In 2018 Westport had a problem. A collapsed supply tunnel meant the northern West Coast town of about 4600 people was having to constantly pump water. Pumping was expensive and unsustainable, but finding a solution proved a headache for the Buller District Council. Teresa Wyndham-Smith explains.
Westport’s raw water supply has come from Giles Creek since 1903. The 2.5-kilometre reticulation is made up of four hand-dug tunnels linked by timber flumes and bridges, open channels and concrete pipework through native bush and protected wetlands.
Its construction was an amazing feat of engineering using the mining expertise for which the district is famous.
In 2014, however, the main tunnel began to fail. In early 2017 it totally collapsed blocking all water flow.
Given the difficulties and dangers of clearing the collapse it seemed the pipeline would have to be re-laid 3.8 kilometres over ground.
For 18 months the council wrestled with what to do. Then Timaru company Hadlee & Brunton stepped up. The family-owned and run company had previously discounted the job as too risky, but new technology made it possible to fix the tunnels without putting workers inside.
It wouldn’t be a cheap fix, the cost was over twice Council’s budget, but it could be done.
Late in 2018 councillors voted unanimously to accept Hadlee & Brunton’s tender to pipe the supply tunnels.
The company has been around almost as long as the tunnels, beginning in 1906 as Hadlee & Clough – plumbers, gasfitters and bell hangers.
Today brothers David and Andrew Brunton, father Ross, and staff take on large national infrastructure projects though their core business remains plumbing and gas fitting.
They began Westport’s $6.3 million project in February 2019 meeting with locals who had worked on the tunnels.
Dave Brunton says this was invaluable. It enabled them to hear at first hand the challenges of what lay ahead as well as providing an opportunity to detail their approach and get feedback.
The Westport project was about reinstating the collapsed main tunnel, improving resilience and restoring gravity flow through a new, fully enclosed pipeline.
Fixing the first tunnel was the biggest challenge. At 1.2 kilometres long, and up to 200 metres deep, it’s the longest of the four. The collapsed section was about 200m long, around 500m from the entrance.
The work required immense preplanning. Cutting edge technological solutions to track equipment in the tunnels without manned entry were invented. A system was developed to remove collapsed hardwood shoring and rock while installing 360 tonnes of pipe and straightening rock walls.
Some of the specialised gear came from Germany, Scotland and Switzerland. Everything was designed around two Herrenknechts; one a 200 tonne horizontal maxi drill rig, the other a 500 tonne pipe thruster. These were dismantled for transporting across Arthurs Pass and up the winding West Coast roads. Polyethylene pipe, machinery and other supplies were helicoptered in. Former goat tracks had to be rebuilt to allow for trucking of larger machines.
The first job was to establish tunnel access.
About 20,000 cubic metres of rock was removed from a hillside where tunnels one and two intersect at a depth of over 30 metres. The portal junction worksite created was protected with rock anchors, structural mesh and rock canopies.
On the other side tunnel, one exited a cliff face directly above a river. A junction was dug 20 metres back to connect with the intake. A small shelf was hand dug in front of the opening and a 1.8 tonne excavator with rock breaker helicoptered on to it.
The shelf was enlarged with eight 25-millimetre rock anchors grouted in. A 40 metre Mabey bridge was built in the bush then cantilevered out using precast concrete blocks and water filled IBCs. Mounting brackets with 30-millimetre holes had to be landed directly over the anchors.
Hadlee & Brunton had a secret weapon, a movie industry expert known as ‘Fox’. He developed camera systems that could provide live remote footage of the drilling head from the tunnel to the drill operator.
After the portal, bridge and camera systems were established the 200 tonne maxi drill began work. It fed 1.25 kilometres of oilfield rods from the portal excavation through to the bridge, navigating hardwood columns and major collapses.
Fox’s camera system enabled workers to guide the 200-millimetre diameter rods between timber supports sometimes only 500 millimetres apart. The drill was then taken to the other side of the hill and connected back onto the rods at the bridge. The 500 tonne thruster was installed in the portal. Huge concrete and steel anchor systems were installed on both sides to take the combined 700 tonne force produced by the machines.
