With the connection of Watercare’s 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 km watermain began 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.
Watercare 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 m to 1.9 m, it carries huge volumes of water – up to 3000 litres per second,” said Webster.
“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.”
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 said.
“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.”
Tunnelling specialists McConnell Dowell constructed the final section of the pipeline, from Epsom to Khyber Pass, connecting the final bend on June 23.
McConell Dowell’s project manager Richard Atkin said Hūnua 4 has been a technically challenging project so seeing construction reaching completion is immensely gratifying.
“The hard work and perseverance of the team has been phenomenal, and we are all very proud to have helped deliver this important new water pipeline for Aucklanders,” said Atkin.
The project set two pipe-jacking records for the longest single drives in the Southern Hemisphere by a TBM greater than 2.6 m in diameter in 2020. The longest was a 1296 m record set by the Herrenknecht AVN2500 mTBM during the third drive.
Watercare project manager David Moore, who has worked on the project for the past seven years, found the complexities rewarding.
“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,” said Moore.
“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.”
Approximately 27 km of the pipeline was laid by open-trenching, and 1 km is suspended under the south-western motorway where it crosses the Manukau Harbour.
“The last 3 km 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 said.
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.
Watercare 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,” said Webster. “This is why we look far into the future to assess our growing city’s needs and make sure we can cater to them.”
Subscribe to Trenchless Australasia for the latest project and industry news.