BIG POWER SCHEME

Grey River Argus, 4 December 1940, Page 8

BIG POWER SCHEME

Canterbury Extensions CHRISTCHURCH, December 3. The construction of a dam and hy-dro-electric power station at Lake Tekapo is the first step toward the complete harnessing of the latent power in the lakes and tributaries of the Waitaki river, said Mr. T. G. Beck, district engineer to the Public Works Department, in an address to the Christchurch Businessmen’s Club yesterday. Mr. Beck explained that the principal projects at present in hand for the development of hydroelectric power in Canterbury were the Tekapo scheme and the combined irrigation and power scheme which involved the diversion of waters from the Rangitata across the plains to the Rakaia river at Highbank. The normal flow of the Waitaki river, with the measure of storage provided by the dam at Kurow, was sufficient to operate two of the five generators for which the Waitaki station was designed, said Mr. Beck. To operate the five machines it was necessary to provide for the storagof flood water. Each machine required 3.000 cubic feet of water a second, or 100 times the flow of the Avon river. The first step in the scheme for such storage was the development at Tekapo. This would enable a given quantity of water to be used twice over. Not only would it provide 25,000 horse power for the driving of the turbines of the Tekapo station, but the same water would be sufficient to operate one of the five units at Waitaki. The development, of similar schemes at the other lakes was being kept in view, but at present it was no more than a paper project. Mr. Beck described the method to be used in the driving of the 6,000 ft. tunnel ’from Lake Tekapo to the power station on the river-bank, a method successfully used overseas, but new to New Zealand. The tunnel would shortly circuit the river across a bend in Which there was a 90ft. loss of head. The construction of a dam would block the natural outlet and raise the level of the lake a maximum of 12 feet.

The tunnelling would be done from within huge cast-iron cylinders, which would be pushed forward by hydraulic jacks. These shields were now under construction in the department’s workshops at Temuka, the jacks were being made in Auckland, and other work was being done in Christchurch. There would be 26 100-ton jacks in each shield, and by operating only half their number the shield could be made to , turn either vertically or horizontally. As the shield advanced it would leave behind a cylinder, inside which a ring of concrete blocks would be assembled. The jacks would obtain their purchase for the next advance of the cylinders from the assembled ring of blocks. These cylinders would enable three feet of tunnel to be completed from each end in an eighthour shift, said Mr. Beck. This would be 18 feet a day, which was extraordinarily fast for the conditions. Everything would be mechanised. Pneumatic picks and spades would be operated inside the shields at three levels, and the spoil would automatically fall through chutes on to conveyor belts, which would carry it to the line of railway trucks. Each concrete block, of which there were 13 to the complete circle, weighed 1,900 lb., and they would be lifted mechanically from the trucks by means of a rotating and expanding arm. As an example of the many little difficulties which could cause trouble, Mr. Beck mentioned the bolts, two inches in diameter which will be used to join the blocks at the point of highest bursting pressure. It was estimated that 32,000 lb. of "pull would be required on each bolt, but before the necessary spanners were constructed some estimate had to be made of the counteracting friction on the thread of the bolt and the bolthead on its washer. As this was not predictable with any accuracy, it was decided that practical experiments would have to bb made. The Canterbury College Engineering School had come to the assistance of the department in carrying out these experiments.