WAITAKI SCHEME

Press, Volume LXVI, Issue 20036, 18 September 1930, Page 14

WAITAKI SCHEME

POWER FOR CANTERBURY. CRITICAL STAGE REACHED. DANGER OF SPRING FLOODS. f Two gigantic holes where hundreds of workers toil like ants, the one right in the path of a swift-flowing river, the other on its bank, but joined to the first, save for a gap of swirling water, by the beginnings of a canal soon to be much deeper—that is the first mental impression conveyed by the Waitaki power scheme. But the simile might be carried much further, and the workers subdivided into digger ants, engineer ants, builder ants, and their industry likened to the toil of a whole colony of ants, each section of which performs its allotted tasks, yet is united to its fellows by the consciousness of a single scheme which pervades all. There, perhaps, the comparison may end, for looking down into those vast pits the observer is conscious of a ceaseless noise, which no colony of ants ever made —the machine-gun rattle of pneumatic drills, the panting of pumps, the shriek of whistles, the roll of wheels on rails—and the mastery which man holds over machines, to promote just such designs as this. To grasp the immensity of the scheme and to inter-relate its parts, even crudely, takes the layman unfortified by a previous study of charts and plans the uetter part of a day; to reach an understanding of it in something like detail would occupy even the brightest minds nearly a week. Briefly, then, the Waitaki river at the dam site is in a deep single stream confined between rock banks, the one on the southern side shelving away to a high terrace, and the other rising sharply in a hillside direct from the water's edge. Steel sheath piles were driven, almost is the form of a square, to join with the Canterbury .side, and by the building of walls of sandbags filled with clay, and- the accumulation of an immense quantity of spoil, the area of the river so enclosed was rendered comparatively water-tight and was pumped out, to enable work to be commenced on the foundations for the northern section of the dam. The word "comparatively" is used advißedly, for water continues to stream into the area, now a giant pit, at the rate of nearly 500,000 gallons per hour, which is not greater than was anticipated. It is held safe, however, and soon the concrete work will have reached a height deemed sufficient for the time being.

Spanning the Elver. Then the work done will be repeated by the blocking of the second half of the river, all of whose volume will be diverted through the channels or sluiceways piercing the northern half of the dam, made for this purpose. Once the river is safely disposed of in this fashion, work will proceed on the construction of the southern sector of the dam and on the completion of the portion joining the Canterbury bank to its maximum height, and it will be continued in a great wall to the powerhouse, several hundreds of yards across the river flat.

I When all is in readiness, the sluicegates to cover the channels already mentioned will be closed, and the river will be allowed to back up into a lake, which will extend up the valley for five miles. . Eventually it will pour over the spillway at the power-house in * great cascade; and turn the machinery which will develop 46,000 horse-power and, when necessary, more, rendering Canterbury and North Otago independent for all time, it is hoped, of the present supply. . Prom the present until some time in November will be the critical period in the whole undertaking, for a casual glance reveals what havoc a high flood, such as would be welcomed at Lake Coleridge, might work at the Waitaki dam. "If we do not complete the present stage before the summer floods," Mr B. H. Packwood, the engineer in charge, told a representative of Thb Pbbss, "we may not be able to finish it for a year." With a continuance of the favourable conditions experienced for many months, and of the electric power supply, the Waitaki river should be producing electricity by the winter of 1932. "We could weather a flood aa big as any we have experienced since January, 1929," said Mr Packwood. This occurred five months after the scheme was commenced, and did serious damage. It is obvious that a heavy flood would submerge some of the works, even if it did not carry away any of the plant and structures, and it would almost certainly bring about a gtfeat increase in the quantity of water reaching the excavations.

Worse, possibly, in itß effects, would be the precipitation of silt, which the river would leave behind it. Fortunately trees are not plentiful on the Waitaki watershed, and the river never carries much debris.

