Central Interceptor: Haycock Flume/Pump Station 23

The Auckland, Tāmaki Makaurau, Watercare’s Central Interceptor project is massive by any standards.

Started in 2019,and scheduled for completion in 2026, it will be New Zealand’s largest wastewater tunnel. It will lie between 26 and 110 metres below the surface, from Pt Erin in Herne Bay to Māngere Wastewater Treatment Plant.

Along with two smaller-link sewer tunnels also under construction, the main CI tunnel will collect wastewater from the existing network and take it to Māngere, with a controlled flow rate. The tunnel slopes at a gradient of 1:1000 taking its content to their destination.

Currently, in older parts of the city, wastewater and stormwater flow into a combined network of pipes. Heavy rain, and stormwater can overwhelm the ageing system, resulting in wastewater overflows into creeks and streams.

The Central Interceptor will significantly reduce this threat to the environment. And to people.

A project this significant is not without its challenges. And there are many steps along the way. In addition to effectiveness, keeping costs down, minimising disruption, and staying on schedule are vital.

Haycock Avenue

Collaboration was the key to success at one step in the progress – the Haycock Flume (Haycock Ave). “Pioneering to get it sorted” is how BurrowTech’s Hayden Powell describes it.

Haycock Ave required a manhole chamber in the roadway and installing flow control gates into the existing Western Interceptor and new pipelines on the site.

“Watercare wanted to avoid over pumping because of the risk and expense.”

Michael Pilkington, Senior Project Engineer, Ghella Abergeldie Joint Venture, says they needed to install flow control on existing pipelines (Western Interceptor and Onehunga Branch sewer). Varying pipeline sizes and flows meant a bespoke solution was essential.

Hayden says Michael knows the job “inside and out” and working with him, they found a very effective answer.

“Using the flume there was no interruption to the wastewater flow.” The flume diverts the flow of liquid through steel pipes with inflatable seals which join the flume and the existing pipe either side.

It was a very precise task and a lot of work went into planning and design – from laser measurements of the pipe, to drawings, the manufacture of the steel, and the all-important seals.

Hayden says it takes a fair bit of planning. “You can’t be even 10mm out.”

And, as for Michael, there’re no complaints.

“It’s been going well, and as planned – no issues at all.”

Pumping Station 23

The PS 23 site is also on the main CI project tunnel alignment. At this point, the tunnel will cross underneath the Manukau Harbour between the PS 23 site to Kiwi Esplanade.

The Manukau Harbour is of great importance to mana whenua, historically, presently and into the future.

Michael Pilkington says, while the flow was lower than for the Haycock flume, it was still a challenge.

He says while they could’ve had other things fabricated, getting the exact inflatable seals for the pipework meant BurrowTech were the right people for the job.