ARAPUNI HYDRO-ELECTRIC-POWER WORKS (STATEMENT BY THE HON. W. B. TAVERNER, MINISTER OF PUBLIC WORKS, REGARDING THE).

Appendix to the Journals of the House of Representatives, 1930 Session I, D-01a

D. —1A

1930. NEW ZEALAND.

ARAPUNI HYDRO-ELECTRIC-POWER WORKS (STATEMENT BY THE HON. W. B. TAVERNER, MINISTER OF PUBLIC WORKS, REGARDING THE).

Laid on the Table of the House of Representatives by Leave.

In accordance with the undertaking I have recently given to the press, I desire to make the following statement to the House regarding Arapuni : — At about 4 a.m. on the morning of Saturday, the 7th instant, water was noticed on the floor of the battery-room at the back of the power-house, having found its way in through the power-house drainage system. On the officer at the pumphouse end of the penstock structure near the spillway weir being communicated with, he found a crack approximately 2 in. wide between the end of the spillway proper and the structure adjoining same. Other water was found issuing from a number of points on the cliff behind the power-house. Wellington was immediately advised, and some of the principal officers of the Department left immediately for the scene, arriving the same night. In the meantime a crack had been traced on the surface of the ground running from the, one first observed through the hill between the old gorge of the Waikato River and the present headrace. This crack was not continuous, but was observed in a number of places all trending much in the same way and ending a short distance below the Falls where the water from the headrace drops back on to the Waiteti Flat. Wherever these cracks existed in alluvial ground they disappeared during the first rain which fell afterwards. After observing the flows through the hill and the movements, it was decided that it was advisable to lower the water so that it would not overflow the spillway, and thus give an opportunity for better examination. Accordingly the gates in the diversion tunnel were opened, and by the following morning the spillway ceased to overflow, and further examination was made. In the meantime I had departed for Arapuni, and with the engineers made a thorough inspection ; and, after carefully going over all the evidences of earth movement, a decision was arrived at that the water should be drawn down unfcil the headrace was dry. This was done, the lowering of the water to this extent being accomplished by Sunday, the 15th instant. On the water leaving the headrace and. forebay it was found that the cracks already observed ran approximately on the lines of the headrace for several hundred feet farther than had been observed on the dry land, and the drainage water was disappearing down these cracks. As the water in the headrace lowered during this week the leaks through the hillside at the back of the power-house and

I—D. la.

D.—la

2

elsewhere had decreased in sympathy, and shortly after the complete emptying of the headrace they fell away very greatly, and by Tuesday, the 17th instant, had entirely ceased. Certain cracks were observed in the back of the power-house on the first morning of the trouble, and a small quantity of water was seeping through these. This, of course, stopped when the other leaks stopped. As the water in the forebay and headrace was lowered, the cracks tended to close, and when the water pressure was entirely removed it may be said that in a general way the cracks closed up to half the width at which they were at the maximum. The maximum width of the cracks was 2 in. at one point, gradually fading away to a hair crack at each end. This is now I in., and fades away to nothing in a shorter distance than previously. Very careful measurements both by direct measuring from known fixed points and by triangulation from parts of the country remote from the scene of movement all indicated that the movement, small as it was, was definite and in the direction from the penstocks to the tailrace —in other words, towards the gorge in which the Waikato was running prior to the diversion in 1928. At the time of my visit on 9th June investigations indicated that some movement had taken place in connection with the power-house, the turbines being slightly out of true level. It was also ascertained that the high-level suspensionbridge spanring the gorge had sagged to some extent, presumably on account of movement of one of the supporting towers. Also, the heavy-traffic low-level bridge just below the power-house gave indications that movement had taken place there. All these displacements support the theory that whatever movement took place was inwards towards the old gorge. 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 for a considerable period. The entire emptying of the lake was therefore decided upon, and the lake was finally drained on the morning of the 24th June. As the water in the lake was lowered certain overhanging material from the cliff wall above the intake to the diversion-tunnel slipped away at intervals during the night of 13-14 th June with the result that the gates of the diversion tunnel became blocked on three occasions. The blockage was overcome by raising the gates and thereby increasing the opening, the pressure of water sweeping the slipped material through the diversion-tunnel. Apparently the gates were not affected by these blockages, as they were successfully operated again immediately afterwards. On Friday, the 20th June, certain cracks, one-fiftieth of an inch in width, were reported as having been discovered in the floor of the power-house round No. 2 unit, and, on telegraphing for further particulars as to the positions and directions of these cracks, the information was received next day that they had become visible round all three machines, and extended from the upper machine-floor down approximately to the top of the turbine scroll cases. These cracks were believed by the staff to have developed in the last few days, as with quite a number of men constantly looking for signs of damage it seems inconceivable they could have been missed previously if there. As soon as it became evident that 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 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 the power available from 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, which occurred on Wednesday, the 11th instant, at 3.40 p.m., the load was taken up by the plants indicated above in addition to the Department's station at Horanora, and has been carried in this way ever since.

