Mapping spatial variability in shoreline change hotspots from satellite data; a case study in southeast Australia

This study demonstrates how a large-scale satellite-derived dataset can be used to investigate statistically robust trends in shoreline position over a 31-year period from 1987 to 2017, at a regional scale. Regional patterns of shoreline behaviour are important for resolving consistent or, alternatively, dissimilar patterns of past shoreline change. Such patterns are best explored using temporally frequent and spatially extensive datasets. Here we analyse satellite-derived shorelines to identify spatial patterns of hotspots of coastline change on the wave-exposed coast of Victoria in south-east Australia where rates of change exceed 0.5 m yr⁻¹. Analysis of shoreline position changes at a 50 m alongshore interval along 900 km of the 1230 km coastline reveals a number of distinct behaviours related to coastal type (rock vs sand coast), landform, shoreline orientation and/or anthropogenic drivers of change. Overall the results show that statistically significant change in shoreline position has affected only a relatively small proportion of the study region over the last 31 years; that the proportion and rate of progradational and recessional change is similar; and that change is localised but dispersed widely along the Victorian coast. Coasts located at the entrances to large tidal inlets have shown the greatest change. The association of hotspots with embayed sandy beaches and adjacent to headlands points to the importance of geological control on shoreline behaviour. Consistent with other regional scale studies of shoreline change, this study found little regional coherence in shoreline behaviour. Instead change is predominately attributed to local factors such as the geological framework of the coast, localised hydrodynamic conditions and anthropogenic influences. Collectively, these results indicate that there is strong geologic control on shoreline erosion in Victoria due to the high diversity of landforms along the coastline; and that further analysis is required to tease out the seasonal to interannual sensitivities to changes in the historical wave climate and the secondary interaction of sediment supply for headlands and hydrodynamics for tidal inlets.