Tide gauge vertical reference datum updates

By jnally on 23 January, 2026

A diagram with various horizontal and vertical lines to represent various measurements derived from tide gauge stations — *How the water level will be reported once the vertical reference datum is changed from Chart Datum to Lowest Astronomical Tide. Credit: DTMI.*

Selected tide gauge stations across Western Australia are having their vertical reference datum updated.

The Western Australia Department of Transport and Major Infrastructure (DTMI) has announced that it is updating the datum from Chart Datum (CD) to Lowest Astronomical Tide (LAT).

The change applies to tide gauges at these locations:

Bremer Bay
Busselton – Port Geographe
Caddadup
Cape Bouvard
Harvey Estuary
Jurien Bay
Mandurah
Peel Inlet
Two Rocks

According to the DTMI, users might notice that reported tidal levels and predictions seem lower than they did previously.

The Department points out that “the total measurement from the water’s surface to the seabed is not changing. Only the tide gauge ‘zero point’ is being updated. As a result, tide heights will appear lower, while charted water depths will appear higher.”

The update brings DTMI’s tidal datums into alignment with those used by the Bureau of Meteorology and the Australian Hydrographic Office.