A VISIT TO MANCAHAO HYDRO ELECTRIC WORKS.

Manawatu Herald, Volume XLIII, Issue 2271, 3 May 1921, Page 4

A VISIT TO MANCAHAO HYDRO ELECTRIC WORKS.

fFrom The Levin Chronicle.)

To (lie average newspaper reader the Mangahao tiydro-eleetne - power scheme, notwithstanding all that has been written about it, is still little more than a name, and stands merely lor a more or less shadowy impres- • sion that at some time in the dim ‘ inline the countryside is to draw ‘ power and light from the distant lulls. It is ditncult for anyone who has not actually visited the works to imagine either the magnitude of the undertaking or the vigour and enthusiasm witti which it is being prosecuted. Already toiling human hands and the magic of men’s brains have wrought a transformation in what a 1 year or two ago was the unelmlleng-' ed domain of the wild pig and pigeon. Man is imposing his will upon the mighty forces of Nature, and turning them into beneficent and fruitful channels. The tusk is a gigantic one, but il is being solved j with courage and determination, and i already the day is within measurable j distance when energy generated away beyond the mountain ranges will he brought to the aid of industry in the cities, towns and counties of the Wellington district. Itecentiy an opportunity given by the vigilance Committee of the Mangahao Hydro-Electric Power League to visit the works was gladly embraced by a Chronicle representative, and a most interesting and informa- j tive expedition into the -recesses of! the ranges behind Shannon was the result. The party assembled from north and south at Shannon, and it. set out in five motor cars, headed by the. Engincer-in-Charge, Mr A. Dinnie, who was closely connected with the Otira tunnel works. THE SHANNON END. Immediately on leaving Shannon the site of the surge chamber is in- \ dieated by the work that has been ! commenced on tiie face of the hill for the pipe lines. After a short run the first instalment of the works are reached on the flat at the foot of the lulls. Here the main power station is lo he built. A big provisional jiower house has already been erectcu litre. It will supply steam-gene-ra tea electricity for all the light and power needed at the surge chamber and in the Arapeti \ alley. The necessary machinery, winch has been on j aider ior twenty months, has just neen set up. The huge boiler operates a lOOh.p. electric motor, which in turn supplies the power for the compressor that will drive the drills in the tunnel, it charges the small electric locomotives that are to be used in the tunnels and for haulage purposes, and it lights up the administrative buildings both at the Shannon end and in the Arapeti Valley. The works now in hand at the Shannon end include the excavation of the site for the permanent powerhouse, the completion of a garage for six lorries, a big machine shop, and comfortable huts for the men. THE FIRST VALLEY. Leaving the Shannon camp, the next stage of the journey took the visitors over the saddle separating the J okomaru-Arapeti . Valley from Shannon. The road winds tortuously up tiie steep hillside, giving charming glimpses of fern-filled gullies and majestic native trees. On the top one looks back down the valley and sees, broadening out beyond, the fertile plain stretching to the coast, a coiouriul patch-work of greens and blues, bounded by the waters of the Tasman Sea. The descent on the other side is even more circuitous and difficult, and demands of the motorist an alert eye, quick judgment and firm hand. Here the party found Mr Miller, one of the engineers, and Mr Campbell, the Y.M.C.A. secretary, awaiting them, and after lunch pro ceeded under the former’s guidance to view the points of interest in the Arapeti Valley. This is the site of the second storage dam. The water is to come from the Mangahao into the dam through a mile-long tunnel, and thence goes from the dam through a second tunnel over a hundred chains in length to the surge chamber, from whence a pipe-line takes it down a 900-foot drop to the power-house, at the. foot of the hills on the Shannon side. Good progress lias already been made with this second tunnel, which was -500 feet in • from the Arapeti side. The formai tion is easy, and is being brought j 'down by shots, the holes for which ! are drilled by hand. When comi pressed air is available shortly, fast-

DETAILS OF A GREAT UNDERTAKING.

