TAWA FLAT TUNNEL

Dominion, Volume 22, Issue 288, 31 August 1929, Page 6

TAWA FLAT TUNNEL

UNDERGROUND RESERVOIR ENCOUNTERED

WORK IMPEDED

The conartcors for the longer of the two Tawa Flat railway tunnels arc encountering difficulties through the broken nature of the ground, but on Tuesday night ran into more serious trouble when a reservoir of water was on the southern drive at the shaft sunk between the Tawa Flat exit and the Ngahauranga Gorge entrance. The underground lake presented a serious problem, as it delivered a flow of about 20,000 gallons an hour. Three Cameron pumps were unable to keep it down, and on Wednesday afternoon the water had completely filled the heading, 10ft. x Bft., and had backed up the rails for about sixteen chains. It was then gaining at the rate of two inches in level every hour, the flow averaging 15,000 gallons per hour. As the tunnellers are working on a downhill grade of 1 in 124, and the water is still flowing, it is only a question of time, unless the flow ceases, of the flooding of the foot of the shaft, when the problem of dealing with the water will be rendered more diflicult. The Cameron pumps at present attempting to bring the level down are working at the face end of the tunnel, and are well buried under chains of water, but fortunately they are dependable machines, and, unless the unusual happens, will continue pumping. It is most unusual in such eases for an underground stream of large dimensions to be encountered. It is thought that the water in this case is coming from a reservoir, which may have now drained itself, in which case the pumps will soon get it down. If not, extra pumps will bo put on. _ The necessity for timbering the broken ground being encountered is also slowing the work, as this has to be' kept up right to the face. It is considered that earthquakes have been responsible for shattering whole parts of the hill. .