ARAPUNI RESTORATION

Taranaki Daily News, 26 March 1932, Page 7

ARAPUNI RESTORATION

x REFILLING OF THE’LAKE GIGANTIC’ SCHEME COMPLETED. POWER EARLY NEXT MONTH. After being dry for a year and ten months, the re-filling of Arapuni Lake was commenced on Thursday, when the gates in the diversion tunnel were partially closed. In a little over a fortnight the great hydro-electric works will once more be in operation, generating electricity for the use of the entire Auckland Province, including the city of Auckland.

The re-entry of Arapuni into the active field of jndustrjr is an event of first importance.- Upon it, the province depends for 45,000 kilowatts of electrical energy. This is the output of the three generators which were in operation when the power station was closed for repairs in June, 1930, and when the fourth generator is working the capacity of. the station will be 60',000 k.w. This will give it a larger output of power than any other hydro-electric station in the Dominion and will provide the province with industrial and domestic power on. a scale not excelled in any part of the world and equalled by few of the larger and older countries. MAGNITUDE OF THE TASK. The engineering magnitude of Arapuni gives the scheme a nation-wide interest, harnesses New Zealand’s largest and longest river, navigable for 100 miles along its 170-mile course from Lake Taupo, it boasts the most formidable artificial Jani ip the country, its electrical machinery ‘ and equipment are by far the most modern and elaborate problems of a difficult and interesting nature were involved'in the undertaking. It has been estimated that when fully developed the total cost, irrespective of the cost of the repairs, will not exceed £l3 15s per electrical horse-power of plant installed. This is believed to be a record under post-war conditions. A-great deal of'discussion has raged round the selection of the site of the works in view of the volcanic character of the .surrounding country. It is interesting to recall, however, that long before the Government decided upon Arapuni Gorge as the most suitable locality for the principal hydro-electric scheme in. the Auckland province, the identical site was considered as a likely proposition by the Waihi Gold Mining Company, which ultimately developed the Horahora scheme a little lower down the river. EARLY EXPLORATIONS. The Government first explored the Arapuni site iu 1914, when small groups of engineers camped beside the remote gorge and deep bores were sunk beneath the river-bed *to ; test the nature of the country. A tunnel was driven under the river and a pilot, tunnel was carried through the ground on the line the diversion tunnel now takes. Galleries were driven deep, into the cliffs on either hide of the gorge and shafts were sunk on both sides of the dam site to a depth of 59 feet below the river level. Mr. Evan Parry’s plan for a chain of liydro-electric stations throughout the Dominion, together with a recommendation in favour' of a dam across the Waikato. River at Arapuni Gorge, was adopted by the Government in 1918,-and in July, 1921, the expert commission’s recommendation for the construction of the Arapuni scheme were approved. The contract was let to Sir W. G. Armstrong, Whitworth and Company, in 1924, the contract price being £1,170,891,- and operations weta commenced on September 14 of that. year. The actual cost ■ was £2,300,000, which includes the cost of the transmission lines. A BREAK IN THE COUNTRY. The first unit came into operation in May, iax9, and on June 2 power from the station was first used in Auckland. It was delivered uninterruptedly to Auckland and the various power boards throughout the province for over a year. Then, at 1.30 a.m. on .June- 7, 1930, a block of country embracing the penstock tunnels, between the. spillway and the power-house, developed a fracture along the front of the tunnels and up the head- f . face. Water poured into the fissure, developing hydrostatic pressure, which tilted the block, including the power-house, toward the river. The bending move- , ment occupied two days, while the base of ire cracks filled up with grit, allowing fuller development of the pressure.

The fault in the country had nothing to do with the vibration that occurred in the third generator; trouble had been experienced, with that unit at least a month earlier. The chief engineer of the Public Works Department, Mr. F. W. Furkert, the assistant-chief engineer, Mr. C. J. McKenzie, the chief electrical engineer, x Mr. F. T. M. Kissel, the district electrical engineer, Mr. T. MacLehnan, and the Government geologist, Dr. J. Henderson, immediately hastened to the scene, and the diversion tunnel was opened, relieving the. pressure of water over the spillway. ARRIVAL OF SWEDISH EXPERT. The immediate effect was a movement of the block of land back, to nearly its original position and the leaks which occurred were reduced proportionately. It was obvious, however, that remedial measures of a comprehensive' character would have to be undertaken. The works were closed on June 11, the lake was emptied, and a thorough inspection of the bed of the headrace was made by the engineers and the Minister of Public Works.

On August 27, 1930, Professor P. J. Hornell, the noted Swedish civil engineer, arrived in New Zealand under commission .to the Government to report on the unexpected development and suggest the most satisfactory remedy. He stated that the fracture was due to the fact that the headrace was not made a watertight channel. He that the headrace should be concreted and surface cracks grouted, and suggested that a more satisfactory job would be effected if the falls, over which the surplus water from the spillway weir escaped, were also concreted. COMPLETION OF THE WORK. All these recommendations have now been carried out, the cost, as estimated at the time, being £500,000. The entire co'st of the scheme has thus been raised to £2,800,000. Professor - Hornell’s recommendations fully bore out the opinions already arrived at by the Public Works engineers. Not only have all the measures suggested been carried out with great thoroughness, but steps have been taken to insert an additional valve in the diversion tunnel. The shaft is already in course of construction and will be completed when the tunnel is closed. When the dam was previously filled,, in December, 1927, a month was occupied in the process, but at that time Auckland and the province were dependent on Horahora for electric current --'and sufficient water passed through the tunnel at Arapuni to enable Horahora. to continue operating. On this occasion Horahora will be nartiaUy closed and

power for nearly all requirements will be supplied from the King’s Wharf station in Auckland. This coal-burning station will close definitely as soon as Arapuni power is again available, the plant being retained purely as a standhy-