EXPLORING BOTTOM OF SYDNEY HARBOUR

Sun (Auckland), Volume II, Issue 541, 19 December 1928, Page 15

EXPLORING BOTTOM OF SYDNEY HARBOUR

HYDROGRAPHERS’ WORK Within 12 months hydrographic surveyors of the Sydney Harbour Trust will have conipleted the first actual survey of the whole of Port Jackson. Of the 22 square miles of navigable waters they have already sounded 13 square miles, embracing the deepest and most difficult sections. The value of the work was demonstrated a few days ago, when G. E. P. Hart and his party located an obstruction lying in 38ft of water at the entrance to Taylor's Bay. Though not in the fairway, the obstruction would constitute a danger to shipping seeking an anchorage in that locality if its presence were not disclosed on the charts. Other officers of the Trust have identified the obstruction, which is 600 square feet in extent, as the remains of the steamer Centennial. The vessel foundered more than 30 years ago, after being in collision, and was believed to have been broken up by explosives. The surveyors are now working in the outer section of the harbour, and have yet to chart Middle Harbour and parts of the Parramatta River. All soundings are taken by hand, which is claimed to be a quicker means than those provided by mechanical methods. Many thousands of soundings are taken in a comparatively small area, hut the crews have acquired a wonderful deftness, and are able to cover big areas of water in unbelievable short periods. One of the every-day responsibilities of the hydrographers is the maintenance of a minimum depth of 40ft at low water in the channels. At their direction the dredges cope with the evil of constant silting. The fact that 1,700,000 tons of silt was lifted from the bed of the harbour in one year shows the need for their vigilance. It is their duty, too, to establish the character of the strata at the harbour bottom where a dredge is to operate, and to rechart the bed after the silt has been taken away. At the present time the dredge Triton is removing the southern portion of the Sow and Pigs shoal area, so that an awkward corner will be eliminated from the eastern channel and the fairway extended to 700 ft. Some interesting facts have been established by the surveyors. They say, for instance, that the deepest

point in the harbour is between Dawes I and Blue’s Points, a little to the west- j ward of the site of the bridge, where j they got a sounding of 159 ft. The en-1j trance to the harbour is almost a mile ] wide, and the channel has a depth of SOft. The average range of tide, the ' recording of which is a duty of the i Trust, is sft, and the greatest known ; range is 8.26 ft. More than 1,000 acres are suitable as anchorages for vessels ; of the deepest draught.