Rapid shoreline erosion and dunefield Change, Salmon Hole, South Australia

Since the 1940's, rapid shoreline and dunefield changes have been ongoing at Salmon Hole, an embayment situated near Beachport in the SE of South Australia. Storm induced erosion has nearly removed the entire dunefield and created a lagoon confined by a calcarenite reef. This study examines the progress, dynamics and causes of the erosion to determine why it has been so severe, using historical aerial imagery, wave reanalyses data, Digital Surface Models (DSM's) from drone surveys and through the volumetric analysis of topographic profiles. The results gained through analysing shoreline change at Salmon Hole are then discussed based on Phillips (2009) change assessment system. This study found that a combination of the formation of the 'lagoon' between the mainland/dune system and the offshore reef and the resultant breakthrough of the tombolo that have led to the acceleration of the erosion processes seen at Salmon Hole. The formation of the lagoon initiated a divergent evolution that continues in the form of a significant geologically controlled longshore current and terminal rip that enhances removal of sediment during and following erosion of the dunes. It appears that each time the lagoon widened post storm erosion it resulted in an increase in the efficiency of the current, resulting in a positively reinforcing feedback loop furthering the erosion level during each successive storm. The profiles taken from the drone survey DEM's reveal the processes involved in scarping and demonstrate how dune systems with zero sediment supply will respond to future climate and wave conditions. Coastal systems experiencing a deficit in sediment supply will not be able to translate landwards/upwards resulting in their removal. If the current rate of erosion at Salmon Hole is maintained into the future, the entire system is likely to be fully eroded within the next 30 years.