THE SIDE-TRACKED WAIKATO.

Poverty Bay Herald, Volume LII, Issue 17008, 15 April 1926, Page 9

THE SIDE-TRACKED WAIKATO.

MAN’S CHALLENGE TO NATURE. FOREST GHOSTS AT ARAPUNI. f NEW ARMSTRONG WEAPON: THE WATER-GUN. Tho main principle of the Arapuni hydro-electric power scheme is to dam tho Waikato river to a height that will compel if to run into its own old bed, at an elevation of about 150 ft. above its present bed. The old bed is being unproved -by about 75 chains of tunnelling, making a channel about (iOft. wide and 12,f1. to loft. deep. When the old bed thus improved, reeeives the waters ol the dammed Waikato, it will be called the ‘ ‘ head race. ’ ’ The river will be wholly diverted into this old bed; but at a point on the old bed a “penstock weir” is being built, for the purpose of again sidetracking Ike river for as much of its waters as the engineers covet) into the penstock tunnels.

AivTl.FI 01A1, TO RR ENTS I’ROJ)L CE

POWEI^ Tho water that gors over the weir continues its course till it rejoins its old bed. But the water that enters the penstock tunnels goes back to the old bed by a much shorter and steeper route. The penstock tunnels drop 175 ft. in 400 ft., and it is thus that the required power is developed.

Three penstock tunnels are included on the present scheme, and the water m each will operate an electric set equal to 20,000 horse-power. Approximately, three-eights of the river will be taken into the penstock tunnels, generating 00,000 horse-power. The ultimate development would comprise live mode of these tunnels and live more sets, or 100,000 horse-power all told. Meanwhile, the bulk of the.Waikato will continue to pass over the weir, and will gravitate back to the old bed by a course much less precipitous than ,175 ft. in 400 ft. Nevertheless, its course will be steep enough to require special provision against erosion—such provision as concreting of the floor and sides of the channel in parts, and constructing the spillway in such a manner that the water finally falls into a basin specially designed to stand the shock. The basin will provide a “water cushion,” which seems to be the best sort of surface on which to receive every second a few thousand tons of falling liquid. The penstock tunnels* which take the power torrents, are circular tubes built of concrete .with a steel lining. The diameter of each tube is 12ft.

STANDING DEAD FOREST AND A SUPER-SLUICE.

The main. dam that is to lift the Waikato back into its old bod will bo a wonderful piece of engineering skill, but after all a dam is just a dam. Even more wonderful in a way was the discovery of a dead but still standing forest covered by silt in the old bed. Apparently the once live forest was killed and partly covered by volcanic action, for a great abundance of charcoal was found in places, and the trunks, whether .still standing or prostrate, were partly charred. Then water-borne (not necessarily riverborne) silt accumulated, and covered over the slain forest without upsetting its perpendicularity. There it stood for goodness knows how many years until Armstrong-Whitworth’s navvies, intent on channelling the old bed to tit it for further service, embedded tludr picks in the-ancient trees. The discovery was of great geological interest, but the navvies, being neither geologists nor archaeologists, were not pleased. Nor was the Armstrong'Whitworth management pleased when it found that excavating a buried forest was likely to bo much more costly than removing mere earth. Somebody with a brain-wave came along and suggested sluicing away both silt and trees by means of a super-powered hydraulic outfit. Under big pressure a it-inch -pipe combined with a 2-inch nozzto gave > a jet. of water that tore flown everything in its course. It is estimated that the pressure was 1301 b. to the square inch. In the portion of the channel obstructed by the dead forest, this water-gun cleared a course at a cost of about one-twelfth of that which, would have been entailed by ordinary manual methods of excavation. BIGGEST DIAMETER TUNNEL SOUTH OF LINEc One important work has not been mentioned, it is the diversion tunnel. The purpose of the diversion tunnel is to take the waters of the Waikato while the main dam is being built. The diversion tunnel will be 720 ft. long, but its other dimensions are much more impressive than its length. It is 2Sft by 28ft unliued, and 24ft by 24ft lined. In this respect it is the biggest tunnel in the Southern Hemisphere: It is wide enough to take horizontally an average cottage, ami is high enough to take vertically a two-storeyed house. It is arch-shaped. Air. Darby, a pioneer settler in the vicinity of Arapuni hydro-electric station, claims that, except the Niagara, and the Zambesi, no river in the world can develop, in a distance of 70 miles, as much hydro-electric power as can the Waikato oetween Taupe and Cambridge. The honor of designing the whole undertaking belongs to the Public Works Department and its Hydro* Electric Branch. Throughout the work the Dominion’s interests arc being carefully watched, by the departmental officers.—-Dominion.