WAITAKI SCHEME

Evening Post, Volume CXVIII, Issue 34, 9 August 1934, Page 14

WAITAKI SCHEME

SOUTH ISLAND POWER

NEARING COMPLETION

BUILDING IN A EIVEH

The programme for hydro-electric development in the Dominion will bo advanced a long step when, probably before tho end of the year, the Waitaki River system is joined into the South Island chain —Coleridge, Waitaki, Waipori, with Waitaki the greatest of them all.

The decision to develop power from the waters of tho Waitaki Kivcr was made only after long investigation and long district and political squabbling and wrangling. North Canterbury insisted that the Waimakariri River1 was tho ideal location —absolutely nothing could touch it; it was Nature's ideal offering to tho engineer, and so on. South Canterbury laughed the idea of Waimakariri right out of (South Canterbury's) consideration; why pass Lake Tekapo, so obviously superior that Waimakariri advocates must surely \je blind? Otago had not so much to say, being occupied with the idea of developing Waipori independently of the Government, a plan not fulfilled, for later Waipori became a State station. The Public Works Department concerned itself as little as possible with politics and kept on investigating. Its decision was that the -Waitaki offered most, and serious work was done over a Jong period, commencing in 1926, in investigating the possibilities of a dam site above Kurow, 40 miles or so back from Oamaru. General plans, then detailed plans, followed, the construction work was commenced in 1928, and to-j day the work is taking almost final shape. Each liydro-electric development differs- from the rest, and particularly has that been so in tho New Zealand stations. Entirely different sets of problems, duc-ito differences in country contours, of rock formation; of river flow, consistent or violently fluctuating, and to tackling new problems in new ways, have given tho engineers at Mangahao, Arapuni, Waikarcmoana, and at Lake Coleridge and Waitaki, in the South Island, not so much electrical problems as problems of civil engineering, for though each station has speciallydesigned electrical equipment, it has been the civil engineer who has been tho big chief in determining station development. . FED FROM THE ALPS. The source of the Waitaki River is far back in the eastern slopes of the Southern Alps, in the snowiiolds and many glaciers, including Tasman, from which the three lakes, Ohau, Pukaki, and Tekapo are fed. The outlet streams from these lakes, which serve as a magnificent natural storage, meet in a common point, and in addition to tho lake supply the Waitaki has a drainage area of: about 3000 square miles above tho darn site. It is a very big river. The lowest flow recorded was 3000 cubic feet per second, but the usual minimum is 5000 cusecs, say, 31,000 gallons per second, a lot of water. The record flood flow was 85,000 cusecs, but there may be a greater flood, and tho engineers have got ready for it, for the spillway at the dam can take care of a flood of 190,000 cusecs. Tho dam is 1730 feet long, founded on solid rock and butted into solid rock at each end. It is not a particularly lofty dam, about '70 feet, as compared with Arapuni's 140..ic0t, 'but it catches up on length, for it is almost three times as long as the Arapuni dam. The powerhouse is built in the dam wall itself —at Arapuni it is over a mile away, at Mangahao it is miles from the dams, and at Waikaremoana it is at the bottom of a steep valley and the. lake is at the top. WHAT THE ENGINEERS FACED. To make possible the building of the Arapuni dam it was necessary to lead the Waikato Kivor past the working point by a diversion tunnel —itself an engineering work of real magnitude — driven through solid rock; the whole flow ran through the tunnel, leaving the dam site dry, or what an engineer calls dry; at any rate,.- dry enough to lay concrete. The country about the Kurow dam site is comparatively flat and the river could not be diverted. Instead, the river was dealt with in sections, by means of three great coffer-dams, behind the barrier of each of which excavations to bedrock were made, concreto poured, and the dam section built up, with sluices to let the river through, not past, when tho third section came to be built.

It was this method of attack that differentiated Waitakl from all the other hydro-electric developments in New Zealand. At Arapuni stubborn difficulties were fought all the way before the Waikato Biror was controlled; at Coleridge a ticklish, almost daring, course was followed to tap the lake, by a. tunnel driven through a hill and up through the lake bottom; at Mangaliao there wero the complications of devastating floods; at Waikarenioana there is the possibly unique- problem of sealing the great leak face. Waitaki' went ahead apparently straightforwardly, but the engineers wero well aware when they drew their plans of the difficulties and the risks of building actually in the stream course. Extreme caro in planning for all possibilities, andI—they1—they admit it —good flood fortune, saw the work past the risks with no more trouble than \had been prepared for. SC^ME FIGURES. If figures convoy much the Waitaki figures will amply bear out that the work has been on a magnificent scale. Bound about 50,000 tons of cement have been used, half a million tons of spoil have been shifted, and five million superficial feet of timber have beon used, mainly in boxing,for concreto work. A special railway had to bo built for handling materials to the site, and about the dam there was a network of conveyer lines. Much of the gravel and sand for the concrete camo from the working site, whereas (ilscwhoro it had, as at Arapuni, to be brought from considerable distances. The lake will extend back for about six miles and an incidental expense was the building of a bridge, costing £15,000, to provide access to back, country land, the former road being cut, off by the lake. TURBINES GENERATORS. The station will commence to operate with two turbines, each developing 20,000 horse-power, but eventually tho development' will reach, according to present plans, 100,000 horse-power The turbo-generator is in two sections. Tho turbine captures the power of the water; the generator transforms that power expressed in horse-power, into electrical power, expressed in the magical letters "k.v.a." Only engineers really know how. to explain for popular consumption what those letters mean. Anyhow, the Waitaki generators will each develop continuously 16,660 k.v.a. at a. 90 per cent, power factor, which is still more magical and had better bo left.at that.

Tho turbines, coupled direct to the generators, will run at 125 revolutions per minute. Each is over thirteen feet in diameter and weighs 21J tons. The generator is bigger gd.ll, about thirty