Coastal Hazards

Because of Australia's natural location and geography, the whole country is in a potentially at risk for coastal hazards. 

Coastal erosion (or shoreline retreat) is the loss of coastal lands due to the net removal of sediments or bedrock from the shoreline.

Coastal erosion can be either a:

• rapid-onset hazard (occurs very quickly, a period of days to weeks)
• slow-onset hazard (occurring over many years, or decades to centuries).

 Coastal erosion is typically driven by the action of waves and currents, but also by mass wasting processes on slopes, and subsidence (particularly on muddy coasts). Significant episodes of coastal erosion are often associated with extreme weather events (coastal storms, surge and flooding) but also from tsunami, both because the waves and currents tend to have greater intensity and because the associated storm surge or tsunami inundation can allow waves and currents to attack landforms which are normally out of their reach.  

Coastal erosion is a natural process which occurs whenever the transport of material away from the shoreline is not balanced by new material being deposited onto the shoreline. Many coastal landforms naturally undergo quasi-periodic cycles of erosion and accretion on time-scales of days to years. This is especially evident on sandy landforms such as beaches, dunes, and intermittently closed and open lagoon entrances.

Human activities can also strongly influence the propensity of landforms to erode. For example, the construction of coastal structures (such as breakwaters and seawalls) can lead to changes in coastal sediment transport pathways, resulting in erosion in some areas and accretion in others. The removal of sediments from the coastal system (e.g., by dredging or sand mining), or a reduction in the supply of sediments (e.g., by the regulation of rivers) can also be associated with unintended erosion. At larger scales, natural and human-induced climate change can modulate the likelihood and rate of coastal erosion. 

Along the Australian Coast:

Rapid onset:

·      The NSW coast has a long history of experiencing coastal erosion events dating back to 1857. Single storm events have caused coastal erosion, such as that associated with East Coast Low storms in 2015 and 2016 that damaged beachfront properties in Sydney. A series of large storm events in 1974 led to even more extensive damage to coastal properties and infrastructure in this region.

Slow onset:

·      The Twelve Apostles along the Great Ocean Road are a result of landscape change and coastal erosion over millennia. There were originally 12 limestone features with 8 now remaining. These structures remain vulnerable to further erosion from waves.

·      Around the Australian coast, nearly 39 000 buildings are located within one hundred meters of 'soft' shorelines and are at risk from accelerated erosion due to sea-level rise and changing climate conditions (as at 2011).

Destruction to Sydney's expensive coast during a King Tide in early 2019 (Left) Coastal erosion on the Southern Shores of Australia (Right)

Source: https://www.ga.gov.au/scientific-topics/hazards/coastalerosion