Modelling seasonal to multi-year shoreline change at a sandy embayment on the Australian east coast

There are several methods presently available that can be used to predict shoreline variability and evolution, ranging from the simplest linear shoreline regression models to highly complex, numerical physical process models. The motivation for the present work was to assess the applicability of an existing empirical equilibrium-based model to predict the evolution of shoreline position extending from storm to inter-annual time-scales, at the distinctly embayed Narrabeen-Collaroy beach in Sydney NSW. This type of approach seeks to incorporate the key physical characteristics and phenomena being modelled, without seeking to model each and all of the individual processes that underlie the observed behaviour. The shoreline model presented was previously and successfully validated for a contrasting long, straight, open coast beach at the Gold Coast, Queensland. In this new work, six and a half years of weekly image-derived shoreline data were used to calibrate and test the existing model, with several weaknesses identified. A newly improved and more generic model formulation is presented. Calibrated and hindcast shoreline time-series at both the long, straight Gold Coast and distinctly embayed Narrabeen sites are presented. Modelled shorelines are compared with weekly measurements to critically assess model accuracy and improved predictive skill.