The vertical wall sections at Point Lonsdale are subject to direct wave forces during storm conditions; this is reflected in the overtopping results. This is also consistent with visual inspection of the wall during the April 2013 site visit, which saw some sections of the bluestone façade removed during a recent storm event. This would be expected with discharges in the order of those presented for Locations 1-3 for the 0.0 m SLR scenario in Table 6-7. It is noted that the overtopping volumes relate to a failure under a SLR of 0.5 m, however, the volume discharges for the lesser SLR scenarios are still very high and would be expected to cause significant damage. Thorough maintenance of this area is required to ensure the viability of the wall. The western wall section has limited beach fronting it, making it more vulnerable to wave impact and undermining.

The revetments have a higher standard of protection in terms of overtopping discharge than the vertical seawall. This is for two reasons. Sloped (non-paved) revetments are designed to absorb wave energy, this reduces overtopping discharges. Also, wave energy dissipates as it enters Port Phillip Bay and the effects of open coast swells lessen with distance from the bay entrance. This reduces wave heights with distance from the entrance, and thus overtopping discharges. The crest elevation is higher at Location 5 and is representative of the newer section of the rock revetment beyond Lawrence Road, which also reduces the overtopping discharges. During the April 2013 site visit, it was noted that the revetments are showing some evidence of out-washing of material as it appears there is no geotextile layer beneath the armouring. This leaves the structure vulnerable to wave action, resulting in erosion of the land beneath / behind.

The management triggers are presented in Table 6-9.

Table 6-9     Management triggers - Point Lonsdale and Lonsdale Bight

Information from Borough of Queenscliffe indicates that water pools in depressed areas during high rainfall events, and upgrades to stormwater infrastructure will be carried out to remedy this. As Figure 6-18 shows, the Fisherman’s Flats area of Queenscliff is vulnerable to inundation under present day storm-tide conditions. Although some shore protection exists in the inner bay area, these are low retaining walls that are not forming a consistent barrier. They are canaled in some locations to allow for surface water to drain, however under storm-tides, these will likely become flood routes. Under the higher sea-level rise inundation events of 1.1 m and 1.4 m, flooding from the main front beach and Fisherman’s Flats is expected to join.

The management triggers are presented in Table 6-10.

Table 6-10     Management triggers - Queenscliff

Lakers Cutting links the southern end of Swan Bay to the newly established Lonsdale Lakes estate, the Bellarine Highway and Shell Rd. This area was dynamically modelled due to the complexity of the inundation mechanisms. This area also includes the area where the Bellarine Highway links to Flinders St in Queenscliff. This is the only way in or out of Queenscliff, other than the ferry.

The Lakers Cutting and Lake Victoria coastal inundation extents are presented in Figure 6-19. This shows a complex network of channels and overland flow paths. Under the 1% AEP event + 0.2 m SLR the inundation extent increase significantly and starts to impact shoreline assets.

For Swan Bay, the inundation hazards are less significant in the short-term. Much of the wider shoreline of Swan Bay is agricultural land, therefore asset vulnerability is low. One key area of note is the Swan Bay Holiday Park, which is positioned on the shoreline at the end of Swan Bay Rd Figure 6-21). The key issues will be related habitat resilience. The surrounding land areas rise gradually to higher land, therefore there appears to be nothing inhibiting any natural roll-back with sea-level rise.

The northern end of Swan Bay includes the southern end of St. Leonards (Figure 6-22). This area is likely to be subject to estuarine flooding from Swan Bay, as well as normal coastal inundation of the shoreline. This will occur under a 1% AEP event + 0.2m SLR, but will be most significant in a 1% AEP event + 0.5 m SLR and above, due to potential depths.

The management triggers are presented in Table 6-11.

Table 6-11     Management triggers - Lakers Cutting & Swan Bay