HARNESSING THE LAKES

Nelson Evening Mail, Volume LXXIII, 5 December 1940, Page 9

HARNESSING THE LAKES

ELECTRIC POWER FROM TEKAPO The construction of a dam and hydroelectric 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. Mr Beck explained that the principal projects at present in hand for the development of hydro-electric 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. NEW TUNNELLING METHOD He described the method to be used in the driving of the 6000 ft tunnel from Lake Tekapo to the powerstation on the riverbank, a method successfully used overseas, but new to New Zealand. The tunnel would shortcircuit 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 eight-hour shift, said Mr Beck. This would be 18 feet a day. which was extraordinarily fast for the conditions. “EVERYTHING MECHANISED” 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 19001 b. and they would be lifted mechanically from the trucks by means of a rotating and expanding arm.