We have welcomed the findings of an
independent report conducted by engineering consultancy WSP into the cause of the Ōrākei main sewer collapse and are focused on implementing its recommendations.
The report sheds light on factors contributing to the incident, known colloquially as the Parnell sinkhole, while also highlighting areas for improvement within our operations.
Chief executive Dave Chambers says the company openly acknowledges the impact of the incident on the environment, iwi, and community.
"When the sewer collapsed, wastewater overflowed into the Waitematā Harbour for several weeks. Understandably, this was very distressing for iwi and our community, and we apologise wholeheartedly.”
We prioritised public and environmental health in the period following the incident, swiftly initiating measures to mitigate the overflows.
"Our immediate focus was to halt the overflows and safeguard the environment. I’m incredibly proud of our staff and contractors who worked quickly to construct one of New Zealand’s largest pump stations within three weeks,” says Chambers.
We engaged WSP to conduct a comprehensive review of the incident to find its root causes and to action learnings from it.
The resulting report identified seven contributing factors to the collapse and that the interplay of all seven lead to the collapse. The factors included the condition of the pipe; extreme rainfall events in 2023; and weakened concrete blocks at the failure location.
"We are pleased to receive the detailed report. It has valuable guidance and we’re committed to implementing its recommendations," says Chambers.
The report highlights areas for improvement in sewer condition assessments and renewal practices, including enhanced inspection techniques and the development of comprehensive assessment and intervention strategies.
"We agree there is a need to lift our inspection techniques, and therefore we will be investing in more detailed inspections and profiling reports moving forward," Chambers says.
“Fortunately, the quality and capability of CCTV has improved in recent years. 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.”
We did not wait for the report to take proactive steps to enhance its condition assessment strategy, with plans being developed for implementation by July. Additionally, we are committed to investing more in pipe renewals during the next two decades, as outlined in its latest Asset Management Plan.
“We are already ramping up our planned investment in wastewater renewals,” Chambers says. “Programme development is underway, and within the next few years we expect to be spending some $100m per year.”
The report was presented at a meeting of our Board of Directors on Tuesday 5 March, and made available to the public on Thursday 7 March. We also commissioned independent environmental impacts reports which we expect to release in the coming weeks when they are finalised.
Work to rehabilitate the damaged section of the Ōrākei main sewer well underway
Chief operations officer Mark Bourne says construction work to rehabilitate the damaged section of the Ōrākei sewer is 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.
“With this technique we can keep wastewater flowing through the sewer while relining work is underway.
“We’d like to thank the Parnell community for their patience while we carry out this critical work.”
We are planning to reline about 1.6 kilometres of the sewer – from close to the Parnell Train Station to the end of Logan Terrace – in the next few years. This $86.74 million investment will significantly reduce the risk of future sewer collapses in Parnell.
