WATER POWER.

Press, Volume LXIII, Issue 19138, 22 October 1927, Page 15

WATER POWER.

CANTERBURY AND OTAGO. WAITAKI TO BE HARNESSED NEXT. [THE PEBSB Special Serrlee.] "WELLINGTON, October 21. In the annual reiwrt of the Chief Electrical Engineer attached to the Public Works Statoment there are inesting references to investigations in connexion with the future power supply in Canterbury and Otago. Mr Kissel says the first, point for consideration is the prospective load for a considerable period ahead and the capabilities of the existing plants to supply tho demand. The value of comparatively large generating plants inter-connected by transmission lines is now generally accepted. The obvious adoption of this policv on the eastern side of the South Island (Canterbury and Otago) is that we should have an extra high tension main transmission line running from north to south through Canterbury and Otago, and that this transmission line should be tapped at various points by main substations to supply the various load centres, and supplied with power at various points where such power can be most economically supplied.• Beaching Capacity. A forecast of the probable growth of load is shown ill a graph, l'rom this graph it is fairly evident that the present Lake Coleridge power station of 27,000 k.w. capacity will bo fully loaded about 1931, and that Waipori (Dunedin) will have reached its capacity (assumed at 20,000 k.w.) about three years later, lb would appear that, neglecting Otago for tho time being, by 1940 there should be a load available of about 65,000- k.w., or 38,000 k.w. in excess of the present Lako Coleridge capacity. Similarly, it would appear that there should be a load of 12,000 k.w. over and above the estimated capacity of Waipori available in the portion of Otago supplied from that source. There is also undoubtedly a very considerable prospective load in Otago Central, which would bo quite economically supplied by the generating station where located on the Waitaki river. Next Station on Waitaki.

"Taking all points into consider- j ation," says Mr Kissel, "there is no difficulty in recommending that the next main hydro-electrio development feu- the South Island should bo on the VVaitaki. The Waitaki river has decided advantages over the Waimakariri when the question of dams has to be considered. In the first place, on account of the large amount of lake area in the drainage basin, the flood flow, as compared with ordinary mean flow, is very considerably reduced. For the same reason the amount of shingle travelling in the stream and tending gradually to reduce storage values is very much less than in the case of the Waimakariri or the Raka'ia. As the minimum flow in the river is about three times the minimum flow in the Wamakariri, the same height of dam affords at least three times the amount of power. The long crest of dam available for overflow reduces very considerably the depth of water flowing over the dqim in times of flood, and so reduces the possibility of erosion and damage behind the dam." It is estimated that a complete deveir opment at this point to a capacity of 30,000 k.w., and including transmission lines to link up with the main line, one at Oamaru and one at Timaru, would cost about'£l,2oo,ooo. In the initial development this might be reduced to £1,000,000 by the omission of one unit and one transmission line. By building subsequent low control dams at the outlet ; of each of the lakes tlh© capacity of this one station could be brought up to 75,000 k.w. on a 50 per cent, load factor basis. Further power, both above and below this station can be developed qn t!he Waitaki.River.and at the different lakes if necessary at a later date- without in any way interfering with the output from this station. To develop the station indicated aibove to the 30,00 k.w. stage would take, about three years from the date construction is commenced. . Another Unit at Coleridge.

When the Coleridge duplication works (completed last year) were designed, provision was made for the installation of a third unit of 7500 k.w. in the station. This can,he.installed at a cost of about £65,000; and if the scheme proposed above is adopted this unit should be installed at Coleridge somewhat in advance ofstlie major develqpment_ at Maitaki. The per kilowatt cost is low, and as it can bo installed more quickly than can the main development, its installation would obviate any risk of short supply and allow the main construction and expenditure to be delayed by about a year. The amount of water available at Coleridge woul dwant careful watching if a dry year were struck, and we would probably have to draw considerably on the storage until the Waitaki was ready, The Waitaki site outlined above appears the most suitable, available and is certainly preferable to the Waimakariri or Lafee Tekapo proposals.