Shoreline Movements Geographe Bay Western Australia

Small scale coastal protection works constructed during the past 25 years to control beach erosion at various locations along the 32km shoreline of Geographe Bay between Dunsborough and Wonnerup are described. These include groynes, seawalls and an experimental Longard sand tube installation. Recent research, including analysis of aerial photographs and a detailed geological investigation, has contributed to a better understanding of the causes behind shoreline movements in this area. From this research an hypothesis is presented which describes the probable mechanism of shoreline movements. It is concluded that these movements are part of a complex natural system in which swell waves transport sediment shorewards along regularly spaced furrows cut through the offshore seagrass meadow and build nearshore sandbars which are aligned at a more acute angle to the shoreline. These bathymetric features largely control the location of shoreline erosion and accretion.