Assessing Shoreline Change using Historical Aerial and RapidEye Satellite Imagery (Cape Jaffa, South Australia)

The coastal zone is a dynamic area which can experience substantial natural change in short time periods, but changes are also associated with human modifications to the coastline. This case study is focused around assessing shoreline change associated with the Cape Jaffa Marina and canal estate in South Australia. The research comprises a GIS based analysis of shoreline change utilising aerial imagery from 1975 to 2005, which provides information of the morphological coastal trends prior to construction in 2008 of the marina/canal estate. In addition, imagery collected by the RapidEye satellite constellation was used to assess shoreline changes in the decade since construction, 2009 to 2019. The shoreline change statistics over the past few decades were calculated using the Digital Shoreline Analysis System extension of ESRI's ArcGIS. The image analysis workflow is based on the objective extraction of shoreline proxies from individual image statistics in a semi-automated process and is used to identify the waterline and edge of vegetation shoreline proxies in a time series analysis. The results provide a case study of a historically progradational sandy coastline experiencing substantial amounts of alongshore sediment transport, the corresponding obstruction from coastal infrastructure, and the resulting morphological changes to the Cape Jaffa shoreline. Shoreline change trends were altered from a predominantly accretional shoreline before the construction of the marina to one oscillating between extremes of erosion and accretion. The results showed significant accretion occurring updrift (Net Shore Movement (NSM) of 106 m) and significant erosion downdrift (NSM of -80 m) of the marina's training walls and entrance. The information derived from Earth observation satellites, such as RapidEye, can provide valuable insights into trend analysis due to their relatively high spatial (5 metre) and temporal resolution (5.5-day revisit).