Not a motor is now turning on the job, or a unit of electricity being used that is not essential at this critical stage of the work, and any further curtailment would have the effeet of slowing down the progress being made with the undertaking. At present the total number of men employed is 1220, and this is within a score of the irreducible minimum necessary to carry the scheme past the peak. The number may rise to 1300, but that will be only a passing phase. To employ on full time the 1220 necessitates the running of the minimum amount of plant now in use; pome would'have to be discharged if there was a reduction. A constant stream of men seeking work visit the dam now, and the engineers are anxious that the problem should not be increased. Power Economies. Awakino, the workers' settlement, is just as dark at night as any Christchurch suburban street, and men coming off shift climb the narrow paths to their huts without the aid of the electric lights with which they were formerly brilliantly illuminated. To reduce the number of lights round the dam and power-house sites, however, would be to endanger life and limb. Such good progress has been made on the dam that the centre block has been completed in the last fortnight to the height provided for this year, and when the section on the Canterbury side is finished, which should be by November, it will be approximately halfway up, or within 53 feet of the top. The excavation for the dam is about 270 feet long, 230 feet wide, and 80 feet deep, the bottom being 40 feet below the level of the surface of the water. For the whole of its length of

1700 feet an inspection gallery will run through the dam, and-in the piers under construction it may already be seen. The spillway section, which win be 105 feet high from rock bottom, win nave a length of 1200 feet. The base of the dam will be 100 feet wide,.and a toe block of concrete six feet thicK will protect the rock on the downstream side of the spillway. Frames for the sluice gates nave already been railed to the site.

Hump Tracks. The principle of the hump track at the Middleton railway yards has been followed for propelling the bins of concrete, mixed on the south bank, along the rails crossing the two trestle bridgeß which span the river, and each has been so designed that the tubs will travel without human aid right to tne north bank. Men leap on the bins ana brake them with a piece of timber opposite the chutes, which reach UKe great tentacles down to the piers. Wet cement sacks placed on the rails are also very effective. Concrete pours down the chutes in an endless stream, and the consumption of cement must be enormous. While some of the men spread it to fill the boxing, others with pneumatic drills, picks, and shovels, and wearing gum-boots, clear the gravel off the rock bottom in the bed of the streams coursing towards the pipes which, suck up the water for discharge through the sheath piling back into the river. The steel piles have not been driven down to the rock, but only to a depth at which it is economical to pump. The workmen are assistfed by a dragline excavator, the bucket of which is drawn backwards and forwards along a stout steel rope, stretching right across the excavation, and by bins which, when filled, are drawn up rails to the spoil tip by a wire rope. High overhead, on the south bank, a puffing locomotive, running on a track constructed over a wooden bridge, draws trucks of gravel which are tipped on to the screens above the concretemixers, and a stone-crusher operates nearby.. No less interesting than the work on the dam are the preparations for the erection of the power-house, which will be 340 ft long, 134 ft wide, and 130 ft high from the foundations to the roof. The site is dominated by. an immense ■teel crane, which swings its great arm over the Blue the huge cavity into which the power-house will be built is called.

Power-House Equipment. Three steep stadium-like structures of timber and reinforcing rods next command the attention, and one'is astonished to s learn that they have been first assembled in the timber yard some distance away, and transported to their final position, each in over 80 sections. They are the form work for the penstocks, which will lead the water into the scroll. In its turn the scroll will feed the Water to the turbine runners, causing them to rotate the shaft which drives the generator. After turning the runners the water will flow through the draught tubes into the tail-race, and so back into the river. The two turbine runners have been delivered near the power-house site, and the two draught tubes, which are of fabricated steel, have been assembled, and the first is in place at the foot of its scroll case. Soon the second will also be lowered into place by the huge crane.

To stand the stresses of such an operation and those exerted by the concrete with which they will be encased, each has been stayed inside by a timber framework. It is only necessary, to convey some idea of the size of these giant tubes, to state that the diameter of each at the top is 15ft, and they are about 40ft across at the outlet. Only 'two units will be installed in the present scheme, although provision is made for five ultimately. The best view of the power-house site is obtained from an access tower, which must be nearly 80ft in height. When the boxing is ready for the pouring of the concrete and the maximum quantity is being mixed, three machines will: be in operation. On the terrace overlooking the job ten concrete bloek cottages are being erected for the power-house staff by Messrs Shillito's, Ltd., and the foundations have been constructed for a x big hostel, to provide accommodation for the single men. Later a block of six garages and another of ,two will be commenced. The houses all have a dampcourse of malthoid and felt, and are very, attractive in appearance. They are now approaching completion. Down on the flat 13 workmen's huts, painted red, have been erected close to the liver's edge. Each is supplied with a fire Jiose, a high pressure water supply having been laid on. Any City person inclined at present to pessimism and a b'elief that the depression is universal would change his views after a visit to the dam site and Awakino, where the Dominion's greatest electrical station is in the making, and over 1000 men, a big proportion of those married having their wives and families with them, have formed a little community which has rapidly established , the principal amenities of civilisation.