Moa Point wastewater plant had overflow hours before major flood
Wellington’s Moa Point wastewater facility suffered an “overflow event” less than 24 hours before it catastrophically flooded, new documents released by Wellington Water reveal.
An incident report released to Newstalk ZB under the Local Government Official Information and Meetings Act shows crews were forced to abandon work after a high-flow alarm was triggered on the afternoon of February 3.
The incident, which saw wastewater overflowing from an isolated channel undergoing maintenance, was logged as a “drowning / asphyxiation” risk and caused the site to be shut down for the day.
Less than 12 hours later, the plant flooded, causing tens of millions of dollars’ worth of damage and sending raw, untreated wastewater into the city’s South Coast.
The report said the high-flow alarm first activated at midday.
“We then took lunch and monitored conditions to see if flows would settle; however, they did not,” a consultant for engineering firm Stantec wrote.
“At approximately 3pm, we had an overflow event, and the decision was made to shut the site down, with works finishing at 4pm,” the report said.
The file said there would be ongoing discussions about how to minimise these events.
Tiaki Wai, the capital’s new water entity which has since taken over from Wellington Water, would not put chief operating officer Charles Barker up for an interview and would not answer questions about the earlier overflow.
In the days following the disaster, Wellington Water boss Pat Dougherty conceded the organisation may have missed early warning signs in the lead-up to the failure.
In a radio interview, Dougherty linked the failure to earlier channel overflows, saying previous issues may have been a symptom of the major issue to come.
Following that interview, Dougherty was stopped doing media interviews about the Moa Point incident and subsequent communications have come from Wellington City Council.
Wellington Mayor Andrew Little declined to answer questions on the overflows, saying at the time it was “not helpful to speculate”.
A subsequent hydraulic report found trapped air in the system was a likely cause.
It found a design fault that meant air bubbles could become trapped in the pipeline, disrupting the flow of wastewater, pushing it back up into the plant.
The treatment plant won’t be fully back up and running until February next year.
Current estimates suggest work to repair the plant will cost $53.5 million, the council’s chief financial officer Andrea Reeves said, but she noted the facility is insured.
The Government announced an independent review into the sewage plant failure in February.
An interim report by a Crown review team was due back on June 30 but has not yet been made public.
Tobias Macintosh is a Newstalk ZB Multimedia Journalist, based in Wellington. He joined NZME in June 2025, after obtaining a Bachelor of Broadcasting Communications at the New Zealand Broadcasting School in Christchurch. Putting a spotlight on all things happening in and around the capital, he also has a keen eye on local politics, crime and justice, and foreign affairs.