ARAPUNI & HAMILTON.

Waikato Times, Volume 108, Issue 18157, 23 October 1930, Page 9

ARAPUNI & HAMILTON.

RECOMPENSE ASSURANCE DESIRED BY COUNCIL. .-SHOULD MORE TROUBLE OCCUR. The suggestion that the Hamilton Borough Council should seek an assurance from the Government that the council would bo fully recompensed for all damage done should further trouble occur at Arapuni . was contained In a letter from the borough engineer (Mr R. Worley) which was read at the council msotlno last evening.

• In his letter Mr Worley said — I have read with considerable interest Professor Hornell’s report on Arapuni, and . while I do not in any way wish to convey the slightest suggestion that I am attempting to criticise It there are' some aspects of the question as stated by the Professor that in my opinion should be considered by the Hamilton Borough Council. ... , The cause of the failure is attributed by Professor Hornell firstly to capillary attraction for water of the columnar rhyolite underlying the spillway and the lower portion of the headrace; secondly, to the fact that such columnar rhyolite expands when it becomes saturated; and, thirdly, that the stresses caused by such expansion between the upper and lower stratas eventually brought about a break in the country. Remedial measures include the grouting with concrete of the existing crack, the repair of the spillway and intake, the lining of the lower portion of the headrace from the spillway to a point 350 feet above the apparent termination of outcropping columnar rhyolite, the construction of drainage tunnels to prevent the accumulation of water in the lower levels of the crack that will not be grouted, and the lining of the upper portion of the headrace where it leaves the main dam. The Professor considers that if water under pressure can be prevented from entering the rock underlying the headrace there would be no further danger. It will be seen from the above, however, that it is proposed to leave as it is, without any lining, the greater length of the headrace, probably on account of the different country and to the fact that the ridge separating the headrace from the gorge is much wider on the proposed unlined portion. However, the Professor states as follows: “From the point of view of absolute security there is no doubt that it would be advisable to extend the lining to the foot of the cliff that serves as abutment, for the main dam; but I cannot advise it, because I believe that there are fair prospects of gaming at less cost a satisfactory result.” In short, the Professor considers that the,.natural conditions are such that it is well worth a gamble in not lining the whole of the headrace; and no doubt he is right. I would quote another paragraph from the report dealing with .the porous layer under the proposed plastic lining of the lower portion of the headrace. "The more importance I give to the aforesaid porous layer, the more strongly I recommend that it be arranged with proper care and with the use of proper materials. There is a theoretical possibility that it might partly clog on account of weathering of the underlying rhyolite rock. I feel, nevertheless, convinced that it will serve its aims if properly carried out..

Possibility of Earthquake. In order to guard against the unexpected happening it is proposed to install duplicate gates in the diversion tunnel and to condition the tunnel so that it may be able to be used at any time to - its full capacity in lowering the level of the lake, and to install an automatic alarm signal in the event of the water in the drainage tunnel being excessive.' Finally, Professor Hornell makes it quite clear that in his opinion a sudden rupture of a portion of the ridge between the headrace and the gorge would only be possible in the event of an earthquake, and that the question of the possibility of earthquakes occurring does not fall within the scope of his inquiries. It is to be noted that Arapuni is only forty miles in a direct line from one of the major geological fault lines in New Zealand, and I think the omission of this aspect from his scope of inquiries is regrettable. Having in view the trouble we have experienced in the past, due to the Arapuni operations,-and in view of the above-mentioned aspects of Professor Hornell’s report, I feel that the Hamilton Borough Council would be wise to seek an assurance from the Government that the council would be fully recompensed for all damage done should any further trouble occur. The Mayor (Mr J. R. Fow) remarked that it was a matter on which the council had to be guarded and careful, but no harm could be done by sending a diplomatic-letter to the Government. The one big factor to cause further trouble, and the only one likely, was that of earthquakes, and if anything did happen the council desired to be recompensed if at all possible.. The previous time the council had been recompensed to the extent of only £looo—a totally inadequate sum —and a great v strain had been placed on the town and on the borough staff. It was decided that the town clerk (Mr W. L. Waddel) should forward a letter to the Government as suggested by the Mayor.