Coastal Storm Data Analysis: Provision of Extreme Wave Data for Adaptation Planning

Client: National Climate Change Adaptation Research Facility: Settlements and Infrastructure (ACCARNSI)
Year: 2011
Project Reference: 10077
WRL Research Report: Coastal Storm Data Analysis: Provision of Extreme Wave Data for Adaptation Planning (Research Report 242)

Example of a long duration storm event observed at the Rottnest Island wave buoy caused by a single storm system.

The Australian coast is subject to a spatially and seasonally variable mean wave climate and periodically impacted by large wave events. These large wave events, particularly when they coincide with high water levels, may cause widespread coastal inundation, beach erosion, damage to property and marine structures, and risks to public safety. Having accurate statistical characterisations of the likelihood and magnitude of large wave events is necessary for the quantification of extreme beach erosion and inundation, design of nearshore structures, and for climate change adaptation planning.

This project reviews Australian coastal storm climatology and previous extreme wave analyses undertaken using instrument and numerical data. Wave data from eight wave buoys Australia-wide has been assessed and trends in mean monthly wave height and in the frequency and magnitude of storm events has been statistically analysed.

Changes in buoy location and exposure over time has been found to notably influence results, with small changes in buoy position able to introduce apparently significant but fictitious trends. Overall, both the east and west coast buoys exhibit non-statistically significant upward trends in mean wave height of up to 2 mm/year and 7 mm/year respectively; and the south coast buoys exhibit downward trends of -1 to -5 mm/year. No statistically significant temporal trends in storm magnitude were found and one east coast buoy showed a small increase in storm frequency.

Using this wave buoy data, extreme wave heights, wave periods and cumulative storm energy have been estimated for a range of return period events. Typical storm shapes were assessed and all buoys were found to exhibit a moderate positive skew, indicating a faster increase in wave height before the storm peak than decrease following the peak.

This storm shape was combined with extreme wave height, period and energy information to construct synthetic design storm time series for each buoy for average annual recurrence intervals of between 1 and 100 years. Spatial differences are noted in the derived events as a function of the dominant storm climatology for the different regions around Australia.

Examples of 100yr ARI synthetic design storm events for each assessed buoy.