1University Of Tasmania
Contemporary climate change-induced global sea-level rise will lead to increased recession of soft coasts. Most beaches have not yet shown such a response because confounding processes including storm erosion and swell-driven recovery cycles are still of larger scale and prevent the emergence of a sea-level rise signal in beach behaviour. However, I ask whether some coastal landforms are particularly susceptible to responding early to sea-level rise with a detectable change in long-term behaviour, typically from stability to recession. I analyzed air photo records of shoreline position over 70 years for 35 soft shores around Tasmania, where climate change-induced sea-level rise is the dominant component of local relative sea level variability. Ten of the shores studied show a long-term change of shoreline behaviour. Sea-level rise and in some cases increasing wind speeds are the only known drivers able to account for the changes at 8 of the 10 sites. These 8 sites have active net sediment sinks capable of sequestering increasing eroded sediment as shoreline erosion increases in response to more frequent higher wave attack at higher sea levels. I identify this as a key condition for early shoreline response to sea-level rise, which occurs at only some swell-exposed sandy beaches but is common (via differing processes) for soft-rock coasts and for sandy shores within tidal but swell-sheltered estuaries and lagoons. High local wind-wave exposure is also critical for early shoreline response within swell-sheltered tidal re-entrants where local wind waves are the primary agent of shoreline erosion.
Chris Sharples is a geologist who has specialised in coastal geomorphology for over the last twenty years. Based in Tasmania, he has recently completed a Ph D study exploring the extent to which sea-level rise impacts are or are not yet being seen in the physical behaviour of soft coastal landforms. This study, which is key to coastal hazard recognition, is the subject of his presentation to this conference.