ARAPUNI

Hawke's Bay Tribune, Volume XX, Issue 161, 27 June 1930, Page 8

ARAPUNI

QUESTIONS IN THE HOUSE MINISTER'S STATEMENT. GEOLOGIST'S INVESTIGATION. Wallington, June 26A number of questions relating to Awapuui were asKtxl in the House of Representatives this afternoon. Mr K. Semple (Wellington East) gave notice to move for a Parliamentary investigation and the production of all documents and plans, including correspondence with Armstrong, Whitworth and Co. over its refusal to go on with the building of the power-house on the present site. The Minister of Public Works (Hon, W. B. Taverner), in his statement, said that it was apparent almost from the very first that extensive work would be necessary to make good the position and that the plant would of necessity have to bo shut down for a considerable period. The entire emptying of the lake was therefore decided upon. As soon as it became evident it would be necessary for the plant to shut down, Auckland was communicated with and arrangements made with the Power Board for it to take up its own load at its King’s Wharf steam plant, and arrangements were also made to get up steam on the department’s steam set at Grand Junction, and also to ensure that Jic department’s Diesel plant at Wnrose was ready for immediate service. Jt 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 plant 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 Horahora, and has been carried on 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. GEOLOGIST’S SURVEY. The director of the geological and survey branch of the Scientific and Industrial Research Department proceeded to Arapuni immediately after the trouble occurred, and after a further examination, when the headrace was laid bare, he consulted with the head of his department, and the Minister in charge of that department agreed that a technical committee, consisting of the head of the department, Dr. Marsden, Dr. Henderson (director of tho geological survey branch). Dr. Marshall (a 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. A summary of it is as follows:— A block of country near the penstock tunnels, between the spillway and the power-house, broke awav at 1.30 a.m. on the 'th inst,, developing a crack extending along the front of the penstock tunnels and the spillway. Water*poured into this crack, developing hydrostatic pressure, which l>cnt the block, including the power-house, progressively over towards the river. This bending extended over two days, while the base of the cracks filled up with grit, allowing fuller development of the pressure. It is evident that the block moved about the base well below the river level—i.e., some 300 feet below the penstock head. After the diversion tunnel at the dam was opened and the level of the water in the penstock head began to recede, the block moved slowly back by about threequarters of its original displacement and the leaks were reduced in greater proportions ALTERNATIVE EXPLANATIONS. It appears evident that the movement of tho crack after it, original formation can be accounted for by the hydrostatic pressure of tho water entering tho cracks ,and ..the question naturaTly arises as to the origin of tho original crack and whether or not further disturbances arc likely to occur. Several alternative explanations may be advanced to account for the original rupture:— I (1) The whole block of country, may have been in tension from natural causes and extra excavations for the new power house, together with hydrostatic thrusts in the penstock head, may have just caused the limit of resistance to bo overcome. This seems the more likely explanation. Alternatively it is possible that water leaked into deep vertical joints below the penstock head, developing sufficient pressure to cause tho rupture. No evidence, however, can be found for such joints in tho absence of deep borings. The third possible explanation is stress caused by a possible earthquake wave, which, owing to the fact that the power house and the penstock head were rigidly tied, might possibly cause such a rupture. Against this is the lack of observation of any such tremor. It is true that the initial movement of tho block caused tremors and vibrations of the block, which were observed by a man living in a hut near the penstock head. These cracks in tho power house, however, do not necessarily indicate disturbance of the power house foundations, since they consist of a transverse crack of the whole building at a point where its width changes suddenly and cracks round the supports of the heavy generators and turbines (350 tons). Rock surfaces visible indicate no movement of rock masses relative to one another. The whole occurrence might well bo unforeseen and due to unexpected weakness of the support of tho whole block which has moved. This supporting material is only just strong enough to withstand the weight' of overlying rock without failure. Further, buttressing of the whole block would appear necessary to prevent a recurrence of the movement and leakages of water from the forebay. The geologists are of opinion that there was no undue water percolation from the spillway into the block of roek between the spillway and the gorge ari'i the power house previous

to the formation of the crack. Thus the initial movement is unlikely to be due to this cause. Tho Minister added that, realising the magnitude of the issues at stake and also tho uneasiness which had arisen in the public mind, the Government had decided to obtain the very best engineering advice, and has been in communication with the High Commissioner for New Zealand in London, the president of the Institute of Civil Engineers and organisations elsewhere in order to select the most suitable man. “Until such time as the report to be made by this engineer has been received,” said the Minister, “I have felt it my duty to advise Cabinet to discontinue any further works at Arapuni. Further investigations will include a survey of the financial position of the scheme, and will deal with the economic aspect,. AMOUNT INVESTED. Meantime I wish to make the following observations:— “The amount already invested in the Arapuni scheme, including substations and transmission lines and works in progress, is £2,500,000. In the previous year before Arapuni came into operation tho working charges for the Waikato system amounted to £76,231, aud standing charges for interest and depreciation and renewals were £74,571, or a total of £150,802. For the year ended March 31 last the respective figures were £62,702 and £195,752, altogether £258,454, so that the difference, amounting to £107,652, represented the additional total opera tion costs of Arapuni for the year. Units sold for the year from the whole Waikato system were 191,000,000 and the net revenue after paying working expenses of £62,702 was £162,981. “The average operation capital for tho year was £2,649,000, so that the net revenue over and above working expenses was 6.15 per cent on the operating capital, notwithstanding that tho plant installed was insufficient to take the whole available load during the earlier months of the year. The present installed capacity of Arapuni station is 45,000 k.w. and consists of three units. The fourth unit ! a now in process of shipment from England and had the course of events not been interrupted would have been installed on arrival, thus bring the total capacity of the Arapuni plant to 60,000 k.w. In a subsequent statement details will bo given showing the cost involved in calling into opera tion stand-by plants and other stations, which were required to take the load when tho supply ceased from Arapuni, but it may be remarked that the estimate at present for generating costs st those stations is at tho rate . of £85.000 per annum, as against £12,000 fcr generating costs had Arapuni continued in commission. Replying to Mr W. L. Martin (Raglan), Mr Taverner said he proposed to call a conference of all power boards concerned to consider the position created by the trouble at Arapuni.