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MANGAHAO HYDRO-ELECTRIC SCHEME.

A writer in the Levin Chronicle publishes some interesting details of the above scheme, from which we cull the following:— The Mangahao river, fed from the snows of Dundas, flows some 1,200 feet above sea level. A record of its flow taken over a long period gives a variation of, say, some 00 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 unknown. 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 1,300 million gallons, to tide over the drawing off of 260 cubic feet when the river supply is, say, 200 cubic feet. The height of one .dam on the river necessary to hold the storage would be too great for 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 some 2,000 feet separates the river from the Tokomaru Valley. The Mangahao tunnel, one mile in, length, becomes necessary to pierce this and to tap the bottom of the lower dam. The Mangahao river 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 necessax-y. The A raped tunnel then leads fi'om the bottom of the Tokomaru Lake, tapping in its purpose the storage of 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 the friction of the concrete walls. Waters of the river diverted to the mouth' of this final tunnel pass through a surge chamber with .sonic 900 feet fall through two six feet diameter steel riverted -pipes, and four-feet pipes down 3,600 feet of incline to impinge in .jets on the pelton wheels of the power-house, liberating 24,000 horsepower for transmission to (he province. The concrete walls of the l-iver dams pi-ovide no less an undertaking. 'fhe river may be diverted, in tunnels to the side of the foundations, but the spi-ingtime floods 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 Mangahao River, feeding en route the Tokomaru Valley works, and tapped by the hoisting tramline to the tunnel faces and the top of the pipe-line 900 feet above it. Housing, the construction of storage buildings for materials, of "en-

gine sheds, blacksmith and workshops, of tramlines and of scaffoldings, require timber. The forest of the Tokomaru Valley has been tapped bv the ever.-encroaching tramlines of the sawmill, and the felling, hauling, trucking, cutting and transport have made an inroad of over one million feet of 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 the faces directed to meet. The one and onequarter mile Ax’apeti tunnel is some 23 chains under the range on one side, and is tapped at its adits and exit.

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 ti-ansformed. The power is used to drive the numex-ous (Concluded on page 4.)

Permanent link to this item
Hononga pūmau ki tēnei tūemi

https://paperspast.natlib.govt.nz/newspapers/MH19220128.2.2

Bibliographic details
Ngā taipitopito pukapuka

Manawatu Herald, Volume XLIV, Issue 2385, 28 January 1922, Page 1

Word count
Tapeke kupu
632

MANGAHAO HYDRO-ELECTRIC SCHEME. Manawatu Herald, Volume XLIV, Issue 2385, 28 January 1922, Page 1

MANGAHAO HYDRO-ELECTRIC SCHEME. Manawatu Herald, Volume XLIV, Issue 2385, 28 January 1922, Page 1

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