Flames, Deluges, and Deadly Waves Down Under: Insights from a Burnt, Flooded, and Eroded Australian Coastline (Surveyed During a Pandemic)

Abstract:

The unprecedented bushfire season in Australia this past year was extinguished in New South Wales by a catastrophic storm, which was later followed by a tight cluster of erosive events along the east coast. This presentation aims to share preliminary insights from surreal fieldwork of students and volunteers surveying over 600 km of the New South Wales coast. The catastrophic bushfire season, colloquially referred to as the Black Summer fires, started early in September of 2019 and raged through the southeast until March of 2020. Analysis has shown that they surpassed records related to extent, severity, and devastation. The fires were brought under control in the beginning of February by an intense low-pressure system called an East Coast Low (ECL - sometimes known as east coast cyclones). While the event put out flames, it resulted in significant property damage to the extent that it was classified as a catastrophe by the Insurance Council of Australia. The greatest impacts from this ECL came from wind and wind-driven rain, causing localised flash flooding. Coastal erosion also occurred due to the combination of spring high tides (~2 m above MSL), storm surge (>1 m above MSL) and waves (maximum height of 14 m and significant wave heights ~ 7 m). This data suggests rain volumes and coastal wave conditions were equivalent to a 5-to-10-year event magnitude event. Then within three weeks during July, two successive ECL storms caused NSW’s worst flood in 29 years and substantial coastal erosion due to the clustering of these events. While it was determined that the July ECLs had return periods of four years and less than one year, respectively, the cumulative effect of these storms on beaches that had not fully recovered resulted in erosion that in places far exceeded what is expected (combined, the amount of erosive potential was that of a single ECL with a return period of approximately seven years). This poster aims to present preliminary insights from post-storm surveys carried out in July. Contextualizing this erosional event by comparing it to those preserved in the geologic record of coastlines that have prograded over the Holocene. Exploring the potential for the stratigraphy of these prograded barriers to preserve a 7,000-year record of fires and floods similar to that observed on the beach and dunes in July.