Position Still Grave

Evening Star, Issue 20510, 14 June 1930, Page 13

Position Still Grave

{©rami. so ms ‘Stas.’]

Strain on Diversion Tunnel Dangerous Work at Arapuni Driving Emergency Tunnels

The petition at, Arapuni is practi-‘ cally unchanged. The level of the'lake, is being gradually lowered,;And about a-quarter of its contents has already been discharged*. . Water has practically ceased to . flow into the now channel towards the spillway, and the’head race should be sufficiently dry on Sun : day or Monday to ©liable a thorough examination to be made of the concrete buttresses and penstock intake structure to their foundations in the bed of the channel. The diversion tunnel, a huge' conduit measuring. 24ft in height by 24ft in width , which has hash gradually opened from 2ft 6in on Sunday to' between 6ft and 7ft yesterday, is taking far more water through it than the normal flow of the river, in order to lower the lak© and finally make it disappear completely, leaving' only the natural flow of the river above the dam. 1 ' ■ ; The dewatering process will .taka some weeks, and as tho pressure is gradually minimised, the gates will be given more “throttle.” This tunnel is the key of the whole situation, and the engineers are anxiously watching .the effect of the torrent through this “hole in the wall,” as all future remedial measures are dependent upon it standing tho strain imposed on it by a velocity of sixty miles an hour. On a former occasion the. tunnel proved unequal to tho task of taking a volume or water much greater thin the normal flow of the river, and a steel lining was inserted for protective purposes. Even this proved ineffective, and hundreds of bolts were torn out by tho tremendous force, of, the inflow. Since then the bolts have been welded, and some months ago the tunnel stood a five days’ test, and showed no signs of trouble. Since, the agates were opened for emergency purposes last'Sunday, the water has. surged through at a velocity calculated at approximately sixty miles an hour, and so far there has been no sign of the tunnel not being ,able to complete its' task. Since the, turbines have ceased work the lake waters are not discharging so rapidly as then.

THREE EMERGENCY TUNNELS. ? In th® meantime emergency measures are being taken in case of anything going wrong. Three tunnels are being driven, one into the bank to the east of the spillway, and just below the weir; one in the vicinity of the old falls, close to the submerged forest ; and one some distance above the spillway. Work is continuous in these tunnels, three shifts a day having; been arranged. It is dangerous work i for those engaged in the. tunnelling,. and on account of the uncertain char-; actcr of the land and the risk of vibra-' tion causing further earth movement, explosives cannot be used. 1 The tunnel above the spillway is being continued to a junction with an emergency penstock known as *No. 7, while the drive: in the vicinity of the falls is cutting back to No. 4 penstock. Both of these drives are 'in the vicinity'of the surface cracks that have made their appearance, simultaneously with the fracture of the north-eastern corner of the spillway weir. The tunnel below the spillway is for exploration purposes to trace the fissure through the adjoining bank,; separating the old and new river channels. Until all the fissures are traced, and the surveys completed, it will not be known whether the “tilt” that has occurred is towards the powerhouse in the gorge, or towards the spillway, DANGER TO WORKMEN. The gorge between the powerhouse and the dam, which is now the river, is running like a millrace,, and a certain amount of erosion seems to be taking place on the up-river side, immediately adjoining the. powerhouse. The new emergency pfenstocks. emerge in this vicinity, and the water . has backed into the" openings, and has even penetrated into the powerhouse and flooded the excavation, where a fourth turbine is being provided for. The whole situation is still grave, and the engineers will be most anxio ■; until the lake has discharged the whole of its contents. Then h proper survey will be possible, and much data will be available by then as to earth movements, - ‘ and the extent of the cracks. The men who are working in the various drives and tunnels are facing extreme danger every minute of the day and night.