What is coastal erosion?
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).
What causes coastal erosion?
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. On coastal headlands, such processes can lead to undercutting of cliffs and steep slopes and contribute to mass wasting. In addition, heavy rainfall can enhance the saturation of soils, with high saturation leading to a reduction in the soil's shear strength, and a corresponding increase in the chance of slope failure (landslides).
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. However, human activities can also strongly influence the propensity of landforms to erode. For example, the construction of coastal structures (such as breakwaters, groynes 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.
Coastal erosion becomes a hazard when society does not adapt to its effects on people, the built environment and infrastructure.
Where does coastal erosion occur in Australia?
The most vulnerable coasts are those made up of unconsolidated sediments, such as beaches, dunes and sand cliffs, on open coasts that experience net longshore drift of sediment and on the shores of coastal lakes and lagoons.
The Smartline national dataset maps record the location of those coastal substrates and landforms that have greater or lesser sensitivity to potential coastal impacts of climate change and sea-level rise (IPCC 2013), such as accelerated erosion and shoreline recession, increased slumping or rock fall hazards, changing dune mobility, and other hazards.
Reference: IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp
- 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 millenia. 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 metres of 'soft' shorelines and are at risk from accelerated erosion due to sea-level rise and changing climate conditions (as at 2011).
What is Geoscience Australia's role in reducing risk to Australians from coastal erosion?
Geoscience Australia is committed to support Australia's capability to managing the impact of natural hazards, including coastal erosion. Geoscience Australia:
- develops an understanding of natural hazards and community exposure to support risk mitigation and community resilience
- provides authoritative, independent information and advice to the Australian Government and other stakeholders to support risk mitigation and community resilience
- maintains and improves systems for effective natural disaster preparedness, response and recovery
- contributes to Australia's overseas development program.
In particular, Geoscience Australia:
- develops national-scale datasets as a fundamental input to coastal erosion hazard and risk assessments
- develops methods and tools that can support the development of coastal risk assessments
- supports national initiatives to manage the coastal environment.
- Geomorphic classification of the Australian coast
- Coastal sediment compartments
- Ground penetrating radar
- Marine Sediments Database (MARS)
- Interactive maps
- stormwavecluster - a collection of R scripts and data used for statistically modelling of coastal storm waves (supported through the Bushfire and Natural Hazards CRC)
- A Nationally Consistent Geomorphic Classification of the Australian Coastal Zone
- The Australian Coastal Sediment Compartments Project
- A Framework for Modelling Shoreline Response to Clustered Storm Events: A Case Study from Southeast Australia
- Improved treatment of non-stationary conditions and uncertainties in probabilistic models of storm wave climate