FRACTURE AT ARAPUNI

Stratford Evening Post, Issue 86, 27 June 1930, Page 5

FRACTURE AT ARAPUNI

STATEMENTJN HOUSE MEMBERS ASK QUESTIONS HISTORY OF THE TROUBLE WELLINGTON, June 2G. When Parliament assembled yesterday Mr R. Semplc ashed whether the Government would appoint a Coiningsion consisting of representatives c? all parties of the House, with power to appoint, outside experts, to inquire into the causes of the recent earth movement at; Arapuni. Mr J. G- Coates asked whether ttoc Government would appoint a Royal Commission, with a judge as president, to inquire into all matters connected with the inauguration, construction and working of the Arapuni power scheme. Mr Forbes said that the Government desired to take the House into its full confidence in regard to Arapuni, and all available information on the subject would be placed before member shortly. The question whether any Inquiry should be conducted by a Royal Commission or by a Commission of members of the House was one for iuture decision.

Statement By Minister In reply to several ons address ed to the Minister of Public Works on the question of the position at Ara puni, the Hon. W. B. Taverncr in u statement traced the history of the trouble from the time the cracks first developed. He added that it was apparent almost from the first that extensive work would be necessary to make good the position and that the plant would of necessity have to be shut down lor a considerable period. The en'are emptying of the lake was therefore, decided upon. As soon as it became evident that it would be neees sary for the plant to shut down Aucfc land was communicated with and arrangements made with the Power Board for it to take up its own \om\ at its King's Wharf steam plant, and arrangements were also made to get steam on the Department's steam set at Grand Junction and also to ensure that the Department's Diesel plant at Penrose was ready for immediate service. It was also arranged that all power available from the McLaren's Falls plant, which belongs to the Tauranga Borough Council, from which the Department, has in the past taken power over a considerable period should be drawn upon. Further the Government's p nt at Rotorua, which has been shut down for some time, was also got ready for immediate action. As a result -when the water fell too low for the machines at Arapuni to operate the load was taken up by the plants indicated, in addition to the Department's station at Hora Hora and 1 s been carried in this way ever since. The total estimated amount of power available is 19,150 kilowatts and the amount of the present load' is 18,000 kilowatts. Thus there is at present an estimated surplus of approximately 1150 kilowatts.

The Director of the Geological Survey branch of the Scientific and Industrial Research Department, said Department agreed that a technical committee consisting of the head of the Department, Dr- Marsden, Dr. Henderson (Director of the Geological Mr Taverner, proceeded to Arapuni immediately after the trouble occurred and after further examination when the head-race was laid bare he consulted with the head of his Department and the Minister in charge of that Survey branch), Dr. Marshall (member of the staff and at one time professor of geology at Otago University) and Professor Bartrum (professor of geology at Auckland University) should further examine the position and make a joint report. This they have done.

The Experts' Report A summary of it is as follows: The block of country near the penstock tun nels between the spillway and the power-hou broke away at 1.30 a.m. on 7th. instant, developing a crack extending along the front of the penstouK tunnels and the spillway. Water poured into this crack, developing hydrostatic pressure which bent the block, including the power-house, progressively over towards the river. This benuiug extending over two days while the base of the cracks filled up with grit, allowing fuller development of the pressure. It i« evident that the blomc moved about the base well below the river level, i.e., some, 300 feet below the penstock head. Alter the diversion tunnel at. the dam was opened and the level of the water in the penstock hau began to recede the block moved slowly back at about three-quarters of its original displacement and the leak;-, iVimc reduced in. greater proportion. T| appears evident that the movement of the crack after its original formation can be accounted for by the hydrostatic pressure of the water entering the cracks and the question naturally arises as to the origin of the original crack and whether or not further disturbances are likely to occur. Severar alternative explanations mav be aovanccd to account for the original nip ture: (1) The whole b'ock of country may have been in tension from natural causes, and extra excavation for the, new power-house together with hydro- , static thrusts in the penstock head, j may have just caused the limit of resistance to be overcome This seems the more likely explanation. Alternatively, it is possible that, water leaked into the deep vertical joints below the penstock head, developing sufficient pressure to "cause the rupture. No evidence, however, can be found for such joints in the absence of deep borings. A third possible explanation is thet stress caused by a possible earthquake