File photo. Crews at the sinkhole in September 2023. Six months later a temporary pump site is being used to reroute wastewater. Photo: RNZ / Jordan Dunn
Heavy rain, weak concrete and 100 years of deterioration have been blamed for a huge sinkhole in Auckland's Parnell.
The Orakei Main Sewer line collapsed in September 2023, leaving a massive sinkhole on St Georges Bay Road that has disrupted businesses in the area for nearly six months.
Crews are still working at a temporary pump site to reroute the wastewater uphill, but Watercare promised it would start installing a new glass-reinforced liner from mid-March.
Following the catastrophic collapse which caused waste to overflow into the Waitematā Harbour, Watercare admitted its inspection techniques weren't up to par.
"When the sewer collapsed, wastewater overflowed into the Waitematā Harbour for several weeks," chief executive Dave Chambers said in a statement.
"Understandably, this was very distressing for iwi and our community, and we apologise wholeheartedly."
He said he was "incredibly proud" of staff and contractors' construction of a temporary pump station to redirect the overflowing sewerage.
Businesses near the site of the huge sinkhole had to cope with an ongoing smell and associated disruptions. Photo: RNZ / Felix Walton
Chambers said Watercare would enhance its condition assessment strategy and start implementing changes by July.
"We are already ramping up our planned investment in wastewater renewals.
"Programme development is underway, and within the next few years we expect to be spending some $100m per year."
A failure analysis report by consultancy firm WSP released on Thursday noted the collapse was likely caused by a combination of factors.
The wet weather in early 2023 was thought to have weakened the sewer line, but that damage was helped along by 110 years of "general deterioration" and crumbling blockwork, WSP said in its report.
It noted Watercare's CCTV surveillance, which also included laser scanning and sonar, did not provide a sufficiently clear view of the pipeline's defects.
Chambers said Watercare had taken proactive steps even before seeing the report this week.
"We will be investing in more detailed inspections and profiling reports moving forward. The type of CCTV the report recommends - which can pan and tilt - isn't readily available in New Zealand, so we'll be looking at the options to get it here."
Watercare chief operations officer Mark Bourne gave no deadline for repairs to the damaged sewer line but said rehabilitation was well underway.
"We've been busy preparing the site so that we can start installing the new liner from mid-March, which is made of glass-reinforced plastic and will extend the life of this section of the sewer by 100 years.
"The new liner will be installed by 'slip-lining' - where you install a slightly-smaller diameter pipe in the old pipe, grout the space in between the new and old pipe and seal it at the ends."
The technique allowed wastewater to keep flowing through the pipe while it was being relined, he said.
Over the next few years, Watercare planned to reline 1.6km of the 13km sewer for a total cost of $86.74 million.