Fifty metres beneath a river, only 5.5 metres lies between me and disaster

“Don’t touch,” warns guide Kim Johnstone, as she opens what looks like a small cupboard door in the tunnel-like gallery 49 metres under the surface of the Clutha River/Mata-Au. Inside a fine cord is hanging: it’s a seismometer and if it moves all hell could break loose.

The Clyde Dam, containing 430 million cubic metres of water and built with 1 million cubic metres of concrete – enough to lay a footpath from Clyde to New York, according to the tour fact sheet – is built on a fault line. Although a thorough geological survey at the time of construction indicated the risk of an earthquake on the Dunstan Fault in the next 100 years is low to very low, standing in front of the instrument is unnerving. In this dark, dank gallery, there’s only 5.5 metres of concrete between me and potential disaster.

Unlike many other dam tours, this small group tour takes you deep inside its workings – into the control room, the throbbing turbines and underneath the spillway where excess water is released. For anyone interested in a better understanding of the technologies that power our light switches, fridges and TVs, this tour is an eye-opening adventure that will leave you in awe of the power of water, concrete and nature.

I’m in Otago in New Zealand’s South Island to cycle three of the Nga Haerenga – The Great Rides of New Zealand, an adventure designed to experience as much of the outdoors as possible. Going underground wasn’t part of the plan, but as we descend to the historic mining town of Clyde at the end of the 55 kilometre cliff-hugging Lake Dunstan Trail, the massive dam dominates the view. I’m keen to get a closer look.

After we’re fitted with hard hats and hi-vis jackets and complete the safety induction, our small group is taken to the control room, where staff monitor the energy market and the system frequencies. On one screen we can see how New Zealand is being powered with a combination of geothermal, sun, wind, hydro and a small amount of gas, diesel and coal. As we watch the screens flicker, the graphs show the country is currently running on an impressive 99 per cent renewable energy. Underneath my feet, I can feel the vibrations of the turbines creating some of that electricity.

Johnstone was running a cafe in Clyde when she came up with the idea of the tour. When she approached Boyd Brinston, the head of operations at the dam, he was perplexed. “Who would want to come on a tour?” Johnstone recalls him saying. Plenty of people, it turns out. Since the tours launched in December 2022, more than 1600 have visited the dam. Ten per cent of the ticket price goes to a local charity. “I was really clear that it had to be of circular benefit for the entire community.” So far, the funds have contributed to a community garden and medical equipment.

After leaving the gallery, we walk to the spillway, where the excess water creates a powerful waterfall into the river, the second longest in New Zealand. We can barely hear each other over the roar of the water and I’m getting drenched, but the massive rainbow framing the view of the valley is worth it.

Just when I think there’ll be no more tunnels, Johnstone leads us to another entrance to the dam wall. At the end of the narrow opening is the concrete expansion joint that will protect the dam in the event of an earthquake. At the point where the two sections of the dam wall meet, the joint soars like a brutalist sculpture. Held in place by the pressure of the water behind it, it gives the walls flexibility to move without breaking. Although it has never been tested, it is designed to withstand an earthquake measuring seven on the Richter scale. For anything under that, “It’s not going to be a problem,” says Johnstone. Then she says, “In theory, right?”

THE DETAILS

VISIT
Clyde Dam tours run daily. A tour takes around 2.5 hours including check-in and safety briefing. Tickets $NZ125 ($102) (adults), $NZ75 (children 5-14), or $NZ375 (two adults, two children). See clydedamtours.co.nz

STAY
The Olivers Collection in Clyde includes a brewery, cafe and restaurant and two restored historic luxury accommodation options with breakfast at The Lord Clyde (rooms from $NZ320/$265) or Olivers Lodge & Stables (from $NZ300) on Clyde’s main street. See olivers.co.nz

FLY
Virgin, Qantas, Jetstar and Air New Zealand offer flights to Queenstown from Sydney, Melbourne and Brisbane. Sixt car rentals (sixt.com.au) are available from Queenstown airport.

MORE
centralotagonz.com

The writer was a guest of Ngā Haerenga – The Great Rides of New Zealand.