Council knew about unstable land at Birkenhead slip for years, earlier decision reveals

Auckland Council has known for years about stability issues below a carpark site in Birkenhead where a large slip has swallowed about 50m of land.

The slip has nearby residents worried, but last night council gave an assurance that the land appeared to have stabilised and posed no immediate threat to homes.

The Herald has obtained a 2010 decision by council officers not to lease the reserve below the carpark to the Great Chelsea Gardens Trust for a number of reasons, including "the unstable nature of the land and its importance for stormwater flows".

"The gully is unsuitable for tree clearance, excavation or earthworks due to its inherently unstable underlying structure ... the area has serious issues of site stability," the decision said.

Last night, Auckland Transport, which manages the carpark, said it first became aware of stability issues in mid-September when a crack appeared and an area of the carpark was cordoned off.

The carpark was built by the former Birkenhead Borough Council, probably in the 1960s, an AT spokesman said.

The slip has resulted in 25 of the 116 car parks being lost and 29 cordoned off.

Auckland Council said in a statement last night that investigators were at the site yesterday assessing neighbouring buildings and establishing if any are at risk as a result of the slip.

"As a result of those assessments, we have reduced access to parts of a neighbouring construction site," said a spokeswoman.

She said assessments are continuing and appropriate measures will be taken if any further risk are identified.

Auckland Council's manager for regulatory compliance, Steve Pearce, said there was no evidence so far nearby construction work had caused the slip.

"This will be considered in our investigation. However, initial indications suggest that it was probably caused by the car park being built on old and potentially poorly compacted fill, combined with an unseasonably wet winter."

Access to the construction site on Rawene Rd had been reduced following council investigations as a precaution.

Further investigation's would continue and were expected to take "some time".

No damage to apartments had been discovered during a walk-around investigation, Pearce said.

"The slip remains active, but appears to be slowing down. Buildings and apartments adjacent to the slip site are not in immediate danger, and we are monitoring the situation in case of the unlikely event that it deteriorates significantly."

Given the scale of the slip, it was unlikely any official intervention could have prevented it, he said.

Part of the Rawene car park slipped away in the past few days after heavy rain in recent months.

Claire Belfour, chairwoman of the Mokoia Ridge Apartments bodycorp, surveys a large slip that has taken out a carpark behind the Birkenhead shops. Photo / Lincoln Tan

Mokoia Ridge Apartments body corporate chairwoman Claire Belfour said the slip was snaking towards residents.

"The carpark was built on flimsy ground and this is just waiting to happen," she said.

Belfour said she had tried to report the cracks since they appeared last Friday, but did not get any response from either Auckland Transport or the Auckland Council earlier.

Nim Tucker, 26, a resident in one of the apartments, watched the slip happen on Sunday.

"There was a loud cracking noise, and then everything just fell in," Tucker said.

"It looked like a horror movie and something was sucking all the trees and carpark from underneath, very scary."

Mokoia Ridge has 26 apartments, which were converted from a toy factory about 20 years ago.

A cafe operator, who wanted only to be known as Mrs Kim, said she was worried that if the collapse got closer to the shops, the telephone exchange could also go.

Auckland Council and Auckland Transport met concerned business owners and residents yesterday morning.

Geotechnical engineers were also at the carpark.

Auckland Transport said it was too early to say what caused the slip.

Aerial view of a large slip that has taken out a carpark behind the Birkenhead shops on Auckland's North Shore. Photo / Chris Tarpey

Birkenhead Town Centre Association chairman Pete Taylor said the disaster came at a busy time for the suburb, which is a major attraction for the Auckland Heritage Festival starting on Thursday.

"We are advising the public to enjoy the horse-and-cart rides and other entertainment in Birkenhead, perhaps a walk through LeRoys Bush and make the most of what Birkenhead has to offer, just perhaps catch a ferry over from the city or enjoy a bus ride over the harbour bridge into the Birkenhead Village."

Auckland Transport chief infrastructure officer Greg Edmonds said engineers had been monitoring the site for several months.

"We closed off more of the car park this morning and the road which runs behind it to ensure the area is safe.

Northcote MP Jonathan Coleman, whose electorate office is near the slip, said it would be impossible to say if the new developments in the area had contributed to it until Auckland Transport had investigated.

He promised to follow developments "very closely" and would keep business owners and residents updated.

The city of slips

This year's big wet has caused bit slips and sinkholes in Auckland

March: Weather bombs lead to giant sinkhole opening up in New Lynn and slips in the Hunua Ranges pouring more material into the water reservoirs than slips caused by the Kaikoura earthquake.

April 4: An avalanche of mud slides down a cliff and slams into San Remo Apartments in Kohimarama following torrential rain.

August 30: A large slip and a number of trees smother a section of Scenic Drive, near Titirangi.

October 1: A slip closes Scenic Drive, just south of the intersection with West Coast Rd.