ARAPUNI WORKS

Greymouth Evening Star, 14 June 1930, Page 12

ARAPUNI WORKS

A REVIEW OF THE POSITION.

[special to “stab.”] AUCKLAND, June 13. The position at Arapuni is practically 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 new channel towards the spillway, and the headrace should be sufficiently dry on Sunday or Monday to enable 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 .n height by 24ft in width, which has been gradually opened from 2ft 6m 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 lake, and finally make it disappear completely, leaving only the natural flow' of the river above the dam. The watering process will take some weeks. As the 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 the strain imposed on it, a velocity of 60 miles an hour. On a former occasion, the tunnel proved unequal to the task of taking a volume of watei’ much greater than the normal flow of the river, and steel lining was inserted for protective purposes. Even this proved ineffective, and hundreds of bolts were torn out by the tremendous force of the inflow. Since then the bolts have been welded, and some months ago they stood a five days’ test, and showed no signs of -trouble. 4 Since the gates were opened tor emergency purposes last Sunday the water has surged through at a velocity calculated at approximately 60 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 the inflow is not reaching the penstock intakes, and these were calculated to take about one-third of the flow of the river.

In the 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 for those engaged in tunnelling, and on account of the uncertain character of the land and the risk of vibration causing further movement explosives cannot be used. The tunnel above the spillway is being continued to 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 nortbi-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 surveys completed, it will not be known whether the “tilt” that has occurred is towards the powerhouse in the gorge, or towards the spillway.

The gorge between the powerhouse and the clam 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 penstocks 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 anxious until the lake has discharged the whole of its contents. Then a 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 in extreme danger every minute of the day and night.