Manapouri Power Station

Machine hall in the Manapouri Underground Power Station.
Machine hall in the Manapouri Underground Power Station.

Luxuriant rainforest reaches down from mist-shrouded peaks to the edge of mirror smooth lakes and fiords. The only sounds are birdsong and tumbling waterfalls.
According to Maori legend, demi-god Rakaikaitu carved out the great lakes of New Zealand’s South Island, including Manapouri and Te Anau, with his ko, or digging stick. The Maori named the area Te Wahipounamu, “place of greenstone”. Tribal expeditions journeyed south in their waka, or canoes, in search of the semi-precious greenstone (jade).
The geological explanation for Fiordland is glacial action eroding the steep sides of the granite mountains over the last two million years. The last ice age ended just 14,000 years ago.

Waterfalls and luxuriant rainforests are shrouded in the mist of New Zealand's Lake Manapouri. A road leading into the dense forestry is one of the most expensive built in New Zealand, leading to the largest hydroelectric power station built there.
In 1990, Fiordland National Park was declared a World Heritage Area. It’s awesome majestic scenery, a slice of Middle Earth – and the last place you would expect to find a power station.
It’s also a place of high rainfall, with 200 rain days and between 179 and 306 inches of rain a year. It’s for this reason that engineers chose Lake Manapouri as the site for a hydro power station. That and the lake’s elevation 583 feet above sea level at Doubtful Sound, on the west coast. This eliminates the need for a high dam; instead, the water can be channeled downwards by gravity, and used to harness energy.
Imagine the foresight and vision of surveyor P.S. Hay, who stood in this wild place in 1904, and envisaged such a hydro scheme. Technological limitations meant the scheme could not be seriously explored until the late 1950s. Then, the New Zealand government invited Consolidated Zinc (now Comalco) to investigate developing a power station to generate power for an aluminum smelter. Work on the power station, at Lake Manapouri’s West Arm, began in 1963.
It would become New Zealand’s largest hydroelectric power station. The project took eight years to complete, in the harshest conditions. Controversy erupted over the impact the power station would have on its pristine surroundings, but in the end it was a battle in which both sides could claim victory.
Today, Manapouri Underground Power Station is a tourist attraction. More than 40,000 people a year take the boat trip over Lake Manapouri to marvel at the power station, and are then bussed over Wilmot Pass for a refreshing cruise on the still waters of Doubtful Sound.

A view from Wilmot Pass into Doubtful Sound. A ship was moored in the sound during the construction of the power station.
Meridian Energy, the power station managers, invited The Chief Engineer to visit the heart of the underground station, so see how it functions in practice, and to meet the men and women who work in this remarkable environment.
The day started at 5:30 am at Lake Te Anau. After a quick coffee and breakfast, it’s a 15 mile drive to Pearl Harbor at Lake Manapouri, arriving in time to catch the 6:45 am “Z boat”. It’s so called because power workers can catch up on their “Zs”. As the boat chugs across the still dark waters of the lake, recumbent forms say not a word as the sun comes up revealing the looming shapes of mountains on this most scenic of commutes.
At 7:45 a.m. we arrive at West Arm, where Meridian Energy team leader John Twidle greets me. Rising up on the west, native forest and swirling mist surround the power station – what you can see of it. Massive cables span the bay to link up with towers on the east side. Three-foot diameter colored balloons are attached to the cables. They are a visual warning device: a few years ago, a helicopter slammed into the cables, killing five.
All vehicles run on diesel fuel. John takes me in a pickup to the main control room, where he signs me in and briefs me on the station’s history and operation.
Amid the display of photographs showing the project’s construction are cartoons and even some poetry.
One visitor was Gillian Anderson, of The X Files fame, whose signed portrait is on display along with the words, “Electricity: I believe in it!”
It’s a satisfying and stimulating place to work, says John Twidle. He still finds it amazing, likening it to a James Bond movie set: a mountain in a remote location opening up to reveal a massive power station.
“ The solution was quite unique, to actually harness that energy by placing the power station 750 feet underground. It was a huge challenge to build it, it’s actually quite phenomenal just to conceive it when you consider the technology of the day and people sitting in the middle of Fiordland. How do you imagine something like that? It’s not the first sort of thing that would spring into my mind.”

With rain falling 200 days a year, waterfalls and lush fern thrive in the environment. An average between 179 and 306 inches of rainfall a year makes this place ideal for hydro power.
Construction required pinpoint accuracy. In an era before high-powered computers or GPS navigation, engineers used analog calculators to precisely measure where tunnels would meet. “When they drilled the tunnel from one end to the other, they had another tunnel team drilling in the opposite direction, and they met in the middle of the mountain, and I think they were something like five eighths of an inch apart.”
Work was dangerous. “Quite a challenge, not just from the power station point of view but the logistics point of view of actually getting yourself into position to build a power station. And then there’s the weather – the reason the power station is here is because it rains a lot. And the sand flies.” These pesky insects plague both tourists and locals alike.
Just getting to the site was difficult. “We’re a long way from anywhere, we’re a long way from what you would see as civilization, there are no towns here. So everything had to be built.”
Workers built a road over Wilmot Pass, linking West Arm with Deep Cove in Doubtful Sound. In its day, this was the most expensive road, mile for mile, in New Zealand.

