To determine wave conditions along the open coast, a global WaveWatchIII wave model was used to compute the wave conditions along the boundary of a coarse SWAN model. The SWAN model extended from Cape Otway to Wilson’s Promontory. Within the coarse grid a finer resolution grid was nested from which model results were extracted at points in 10 m water depth along the study area coastline. The model was run for 85 storm events spanning 33 years from 1979 to 2011 from which extreme conditions and the variation in wave climate along the open coast could be determined.

The wave climate for the open coast was determined by deriving the relationship between the model-derived values at Point Nepean and each extraction location from Breamlea to Point Lonsdale. An additional relationship between the modelled and measured data for Point Nepean was then derived from which the wave climate at each location was determined. It was assumed that the wave period remained constant for all locations.

An extremal analysis was performed to determine the AEP for significant wave heights (Hs) at Point Nepean, Table 4-4. The same relationship used to determine the wave climate for each extraction point was also used to determine the extreme values for the open coast at 30 locations. These values were used to inform the subsequent joint probability assessment to determine the final design conditions for the hazard modelling. Appendix A gives more details of the wave analysis.

Table 4-4     Extreme wave heights for Point Nepean

The wave climate within Port Phillip Bay was available from models used in past projects with minor editing to grid coverage, and inputs. As swell from Bass Strait penetrates only a short distance through the entrance of Port Phillip Bay (Cardno, 2011), waves in the study area within the bay are generated by local winds (i.e. fetch-limited waves). A wave climate for the study area from Edwards Point to Avalon was derived using measured wind data from Point Wilson. The wave climate was obtained by applying a 1% AEP wind in the model, from various directions, based on Australia design wind standards (AS/NZS 1170.2:2011).

An additional dataset of measured wave heights off Portarlington was received from Water Technology for March 2010 to March 2011. This data was from a pressure gauge and was used as a check on the wave heights in the Portarlington area. This was not a formal model validation exercise.

Due to the dominance of the current fields near the heads area and the swell conditions, the corresponding wave climate from Point Lonsdale to Edwards Point was modelled under flood-tide conditions with swell applied to the model boundary.