TEKAPO SCHEME.

Press, Volume LXI, Issue 18571, 22 December 1925, Page 5

TEKAPO SCHEME.

HYDRO-ELECTRIC POWER. POTENTIALITIES DISCUSSEP. (SPir-IALLT written fob "the PM3S.") (13y Herbert Hall-) . Since 1204, when a comprehensive survey was made of the water power possibilities of New Zealand for the purDoses of a Parliamentary report, South Canterbury has been recognised as particularly favoured by Nature with sreat lakes and rivers capable of devclopiivs power &o an almost unlimited extent. The main, backbone of the Southern. Alds rises to its maximum height on South Canterbury's western boundary, and bedded in its gorges are the largest glaciers in tho Southern Hemisphcie; tjiese permanently feed Lakes Ohau, Pukaki, and Tekapo and form the headwaters of the Rangitata River. South. Canterbury's northern boundary is the snow-fed river, Rangitata, and its southern extremity is bounded by tha Waitaki River, fed from three great lakes. It is apparent even from a casual survey that the hydraulic possibilities from these lakes and rivers are very considerable. The lakes are of nreat altitude and might be utilised £or high-head schemes, and the river banks are of suitable formation for tho construction of low-head power plants alone: the lines of those so successfully used in Switzerland and Sweden, where rapids of as little as six or eight feet fall are use.-l for tho economical generation of power. It was probably the fascination of considering the possibility of constructive a super-plant of hundreds of thousands of horse-power capacity that 20 years aao led to the neglect of smaller themes more suitable for the requirements of tho present time, and within tho financial resources of tho South Canterbury people. While it makes engrossing study to contemplate tho full utilisation of the latent power in South Canterbury's lakes and rivers, the practical issue should 'be one of devising comparatively small and economically designed schemes suitable for supplying the consumptive demand at the present time, and also capable of progressive development as tho understanding of, and demand for, electricity grows in both town and country. _ A typical scheme of suitable dimensions ijnd of, small cost is the one oronosed and already carefully investigated at the mouth of Lake Tekapo, fifty miles from tho port of Timaru. Scheme Explained. This development is on the low-head principle, which is largely adopted in Canada and Sweden, where similar conditions exist. No consideration is to be given to the altitude of the lake, nor is a tunnel required; it is rather the river immediately below the lake outlet than the lake itself which it is proposed to utilise. This is made feasible and easy, in an engineering sense, by the singular "S" bend in the river's course just below the foot of tho lake. At its commencement the river flows southwards through a gorgo 150 foot high for three-quarters of a mile, to issue upon a series of morainic shingle flats. Around these tho river takes an extremely winding and rapid route; two complete loops form the "S" bend, its tail is only a mile from the lake, while tho course to form its convolutions is three miles and a half long. Across tho foot of tho shingle flats, whose general level is twenty-five feet above the river-bed, a power canal is to be cut to short-circuit the loop. At the gorge mouth a crib-dam of timber and largo boulders will bo constructed to divert the river w.'itcr or such proportion of it as may be required, into the power canal, but it will allow the surpl.is .and flood waters to pass over its crest. The canal-cut will cross the

shingle flat at the foot of the hill, to join the loop of the river 011 the further side. By this means the river makes, as it were, a new straight course half a mile long, with a. fall of about eight feet in that distance, in place of its natural winding course of about two miles with a fall of 75 feet. This diversion of the river thus makes an artificial waterfall 68 feet high; the actual net working head for the turbines being 55 feet. The canal will be controlled at its intake by floodgates and a spillwav, and at the power station end it terminates into open concrete chambers, in which the turbine runners will be placed; these will in their turn be directly coupled to the electric generators' units.

Capable of 20,000 H.P. The hydraulic conditions are favourable for "a simple type of low-head river development; the bend as described allows a medium head to be obtained with onlv a half-mile long canal, without a retaining-dam in the river-bed, or pipe lines to the turbine. The usuai difficulties of shifting shingle and heavy flood-water have already been mastered bv tho natural provision arising out of the position of the lake immediately at the back of the river bend. The great area of tho lake—over 3G square miles holds and controls the floods from the mountains beyond; the narrow outlet to the river, scarcely four chains wide over a high natural bar, holds back the excess water and regulates the discharge into the river. Tho lake fulfils tho functions of shingle-trap, floodbuffer, and water reservoir. With the 55 feet head available and the minimum flow of ~ oou cubic feet per second, 10 000 h.p. will be developed. The scheme is capable of easy extension up to 20,000 h.p. by the artificial conservation of the flood-waters in the lake by the construction of a simple j

type of timber weir, about five chains long, placed over the bar at the lake outlet. This does not exhaust the possibilities of progressive development along the lines described; only one loop of the bcrnl will be used in the initial developmu>t, allowing the same water to be reuse d by diversion across the second loop in the lower reach, with a corresponding duplication of water-power, when the demand for electrical energy necessitates future extensions.