MANGAHAO FROM A NEW ANGLE.

Shannon News, 27 January 1922, Page 4

MANGAHAO FROM A NEW ANGLE.

HOW ENGINEERING SCIENCE IS SERVING THE COMMUNITY. (Specially written for the News) The need of the railway has pierced the heart of the mountain. The engines of industry have wrested the coal from a thousand feet beneath the surface. The growth of the city has reared the towering skyscraper and the call of its people has dammed the in its mountain lastness. The passage of the mercantile marine has cut a continent in hall. And each struggle and each conquest has been a stepping-stone in the corridors oi knowledge. In the construction world of to-day we measure our greatness in terms oh the monuments we can built, rather than the monuments we have built. The ancient Egyptian pyramid v>l Gizeh was the work oi 100,000 slaves lor 30 years. The 500-feet high, ferro-concrete structure of New York is the work of 200 to 300 men for twelve months.

The colliery towns of South Wales, of Lancashire, of Yorkshire, have toiled' in the underworld for 200 years. The explosive firedamp or marsh gas came first, the safety lamp came after. The sudden floods of the underground waters was followed with the perfection of the pump. It has taken the mining engineer 200 years to comprehend the slope of ins seams oi coal, to know when to raise or lower his adits; and it has taken the colliery towns of Britain 200 years to hoist their 250 million tons \ per « *• year. * The manufacture of the electrical unit which has taken the field later in the day takes the advantage of the knowledge of its -predecessors in power.

Primarily in the construction of a scheme such as the Mangaliao comes investigation. The Mangahao River, fed from the snows of Dundas, flows some 1200 feet above sea level. A record of its flow taken over a long period gives a variation of, say, some 60 cubic feet of water per second in the very dry season, to, say, some 20,000 cubic feet in the excessive floods. Its capacity is known. : It has a potential supply of 260 cubic feet per second. Dams are necessary to store up its waters to give it a reservoir of a known capacity of nearly 1300 million gallons, to tide over the drawing off of 260 cubic feet when the rivetsupply is, say, 200 cubic feet. The height of one dam on the river necessary to hold the storage would be too great lor economic construction; two dams are then required,' the upper to replenish the lower by means of sluices, the development of the potential of the inland lakes requires its fall. The shortest route is chosen. A range rising to some 2000 feet separates thk river from the Tokomaru Valley. The Mangahao tunnel, one mile in length, becomes necessary to pierce this and, to tap the bottom oi the lower dam. ’ The Mangahao Rivei is thus diverted into the Tokomaru Valley. The Tokomaru dam serves its purpose of holding back the water of the river and of including its storage in the amount necessary. The ,Arapeti tunnel then leads from the bottom of the Tokomaru Lake, tapping m its purpose the storage of the' three lakes, and pierces the subsequent range for one and one-quarter miles, having in its progress a slight fall to allow the momentum of its waters running at full bore to overcome ths friction of the concrete walls. Waters of the river diverted to the mouth oi this final tunnel pass through a surge chamber with some DUO feet tall through two six feet diameter steel riveted pipes, and four-feet pipes down 36(11) feet’of incline to impinge in jets on the Belton wheels of the power-house, liberating 24,600 horsepower for transmission to the province.

Conception is the dream, but construction is a maternity different matter. Have you stood on the banks oi a river and watched the swirl of ihe waters against the piers of a bridge/ Can you imagine levelling the bed cl the river and lilling in concrete, working in pneumatic caissons twenty ieet below the river surface under air pressure, while for the first few hours the walls seem to reverberate like the beating of drums? The concrete walls of the riverdams provide no less an undertaking. The river may be diverted in tunnels to the side of the foundations, but the springtime hoods speeding twenty to thirty feet high bank to bank will have a voice of authority. Access is primarily the first feat of construction, the forming and upkeep of the hilly road leading over ten miles from Shannon, feeding its materials and supplies down the precipitous tramline to the works of the Mangahau River, feeding en route the Tokomaru Valley works, and tapped by the hoisting tramline to the tunnel faces and top.’n.f the pipe-line ( JUD feet above it. Housing the construction of storage

buildings for materials, oi engine sheds, blacksmith and workshops, of tramlines and of scaffoldings, require timber. The forest of the Tokomaru Valley has been tapped by the everencroaching tramlines of the sawmill,, and the felling, hauling, trucking, cutting and transport have made an inroad of over one million feet on its virgin rimu growth.

Tunnel construction has become one of the principal factors of the scheme. The mile-long Mangahao tunnel has been pierced some 14 chains on either side, with faces directed to meet. The one and one-quarter mile Arapeti tunnel is some 23 chains under the range on one side, and is tapped at Us adits and exit.

Tunnelling has become a process. It lias passed through the stage of the early Carthaginians and their Contemporaries in their primitive search lor gold with slave labour, through the colossal undertakings such as the St. Gothard, the Mont Vaiion, the Simplon of the Alps, and has become more or less a routine.

Electrical power generated by a steam plant is transmitted to the works of the adits and outlet, to the Tokomaru Valley, and to the River Works. It is transformed. The power is used to drive the numerous 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 , lace already advanced a quarter mile under the hill. Bars are set across the tunnel about one foot from it. The air pipe laid to the face has in it a potential of air undei' 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 fl\fe 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 or six feet oi 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 tunneling 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 fine anchorages and smaller works will consume over 40,000 cubic yards of concrete.

Of the constituents, cement, stone and sand, 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 dial are dammed will become our lakes, harbouring the duck and the trout. f And so whilst the angler trails Iris float on the bosom of the waters and explains how he lost a six-pounder the week before last, from underneath 260 cubic feet a second will be eddying away and discharging in headlong rush on to the plains of Shannon. In the caoital 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.