The idea to build a hydroelectric power station at Lake Coleridge came during a time when New Zealand was beginning to take electricity use seriously.
During the 1880s and 1890s, growing interest in electric power led the Christchurch City Council to consider building a hydroelectric power station on the Waimakariri River. However, this never came to fruition thanks to an uproar from ratepayers following the passing of the City of Christchurch Electric Power and Loan Empowering Act 1902. The Act authorised the Council to raise costly loans to construct and maintain the proposed Waimakariri station, which placed the financial burden squarely on the Christchurch City Council and ultimately the ratepayers. The real sticking point was that any outlying areas that tapped into the power supply would not pay the same price, and so the project was brought to an indefinite halt.
At the end of 1903, American engineer L M Hancock produced a report for the New Zealand Government that proposed an alternative plan that would cause less controversy and provide more benefits. That plan was for the construction of a hydroelectric power plant at Lake Coleridge.
While the lake sits just outside our District’s boundary, northwest of the Rakaia River, the success of the hydroelectric power plant there was not just a win for Christchurch and Selwyn District. Ashburton benefited from Coleridge too, alongside all of Canterbury.
The work begins
Back in 1901, a party of seven journeyed from Christchurch to inspect Lake Coleridge and measure its usability for hydroelectric power generation. The group concluded that while it was possible, a hydro station at Coleridge would “involve a very considerable expense” and that diverting the Harper and Wilberforce Rivers to provide a greater flow of water would be costly and difficult.
The idea was shelved until Hancock’s report in late 1903, which managed to convince the Government that Coleridge was the best spot for a power station close to Christchurch. The Council expectantly waited for the Government to make a start, but it would be another seven years before the project kicked into gear. Following another series of bureaucratic hold-ups, a party was finally sent to Coleridge in late 1910 to prepare the site for the proposed works.
According to Rosemary Britten’s book on Lake Coleridge, the area was “busier than it had ever been, or is likely to be again” between 1911 and 1914. Coleridge power station was built largely by hand, and steam shovels were relied on for some of the heavier work. The construction effort was immense; there were up to 400 men working at one time, yet the sheer volume of manpower did not prevent problems from arising during those busy years.
Lake Coleridge power station was the first in the world to be built entirely on glacial moraine, which led to some problems and mistakes.
These problems are best explained by Rosemary Britten: “The powerhouse foundations were made with a deep concrete block for each turbine unit and shallower foundations for the rest of the building, all capped with a thin layer of concrete. When the machines were started, concrete cracked, foundations subsided to varying depths, and the whole system became out of alignment. This caused trouble for ten years, until pressure-grouting with many tonnes of cement under the floor finally consolidated the loose shingle and obtained a solid foundation.”
Loose gravel made work in the tunnel and surge chamber “difficult, slow and dangerous.” The pipes crept up and down as much as 15cm daily due to temperature fluctuations, which caused the anchor blocks to become dislodged. This caused delays, as they had to be redesigned to include expansion joints.
On 1 September 1914 the station’s tunnel filled with water for the first time, unexpectedly and accidentally. An unusually strong gale took off the top two layers of the bag dam, which kept the water out of the intake construction work. Waves whipped up by the wind poured down the tunnel and filled the surge chamber to lake level. It was found that the tunnel leaked so badly that work was held up in order to fix it.
Success at last
The opening ceremony of the Coleridge power station was held on 25 November 1914. Prime Minister William Massey opened the valve which let the water flow into the first turbine, which heralded the conclusion of a long and drawn-out project.
Rosemary Britten states in her book that Coleridge “was the first New Zealand scheme built under the Aid to Water Power Works Act 1910. As well as being the first in the world to be built on such an unstable foundation, the powerhouse itself was the first large building in New Zealand to be constructed entirely of reinforced concrete. It was also first in the world to introduce air-vented draft tubes on the turbines.”
Outages and supply cuts plagued the early days of Coleridge. Some adverts in the Ashburton Guardian during the early twenties advertised gas lamps with the tagline “don’t depend on Coleridge!” Eventually, failures became less frequent and the system became more reliable.
Coleridge was opened with three operational turbines and had nine by 1930. Since then, four have been decommissioned. However, Coleridge’s power output is much higher today than it was in 1930 thanks to computerisation and modern redesign.
Sometimes it’s easy to forget that there are vast systems of infrastructure that make our lives easier. Next time you flick on a light, put the kettle on or sit down to watch TV, remember that it’s thanks to the hard work of many experts, past and present, from all sorts of different fields.
By Connor Lysaght
Unless otherwise stated, photographs and research materials on this page are owned by the Ashburton Museum & Historical Society Inc. This post was modified for this blog and was originally published in the Ashburton Guardian, 15 January 2022.
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