The Evening Star THURSDAY, FEBRUARY 1, 1934. WAIPORI HEADWORKS.

Evening Star, Issue 21634, 1 February 1934, Page 8

The Evening Star THURSDAY, FEBRUARY 1, 1934. WAIPORI HEADWORKS.

The steep hillside above the power house at Waipori Falls is an asset in power-production. Its presence was one reason for selecting the site for a hydro-electric headworks. At the inception of the scheme, when, in the day of small beginnings, there was no thought of storing water, it was realised that the dry-weather flow of the stream was small, but the exceptional head of vertical pressure obtainable within a small horizontal distance was regarded as ample compensation for deriving horse power through the medium of Pelton wheels. (At the Waitaki power station the reverse conditions hold, the fall giving the pressure, to operate the turbines being relatively small, but the volume of water available being virtually inexhaustible.) However, the Waipori hillside is also a liability. This was experienced from the outset. Originally a wooden flume led the water from the weir to the penstock, traversing the sideling above the river bed. There were recurrent interruptions to the power through boulders above becoming dislodged and crashing through the flume, or by minor slips carrying away sections of the flume. That disability was eliminated once and for all by tunnelling through the hill between the weir and penstock. At the time it appeared an ambitious undertaking, but it had been made worth while because in the meantime the necessity for water storage had been realised, and the minimum flow through the tunnel sufficed to operate a larger generation plant than that originally conceived. (It may be as well to remind the younger generation of our readers that the Waipori rights were originally acquired from private enterprise merely to provide power for the operation of Dunedin’s then new electric tram system, estimated to require about 900 h.p.) As more units were installed in the power house the system of pipe lines down the hill grew, but there has been occasional trouble with them- owing to the insecure foundation provided by earth lying at so steep an angle. The best remembered interruption to the service occurred some years ago (1929), and lasted three weeks. Loss of revenue, let alone loss of prestige, from such a cause is a rather serious matter, and there has been long deliberation at the Town Hall over preventing such a recurrence by giving absolute permanence to the pressure supply to the power house, as had previously been done in the conveyance of the water to the spot where it was to begin to do its work by replacing the flume by a gravitation tunnel. Last night the City Council decided to replace the pipe lines by a pressure tunnel. The latest of the lines installed will therefore only have completed a very short life, and the expense of sinking an inclined shaft from surge chamber to power house would appear premature were it not for the fact that a fifth 3,000 k.w. generator unit in the power house should in 1929 have been connected with a new pipe line, but the line was not installed because the slip had destroyed confidence in the reliability of that form of connection. Since that time, it appears, the stability of the hillside has been constantly under observation, as a result of which boring and a geophysical survey were undertaken. The conclusion reached by the E.P. and L. department’s consulting engineer was that not only would a pressure tunnel remove anxiety on the score of reliability, but it would prove economical in the long run. The estimated cost is £58,000, and in view of the ratio of this figure to the capital expenditure to date on Waipori (the loan capital is stated in the latest council Year Book as £1,419,000) that figure does not appear excessive, particularly as it is not proposed to borrow for the purpose, but to charge the amount to renewals and draw on the fund established for such purposes. It is expected that by the time the tunnel is completed, about two years being required for the work, power will be available from Waitaki, and this will carry Dunedin’s load during the presumably brief interval while diversion of the water from pipe lines to tunnel is being effected, thus averting any cutting off of current. It will be a matter of interest to the Dunedin public to see which work will be accomplished first—the Waipori pressure tunnel or the Waitaki scheme. On the whole, the latter has experienced favourable conditions—i.c., an absence from floods—for the difficult part of the engineering work on'the dam, and

the work is now so far advanced that comparative independence of high river effects can be expected henceforth to the completion of this great undertaking. Apart from the somewhat captious attitude of one councillor on the grounds of a snap vote, the only matter in dispute last night was on the hoary issue of day labour versus contract. It is refreshing to see that veteran councillors are by no means ignorant of the uneconomic results attendant on the day-labour system which has from time to time marked various Waipori extensions. The accumulation of unsaleable plant was by no means the only form of waste.