Large waves, elevated water levels and strong winds generated by a storm can cause coastal erosion and inundation. Erosion and inundation commonly occur as a consequence of increased wave height and storm surge, which can cause the sea to rise to levels much higher than normal due to the action of on-shore winds (wind setup) and a lowering of the barometric pressure.
Wind blowing onshore over the ocean surface drives surface waters before it and against the coastline. This results in elevated water levels in coastal areas, the degree of elevation being higher for extensive shallow areas and semi-enclosed bays.
The reduced barometric pressure that generate storm winds also causes a local rise in ocean level. Providing low pressure persists for a sufficient length of time, the increase in water level amounts to about 0.10 metres for each 10hpa drop below normal barometric pressure (1013hPa).
The effects of storm surge may be intensified if storm surge conditions occur during periods of spring or extreme tides or in association with other tidal anomalies.
Storm surge in NSW occurs as a result of intense low pressure systems offshore of the NSW coast. These low pressure systems include tropical cyclones, ex-tropical cyclones and east coast lows.
Coastal Erosion
Coastal erosion is the loss of land along the shoreline due to the natural removal of beach and dune material in response to changing wave and water conditions. Buildings and facilities located within the ‘active’ beach system, or areas subject to coastal erosion can be undermined and may even collapse.
Approximately 60 percent of the NSW open coastline is characterised by sandy beaches. These beaches are dynamic environments undergoing continual cycles of erosion and accretion in response to the action of tides, wind and waves. In many places, existing foreshore development has been built within the ‘active’ beach system and is at risk from coastal erosion.
The extent of beach erosion during a particular storm event depends upon a variety of factors that include:
- The wave conditions and elevated water levels generated by the storm
- The presence of rip cells
- The condition of the beach
- The condition of dune vegetation which can influence the volume of sand in the dunes which help to buffer the effects of storm erosion
- The presence and influence of adjacent headlands and coastal structures, which can modify local wave conditions and the supply of sediment
Immediately following coastal erosion events on sand beaches, a near vertical erosion scarp of substantial height can be left. If buildings are located close to the vertical erosion scarp, they may be at-risk of structural damage. Instability of the escarpment may pose a hazard to beach users following storms with recorded instances of children and beach users buried by the collapsing sand face.
Coastal Inundation
Coastal inundation is the flooding of low-lying coastal land by ocean waters. Along the NSW coast there are many low-lying areas above the normal high tide level that are subject to coastal inundation. These include wetland and other fringe areas of coastal lagoons and rivers, and the areas behind beach and dune systems. Buildings in low-lying coastal areas can be inundated as a consequence of storm surge conditions.
Emergency Management Arrangements for Coastal Erosion and Inundation
The SES as the combat (lead) agency for storm damage control is responsible for the emergency management of coastal erosion and inundation as a result of severe storms. The SES prepares emergency plans for coastal erosion and inundation and coordinates the emergency response to coastal erosion and inundation.
Warning Systems for Coastal Erosion and Inundation
The Bureau of Meteorology issues Severe Weather Warnings when damaging waves or storm surge conditions are anticipated that may result in coastal erosion or inundation. These warnings are broadcast over local radio stations. Warnings are also available on the Bureau of Meteorology website.
What should you do to prepare yourself
You can take some basic measures right now to prepare for coastal erosion and inundation. These measures include:
- Keeping a list of emergency numbers and assembling an emergency kit
- Developing a home or business emergency plan
- Developing a knowledge of what warning systems are available
What should you do when coastal erosion or inundation is likely
When a Severe Weather Warning for damaging surf or storm surge conditions is issued you should:
- Keep an active watch on the situation
- Stay out of the water and away from areas exposed to surf
- Keep in contact with your neighbours
- Stay tuned to a local radio station for updates and further warnings
- Be prepared to evacuate if the situation worsens
- Follow the instructions of emergency services
- If you require assistance call the SES on 132 500