A large cutting and towing head, which removed all debris in tunnel one, was connected to the rods in the portal then fitted to the 800-millimetre steel pipe.
Dave Brunton explains; “The thruster was pushing steel pipe as the drill was pulling and cutting. If something went wrong wings could be retracted on the drill reamer to push the assembly back through the pipe without having to go in.”
Over 1.2 kilometres of C350 813-millimetre OD steel pipe, 12 millimetres thick, was pushed through the hill in 24 metre sections following the alignment.
It could withstand further collapse, would last for decades and 710-millimetre PE could be inserted when it did corrode.
The 200 tonne maxi rig pulled 208, 6-metre-long rods drawing the pipe through, averaging eight rods (50 metres) a day.
Andrew Brunton says; “It had a maximum pull of 200 tonne, we got up to about 170 tonnes with about 200 tonne additional push from the thruster.
“We also had to install about 1.5 kilometres of 600-700 diameter PE through the remaining damaged tunnels, open earth flumes, timber bridge flumes and old concrete culverts. Putting this continuous pipe string through tunnels two and three was almost as complicated as the tunnel one rehabilitation.
“We threaded the pipeline through dense native bush and rugged terrain into the tunnel portals with very little disturbance. Now, all the way from the intake to the reservoir ponds, there’s a solid connected gravity pipe.”
The existing intake weir was rebuilt and fitted with self-cleaning screens, solar powered Scada controlled automated gates and mag meters. There are no valves or automated air intakes. All air is provided through chimneys welded into the pipe.
Hadlee & Brunton worked closely with local contractors and tradespeople.
“It’s important that the guys who have to maintain and run the system are involved in the construction process”, says Dave Brunton.
“They had the opportunity to make suggestions and tweaks to improve system workability as work progressed.”
Local iwi Ngati Waewae was also represented on the project board. An on‐site karakia (blessing) before the crucial final phase of main tunnel drilling had a big impact on all gathered.
One of the biggest challenges was weather.
Over 100 official rain days were logged during the 300-day construction period. Dave Brunton says this affected portal excavation.
“Every time it rained, we had to shut the operation. We couldn’t risk any of the guys or machinery, so we switched the programme around.
“The second half was going to be work below tunnel four and lining two and three. We did that first and carried on doing tracks and prepping for tunnel one.”
The system has been operating successfully since fully commissioned in December 2019. Whereas original design called for operating capacity of 120 l/s the company’s design delivers over 250 l/s.
The Buller District Council’s group manager infrastructure services, Mike Duff, says the project is a major achievement.
“It’s renewed a vital asset for the town securing the supply for at least another century.”
Hadlee & Brunton’s approach was the safest option, had less impact on the environment and adjacent landholders, was quicker than going overland and ongoing maintenance costs would be lower, he says.
This was confirmed when major slips came down late last year. If the open cut pipeline had been in place as proposed it would have been wiped out.
Buller mayor Jamie Cleine praises the company’s approach. “Their reporting to the council was excellent and that helped build community confidence.”
Hadlee & Brunton kept in close contact with the local daily paper, The News, including taking reporters for site visits. Their articles, and council newsletters, kept the community updated.
Over $1 million, or about 15 percent, of project value was returned to Buller businesses including trade contractors, professional services, retail and hospitality providers. Buller chief executive Sharon Mason says it was fantastic for the town.
“The increase for local businesses really benefitted the community.”
Dave Brunton pays tribute to the council.
“It’s tough for a Council like Buller. They’ve a tiny ratepayer base, huge land area, very old infrastructure. But they were ready to look at it from a different angle – to back us and believe in what we put forward – many other councils wouldn’t have been brave enough to make that call.”
Mike Duff says Hadlee & Brunton carried out the project on time and under budget.
“The equipment, techniques and methodology to complete this work have never been applied before in New Zealand, it’s likely a world first.”
The Buller District Council and its main contractor Hadlee & Brunton won two awards for its Westport Water Tunnel Pipeline Project.
At the 2020 Water New Zealand conference it won the Excellence Award, the highest honour available in the Three Waters sector. It was then highly commended in the Institute of Public Works Engineering Australasia awards in the ‘Best Public Works Project over $5 million’ category.