ARAPUNI SCHEME SOUND

Taranaki Daily News, 16 October 1930, Page 11

ARAPUNI SCHEME SOUND

CRACK NOT A BAR TO OPERATIONS

DAM AND RACE NEED REINFORCING

£560,000 WILL REINSTATE WORKS

? That the site of the Arapuni hydro-electric undertaking is satisfactory and the scheme can be developed to the full extent originally contemplated are the principal opinions expressed in the report of Professor P. G. Hornell, the Swedish expert, presented to Parliament yesterday. He finds that the mam dam is leaking and reports that the.damthe headrace and the spillway must all be reinforced to prevent leakage. The works have been designed in accordance with sound principles of engineering, and the crack which caused the stoppage of operations, was not due to the position or the driving of the plant. There is no reason to abandon the headrace or the power station if the remedial measures he suggests are taken, and there would be risk in bringing the power, station into commercial operation before finally checking erosion m the spillway channel, fhis sec tion of the work could be left until the dam and headrace had received attention, and it might then be found that further work was unnecessary. The Public Works Department estimates at £560,000 the cost of carrying out the whole of Plo J e ® s ® r nell’s recommendations, the . essential first section of the opeiations costing £360,000. . j

: By Telsjraph. —Presi Association. ' ' Wellington, Last Night. ' 'Tlie report of the Swedish hydroelectrical ertgineering expert, Professor p. G- Hornell, on ;the_ Arapuni power scheme was presented in the House of ■ Representatives this afternoon by ,the Minister of public Works; the Hon. W. B. Taverner. ( /- <; Professor Hornell 'expresscs the view .‘that the, general surroundings, and power development ‘possibilities at Arapuni are such that the locality is very suit-, able' for the economic development of hydro-electric' power. Gdncermng the '/'class of country it may be said. that it. by. no means excludes the possibility of creating a successful , water' power ' station on the site. He has no apprehension as to damage likely to .occur fbora water -leaking from the lake by. , w'-ay ,of Acacia'.'Gully. - ,;, , He finds that the main dam is correct •in its . position in' regard to the . ultimate proposed power output, but that as • there- is ■ evidence that the dam •'is-leaking 'at- some places in the foundation, even at the present lowered water level with the river at its original state,- it is essential that the origin of any appreciable leakage be located and. that the leaks • be carefully. grouted - tinder pressure.So as to stop effectively water passing under the dam or through the rock foundation. . Professor Hornell , iA' also ,of,- the. opinion that opportunity should'be taken further to strengthen; the country adjacent to the main dam, particularly on the western abutment, by reinforcing, grouting and waterproofing the sides of the, head race between ’the head race bridge and the junction of the head race with the lake. . In reply to questi.ons relative to the development of the scheme, the p'rofes- - sor states that the; works are sited in such way as to ensure the maximum power available (consistent with reasonable expenditure. “In general,”' he remarks,” it may be said that the works as executed have been designed in accordance with sound principles, of ehgineering. From the civil engineering point of view I have no adverse criticism to pass- upon the general location of the different parts ;of the plant in relation to each.other. On the electrical side of the problem ,1 can make no comment. Ab far as can' be seen from a detailed visual inspection on the site the constructional work has been well carried out. JUSTIFIABLE RISK TAKEN. • Discussing the question as to whether .the crack which took place on June 7 might hay® the professor expresses the qpiniqh that although the original plans'.and-specifications indicate that. the Public Works Department was not unmindful of the possible necessity for lining portions of the race, it took a justifiable risk in, not carryino- out this lining when the work was constructed. He is of the opinion that features such as the driving and operation of the penstock tunnels and the weight of the outdoor transformers’ • statibn. had very little effect' in causing the rupture. . He also holds the view that .the fact that the ■ crack has occurred will have.no effect in preventing the continued operation of the existing power station, and that there is no need for apprehension in extending the power, station in its present site to the full capacity anticipated. He can see no reason for abandoning • the present headrace or power station if the remedial measures suggested by him are carried out. With regard to definite consolidation of 'the falls, the report is not conclusive in that Professor Hornell states that in view of the magnitude, of the works involved he would require further time to make a mor© detailed ex* 1 amination before giving a. finally considered opinion. So far as his investigations have enabled him to go he is or the opinion, that the ..effect of water entering the columnar rhyolite rock between the spillway and the head of the falls may have had a considerable elfect in- causing the rupture at the f aU ®» and for this reason he has suggested the water-proofing of the channel. In ■ making this suggestion he stresses the point that as the power station is further developed the -amount ■ of- water which will be passing over the falls for considerable portions of the; year will be very considerable reduced.

changes at diversion tunnel

In regard to the diversion tunnel the expert is of the opinion that this should not be completely closed up with concrete, but rather that a second gate should be provided immediately above or below the present one so that repairs can be executed to the gates if necessity arises in after years. The professor considers that a considerable amount of grouting should be done in and around the diversion tunnel and immediately up-stream of the main dam, and he further suggests that the diversion tunnel should be plastered with a gunite surface. ' , * Finally Professor Hornell draws attention to the fact tljat throughout ho has done very little by way of estimating the cost of the various sections of.

I ffie work. “I feel that without considerably more knowledge of’local conditions atid prices I could not. dp this with any degree of accuracy,” he states. “In view of the fact that-H-.'have described the-.works proposed in* some detail I have now no. doubt but that tho engineers of the Public Works , Departs tuejit could provide estimates with a fair 'degree .of .accuracy.” - In a further statement upon' Arapuni MriJ Taverner said that after consideration of the .expert’s report he had considered it pdvisable to obtain further information ,4n ; relation to -the consolidation of, th© erosion, below the spillway, commonly .called 'the .'falls. * The locality had considerable bearing upon the- subject. In' a'letter to Professor Hornell, read by him, the Minister asked, that a more definite recommendation should be in regard . to’ 'what should be .done at the falls, and he asked particularly- whether ■ it- was considered-. that there was any risk of further extensive erosion should the plant be ..operated before the complete protective - work-at-the falls, had been carried, out.

BRINGING THE .PLANT INTO USE.

In his reply Professor Hornell said he was of the opinion that if remedial measures' for hampering the speed of destruction in - the spillway were ex.ecuted as outlined in his report there would be no risk .in bringing the power station" into commercial operation before, the final arrestation of the eresive processes in the spillway channel wherever this, should be done. The remedial measures proposed in his report might even be sufficient to make any .consolidation of the- falls unnecessary, 'especially if the power station were soon fully developed to its. ultimate proposed capacity. “Therefore I consider it inadvisable from a technical and an economical viewpoint to apply any scheme of consolidation of the falls without very careful investigation of the different possibilities,” Professor tHorilell said. “In the, event, - however, that in 'the course of time the' final arrestation of the erosion should be deemed necessary, a definite scheme should be worked out beforehand, and as soon as possible,. ready to be applied when the need arises. Preliminary considerations of different possible solutions have made me arrive at the conclusion that the arrangements required could be executed at a much lower outlay than that authorised. ” ' “Finally I would call attention to the important point that the work for the final arrestation of erosion in thej spillway <?liannQlcan, ; be . executed, without affecting the-operation of the power station?’' “Members-will perceive from the perusal of the report that Professor Hornell, for obvious reasons, has been -unable to give an estimate of the cost of his. suggested remedial measures, the Minister said.. “An estimate of the cost has, ••however? been compiled by the Public Works Department at '<£360,000 for the. work recommended by the professor. To this', of course, must be added the cost of consolidation of the-falls, estimated at £200,000, making a total of £560,000.”