The wave climate varies throughout the study area, from smaller wind-generated waves in Port Phillip Bay, to larger Bass Strait swell waves along the open coast.

Within the bay, waves rarely exceed 1 m in height in the study area. However, with strong winds from certain directions, and depending on water depth, they are able to produce wave heights in excess of 1 m. Analysis of wind directions and frequency show that winds rarely occur from the direction of the greatest fetch (north-east), therefore the occurrence of waves from that direction is similarly infrequent. The presence of the Great Sands (Figure 3-5) limits the wave energy reaching the shoreline of the east coast of the Bellarine Peninsula. Similarly, in Swan Bay, the water depths are very shallow with large areas of seagrass. This results in a very low wave-energy environment.

Waves near the entrance to Port Phillip Bay have been studied in the past, and detailed models exist that have provided information relating to swell penetration through the entrance, as well as the effect of the flood and ebb currents on the entrance wave climate.

The open coast and Lonsdale Bight shoreline of the Bellarine Peninsula receive waves from Bass Strait. Measurements of the waves in Bass Strait have been made by PoMC at a site approximately 8 km south east of Point Nepean since 2003. The wave climate is dominated by swell with about 92% of the waves coming from the south south-west and south west with a most frequent direction of around 213 ° (Figure 3-3). This is the direction of waves that are able to propagate through the gap between Cape Otway and King Island from the Southern Ocean and arrive at the coast as swell. Waves with a significant wave height greater than 3 m come from a narrow directional band around the average direction. The largest waves occur when the local wind comes from the same direction as the swell. Some wind-waves come from the south south-east, but these are relatively infrequent.

The measured significant wave height reaches 6.4 m, with at least 50% of the waves being between 1 and 2 m. The average significant wave height over all seasons at this location is 1.7 m. Seasonally, the average wave height drops to 1.6 m in summer and autumn and returns to 1.7 m during winter and spring. The dominant spectral-peak wave period is between 10 and 16 s with an average period of 12.8 s. The average varies from 11.7 s in summer to 13.6 s in winter.

The wave climate changes along the open coast (Bass Strait) of the study area depending on:

Figure 3-3     Wave direction vs. significant wave height (H s ) at the PoMC Point Nepean wave buoy (Cardno, 2011a)

Thirteenth Beach and the Buckley Park coast are almost perpendicular to the dominant wave direction, and experience the highest wave conditions within the study area. Rocky outcrops and shore platforms offer some protection to certain parts of the shoreline. Ocean Grove and the Barwon River entrance are sheltered by Barwon Head. The wave modelling and determination of design wave conditions for this assessment are presented in Section 4.3.2.