Shellharbour - Tharawal (Illawarra South) multi-beam data now available on AusSeabed

NSW Department of Planning and Environment have recently released 2 and 5m gridded bathymetry and 5m backscatter mosaics from Shellharbour multibeam surveys south of Wollongong in 2017. The surveyed area lies within the seacountry of the Tharawal peoples and stretches from the iconic Five Islands and Red Point near Port Kembla to Bass Point south of Shellharbour. The 60km2 of multibeam, combined with the 2018 marine LiDAR, provides the first 100% high-resolution digital elevation model for this the ‘Illawarra South’ Secondary Sediment Compartment. Compartment mapping has been funded by the state’s Coastal Reforms program to provide baseline dataset and map the spatial distribution of seabed types. This will allow us to develop a better understanding of nearshore sediment distribution and transport as well as assess threats/risks associated with erosion events (i.e. East Coast Lows) and changing sea levels.

With a full digital elevation model stretching from 200m inland to a depth of ~60m, the data have already been used in a case study to examine data utility toward improving shoreline change forecasting. Following sediment surveys to interpret backscatter variability, Kinsela et al (2020) examined and compared the observed geomorphology and morphodynamics to theoretical predictions as derived from more traditional wave-driven sediment transport theory. The shoreface geomorphology across the Shellharbour compartment was found to be much more complex than models might suggest. The more accurate definition of sediment distribution and associated dynamics is critical to developing quantitative sediment budgets and providing a more meaningful predictive capability for examining future shoreline change scenarios.

Kinsela, Hanslow, Carvalho, Linklater, Ingleton, Morris, Allen, Sutherland, Woodroffe 2020. Mapping the Shoreface of Coastal Sediment Compartments to Improve Shoreline Change Forecasts in New South Wales Australia. Estuaries and Coasts