MANGAHAO FROM A NEW ANGLE.

Shannon News, 25 January 1922, Page 3

MANGAHAO FROM A NEW ANGLE.

HOW ENGINEERING SCIENCE IS SERVING THE COMMUNITY.

(Specially written for the Shannon News).

The need of the railway has pierced the heart oi the mountain, ine engines oi industry have wrested the coal from a thousand teet beneath the suriace. The growth of the city has reared the towering skyscraper and the call of its people has dammed the river in its mountain fastness. The passage of the mercantile marine has cut a continent in half. And eacn 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 of the monuments we can built, rattier than the monuments we have built. The ancient Egyptian pyramid M Gizeh was the work oi luu.ouu slaves for 30 years. The 500-feet nigh lerro-concrete structure of New York is the work of 200 to 300 men lor iWelve 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 alter. The sudden floods of the underground waters was followed . with the perfection of the pump, it uas taken -me mining engineer 200 years to comprehend the slope of his aeams oi' coal, to know when to raise or lower his adits; and it has taken die colliery towns ol Britain 200 years to hoist their 250 million tons per year. The manufacture of the electrical unit which has taken the field later in me day takes the advantage oi the Knowledge of its predecessors m power. ? Primarily im the construction of a .-'■•neiiie such as the Manganao comes mvesugation. Tne Manganao River, iod iroin tne snows of Dunuas, nows •juhie IRK) feet above sea revel, a record oi its how taken over a long period gives a variation oi, say, some jo cudic leet oi water per second in me very dry season, to, say, some ~u,out) cubic leet m me excessive floods. j's capacity is known, it nas a potential supply oi 250 cubic leet per oecona. Dams are necessary to store up its waters, to give it a reservoir ot a known capacity oi neany 13UU million gauons, to uue over the drawing off of 260 cubic leet when the river ouppiy is, say, 200 cubic leet. The neight oi <one dam on the river necesoary to hold the storage would be too great lor economic construction; two uams are then required, the upper to replenish the lower by means oi sluices. Jhe .development of the potential of the inland lakes requires its fall. The .shortest route is chosen. A range rising to some 2000 feet separates the; river from the Tokomaru Vailp . The Mangahao tunnel, one mile in length, becomes necessary to pierce Hus and to- tap the bottom ol tiie iowier dam. The Mangahao River ,is thus diverted 'into the Tokomaru Valiev. The Tokomaru dam serves its purpose of holding back the water ol die river and oi including its storage in the amount necessary. The Arapeti tunnel then leads from the bottom ol" the Tokomaru Lake, tapping its purpose the storage oi' the three lakes, and pierces the subsequent range for one and one-quarter miles, having in its progress a slight fail to allow' the momentum of its waters running at full bore to overcome the motion ul the concrete walls. Waters ol the river diverted to the mouth ol this final tunnel pass through a surge chamber with some DOO feet tall through, fwo six leet diameter steel riveted, pipes, and . s'our-ieet pipes down TB'JO feet of incline to impinge in jets <m the Pelton wheels of the power-house, liberating 24,000 horsepower i'oi’r transmission to die province. Conception is die dream, but construction. is a materially different- matter. Have you stood on the banks of a river mid watched the swirl of the waters against the piers of a bridge? Can yon imagine levelling the bed cf die river and filling in concrete, working in 'pneumatic caissons twenty feet below the river surface under air pressure, while for the first lew hours the wafVs seem to reverberate like die beating of drums? The concrete walls of the riverdams. provide no. less an undertaking. The. rive* may be diverted in tunnels to die side of the foundations, but the [ springtime Hoods speeding twenty to thirty feet-high bank to bank will l hare a voice of authority, i .Access is primarily the first feat of 1 construction, the forming and up- \ keep of the hilly road leading over | ten miles from Shannon, feeding its ! materials and supplies down the precipitous tramline to the works of the Mangahao River, feeding en route the Tokomaru Valley works, and tapped bv die hoisting tramline "to the tunnel faces and top of the pipe-line 900 feet above it. * Housing, the construction of storage

buiiumgs ior maienais, ox engine sneus, jjiaCksrn.m unu worKsnupo, m Tramlines ana .... scuuuiuuigs, limner. Tne oi me ionomaru vauey nas nee-, tapped ny. me everenciOacmng Ua. ~mes m me bawiuni, u«u me :.auiing, uuumig; calling anu uttibi. . i nave maue an mruau oi over 0..., ninnon ieei oil us virgin rnnu gie..m. luiinei conou ~auii nas become one oi me principal ,actors oi me seneme. ine nme-iuiig .-..aiiganao lunnei nas neon pierceu some 11 cnams on either side, with die mces directed to meet. Tne one ana ohe-quuiier mite Arapeu tunnel is some .o cnams unaer me range on one tme, ana is tapped ai ns adits and exit. Tunnelling nm- become a process, it nas passed imougn me stage of me early carmagiu..iiis and meir contemporaries m .noir primitive searen tor gold with .m.ve labour, through die coiossai un ~.-i laKiiigs such as me St. uomaru, tiic aunt vanuii, me Simplon Oi me .nip-'. <uiu nas necome mure or less a routine. Electrical puver generated by a steam plant is uausmuted to the works of the adits aim outlet, to the Tokomaru Valley, aim to tne River Works. It is transformed. The power is used to drive the numerous electric motors auxiliary to the construction. Part oi it is used to drive induction motors which operate, with a belt drive, compressors sucking m and compressing air to about sm times normal an pressure. This air fluctuates tiirougli pipes to the tunnel faces. Now consider a circular face 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 lace 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 leet. into these holes over one inch in diameter explosives are rammed. The detonation sends iree a volume of gas which in its vast expansion rends the rock to the free tace. The tunnel is trimmed to its true shape. The rock blown out is transported on trucks out through the mourn 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 hie underground. One tunnel is stream mg with underground water. The ioul air of the underground explosi. f - is sucked out through pipes by machinery. The concrete wails of the dams, the tunnels, the power house, the pipe line anchorages arm analier works will consume over m,OOO cubic yards of concrete. Of the constituents, cement, stone and sand, the loaner has to be transported, the otheiw have to he obtained. So in the advance of the tunnels the rock is accumulated in large heaps, and, as the evolution proceeds, it will pass through ct ashing plant, and under rotating hammers which will break it to the sizes ux stone and sand required. It will pass through.»tne mixing machines wmi cement and will be launched into me waifs of the dams. And so with Urn inroads of time tne 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 lie lost a six-pounder the week before fast, 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.