Relief is shown by contours. Depth by isobaths and soundings. Relief is shown by contours. Depth is shown by isobath Hydrographic chart of Port Darwin "Aus 28" Sources: R.A.N. surveys 1925 to 1993 and surveys by Northern Territory Authorities 1970 to 1994. Soundings in upright figures are from old and inadequate surveys. Includes reliability diagram, tidal streams, tidal levels. Depths are in metres and are reduced to Chart Datum: which is approximately the level of Lowest Astronomical Tide. Heights are in metres. Underlined figures are drying heights in metres and decimetres, above Chart Datum: all other heights are above Mean High Water Springs. Navigational marks: I.A.L.A. Maritime Buoyage System - Region A