Auckland bureaucrats were told in February a leaking stormwater pipe was causing cracks to a Birkenhead carpark this year but it was not fixed before the first of two large slips in October.

Council officials now say their investigations suggest it is unlikely that stormwater pipes played any significant role in either slip.

The first slip on October 9 swallowed 50m of the Rawene St car park. A second slip on November 28 sent a drilling machine and more debris tumbling into Rawene Reserve and workers scattering.

The slips have led to the loss of 25 public car parks and had a big impact on local businesses in the lead-up to Christmas.

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We would like to get this issue resolved at the very earliest opportunity before it develops into a more significant repair job

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Documents obtained by the Herald under the Official Information Act contained no information to indicate the stormwater pipe was fixed.

The OIA response showed the stormwater problem was batted back and forth between officials from Auckland Transport and Auckland Council's stormwater division, Healthy Waters.

Cracks to the Rawene car park in Birkenhead. 9 October 2017 New Zealand Herald Photograph by Murray Kirkness.
Cracks to the Rawene car park in Birkenhead. 9 October 2017 New Zealand Herald Photograph by Murray Kirkness.

As part of routine maintenance due to known stability issues below the carpark, AT carried out CCTV work in February which found "the car park has a lot of cracks at the back end which is caused by the leaking stormwater piping".

AT officers discussed the damage to the stormwater pipe after receiving CCTV coverage and a technical report on February 15 and approached Healthy Waters the same day.

When AT had not heard back from Healthy Waters after three months, AT sent two emails to Healthy Waters boss Craig McIlroy and another council officer on May 16 for help "to resolve an issue that has been causing concern since the beginning of the year".

"We would like to get this issue resolved at the very earliest opportunity before it develops into a more significant repair job," AT facilities management manager Peter Bierens said in the email to McIlroy.

On the same day, Healthy Waters northern operations manager Phillip Johansen apologised for the delay and urged Bierens to "log further faults in the northern area . . . so they don't slip through the cracks".

After further to-ing and fro-ing, Healthy Waters principal stormwater manager Craig Mountjoy concluded on July 7 after reviewing the CCTV video that "there are no stormwater pipeline issues that need to be excavated to repair".

An aerial photograph clearly showing the two slips in Birkenhead. Source / Auckland Council
An aerial photograph clearly showing the two slips in Birkenhead. Source / Auckland Council

"As long as the buried manholes mentioned in my previous email of May 23 are exposed and the lids reset so they are accessible after sealing we can repair the faults by patching or lining after sealing is done," he said.

After involving "several teams" over two days last week to a series of questions from the Herald, the council issued a response from in-house geotechnical specialist Ross Roberts saying it was too early to establish the causes of the slips.

"Initial technical investigations, including CCTV inspections, suggest at this stage that it is unlikely that stormwater pipes played any significant role in either slip," said Roberts, saying the investigations are continuing but are being hampered by the instability of the site and concerns for staff safety.

The council refused to say why Healthy Waters was slow to respond and take action after it was alerted to the leaking stormwater pipe and cracking in February.

The council did not say whether the stormwater pipe had been fixed, but a senior official — who did not want to be named — said it had not been.

At a public meeting on December 7, council officers said the cause of the slip had not been conclusively established, but the following areas were being investigated: Level of saturation of the fill; level of compaction of the fill; makeup of material in the fill; higher ground water level in the base of the gully from a natural spring outfall below the fill; stormwater outflow into the gully and water ingress at the top of the gully.

Roberts said the prime focus for council and council-controlled organisations (CCOs) working at the Rawene Reserve site is ensuring the safety of the public and adjacent properties.

"External technical experts have been engaged to investigate and design remedial plans with a view to beginning stabilisation works, which will progress as quickly as is feasible. In the meantime, the site is being monitored for any further movement," he said.

Distressing time for business owners

Birkenhead business owner Brad Boult pictured in front of the carpark that has now been destroyed in the result of a slip. Photo / Nick Reed
Birkenhead business owner Brad Boult pictured in front of the carpark that has now been destroyed in the result of a slip. Photo / Nick Reed

Birkenhead Brewing Company co-founder Brad Boult, who runs a bar in the town centre, said he was surprised council had not taken action earlier after discovering the leaking stormwater pipe.

Boult said not being able to use the Rawene St carpark made running a business tougher, but the Birkenhead Town Centre Association had been working with owners to use some of the private car parks after-hours so the public parks were left available for punters.

The shortage of car parks in the town centre was acting as a deterrent to attracting new tenants to empty shops, he said.

While Boult admitted he wasn't an engineer, he believed earlier action may have helped and urged council to further investigate the causes of the slips.

"They certainly could have stopped the leak or the effects of the leak and stopped the water from getting in there."

Northcote MP Jonathan Coleman said council needed to explain why it appeared to have been sitting on a problem which was a "massive inconvenience" and had caused distress to the local business owners.

"I think a lot of people will be quite angry about that and they need to explain themselves to the public." Coleman said having a shortage of car parks made it harder for the town centre to compete against the big malls.

Additional reporting Nikki Preston