The astronomical tides in the study area vary, with Bass Strait having semi-diurnal with a diurnal inequality, meaning there are approximately two tidal cycles each day; with one having a larger range than the other, whereas in Port Phillip Bay north of the Heads, the tides are classified as diurnal, with one major tidal cycle each day (definitions from ANTT, 2014). The change in tidal character results in different sets of tidal planes being used to describe the tides in the two areas. Hence, in Table 3-1, which displays the tidal planes at Lorne, Queenscliff and Geelong (ANTT 2013, and PoMC, 2013) referenced to AHD, there are different values for Lorne and for Queenscliff and Geelong which are inside the bay. The tidal range for the open coast is 1.8 m in the Bass Strait at Lorne. At Geelong, the tidal range is 0.9 m.

Table 3-1    Astronomical Tides (ANTT, 2013 & PoMC, 2013)

Tidal data is available from a number of tide gauges owned by the Port of Melbourne Corporation (PoMC), Victorian Regional Channels Authority (VRCA) or National Tidal Centre (NTC), relevant to the study area, Table 3-2. The most relevant to this study are located at Lorne, Point Lonsdale, Queenscliff, Point Richards and Corio. This data was used to determine and confirm surge and storm-tide levels for the study area. Section 4.3.1 and Appendix A detail the methodology for determining storm-tide levels.

Table 3-2     Tide Gauges within the wider study area