Storm tide recurrence intervals – a statistical approach using beach ridge plains in northern Australia

The marine inundation generated by Tropical Cyclone Yasi, north Queensland, February 2011, flooded at least 130 beachfront homes and many commercial businesses, becoming the most substantial marine inundation impact in Australia's modern history. As a consequence, guidelines for building in storm tide impact areas have been developed and discussions are beginning on whether Australia needs a national standard for buildings impacted by these events. Central to this will be determining which areas of coastal land need to be subjected to the standard, and this will likely be based upon the magnitude of a particular return interval event. The veracity of the current method for determining these return intervals is difficult to determine as there has been no objective way to assess the accuracy of this approach. One such method is developed here – applying extreme value theory statistics to millennial scale sedimentary records of tropical cyclone marine inundations. The approach is applied to a 5000-year-long beach ridge record of tropical cyclone inundations near Tully Heads and the results suggest that the inundation generated by Tropical Cyclone Yasi here had a return interval of approximately 1000 years. This is a substantially lower figure than the approximately 5000-year return interval suggested by the currently accepted approach. Irrespective of which method is more accurate, the marine inundation generated by Yasi was a very rare event and one that may become more common under a future altered climate