Centennial-scale shoreface bathymetric and sand transport change in response to Tasman Sea wave climate variability

Significant variability in the modality of mean and storm wave climates along the south-eastern Australian coast, has been observed on annual to decadal time scales. On longer timescales of interest to marine geologists, wave climate shifts result in switching of sand transport paths on the lower shoreface and alongshore via headland bypassing. Using a novel approach we use wave climate hindcasting and marine geoscience investigations to illuminate sand supply and transport processes for sections of the eastern Australian coast. The problem is approached through the combined analysis of shoreface bathymetric change and related nearshore, shoreline and spit behaviour, over a 119 year period, together with wave climate variability associated with the Interdecadal Pacific Oscillation (IPO). A rotation in the seabed bathymetry is interpreted as a response to multidecadal processes, including: a rotation in the dominant deepwater south-easterly wave power from 120-140 to 140-160 and changes in modality between La Nina-like to El Nino-like phases of the IPO; and, associated changes in across-shoreface and headland bypassing longshore sand transport. The shift from unimodal mean and storm wave climate in the 1800's to bimodalilty in the 1900's is associated with large scale changes in the windfield over the Tasman Sea. Centennial scale processes can delay dynamic equilibrium over the shoreface, and our results can be applied to understanding Late Holocene shoreface evolution.