LAKE PUKAKI CONTROL

Press, Volume LXXXIII, Issue 25362, 9 December 1947, Page 8

LAKE PUKAKI CONTROL

TESTING OF GATES

WATER LED THROUGH COFFER DAMS After the satisfactory test yesterday of the control gates at the outlet of Lake Pukaki, an adequate supply of water for the four turbines at the Waitaki power station next winter is assured. The installation of these gates, and the erection of a temporary dam will give an extra eight feet of storage in the lake and permit control of the flow of the lake to the power station. The resident engineer (Mr E. D. Kalaugher) estimates that every extra foot of water in the lake can generate 1,250,000 units of power. Full advantage of the expected rise, in the lake level cannot be taken until the installation of a fifth turbine at Waitaki, which is not expected by next winter. The breaking-down of the coffer dam to . divert the water through the gates, scheduled for last Sunday, was delayed. It was hoped that a small trench could be dug to let the water through from the lake in a controlled flow, but the dam was found to be of such soft earth that the amount of earth flowing into the tunnels might have caused a blockage. A siphon was set up during the week-end, and water began to pour on to the gate side of the coffer dam on Sunday morning. By using the siphon, it was hoped to equalise the level of the water on both sides of the dam, so that the dam could be breached withdut fear of excessive scouring. The siphon, however, ceased to work on Sunday afternoon, when the water in front of the tunnels leading to the gates was about five feet below the level of the surface of the lake.

The siphon was then abandoned, and work was begun on laying a drain through the dam. The trench in which the drainpipes were laid was dug with a dragline and water was again running from the lake into the pool in front of the tunnels at 4 o’clock yesterday afternoon. The heads of water on each side of the breached coffer dam were level in a few hours, and last night water was put through the gates as a test. By the raising of the gates, much of the outflow from the lake can now be diverted through the tunnels. Five concrete tunnels, each 10 feet square at the intake, carry the water nearly 100 yards. The gates are set about half way along the tunnels, and in spite of their size and weight are fitted to a fraction of an inch. Another Dam With about half the water flowing through these tunnels, the diminishing outflow along the present course—under the traffic bridge—will enable another dam to be built. This dam will be temporary, and a few yards downstream of the present traffic bridge across the Pukaki river. It will hold the expected eight-foot rise in the' lake’s surface. Consisting mainly of rocks and shingle, the material for the dam will be piled up the banks of the river. In about six weeks, if the work proceeds according to schedule, this material will be pushed into the river by bulldozers and the dam formed.

Work at the lake will not be finished with the construction of this dam as the ultimate plan is to raise the level of the lake S 5 feet above its present level. This will be achieved by building a permanent dam about 200 yards long, roughly in line with the present gate, structure.