Rapid Assessment of Shoreline Changes Induced by Tropical Cyclone Oma Using CubeSat Imagery in Southeast Queensland, Australia

Abstract

Kelly, J.T. and Gontz, A.M., 2020. Rapid assessment of shoreline changes induced by Tropical Cyclone Oma using CubeSat imagery in southeast Queensland, Australia. Journal of Coastal Research, 36(1), 72–87. Coconut Creek (Florida), ISSN 0749-0208.Tropical Cyclone Oma hit the SE Queensland coast of Australia in February 2019. Significant wave heights exceeding 10 m were further amplified by a king tide. Satellite remote sensing of pre- and post-Oma shoreline positions was performed because storms hindered the ability to acquire field-based data. The high spatial and temporal resolution of PlanetScope imagery enabled mapping of the high water line (HWL), which was used as a shoreline indicator across 200 km of shoreline. Given that this is the first use of PlanetScope imagery to map shoreline positions, the positional uncertainty was assessed. Comparison to a temporally coincident, LIDAR-derived mean high water (MHW) shoreline at a distant site showed an average horizontal offset of 9 m with the HWL shoreline. The Oma-affected shoreline uncertainty ranged between ±13.86 and 23.28 m, primarily influenced by the geometric accuracy of the data used, as well as the pixel size of the imagery and the horizontal offset between the HWL and MHW elevations. The net shoreline movement (NSM) was calculated every 200 m along the study area by the Digital Shoreline Analysis System. Only transects with NSM values greater than the uncertainty of their associated shoreline compartment were used to assess change. The spatial distribution of erosion and accretion was similar across the SW–NE-oriented shorelines as the southern ends of Fraser Island and the Cooloola Sand Mass eroded while their northern ends prograded. Wave data shows that the wave direction rapidly shifted 56° in an anticlockwise direction during Oma. Wave propagation came primarily from the SE, and the direction of longshore transport likely turned northward, leading to the shoreline rotation observed in the imagery. This study demonstrates the significant improvement on assessments of regional-scale shoreline changes in the aftermath of an episodic event using new satellite products.