Flumin’ good job!

    

BurrowTech has recently played a part in history by designing and manufacturing a large flume for Watercare’s billion-dollar Central Interceptor project.

The Central Interceptor is a giant 16.2-kilometre-long 4.5m internal diameter tunnel running from Point Erin, Herne Bay, to Māngere Wastewater Treatment Plant. The tunnel sits deep below ground (15-110m) and collects flows from older suburbs where there is a combined stormwater/wastewater network. In dry weather, the network works well. But in heavy rain, the system becomes overwhelmed by stormwater and overflows occur into streams and Waitematā Harbour beaches. The new Central Interceptor tunnel will capture these flows, taking them to the Māngere Wastewater Treatment plant for processing, resulting in a significant improvement in water quality.

It is the largest wastewater infrastructure project in New Zealand history.

Most of the tunnelling has been completed and now crews are working to connect the giant tunnel to existing local wastewater networks. The new flume was installed in December 2024 into a section of the Ōrākei Main Sewer (one of Auckland’s largest wastewater pipes) at the Central Interceptor Tawariki Street site, Grey Lynn. The flume allows teams to safely isolate flows, excavate beneath the Ōrākei Main Sewer, and create a new chamber/connection.

The flume installation was carried out at night, when residents were asleep, and wastewater flows were therefore at their lowest.

The BurrowTech flume consists of six separate sections, and four inflatable rubber seals. BurrowTech’s Hayden Powell says space on the site was tight and the flume was the best solution: “It was the safest and quickest way,” he explains.

Hayden says the flume is likely to be in place for up to 18 months whilst Watercare’s construction partner, Ghella Abergeldie Joint Venture (GAJV) continues the delicate work on the Ōrākei Main Sewer.

GAJV B-grade tunnel manager Mark Tregoweth says safety is the Central Interceptor project’s main priority: “Installing the flume involved months of careful planning and was tightly controlled. We couldn’t allow raw wastewater to enter the excavation chamber where our staff are working, so the flume was vital. In fact, we couldn’t have done the work any other way.”

He added: “The service from BurrowTech was very good. Hayden was super-fast to respond to any query. Multiple things changed, and for Hayden, nothing was a problem. He made it happen, quick. I’d definitely use BurrowTech again.”

Meticulous measurements and zero tolerance designing went into making the flume which slid perfectly into place. It was absolutely “bang on,” according to Hayden.

Once the chamber is built, the flume will be removed.

The Central Interceptor tunnel is designed to last 100 years.

Hayden says: ”Working with a great team makes you really appreciate how even a job with a lot of moving parts can come together perfectly. From project planning, approvals and design to the people on the ground (or in this case, the sewers), doing the hard yards. Everyone is equally important.”

He is also quick to pay tribute to the Watercare and GAJV teams: “BurrowTech is privileged to work on this prestigious project and we are delighted to know that we have played a small but significant part in creating a cleaner Auckland. It’s a legacy we can all be proud of.”