MANGAHAO HYDRO-ELECTRIC SCHEME.

Manawatu Herald, Volume XLIV, Issue 2385, 28 January 1922, Page 4

MANGAHAO HYDRO-ELECTRIC SCHEME.

(Concluded from page 1.)

electric motors auxiliary to the construction. Part of it is used to drive induction motors which operate, with a belt drive, compressors sucking in and compressing air to about six times normal air pressure. This air fluctuates through pipes to the tunnel faces.

Now consider a circular face already a quarter of a mile under the hill. Bars are set across the tunnel about a foot from it. The air pipe laid to the face has in it a potential of air under pressure which in escaping passes through a machine mounted on the bar, causing it to strike and -rotate a drill which gradually eats into the solid rock ahead, several-holes are bored arranged according to the country to a depth of five or six feet. Into these holes over one inch in diameter explosives are rammed. The detonation sends free a volume of gas which in its' vast expansion rends the rock to the free face. The tunnel is trimmed to its true shape. The rock blown out is transported on trucks out through the mouth of the tunnel. And thus another five 01 six feet of tunnel has been driven.

Shift follows shift right through the night, and in the repetition of the process becomes the rates of advance. Auxiliary to tunnelling comes the arduous task of the underground. One tunnel is streaming with underground water. The foul air of the underground ‘explosives is sucked out through pipes by machinery. *

The concrete walls of the dams, the tunnels, the power house, the pipe line anchorages and smaller works will consume over 40,000 cubic yards of concrete. Of the constituents, cement, stone and hand, the- former has to be transported, the others have to be obtained. So in the advance of the tunnels the rock is accumulated in-large heaps, and, as the evolution proceeds, it will pass through crushing plant and under rotating hammers which will break it to the sizes of stone and sand required. It will pass through the" mixing machines with cement, and will be launched into the walls of the dams. And so with the inroads of time the valleys that are dammed will become our lakes, harbouring the duck and the trout.

And so while the angler trails, his float on the bosom of the waters, and explains how he lost a sixpounder the week before last, from underneath 2GO cubic feet a second will be eddying away and discharging in headlong rush on to the plains of Shannon. In the capital City the business man will be boarding his morning tram and wondering if he will again have the misfortune to walk when the power breaks down.