Source: Radio New Zealand
Untreated water is leaking onto the capital’s south coast beaches due to the Moa Point Treatment Plant flooding. RNZ / Samuel Rillstone
Sewer robots are being used to patrol pipes elsewhere in the world to keep them from blocking, but what about in New Zealand?
Wellington Water has suggested the main outfall pipe into the Cook Strait was blocked, causing a back-up into the Moa Pt treatment plant, but it did not know how.
“Catastrophic” flooding has damaged perhaps 80 percent of the plant’s equipment and may take months to fix, chief executive Pat Doughtery told Midday Report on Thursday.
It was “as bad as we feared”, he said.
RNZ asked the agency if it used robots in sewers or had looked into using them.
A spokesperson responded, “No. Would it work?That’s probably not an approach we are considering at the moment.”
The pipe has not been inspected internally since its construction almost 30 years ago in 1998.
Dougherty told both RNZ and the Herald they suspected the cause but were checking.
“We have got a TV camera on the site and we will be getting that to have a look at the outfall pipeline to try to understand what went wrong that caused a backup into the building,” Doughterty told Midday Report.
Earlier, he told the Herald, “The outfall wasn’t able to cope with that volume and backed up into our worksite.”
It was inspected annually by divers, but it is hard to get into a pipe that was carrying high volumes of wastewater every day, Dougherty said.
“So I don’t think we have … any regular inspections of that pipe,” he said.
Dougherty agreed that it was a problem.
The agency later on Friday told RNZ it was still working through what happened and there needed to be a thorough investigation.
“It would be inappropriate at this stage to speculate. The outfall pipe is just one of several areas under investigation – ultrasonic cameras and divers are being deployed over the weekend,” it said.
“The long outfall pipeline is only one part of the overall investigation.”
Ultrasonic cameras were being deployed with divers.
Inspection robots
The sewer robot industry has been expanding rapidly.
While using them in an ocean outfall, like in Cook Strait, might be complicated, the robots have been used widely in cities overseas.
Arlington in the US in 2021 completed a survey of 80km of land-based big sewers in 2021 using robots with cameras, laser and sonar.
China has floating robots to both spot damage and others to do repairs.
In London, experts in December held an online forum about using AI to boost robot inspections of the Thames Tideway super-sewer.
“The pipe inspection robot market will expand rapidly between 2025 and 2035 owing to the increasing demand from oil and gas, water and wastewater, sewage and industrial manufacturing industries,” said Future Market Insights.
It could grow to five times the current global size of $8 billion in a decade.
Online promos for one robot said the data was collected and stored on-board for a “fast and objective profile of 900mm to 3,000mm pipes, and information about corrosion, debris under the flow line and surface damage on top of the standard systems deliverables, without the need for anyone to enter”.
Aside from adverts like this, though, a scientific review in December said both that “research on sewer defect detection has grown significantly” and that “research on robotic systems for sewer pipe inspection is still limited”.
It only looked at robots using CCTV – not much use in an outfall – and said they had obvious limitations but also that some of these AI models demonstrated “outstanding performance” for speed and accuracy.
Very highly crictical assets
Wellington Water said it last inspected the outfall in March last year, 11 months ago.
“This is an external inspection for structural integrity (visual) of the exposed portions of the outfall pipe, condition of the diffuser ports, and assessed for erosion or scour around the exposed sections of the pipe,” said a spokesperson.
There was an annual assessment of the rust protection system.
“It is not our standard practice to internally inspect a pipe of this type and age.”
While it regularly used floating cameras to inspect sewer lines elswhere, this was a “different scenario” to an outfall.
These sewer lines were “more prone to blockages” from debris and fat/scum especially in smaller or low-flow pipes. But the outfall discharge came after the treatment processes that removed such debris, scum, and fats.
The agency, which is about to morph into a new government-mandated entity, already had huge stresses on its finances from having to do big fixes to avert more crises, before the biggest one ever hit on Wednesday at Moa Pt.
However, it had recently undertaken what it called a successful if partial assessment of “failure modes” of critical assets.
“The focus of this project meant that all potential ‘showstoppers’ were identified and assessed,” said an internal report.
“By tailoring asset management approaches towards assets that are most critical, Wellington Water is aiming to avoid large scale disruption to communities and environmental damage.”
Another “potential showstopper”, the Seaview outfall, runs from the Hutt to Eastbourne and on to Pencarrow.
Built in the 1962, it had been running at half-capacity and “needs renewing or upgrading with no budget provision for physical works – expected to be around $700m,” said an asset management plan last year.
Both Moa Pt and Seaview treatment plants were “very highly critical” assets, or VHCAs.
They were built and operated under 25-year contracts that expired in 2020.
“The expected lives of many of the mechanical and electrical assets means that a significant renewals burden has arisen post termination of these contracts.
“Failure of these assets heightens the risk of consent non-compliance and unplanned discharges to the environment,” it said.
Seaview’s problems meant higher operating costs and an increase in treated discharges to Waiwhetū Stream, the latest around the same time this weak that Moa Pt failed so drastically.
Moa Pt was rated “poor” and significantly non-compliant with its discharge consents, local residents were told by the agency last December.
The 2025 plan also said “critical wastewater mains are in very poor condition”.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
