FACING DIFFICULT PROBLEMS

Timaru Herald, Volume CXXXVIII, Issue 19941, 27 October 1934, Page 7

FACING DIFFICULT PROBLEMS

Nature, which has been very beneficent to New Zealand in the matter of soil and climate has also provided in upland waters very favourable sources of power for the helping of industries in town and country for public and private lighting and for adding other comforts to life. Some of the streams and lakes in the high country promise in the days of full development—the cheapest power in the world if the requisite load is available. This may come from the development of special industries needing large power or from an increase of population requiring current for many purposes.

PECULIAR NATURE OF WAITAKI RIVER

Method of Attack Described

Each hydro-electric development differs from the rest, and particularly has that been so in the New Zealand stations. Enetirely different sets of problems, due to difference in country contours, of rock formation, of river flow, consistent or violently fluctuating, and of tackling new problems in new ways, have given the engineers at Mangahao, Arapuni, Waikaremoana, 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 specially-designed electrical equipment, it has been the civil engineer who has been the big chief in determining station development. The Waitaki 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 the engineers have got ready for it, for the spillway at the dam can take care of a flood of 190,000 cusecs.

The dam is not particularly lofty, about 120 feet, as compared with Arapuni’s 140 feet, 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 Mangahao it is miles from the dam and at Waikaremoana it is at the bottom of a steep valley and the lake is at the top.

To make possible the building of the Arapuni dam it was necessary to lead the Waikato River past the working point by a diversion tunnel—itself an engineering work of real magnitudedriven 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. It was this method of attack that differentiated Waitaki from all the other hydro-electric developments in New Zealand. At Arapuni stubborn difficulties were fought all the way before the Waikato River 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 Mangahao there were the complications of devastating floods; at Waikaremoana there is the possibily unique problem of sealing the great leak face. Waitaki went ahead apparently straight-for-wardly, but the engineers were well aware when they drew their plans of the difficulties and the risks of buildactually in the stream course. Extreme care in planning for all possi-