KAITAWA WILL SOON HELP N.I. POWER SUPPLY

Grey River Argus, 12 April 1948, Page 8

KAITAWA WILL SOON HELP N.I. POWER SUPPLY

The first unit of the new Kaitawa hydro-electric station at Lake Waikaremoana is already running on test and will probaly soon be contributing its 16,000 kilowiatts to the North Island power supply. The bringing into use of this unit and of another which is expected to' be ready later this year, will be the culmination of a hazardous project, involving tunnelling through the rim of the lake, which was first begun in 1935. The major tunnelling and the structural work at the power house have been completed for several months, and work recently has been concentrated on developing an mlet from the lake to the tunnels and in making the final fittings to the turbine and generator. Water has been by-passed around the turbine, through a release valve. The full flow is now available in the turbine but the unit has only been run without power load so far. Kaitawa may be described as a generating unit deriving its vzater power from a lake set above it and on the other side of a thin rim of broken slip fromation. Previously, the lake has overflowed into the Waikare Taheke stream or seeped into the stream lower down -through fissues in the rim. This water has been used for two other power stations, Tuai and Piripaua, on the hillside below the Kaitawa site. ’TWIN TUNNELS Now twin tunnels, merging into one at the lake end, have been driven through the rim to enable the lake water to be used at Kaitawa in addition to the other stations below. The last move, will be the sealing of the leaks in the lake, so that there will be no normal outlet , from the lake, except the tunnels, and all the water in it will then be available for the three power plants. The lake end of the tunnel was taken to a point 200 feet Inland and about 50 feet below *he normal level of the lake. The surroundings were excavated and faced with concrete in step formation, making a strong inverted cone about the inlet, and then began the removal of the strip of land separating the inlet from the lake. Major problems in this work were the increasing ‘low of water from the lake, which was taken out through the tunnel and the one completed penstock, and a number of huge boulders encountered in the excavations. These had to be broken by explosives. The last stage was the excavating of a final channel to the lake with a dragline. While this channel is not yet to its full depth there is a free flow of water from the lake into the tunnel. The tunnel inlet is now established at 1960 feet above se-" 2 level, about 30 feet below the present level of the lake, and the channel will be taken down accordingly, giving the hydro-electric authorities control over that additional depth of water. So far, this can only be passed through one of the two tunnels into which the main one divides a short distance from the lake. The other tunnel is still blocked by a gate to allow work to be completed on the pipe from its outer mid to the second turbine in the power house. Work has also begun on the final stage of the scheme, the sealing of the natural leaks in the lake. This will be done by covering the affected areas, which have be* 1 ” located by a diver, with successive layers of fairly coarse stone, gravel, sand and clay. The seal then being protected from wave action by a layer of rocx. In most cases this will all have to be done under water, but the fall Oi the lake has exposed a number ,of the leakage the work. _______