The 50 year-old secret of Lake Benmore

May 1965 saw the grand unveiling of New Zealand’s largest earth dam - the Benmore Power Station.

Located in the Waitaki Valley, on New Zealand's largest man-made lake - Lake Benmore - it is the largest hydroelectric station in the Upper Waitaki Scheme and New Zealand’s second largest after Manapōuri.

Generating 540 MW of electricity, the Benmore station could power up to 300,000 homes a year.

The dam was the product of a 10-year, $48 million engineering achievement – the likes of which were few and far between in its time.

It is still marvelled by visitors and locals alike today.

Benmore Opening

Prime Minister Keith Holyoake was joined by media, international guests (such as Swedish royal Prince Bertil), and elected officials to ceremoniously open the station.

In a carefully stage-managed piece of theatre, he pushed a button to see the station roar to life... But did it really?

Behind the Prime Minister, a neon tube lit up a large board with a map of New Zealand, showing the connection between Benmore and the capital, Wellington.

Much to the delight of the assembled crowd and guests, DC power from little old Benmore was powering the capital. Cheering, hugging, whooping and celebrations across the town of Otematata ensued.

But it wasn't actually that simple

The power station had been running smoothly in the weeks and months leading up to the Prime Minister’s visit, however, just a day or two before the grand unveiling, there was a massive transmission line failure.

All three of the station’s turbines malfunctioned on the day of the opening ceremony – meaning the DC line intended to light up both the neon beam, and send power to the North Island, was down.

The power coming through to the neon beam on the night Holyoake pushed the all-powerful button didn’t come from the station at all. Instead, it came from an auxiliary turbine, brought close enough to the assembly for the sound of a whirring machine to be heard as the Prime Minister brought his finger down.

It was in fact, simply a grand (but altogether empty) gesture.

The evolution of a project

Initially, Benmore was touted as being a concrete dam like Waitaki, but advances in dam building techniques meant Benmore was able to be built using earth.

The Ministry of Works (MoW) began construction of the earth dam in 1958.

  • February 1958 - the first group of about 150 men arrived at Otematata to begin work on the dam.
  • August 1958 - more than 10 shopkeepers had opened stores to cater for what was then a growing population.
  • December 1964 - the lake was filled.
  • January 1965 - the first power was produced.
  • By the end of 1965 - there were over 450 MoW employees living and working in Otematata.
  • Sometime in 1966 - less than two years after the first electricity was produced, the plan to build the Benmore power station was approved.

Work quickly began to build a camp for workers to live in.

So what really happened that day?

One of about four dam-building families still living in Otematata today is the Bayliss family, consisting of Alan ‘Taffy’ Bayliss and wife Bev.

Alan, now 85, was a technician in his heyday – working on Benmore between 1964 and ’68. He remembers the opening ceremony well.

He said he can’t remember seeing anyone as flustered and panicked quite as much as his foreman was; his face turning whiter as each turbine was declared out of operation.

Two burst into flames upon starting up; while the other turbine had accidentally been welded to its casing, preventing it from spinning.

He remembers clearly another problem quickly emerging on the morning of the ceremony – there was a limited number of seats in the hall where the opening would take place.

“There was a huge assembly of people and the physical space of the power station couldn’t accommodate all those people.

“All the MPs, the agencies involved, the Territorial Authorities, all invited and there was no room for anyone else – not even for the construction workers,” Alan said.

“That caused an uproar let me tell you . . . but thankfully for us there was another problem. Those running the evening needed security guards, tour guides, car park attendants and all the rest of it.

“So, our boss said, ‘listen fellas, you guys volunteer your services, I’ll pay for a shout.’ I was on the social club and we were already planning a big knees-up that night – so we gladly joined in.

“They got their volunteers and we had a great big knees-up in the gymnasium afterwards, along with some of the nobility invited,” he laughed.

Otematata: A short history

Otematata means ‘place of good flint’ in Māori, and is surrounded by rugged rocks, hills and mountains, as well as the lake itself.

Tōtara Kaimaka/the Benmore Range runs along the western side of Te Ao Mārama/Lake Benmore in Te Manahuna/the Mackenzie Basin.

Tōtara Kaimaka was an ancestor on the Ārai-te-uru waka, which – according to lore – capsized near Matakaea/Shag Point on the Otago coastline hundreds of years ago.

After the capsize, many of the passengers went ashore to explore the land. However, they needed to be back at the waka before daylight to carry on their voyage.

Many did not make it, including Tōtara Kaimaka, and instead transformed into many of the well-known geographical features of Te Waipounamu.

