FOR HYDRO WORKS

Waikato Times, Volume 127, Issue 21187, 9 August 1940, Page 4

FOR HYDRO WORKS

GREAT TRANSFORMATION KARAPIRO BITE PREPARED PROGRESS ON TUNNEL SHAFTS PLANS FOR HUGE DAM Something new in “blitzkreig” is in progress not very far from Cambridge. It is a lightning war against the existing terrain at the site of the new hydro-electrical power station in the preliminary stages of construction at the Crow’s Nest, Karapiro, about four miles upstream on the Waikato River from Cambridge. Bulldozers and other modern mechanical navvying machines are the weapons of a remarkable transformation of the contour of the countryside. It is only five weeks since work first began on the scheme, yet in that time hillocks of age-long standing have tumbled, roads have been hewn out of cliff faces and over rolling pastures, undulating tussock country has been swept into a large flat, and small gullies have been filled. Contrasts in the initial progress on this power scheme and the Arapuni construction which was commenced in 1924 are well defined. Almost overnight modern machinery has transformed the face of the site, whose geological history extends over many years, to suit it as a base for the building of the works, whereas at Arapuni some time elapsed before any great change could be perceived.

Preliminary Shafts The Crow’s Nest power station, when completed, will generate 85,000 kilowatts, but much water will flow through the rocky defile of the natural site before that stage of construction is reached. A start has actually been made on the power scheme proper, however, which will be pushed ahead rapidly from now on while the other work of laying out the adjacent areas and the erection of buildings and living quarters proceeds. The constructional work actually in hand involves the sinking of two shafts as a preliminary to the piercing of the diversion tunnel. The two shafts are being bored at intervals of thirds along the line which the diversion tunnel will follow. One shaft will be sunk to a depth of 120 feet to a point that will become the floor of the tunnel. The second shaft, which is being sunk at a point almost where the dam will be constructed, will have to be bored to a depth of 180 feet to reach the level of the future floor of the. tunnel. The shafts are about 12 feet square, walled with heavy timber as they progress to a greater depth. When completed, they will be fitted with electric lifts to carry the tunnellers to their task in the rocky bowels of the terrain. Drilling Through Rock It is expected that the work of sinking the two shafts will occupy about two months. There are now two shifts being worked on the shafts, but shortly, when accommodation is available, a full three shifts will be worked to keep the boring progressing 24 hours a day. When the shafts have been completed the drives for the tunnel will be commenced on four faces, outward and inward from each shaft. An automatic tip system will carry the spoil from the tunnel. An indication of the nature of land formation at the Crow’s Nest can be gained from the progress alieady made on the shafts. One has progressed to a depth of about 20 feet, yet for some feet the bore has been made through solid rock. The longer shaft has progressed about 15 feet through clay, although rock is expected to be encountered within the next few feet. Compressed air drills are employed on the rock. Fifteen Months On Tunnel Fifteen months is the time estimated for the driving of the tunnel, which will be 1000 feet long. The egg-shaped cross-section will be about 25 feet in diameter. The tunnel will be driven across a rightangled bend in the river, which sweeps through a rocky gorge on a sinuous course. When the tunnel is completed the river will be diverted through it so that a dry bed will be secured for the foundation of the dam, which, from the extreme bottom of the foundation to the road level on top, will be about 170 feet high. The power station will be constructed on the downstream side of the dam on the Karapiro bank of the river, while a switch station will be located on the Maungatautari side of the site. A spillway will be constructed on the Karapiro end of the dam. The construction of a power scheme at the Crow’s Nest will mean the formation of a huge lake from the station to Arapuni. Type of Dam It will be a huge dam that will impound such a vast quantity of water. Construction will be on the gravity-arch principle, the centre being arched, with the thrust taken by heavy gravity sections on either side. The second biggest hydro-electric power station constructed on the Waikato River is thus under way. During the next three to four years great changes will become apparent at this old river course, which for years remained undisturbed until the needs of man demanded more power. Soon little trace will remain of the physical and human history with which the Crow’s Nest site is richly endowed. Signs of the fortifications used by the famous Maori warrior Te Waharoa are fading. Also disappearing is some of the interet>ng geological evidence which has assisted th> reconstruction of the story of the Waikato River, although the work may unearth new geological discoveries.