Safer swimming in the pipeline once Watercare’s Central Interceptor up and running

Checking for black flags on the Safeswim website may remain a sensible precaution, but Aucklanders should have more confidence to take a dip at the city’s beaches once Watercare’s Central Interceptor wastewater tunnel is completed.

Water quality has been a challenge highlighted by January’s flooding and Cyclone Gabrielle, after which many beaches had warnings for weeks on end.

Commercial manager Nigel Varcoe said that was exactly what the Central Interceptor was meant to mitigate.

“Central Interceptor is designed to prevent contaminated water entering the harbour,” he said. “Our ultimate objective is to clean up our beaches.”

In central Auckland’s older areas, a combined network of pipes handles both wastewater and stormwater.

However, during intense rainfalls, the volume of stormwater can exceed the pipes’ capacity, resulting in wastewater overflowing into creeks and streams and contaminating them.

Varcoe said in the recent extreme rain, even the Central Interceptor would have overflowed, however, it will be able to prevent the vast majority of incidents.

“We’re cleaning up 90 percent of Auckland’s overflows in this part of the isthmus, so 90 percent of what happens at the moment would have been cleaned up; what happened earlier this year is a bit exceptional.”

While another of Auckland’s major tunnelling projects, the City Rail Link, had blown out in budget by a billion dollars, Varcoe was confident the Central Interceptor would still come in within its original budget of $1.2 billion.

“We’re on track for that at the moment.

“We had significant contingencies put aside for unforeseen events, and so for the moment, we’re still on track against that number.”

However, with Covid-19 delays, the completion date would be blown out slightly – pushed back from 2025 to 2026, he said.

The Central Interceptor’s boring machine Hiwa-i-te-Rangi has now reached its deepest point, tunnelling 115 metres below Hillsborough after crossing the Manukau Harbour from Māngere.

The boring machine is now at the deepest point of the project.
Photo: Simon Runting,

Tunnel manager Michele Petris said despite all the challenges thrown at his team by the pandemic, they were making good progress.

“It was very complicated to get the people into the country, specialised people, to work.

“But with all these problems, if you look 360 degrees at the picture, we’re going pretty well.”

On Thursday, the machine would have completed 5km of its 15km journey from the Māngere wastewater treatment plant to Grey Lynn.

Petris said the boring machine was excavating 20-25m per day.

“For the length we have, it’s a good production. We expect to continue like this, with this average, until we reach May Rd.”

The May Rd milestone, the halfway point of the project, was now 2.5km away.

Michele Petris on site.
Photo: RNZ / Marika Khabazi

Around August, the team and all their equipment would need to relocate there from Māngere.

Petris said despite the big move, the tools would not be down for long, with tunnelling towards Grey Lynn likely to resume in November.

“Once we reach May Rd, the first section of the tunnel will be stripped to reuse all the rails, lighting, supports, and everything, so we can deliver the first section of the tunnel as soon as possible.”

Watercare also lodged resource consent to extend the tunnel route from Grey Lynn to Point Erin, in order to capture the combined stormwater and wastewater flows from the Saint Mary’s Bay and Herne Bay areas.

Across the city, 16 Central Interceptor sites have now opened, allowing for connections to the main pipeline along the way.

At one of these sites, a micro-tunnel boring machine called Domenica was just one week out from completing a secondary tunnel that would run from Miranda St, Avondale to May Rd, in Mt Roskill.

Senior project manager Bhargava Jinukula said although residents had taken a lot of interest in the project, the team had taken care to minimise disruption.

Meanwhile, the benefit to residents would be obvious once the project was completed, he said.

“They will see a lot less contamination of the beaches of Auckland and probably enjoy more time on the beaches when it’s a clear day like this.”