D.—la

3

Excluding the Auckland load, which is being carried by the Auckland Electricpower Board with its own plant, there is approximately a total load of 18,000 kilowatts to be supplied, and for the supply of this we have the following sources :— Kilowatts. Horahora Government hydro-electric scheme, installed capacity . . 10,300 Grand Junction steam plant belonging to the Government, capacity . 3,000 Diesel plant at Penrose belonging to the Government, capacity . . 3,700 Rotorua hydro-electric plant operated by Tourist Department, capacity . . . . . . . . .. . . 350 And whatever surplus may be available from the McLaren's Falls hydro-electric station owned by the Borough of Tauranga, which has been drawn upon largely by the Government in the past prior to the completion of Arapuni, the available surplus being estimated at approximately .. .. . . 1,800 Total estimated amount available .. .. .. ..19,150 Amount of present load is .. .. .. .. .. 18,000 Thus there is at present an estimated surplus of approximately .. 1,150 It will be seen that, although the margin is small, there is a definite margin. Furthermore, certain industrial undertakings have their own power plant with which they can supply their own loads and may be able in some cases to feed back a small amount into the general reticulation ; also, as the winter passes away, the Auckland City load will fall, and it will then be possible for the Auckland Electric-power Board to supply power back to the Government lines for distribution should it be required to the districts where large milking loads have to be carried during the summer. Realizing, however, that the demand for electricity grows continually even faster than the population, I, immediately the gravity of the position became manifest, cabled to the High Commissioner to make inquiries as to the possibility of securing for prompt delivery a steam plant which could be installed in the Waikato district handy to the coal-mines. Negotiations concerning this are still in progress, and I expect to be able to report before long that a conclusion has been reached and definite arrangements made for the supply and installation of this plant. Considerable inconvenience has, of course, unavoidably been caused to the Auckland Power Board and other Boards on account of interruption of supply, and I may here state that although the Department is, under its agreement with its customers (the Boards) relieved from liability as a result of such happenings as have now occurred, every effort will be made and all expedition used to alleviate the position. The Director of the Geological Survey Branch of the Scientific and Industrial Research Department proceeded to Arapuni immediately after the trouble occurred, and, after closely examining everything then visible, returned to Wellington until such time as the headrace could be laid bare. He then again visited Arapuni and had a further examination, after which he consulted with the head of his Department ; and, at my request, 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 the 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 to the Auckland University) should further examine the position, and make a joint report. This they have done. The full geological report will be published in due course, but for the purposes of this statement a summary of it is as follows : — A block of country near the penstock tunnels, between the spillway and the power-house, broke away at 1.30 a.m. on the 7th instant, developing a crack extending along the front of the penstock tunnels and spillway. Water poured into this crack, developing hydrostatic pressure, which bent 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

2—D. la.

