John Kennedy is in awe of the people who, more than 75 years ago, designed and built hydro dams on the Waikato River.
Mercury NZ Hydro Rehab project manager John Kennedy left and site leader Kiel Adlam on top of Karāpiro Dam. Photo: Mary Anne Gill
At a Karāpiro community celebration last week dam operator Mercury Energy announced Ariki Road – which runs over the dam itself – would reopen permanently this week after closing off and on since August 2022.
It marks the near completion of the $90 million upgrade to the Karāpiro Hydro Power Station, a facility designed before World War II, built during the war, and commissioned in 1947.
The third and final new power generator is now in place, boosting output enough to power an additional 63,000 homes. With the upgrade, Karāpiro now generates more electricity from the same volume of water.
In charge of the barbecue was Mercury senior project manager Bede Geoghegan hoping not to repeat a previous community outing when the barbecue caught alight. Photo: Mary Anne Gill
“Efficiency is way up,” says Kennedy, who lives in Newstead and is Mercury’s Hydro Rehabilitation Programme Manager.
Cambridge News 21 August 2025
This was his first project for Mercury, and he described it as a “once-in-a-generation” job.
“It’ll be my grandchildren that take these machines out next time, or even my great grandchildren. It won’t be my children because this will run for 50 years,” he said.
“It’s amazing. Some of the stuff that we took to scrap has worked tirelessly through this time and when you think everything back then was done on paper, no calculators, it was all done in a design office somewhere with slide rulers and drawings. It would take months to ship across the world with design changes.
Mercury NZ Hydro Rehab project manager John Kennedy takes a community group led by resident Hilma Gill off for a tour of the dam building and the three new Kaplan turbines. Photo: Mary Anne Gill
“What they delivered back in those days is quite astounding really and the fact it has been reliably around for 75 years means it was well designed and well-engineered.”
For every litre of water that goes through Karapiro, the plant now generates three percent more power.
Kennedy’s favourite hydro station of Mercury’s nine on the Waikato River is Karāpiro.
“This was the project that brought me to Mercury and this is the one I’ve been invested in for the last three years.”
Celebrating the road opening, from left Debbie Alexander, mother Hilma Gill and brother Richie Gill. Photo: Mary Anne Gill
Karāpiro-Arapuni site lead Kiel Adlam also has a lifetime invested in the hydro industry – as does his father Magnus, who last year celebrated 40 years with the company.
Born in Hamilton, Adlam moved to Arapuni at age two when his father took a job there. He’s now Mercury’s Operation Readiness Coordinator.
“He’s still here, still telling me I’m doing it wrong,” said Adlam, who now lives in Cambridge.
Mayoral candidates Mike Pettit, left, and Clare St Pierre at the Mercury Karapiro Dam community day. Photo: Mary Anne Gill
The best part of the Karāpiro project has been the learnings on the way.
“We learned a lot of things on the first unit and now the third one. I’d like to think we’re in a much better place now.”
Both men now move onto Maraetai – where all its turbines, generators and governors will be replaced – followed by Ātiamuri and Ōhakuri, projects that will keep Mercury busy for years to come.
Mercury chief executive Stew Hamilton has been with the company four years, the last as CEO.
It was his 50th birthday the day of the community celebration and what a way to celebrate.
One of the community tours gathers on the bridge at Karāpiro Dam on the Waikato River. Photo: Mary Anne Gill
Although born in Auckland, Hamilton grew up in South Island communities where operations similar to the Karāpiro one had a big impact on people’s lives.
“I recognise that over the last few years there has been a life light between two sides of the community (here).”
His announcement that the road would reopen this week was received warmly by staff from Mighty River Domain on Lake Karāpiro, and by locals like mother and daughter Hilma Gill and Debbie Alexander, who can now leave the village and visit the café on the other side of the lake.
“I’m in awe of the people who created this infrastructure that set New Zealand up for 70 plus years,” said Hamilton.
“We need to think seriously about how we’re setting New Zealand up for the next 50.”
Mercury Energy chief executive Stew Hamilton welcomes the Karāpiro community to a barbecue which was to celebrate the road’s reopening. Photo: Mary Anne Gill
The biggest change seems deceptively simple, he said.
“I was walking through the plant just now and if you were there three years ago, there was shaking and vibrating. There was nothing like that. It’s nice and smooth.”
Naming a favourite power station, he said, is like naming a favourite child.
“They’ve all got something but I think this is special for a lot of New Zealanders because they come to Karāpiro lake for all that happens on there.”
Mercury Karapiro Dam community day
What a way to spend your 50th birthday: Mercury NZ chief executive Stew Hamilton at the Karāpiro Dam for the community celebration, a party on him. Photo: Mary Anne Gill
