climate modelling and make those decisions.”

Meanwhile, the Waitematā Local Board is waiting on Auckland Council’s parks team to complete a project scope study on daylighting Tunamau at Western Park.

Deputy chairperson Alexandra Bonham said the board was “very interested” but it would be a slow moving project that would require community engagement and a wellspring of funding.

Have you got a sensational stream flowing through your backyard? Contact jonathan.killick@stuff.co.nz