HARBOUR DEPTHS

Sun (Auckland), Volume III, Issue 874, 18 January 1930, Page 4

HARBOUR DEPTHS

CHECK ON BRIDGE ESTIMATES ADMIRALTY CHARTS WRONG Borings of the harbour h,a the suggested sites for the . posed Waitemata bridge have hU? - so far advanced that the engine?" can now use the data availahu ? check up their estimates of ee** struction costs of the The contractor engaged on soundings still has further the route from North cote and I°* Erin. Twelve soundings taker In' this route reveal that the av^ t 5 depth of mud over the papa bed harbour is 90ft— 10ft less assumed by the Harbour Bride. . 81 soeiation's engineers, who held n opinion that a bridge with a 600-t'oot span on this alignment cost JCSI3.OOO. c Admiralty charts showing h.r bour depths off Northcote haw been proved inaccurate by the t«« soundings. Where the chart, show 12 fathoms the correct., depth is 14 fathoms. |' i, claimed that the deepening has been caused by the harbour re clamation walls, which are also suggested to have changed the set of currents of big and little Shoal Bay so that mangrove banks now show where ten years ago the mud-flats were scarcely dry at the lowest spring tides. An interesting suggestion by the Harbour Bridge Association engineers is that by dredging away the shoal covered by three fathoms of water just beyond Northcote Point, on the Ponsonby side of the channel, the main channel up the harbour could readily be straightened. Thus the bridge could be constructed across the channel, and so eliminate the Harbour Board’s argument that a very wide centre span is needed. Straightening of the channel would improve the bridge construction as its highest point would be about midway, allow, ing for practically equal gradients on either side. The original plan shows the highest span to be over the exist, ing channel close to 'Northcote.