Commuters to the station arrive by boat after an hour's ride, and make the return trip after their shift ends.
A former luxury passenger liner, the Wanganella, was moored in Deep Cove to house workers. Machinery was custom made especially for the power station. Major components were shipped across the Tasman Sea, and workers then had to muscle them up the hill and down to the power station site.
They built another camp at West Arm, and a whole village on the other side of Lake Manapouri. More material was barged across the lake. At its peak there were 200 workers based where the present day township of Manapouri now stands.
A huge underground cavern had to be hewn out of the solid granite mountain, 750 feet underground. Access and service tunnels and shafts had to be dug, as well as a four-and-a-half mile long tailrace tunnel to Deep Cove.

One of the tunnels bored through solid granite to make the vision of surveyor P.S. Hay come to life.
Machinery had to be backed down the main access tunnel, taking up to seven hours. If someone brought something down in the wrong order they had to take it out again, because there was nowhere to store it.
Workers number 22 different nationalities, many from Yugoslavia and Italy, because they had experience in mining and drill-and-blast construction methods. As they worked underground, water poured from the rock face and had to be continually pumped out. They bored holes for explosives, placed the charges in darkness after the lights were switched off for safety, and retreated for the blast.
John Twidle describes the challenges: “Once you start drilling underground, there’s the danger of rock falls, and the water coming in…you need to actually start pumping this back out, and you end up in a situation where you are pumping water not just up and over, but you’re actually pumping it up.”
Earthquakes are yet another hazard. New Zealand, like California, is on the boundary of two tectonic plates. Fortunately, Meridian Energy explains, earthquakes are not noticeable because vibrations move through the solid rock.

Meridian Energy team leader John Twidle looks over the floor of the Manapouri Power Underground Station, a phenomenal achievement not only to conceive of but to build as well.
At 9:00 a.m. it’s time to don full PPE (personal protective equipment) and I meet tour safety co-coordinator Susan Cody. It’s a dangerous working environment, and care is required at all times.
We jump in the pickup and drive to the entrance of the main access tunnel. It’s 22 feet wide and 6,700 feet long, and descends at a gradient of 1:10. This is the only place in New Zealand where vehicles drive on the right, but with the steering wheel on the right, too; this lets you tell how close you are to the rock wall.
We reach the viewing platform. Here there is a commanding view over the Machine Hall. It’s 364 feet long, 59 feet wide, and 127 feet high. The floor is 750 feet below the surface.

An access tunnel road leads 6,700 feet, nearly three-and-a-half miles, down through the mountain into the power station.
Now you can get a good idea of how it all works, although you can see only part of the machinery, explains Sue. “Where we’re standing at the moment overlooking the Machine Hall, standing on the viewing platform we’re 13m (42 ft) above sea level. The floor we’re looking at which is called the generator floor, that’s 6m (19.6 ft) above sea level; the center point of the penstocks where the water is actually coming in is 3m (9.8 ft) below sea level, and then as it leaves the station, for the first kilometer it actually goes quite deep, quite drastically 30m (98 ft) below sea level, and then for about 7 km (11 miles) it just gradually keeps going down.
There are seven machines; each has seven turbines, and seven generators. The blue machines we are looking down on from the viewing platform are the exciters. These boost the generators.
A model explains graphically how the station works: the water comes from the lake via intake gates, pours vertically down large pipes called penstocks, spins the turbines, then goes out to sea.

Control gates at Lake Te Anau regulate water flow into Lake Manapouri. Careful management of the lake is required to avoid damage to the shoreline.
Machinery came from all over the world: turbines from Harland in Scotland; generators from Siemens in Germany. Exciters were also originally from Siemens, but three years ago were replaced with GE versions. These models have no carbon brushing system, so dust in the air is no longer a problem. Cranes and transformers are from Savigliano, of Italy, and switchyard components were made in England.
We descend the stair to the machine hall floor, where engineers are conducting “drop load tests”. These measure how the generator performs when the load is suddenly varied.
Manapouri Underground Power Station is one of the few in the world capable of a “black start” – where override systems enable it to be powered up virtually instantaneously after a shutdown.
Everywhere machinery is massive, with huge spanners, giant nuts and bolts. Safety is paramount, and danger signs and emergency equipment are placed throughout the station. The temperature, about 45 deg in the tunnel – nice for cellaring wine – remains in the mid-70s in the machine hall, but climbs higher if output is increased.

Power station tour safety co-coordinator Susan (Su) Cody. A dangerous working environment such as this requires care at all times.
Now it’s time to put in ear plugs as we descend further down to the turbine floor, which is actually a foot beneath sea level. We capture a glimpse of the massive turbine. This is raw power: It’s spinning at 250 revolutions per minute, turning a set of magnets, the rotor. This is contained within a stationary set of windings consisting of 24 coils, the stator. Action and reaction create electricity (electro-magnetic flux).
Each generator produces 133MW of power – that’s about 178,000HP, or the same as 178 Formula 1 racing cars, or 1,780 family cars.
Generators produce electricity at 13,800 volts. Transformers – one for each turbine – convert it to 220,000 volts, then cables take it up all the way to the switchyard – three cables for each machine – and out through the power lines to the national grid. Homes in New Zealand use electricity at 230-240 volts AC, not the 110 volts used in North America and Europe.

