The day we shall never forget
Trip Start Oct 18, 2010
72Trip End Feb 20, 2011
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Where I stayed
Invercargill to Te Anau
Written Monday 10th January 2011
Saturday was a wash out, we returned to the Catlins, but lost the sun and met the rain again. The Catlin hills are great but we never saw them on a clear day. We did have a very relaxing walk in the town park which is very well kept and a joy to see. Town councils in UK should take note. That night the skies cleared and the wind dropped.
We left Invercargill at 0900 on Sunday, glad to leave this town behind us. We had a lovely drive under clear blue skies and decided to drive into Manapouri to book a trip for the next day to Doubtful Sound
The trip falls into four parts:
- Trip across Lake Manapouri of about 50 minutes at 40knots
- Journey by coach down 200metres below ground into a massive man-made cave to view a hydro-electric power plant, (not every-ones cup-of-tea but a truly magnificent example of mankind’s technical prowess)
- 21km journey by coach over the most expensive road in NZ (10$ per centimetre) to Doubtful Sound.
- 3 hour trip around Doubtful Sound, probably the most beautiful natural place on Earth.
No words I can write can possibly describe the wonderful views we experienced over our 8 hour trip
Captain Cook named it “Doubtful” because he doubted he would get his sailing ship out if he sailed in, he was probably right.
Today we have had a quiet day strolling around the lake at Te Anau in brilliant sunshine and 24/28deg’
You can skip the next two paragraphs if you are not keen on Geography or power stations.
Strictly speaking Doubtful Sound is a fjord, that is to say a sea inlet formed by glacial action during the last ice age. All the lakes in this area are also drowned glacial valleys. Its classic glacier country; steep-sided valleys, truncated spurs and hanging valleys
The power station.
There are seven hydro-turbines driving alternators, each delivering 135Megawatts of power. The alternator output voltage is 13.8kilovolts stepped up via transformers to 225kilovolts for the line transmission out of the station. There are four sets of three-phase lines leaving the station, similar to Didcot.
This requires a lot of water to fall from a great height. They use a 180metre head of water, (Lake Manapouri to sea level), consuming 18 Olympic size swimming pools of water every minute. No chance of water shortage the feed is from two lakes with a combined surface area of 600square miles, with maximum depths of 400metres, the lakes topped up by 9metres of rain per year falling on all the surrounding mountains, total catchment 3000 sq' kilometers. That’s a lot of water. An information board by the lake informs me that if the lakes fall to “low” it only requires three days of rain to top them up
Just to make sure that the turbines receive water with enough force they take advantage of the venturi effect. The water intake for each turbine is 3.6metres diameter, close to the turbine this is reduced to 2.9metres. My mathematics is not up to calculating the speed gain on a 180metre head, it must be awesome. The power station guide tells me that standing next to the venturi outlet is deafening even wear ear-defenders. I believe him, a fact sheet gives the rate as 80 cubic metres per second.
We viewed the tail race as the water from the turbines empties into Doubtful Sound via two huge tunnels. I would gauge the water to be travelling at 20 knots but it is hard to judge. At any one time there is 150million gallons of water within the station complex.
This is a perfect power-generation system, it takes nothing from nature, produces no pollution and with its seven sister stations in this area produces 25% of NZ power. (The only environmental loss was the river that drains Lake Manapouri into Doubtful Sound slowed down a lot). The stations are all un-manned being controlled, via microwave links, from a central control room in the middle of south island
Tedious factoid, 3,200 tons of explosive were used to build the power station and all its tunnels, both road and water.
The road was so expensive because all the power station kit was brought in via Doubtful Sound, the heaviest item close to 300tons, hence a very strong road rising 600metres above sea level.
I Loved It!!
The lady wife was tolerant but unimpressed. Fortunately there were two american power station engineers on the trip so we happily talked about alternators and exciter circuits for 20 minutes. Great.