Impact of Cyclone Yasi on the wreck of the SS Yongala documented by comparative multibeam bathymetry analysis

Abstract

In February 2011, north Queensland experienced one of the largest and most severe tropical cyclones on record. Category 5 Cyclone Yasi caused substantial structural damage not only on land, but also at sea, including to the historic shipwreck of the SS Yongala . The Yongala is of high cultural and natural heritage value and is a major dive tourism attraction. As part of a Queensland Government initiative to document the degree of damage by Cyclone Yasi, changes to its structure were documented by comparative analysis of multibeam bathymetry data of the wreck collected in August 2004 and May 2011 (i.e. pre- and post-Yasi respectively). The storm had a significant physical impact on the c.110m-long wreck. The most pronounced changes occurred in the forward section of the wreck. A 35m section forward of the central deck citadel has rotated around its own axis and the bow dropped more than 5m in depth. Minor deformations were observed at the stern of the wreck and debris was identified on the seafloor around the wreck. The impacts of the cyclone will exacerbate deterioration. It is very likely that the wreck’s hull will rupture in the short- to medium-term, especially if further extreme weather events occur. Together with visual observations, the results of this study will inform ongoing site management by contributing to the identification of key risk areas, and help to establish policies and procedures to address damage to the wreck’s integrity in the future.