| Historical notes: | This was the first tunnel to be constructed under Sydney harbour. It was built between Long Nose Point, Balmain, and Manns Point, Greenwich, from 1913 to 1924 to carry submarine electricity cables for the electric tramway system on the north side of the Harbour. Submarine cables laid across the harbour earlier had suffered damage from ships dragging their anchors.
The tunnel was flooded about 1930, whether intentionally to avoid continual pumping or as the result of a sudden inrush of water is not clear from the records. The cables in the flooded tunnel remained in use until 1969, but are no longer used because ample supplies of electricity are available on the north side of the harbour from Electricity Commission substations.
When it was built, the tunnel was one of Australia's major engineering feats. At the commencement of the work, the necessary compressor was located on the south to supply power for the pneumatic drills. Work was started from three points -Long Nose Point, Greenwich, and a shaft at the extreme end of Mann Point. Progress was rapid for a while -about 25 yards per month at every point. But then residents of Long Nose Point, in letters and protests, caused the abandonment of the Long Nose end after a considerable distance had been excavated. Work, therefore, went slowly on from the north side until about May, 1915, when a big fissure in the rock about the middle of the Parramatta River was met. The only solution was to seal up the tunnel and patch the fissure.
It was then found that the second sealing showed signs of weakness, and it was thought advisable to abandon the top tunnel and go deeper into the rock. A permanent bulkhead was built into the rock and the tunnel was sealed up with about 15 feet of concrete. Then a second tunnel was commenced 50 feet below the first one. The down grade was increased to 1 in 1.3. The work was still being carried out with explosives, and progress was fairly fast; but on arrival at the point immediately below the original break-in, another crevice was struck, and water rushed in. On this occasion, the engineer in chief, R.L. Rankin and the resident engineer, W.R.H. Melville, decided to go with the foreman and have a look at the fissure that had flooded the tunnel. Placing candles on pieces of wood, they swam about 40 feet into the centre of the tunnel.
The break-in was later sealed by placing 6-inch pipes, about 15 yards long, into the crevice, and the whole of the tunnel in the immediate vicinity was packed with bags of clay, tightly rammed. In front of this was placed a steel bulkhead with a steel door, and through the bulkhead three-inch pipes were laid right into the crevice, to allow the water to get out.
A detour was cut at this point to about 6 feet, to get round the crevice, and when the men had passed it they worked back to the original line of excavation.
The section of the tunnel that had been sealed up was cut through, the detour filled in, and the original straight line of excavation restored. After going about 50 feet past the crevice, they struck another small fissure, which was apparently a section of the original one, and water suddenly flowed in at the rate of about 2400 gallons an hour. This was not sufficient to stop the progress of the work, but pumps were installed to cope with the inflow.
Soon after the men began to work on the up-grade, and here great care had to be exercised to prevent the material falling back on them. The material was cut out by channelling machines, which allowed it to be removed without difficulty. Eventually the men broke through at the Long Nose Point side. Their calculations had been made with remarkable accuracy. The centre line, when the tunnel was connected, was only an 1/8th of an inch out, while the levels were absolutely correct.
In 1952 the Electricity Commission took over all power generation but the railways retained the tunnel and cables. The tunnel ceased use in 1969. |