THE PUKAKI SCHEME

Otago Daily Times, Issue 26747, 16 April 1948, Page 4

THE PUKAKI SCHEME

Twenty Million Units Stored For Winter Use

GREAT EARTH DAM

Comparatively remote as they are from Dunedin, the two major hydro-electric schemes at Lake Pukaki and Lake Tekapo are probably little more than a name to most consumers of electricity in the south. Yet they are vital not only to the present supply of power but to the thousands upon thousands of kilowatts that can be produced from the complete harnessing of the Waitaki River.

Without the control of these two lakes—and possibly Lake Ohau—power schemes on the river would be of full use only in the summer when the river flow is great but when the consumption of electricity is comparatively low. The ultimate capacity of Waitaki will be 75.000 kilowatts, but last winter sometimes only one unit producing 15.000 kilowatts was in use. so reduced was the flow of the river Full control of the lakes will enable water to be stored in the summer and released as required during the winter Hence their importance to the power supply of the south in the years before the Roxburgh scheme is completed. Great Storage Capacity The first of the two schemes to affect the power supply will be the Pukaki project. It will play an important part in the coming winter months, because, with the completion of the temporary earth dam and the operation of the permanent sluice gates, already nearly 21.000,000 units are represented in the water that is at present being stored and controlled. The dam has raised the lake level 10ft and through the sluice gales can be drawn off, if necessary, another five feet of water below the normal level of the lake, giving control over a total of 15ft of water. When the main earth dam is completed the level of the lake will be lifted between 30ft and 35ft. This will give a storage capacity of more than 50,000.000 units. Work on the Pukaki scheme has reached an interesting stage. The temporary dam was completed some time ago. five box culverts convey the water to the sluice gates which can now be controlled by temporary winches, and a stilling basin Beyond destroys the energy of the released waters and prevents them from scouring a great hole beyond. There is still a certain amount of seepage—there always is through an earth dam—and at present the temporary dam is being sealed more effectively with fine spoil. 1 At Pukaki the foundation was not suitable for the building of a concrete dam, and so a natural method was adopted—the construction of a huge earth dam. This dam will be 1200 feet in length and the concrete spillway to the north will be 300 feet long, with an overall width of 600 feet. The earth dam will contain half a million yards of material, and by the time the whole job is completed twice that amount of spoil will have been handled. On top

of the dam will be the main highway, which will pass over a bridge above the spillway. Completion in New Year The chief task confronting the engineering staff and the 240 men on the job at present is preparing the ground for the main earth dam. Pockets of pug were found in the area to be occupied by the dam, and all these have to be cleaned out before the dam it built, at present an experimental area is engaging the attention of some of the innumerable carry-alls, tractors, Sheep’s-foot rollers, rooters and dozers on the job. Selected material is being spread, consolidated with the special rollers, watered to achieve maximum consolidation, and tested for density. Soon the pug from a wide hole containing the seepage through the temporary dam will be removed and the main dam begun in earnest. It is expected that the main earth dam will be finished in the new year and that the concrete spillway will be completed in about eight or nine months’ lime. Later a mole will be built at the entrance to the box culverts, marked at present by a vicious whirlpool.