D.-lA

4

development of pressure. It is evident that the block moved about a base well below river-level— i.e., some 300 ft. below the penstock-head. This is evident by the tilt of the power-house, which attained about one minute of arc, and the tilt of one support of the suspension-bridge. The crack on the penstock-head attained to an opening of a little over 2 in. 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 three-quarters of its original displacement, and the leaks were reduced in greater proportion. It appears evident that the movement of the crack after its original formation can be accounted for by hydrostatic pressure of 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. Several alternative explanations may be advanced to account for the original rupture —first, the whole block of country may have been in tension from natural causes and the extra excavation for the new power-house, together with the hydrostatic thrusts in the penstock-head, 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 deep vertical joints below the penstock-head, developing sufficient pressure to cause rupture. No evidence, however, can be found for such joints in the absence of deep borings. Several cracks developed in the blocks between the penstock-heads and the gorge, which rapidly filled with water, and would create extra hydrostatic pressure or facilitate transmission of same. A third possible explanation, is the stress caused by a possible earthquake wave, which, owing to the fact that the power-house and 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 the block caused tremors and vibrations of the block, which were observed by a man living in a hut near the penstock-head. These tremors, together with the tremors caused by the progressive probable jerking return of the block on removal of the water which gave rise to the hydrostatic head, caused vibrations and cracks to appear in the power-house. These cracks in the 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). The rock surfaces visible indicate no movement of rock masses relative to one another. The whole occurrence might well be unforeseen and due to unexpected weakness of the support of the whole block which has moved. This supporting material is only just strong enough to withstand the weight of the overlying rock without failure. Further buttressing of the whole block would appear necessary to prevent recurrence of movement and leakages of water from the forebay. The geologists are of the opinion that there was no undue water percolation from the spillway into the block of rock between the spillway and the gorge and power-house previous to the formation of the crack ; thus, the initial movement is unlikely to be due to this cause. There has not been sufficient opportunity to finish a fuller report covering the whole power-development site, but such a report is in process of compilation. This report will be submitted to the officers of my Department in order that with the information contained therein they might devise remedial measures. Meantime, realizing the magnitude of the issues at stake and also the uneasiness which had arisen in the public mind, the Government decided to obtain the very best engineering advice that could be obtained, and with that object in view has been in communication with the High Commissioner for New Zealand in London, the president of the Institute of Civil Engineers, and organizations elsewhere, in order to select the most suitable man. Until such time as the report to be made by this engineer has been received, I have felt it my duty to advise Cabinet to discontinue any further works at Arapuni. It must be realized that very considerable works were in progress in the direction of installing a fourth unit to increase the

D.-lA

5

capacity of the station in accordance with the growing demand for electric energy, and also work was in hand for securing the position at the point where the water from the headrace falls back on to the normal level of the Waikato. At this point considerable erosion occurred last year, and, although for the last ten months no further erosion has occurred, my predecessor did not deem it advisable to take any risks in this direction, and Cabinet on his advice had decided to thoroughly secure the position by the construction of a drop weir. Plant had been assembled and a certain amount of work done on this, but if the position at Arapuni should be found on mature consideration to be beyond repair, which I sincerely trust will not be the case, then it would have been a waste of money to proceed with the securing of the waterfall. Similar remarks apply to the completion of the fourth generating-unit. As any one reporting on the naturally require the very best of information not only concerning surface indications, but also concerning the lie of the strata below, exploratory tunnels will be carried on until such time as the fullest of information concerning all the surroundings has been obtained. Further investigations will include a survey of the financial position of the scheme and will deal with the economic aspect. Meantime, for the general information of honourable members, 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, the working-charges for the Waikato system amounted to £76,231, and the standing charges for interest and depreciation and renewals were £74,571, or a total of £150,802. For the year ended 31st March 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 operation costs of Arapuni for the year. The 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 operating capital for the 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 the plant installed was insufficient to take the whole available load during the earlier months of the year. The present installed capacity of the Arapuni Station is 45,000 k.w. and consists of three units. The fourth unit is now in process of shipment from England, and, had the course of events not been interrupted, would have been installed on arrival, thus bringing the total capacity of the Arapuni plant to 60,000 kw. In a subsequent statement details will be given showing the cost involved in calling into operation standby plants and other stations which were required to take the load when supply ceased from Arapuni, but it may be remarked that the estimate at present for the generating-costs at those stations is at the rate of £85,000 per annum, as against £12,000 for generating-costs had Arapuni continued in commission. W. B. Taverner. 28th June, 1930.

Approximate Cost of Paper. —Preparation, not given; printing (550 copies), £4 15s.

Authority : W. A. G. Skinner, Government Printer, Wellington.—ll)3o.

Price 6d.}