Auckland’s biggest water project finishes construction

Auckland’s biggest-ever water project – a $400 million water transmission pipeline from Manukau to Khyber Pass – has been completed after more than a decade in construction.

With the connection of our Hūnua 4 pipe to the Khyber Pass reservoir marking the colossal pipeline’s completion, it will now undergo a series of tests before the final stage is put into service.

Work on the 31-kilometre watermain started in 2008 and has been carried out in 11 stages. As each stage has been completed, the pipe has been connected to its neighbouring suburbs, boosting resilience and providing for population growth.

Our chief infrastructure officer Steve Webster says the colossal project caters for our growing population and provides resilience in the event of a natural disaster.

"As far as water pipes go, Hūnua 4 is massive. With a diameter ranging from 1.6 metres to 1.9m, it carries huge volumes of water – up to 3000 litres per second.

"This means that as our city grows, we can continue to provide uninterrupted, high-quality water supply.

"The geographic separation between Hūnua 4 and our other major water transmission lines gives us a great deal of resilience in the event of an earthquake or other disaster that could damage our network.

"It also means we can take our other large pipes out of service for maintenance, without disrupting anyone’s water supply.

"And Hūnua 4 does all this beneath our feet, without us even realising it – she’s a bit of a quiet achiever.”

Photo, from left: Watercare project manager David Moore, McConnell Dowell project manager Richard Atkin and Watercare graduate engineer Hinewai Hosford.

The benefits of the pipe reach as far as the North Shore and west Auckland, as well as the communities it connects to along its route.

"Hūnua 4 carries water from our Ardmore and Waikato treatment plants between our Redoubt Rd reservoirs in Manukau to our Khyber Pass reservoirs,” Webster says. “From there, the water can make its way into town, out west and across the Harbour Bridge, boosting the water supply to the North Shore and supporting population growth in these areas too.”

Our project manager David Moore, who has worked on the project for the past seven years, found the complexities rewarding. Most of the pipe has been laid in the road reserve in highly-populated areas.

"This pipe has three state highway crossings, three rail crossings, crosses the Manukau Harbour beneath the south-western motorway and passes through many arterial roads,” he says.

“The project discovered many lava caves, with one large lava cave at Ngatiawa St in One Tree Hill and others discovered while tunnelling through Newmarket.”

About 27km of the pipeline was laid by open-trenching, and 1km is suspended under the south-western motorway where it crosses the Manukau Harbour.

"The last 3km of the pipe – between Newmarket and Khyber Pass and including a long section under State Highway One – was largely built by a tunnel-boring machine to minimise disruption in this high-traffic area,” Moore says.

Photo: Welding work is carried out as part of the final 'tie-in' of the colossal pipe to the Khyber Pass reservoir.

While construction work began in earnest in 2012, the need for Hūnua 4 had been identified in the late 1990s. Preliminary works were carried out from 2008 to install the section of the pipe that’s tucked under State Highway 20 where it crosses the harbour. We partnered with NZTA on this work to coincide with the highway extension, saving time and money.

"Huge infrastructure projects of this scale typically take 20 to 25 years from the initial concept discussions to the delivery of the project,” Webster says.

“This is why we look far into the future to assess our growing city’s needs and make sure we can cater to them.”