The machine hall: Seven generators are housed in the massive underground cavery, 750 feet below the level of the lake. The hall is 364 feet long, 59 feet wide, and 127 feet high.
On the penstock gallery we are 20 feet below sea level and beneath the massive penstocks themselves. It is incredible that above us water is rushing into the turbines at a rate of 17,657 cubic feet per second.
The “head” of water produces the power. The surge chamber rises and falls depending on how much power is being generated. The higher the water in the surge chamber gets, the lower the relative head.
Once the water has produced all the power, it is channeled through the draft tubes and out the two tailrace tunnels to Deep Cove.
John Twidle then joins us and takes me up the elevator to the control station. At one level we stop and explore a tunnel bored into the solid rock. There are other ways out, but taking the stairs – or rather, climbing ladders 750 feet up to the top is for emergencies only and not for the faint-hearted.

A massive stator in the stages of being assembled. Magnetic coils produce the electricity.
Manapouri was fully commissioned in 1972. However, it soon became clear it could not generate power at peak levels because of greater than anticipated friction between the water and the tailrace tunnel. Peak capacity remained at 585MW, instead of the 700MW hoped for. The solution was to build a second tailrace tunnel.
This has increased output significantly, says Twidle. “The idea was basically like to put a twin exhaust pipe in a car. If you can do that you can free flow the station. The idea is to get the water in and through and out in the most efficient way.”

Each turbine revolves at 250 rpm, producing 133MW of power.
The tunnel was built from 1998 to 2002. A massive 75-foot-long tunnel-boring machine (TBM) drilled through the rock. As a result, the power station generates more power from the same amount of water – enough to power 64,000 homes. It also eliminates emissions of 376,000 tons of CO2 a year.
For the second tailrace tunnel, about three million cubic feet of rock was excavated. At Deep Cove it was shaped to fit the natural contours of the land and replanted with 235,000 native plants.
A huge issue has been the impact of the power station on the environment. Original plans were to raise the level of Lake Manapouri by at least 100 feet.
As construction proceeded in the 1960s, concern grew that this would harm the environment. Lake Manapouri’s wooded islands and fragile shoreline beech forest would disappear.

Alan Bulling, project manager, is responsible for conducting the tests necessary to ensure the station's efficiency.
Pressure swelled, and a petition collected more than a quarter of a million signatures (out of a population of less than three million). It turned into a major election issue, and was a decisive factor in the defeat of the government. In 1972 the new government declared the lake level would not be raised. Electricity would be produced to power the aluminum smelter at Bluff 100 miles away in the far south of the country, and to feed the national grid, with lakes remaining at their natural levels.
The Guardians of Lakes Manapouri, Momowai, and Te Anau was formed to manage lake levels. This is done through a delicate balancing act of control gates and channels between the lakes, and monitoring power generation. If lake levels are too low, beaches lose sand and gravel; too high, shoreline vegetation drowns.
Twidle is pleased at the minimal impact the power station has on the landscape, the result of the protest action by environmentalists.

A memorial commemorates Terence Smith, killed when the road over Wilmot Pass was built. Sixteen workers lost their lives during the power station's construction.
“ Thank God they succeeded, to be honest. One of the more extreme concepts had Lake Manapouri being raised, to such an extent up to Te Anau so it would have been just one big massive lake. Manapouri is a very pretty lake. Therein is the start of our environmental movement in New Zealand. The Guardians of the Lake were formed and they are still active today and we report to them from an environmental viewpoint and they are our watchdog. They have a lot of sensible guidelines in place and we at times have to really work hard to meet those guidelines. But they are all doable…It’s about trying to make the lake perform as if we weren’t here.”
The power station was a finalist in the British 2002 Financial Times Global Energy Awards.
About lunchtime, Sue takes me over Wilmot Pass to Deep Cove and Doubtful Sound – named by explorer Captain James Cook in the 18th century because he was doubtful he would find his way out again (he did). We gaze down on the sound, rays of sunlight dancing on the water – and I inspect the memorial marking the spot where surveyor Terence Smith, a husband and father, was accidentally killed in 1965, at the age of 25.

The road from Deep Cove to the power station was built specifically to serve this purpose. At the time, it was the most expensive road, mile for mile, in New Zealand.
It’s a reminder of the dangers the brave men who built this power station faced daily.
In the cover, we look at the place where the Wanganella was moored, and then at the outlet of the two tailraces, almost hidden by the bush line and the deep green water of Deep Cove. The first tailrace tunnel is about 28 feet wide and three feet above sea level; the second tunnel is slightly higher. Water is discharged at a controlled rate, so as not to damage rare black coral in the cove.
In this setting it seems only natural that human achievement should merge harmoniously with Nature: her power harnessed, but respected, never tamed.

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