Wind waves and their relationship to storm surges in northeastern Bass Strait

Abstract

The wave climate in eastern Bass Strait and its relationship to extreme sea levels occurring along the Ninety Mile Beach are investigated using wave data from Kingfish B platform. The analysis reveals that significant wave heights in eastern Bass Strait are approximately forty per cent lower than those occurring at sites on the west coast of Tasmania and southern Australia and ten per cent higher than those at Eden on the east coast. Wave periods are lower than the western sites and Eden by thirty per cent and ten per cent respectively. Wave events, defined as episodes of significant wave height greater than 2 m for at least half a day, were most commonly associated with winds with a westerly component (73 per cent of cases). Sea level anomalies at Lakes Entrance were positive in 73 per cent of the wave events and greater than 0.2 m in just over half of these indicating that the associated weather conditions also contributed to a storm surge. For the remaining events, which were associated with winds with an easterly component, sea level residuals were in the range of ±0.2 m. Wave model simulations were undertaken for three wave events associated with different prevailing wind conditions to determine how the waves were likely to impact on wave setup along the Ninety Mile Beach. Significant wave heights at the coast were found to be most strongly attenuated in the westerly wind case where winds were directed alongshore compared to the southerly and easterly wind cases where there was a larger onshore component to the winds and hence the waves. However, the highest storm surge events along this coastline occurred under westerly wind forcing suggesting that under the circumstances that are most favourable for storm surges along this section of coast, wave setup is not likely to further elevate coastal sea levels. In the easterly event wave setup is larger, but sea level residuals tend to be low or negative. The event for which the winds had a large southerly component yielded a situation where both wave setup and surge combined to produce larger coastal sea levels