More power to the mainland

The commissioning of the Roxburgh Dam drastically changed New Zealand’s electricity supply. On its 60th anniversary Central Otago reporter Jono Edwards and  videographer Craig Baxter take a look inside the colossal structure.

In a computer-filled office, generation technician Quentin McLean points at a picture of a 1956 newspaper clipping.

"This says it all. It’s from your paper. It says ‘Roxburgh has freed South Island from worries over power supplies’."

Another generation technician, Don Nicolson, says before the dam was built, the South Island had scheduled blackouts.

"It pretty much changed that for the whole South Island."

After a post-World War 1 population boom, an increased demand for electricity pressured the government to create  major new power schemes.

In 1947 the site on the Clutha River, 9km north of Roxburgh, was selected for the country’s first major hydro-electric project.

The first of the eight 40MW electricity turbines was commissioned in 1956, and the rest had been installed by 1962.

The colossal 150m-long structure required 1.5 million tonnes of concrete, much of which was poured by hand.

Health and safety regulations were quite different from today.

"I can confirm about four or five deaths," Mr Nicolson said.

"One guy fell into the concrete of the dam. As far as we know he’s still there."

Mr Nicolson initially thought this was just a "bit of a construction story", but was one day visited by relatives of the man’s friend.

"We learned from ’54 to ’56 they were just about flat out because they really needed to get the system on. Middle of the night they were pouring [concrete] in winter, and he went out to check the concrete was setting, and they say he slipped in and sank like quicksand."

• Outside on the transformer platform the water flowing downstream is swift.

"This is pretty much the start of the Clutha River," Mr Nicolson said.

By this he means water effectively begins to flow after Roxburgh Dam.

"Before this it’s lakes and dams. Contact have been putting a lot of young salmon in. So this is where they’ll end up."

On a basic level the dam works by blocking the river’s water, creating Lake Roxburgh.

The water falls nearly 46m on to turbines,  turning them and powering the generators,  which produce electricity.

An average of 510cu m  of water passes through the dam every second.

This generates enough electricity to power 300,000 homes  a year.

Contact’s Clyde-based head of hydro generation, Boyd Brinsdon,  says most days Otago and Southland’s electricity demand is met by renewable sources.

"Every time 100 people turn a light switch on or off, then these stations will follow that load really closely. Every few seconds they’ll adjust their output, because that’s what you have to do on an electricity system.

"The good thing about these hydro units is, if you push the start button, they’ll start and ramp up to full load in about three minutes."

When flows are low, however, electricity needs to be imported from the North Island, he says.

"The Achilles heel is you can’t be sure you’ll have the water, which is why storage at Lake Hawea is so valuable."

The building’s large machine hall provides a glimpse into the dam’s past.

Its mix of pastel colours and generator hardware makes it look like a 1950s Nasa centre.

In the early days the plant had 42 employees.

Now, with the arrival of new technology and the selling of the Roxburgh Hydro Village, it needs just five permanent staff plus contractors and cleaners.

Over time, much of the machinery has been replaced.

Mr McLean says a major part of his job in the past 15 years has been helping with the many refurbishment projects.

Mr Brinsdon says  the eight large turbines, however, are original, having  been at the dam since its creation.

"You can see that they’re starting to wear, so that’ll be another big project over the next 10 years."

But  the structure as a whole will have a long lifespan, he says.

"You hear these rumours about how a dam can only last 100 years, but we don’t believe that’s true."

Mr Nicolson echoes this sentiment.

"Oh, it could be here for 100, 1000 years. Long after I’m gone."

jono.edwards@odt.co.nz

 

Dam facts

Commissioned in 1956.

• All eight turbines operational in 1962.

• Powers 300,000 homes a year.

• Average water flow of 510cu m a second.

• 320MW capacity.

 

 

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