During the Royal Commission of Inquiry into Ngāi Tahu land claims, Ngāi Tahu kaumātua/elders recorded Tōtara Kaimaka as a kāinga mahinga kai/food-gathering place where weka, tuna/eels, whio/blue duck, and purau/‘Māori onion’ were gathered.

And although Māori used the area extensively in the pre-dam era, it was the influx of MoW workers hundreds of years later who made the area their home.

There were around 450 Ministry of Works employees living in Otematata in the late 1950s, but that number significantly dropped with the dam’s completion.

At the 2001 census, Otematata had a “usually resident population count” of 243.

Alan Bayliss said he’s immensely proud of his and his colleagues’ work.

“I’m proud of what these New Zealanders have built and what they left behind. I take my hat off to one man in particular – Max Smith,” Alan said.

“He was the last project engineer for the MoW. That man started his working life in Roxburgh. When he came here (to work on Benmore) he had a whole number of people willingly help him make the dam into a real recreational space, where people wanted to be.

“Without him there would be no trees, no lasting recreational amenities. We wouldn’t have had boat harbours, toilets, boat ramps – you name it,” he said.

Benmore and Otematata would not be the same place they are today without the foresight of Mr Smith, he said.

What will I find in the area?

In terms of wildlife in the area, the New Zealand falcon/kārearea, sky lark, chukor, California quail and the New Zealand pipit/pihoihoi can all be found. As well as the common skink and common gecko if you look hard enough.

In terms of recreation, Lakes Benmore and Aviemore attract many boating enthusiasts, whether it be power boats, yachting or windsurfing. Jet skis and wave riders are also popular.

The wider area offers walks, tramps, mountain biking, boating, and fishing – Lake Benmore is well-known for its trout, with healthy stocks of both rainbow and brown trout. Chinook salmon and sockeye salmon can also be found.

Above are a few snaps of neighbouring Lake Aviemore

The expansive Lake Aviemore also has good numbers of brown and rainbow trout. Down the road is the Lake Benmore Holiday Park for accommodation needs.

Alan Bayliss said many of his work colleagues moved on to different larger towns with more work, like Twizel – but he stayed on.

“I’ve lived in Otematata all that time – a lot of the crew did move, but not us,” he said.

“Many of my co-workers from back then are still alive. There are only about four families here who used to be involved in the dam build. Quite often though we get people coming through who used to work here.

“A few of the engineers, but mostly the people who come back are coming back for retirement or if they’re driving through. But there are more than a handful living in Twizel too.”

Benmore Range conservation area is home to a number of native plants and shrubs – including slim snow tussock and narrow-leaved snow tussock; as well as an array of alpine herbs along the summit ridge.

The science behind the water

The lake’s water is not only clear, it has a lower level of chlorophyll, phosphorous and nitrogen than other lakes – all signs of a healthy waterway.

The Trophic Level Indicator (TLI) measures three parameters, including water clarity and total nitrogen. From these parameters a TLI value is calculated.

The higher the value, the greater the nutrients and fertility of the water which encourages growth, including algal blooms. As a rule, higher TLI scores mean poorer water quality.

Water quality therein is measured from 0 (very good) to 7 (very poor). Benmore’s most recent reading is a 2.1, attaining a ‘good water quality’ score.

In the Ahuriri arm of Benmore, the TLI is much higher – at or around 2.9, which is right on the edge of being classified as ‘average water quality’.

TLI limits in the Waitaki lakes are set to help achieve community outcomes agreed by the Upper Waitaki Water Zone Committee, which include providing for a diverse ecosystem of plant and animal life, recreational opportunities and customary use.

Can I swim here?

When you’re heading to the local lake this summer, don’t forget to look out for water quality information signs. These will tell you if there’s a health alert in place or whether to avoid swimming if it’s been raining.

It’s important to avoid swimming for 48 hours after there has been rainfall. This is because rain can wash bacteria from roads and paddocks into the waterway.

Environment Canterbury regularly monitors water quality at 100 popular swimming spots around Canterbury. The results are updated weekly, and are available through Land, Air, Water Aotearoa (LAWA), New Zealand's most comprehensive source of water data.

The Upper Waitaki Water Zone Committee, which looks after waterways on behalf of the public, say it is important to look out for each other these holidays.

Upper Waitaki water zone committee Chairman, Simon Cameron, said that with the potential for E. coli contamination over summer, it’s important for tourists, locals and everyone in between to be in the right “mindset”.

“There are other groups sharing the same concerns as us – the Environment Canterbury Navigational Safety Team is one. That’s all around being boat safe and being vigilant around alcohol mixing with boats, as well as the rubbish aspect. All things to think about,” he said.

Enjoy our lakes this summer. If you’re visiting one of the beautiful waterways, we’re counting on you to dispose of rubbish correctly and use the toilet facilities provided.