er progress will bo made. Iwo adits or vertical shafts will also be pul down on to the tunnel line from dips in the formation above it and these will enable tiie work of piercing to be prosecuted from five faces simultaneously. What is known as the Main Camp is located in the Arapeti Valley. Hero tiie second dam will be situated across the ToKomaru River. It will be fed by the Tokomaru and Arapeti streams, and the tunnel from die Mangahao dam in the next valley. Here arc most of the living quarters, the cookhouse, mess rooms, post office, and Y.M.C.A. Light railways have been laid to each tunnel, and will facilitate tiie handling of supplies and excavated material. AT MANGAHAO. In the Arapeti Valley the party again took cars and crossed the tardier range by tiieans of an excellent rolul to the Mangahao side. Leaving the cars there is a dibp down a steep zig-zag to the point where the Mangahao (lows between sheer banks of solid rock, 900 feet below. Here a start has just been made with the* tunnel which will carry the water through from Mangahao into the Arapeti dam. The drills are being operated by compressed* air, and the contractors are skilled Wailii men, who were already 40 feet in. An average progress of 50 leet per week is expected. The tunnel will be a mile long, and it will he attacked from the Arapeti side as well.

Tiie chief other point' of interest is the site of die great dam that, will imprison the waters of the Mangahao. This will he ninety feet high, and it will provide a head of water forty feet in depth at the tunnel mouth. It is located just where the river narrows down and enters the constricted rock channel. A second dam will be put in further up the valley lo serve the double purpose of catching silt, and gravel and relieving die pressure on the lower wall. THE GREAT DAM.

A variation of the original plan has been necessary at Mangahao owing to ‘The geological conditions dial have been encountered. The lower clam was to have stretched across to a jut,iny spur ttiat came out irom the main mil lace beyond it. Trial bores, However, proved that the end oi this spur was really an island of rock, and that between it and the hill on the dinner sate there was a local formation of shingle and waterworn stones mat would not- withstand the enormous pressure of the water imprisoned hell,ml it. Already the bore had gone c.vn over sixty feet, without touching solid rock bottom, and the dam wall will consequently have to be carried l ght, across to the solid rock beyond, at an additional expenditure of probably £50,000. It is of interest, as snowing the bearing of one science upon another, that us long ago as January, 1920, before the Mangahao \ alley had been touched, a theory that has since been proved by investigation was put on record by Mr G. Leslie Adkin, of Levin, an enthusiastic student of the geology of the Tararuas. Mr Alikin held that the area between this island of rock and the hillside was tlie old bed of the Mangahao, now filled by water-borne debris and quite unstable as any part of u wafer-hold’ ing wall. The. theory was elaborated in a paper before the N.Z.- Science Congress at Palmerston earlier in the resent year, and has since befcn published in. jhe Journal of Science and Technology. Its truth has "been demonstrated by subsequent events, and it must be admitted that, had it Leen taken into account at the beginning, a much clearer view of the engineering problem presented would have beerT possible. The condition existing at Mangahao is one characteristic of the formation in the Tararua r ver valleys, and Mr Adkin was led to his conclusions by observations in other parts of the range and the application of his deductions to the Mangahao site. POWER IN 1923. The inspection at Mangahao being completed the visitors returned by cars to Shannon and thence to their respective towns. The visit was a revelation to the party in view of the frequent criticisms of the slowness of progress. About 220 men are employed altogether and they seem to be very comfortably housed. Many are married men with families and already there are several flourishing vegetable gardens to he seen adjacent to their huts.

The visitors were greatly impressed by the enthusiasm of the engineering stuff, their professional zeal, and their willingness to make everything clear lo questioning laymen. Mr Dinnie and his assistants (Messrs Miller, Johnston ami Anderson) spared no trouble to make the visit informative and interesting. One of the most-discussed questions was, of course, the probable date ot completion of the works. It' was gathered that from an engineering standpoint, there was no doubt that—except for some unioresecn contingency—something not at present imagin able—the Ministerial expectation that power will he turned on by Christmas, 1923, will be fully realised.

THE Y.M.C.A.’S WORK. The housing arrangements seemed excellent and generally the living conditions left little to be desired, though admittedly the camps were viewed under the most favourable conditions. Houses with separate cubicles have been built for single men and small cottages for married men with families. Messroom, post office, dry canteen, and change and drying rooms tire provided. .'some tents are still in use. but lints will replace these as soon as timber is available. Arrangements have also been made for medical attention 'and medicine for the men at a.very small cost indeed and a doctor visits the work once a week. The Y.M.C.A. tent is in use, but a hut is being built to replace it. Pictures are shown there three nights a week and readingmaterial supplied. The Y.M.C.A. is undoubtedly doing good work and is assist ing to make life more tolerable for Hie men. One of Mr Campbell's self-imposed duties, pending other arrangements, is that of schoolmaster to the children living with their parents in the Arapeti Volley.