Coastal studies

1. What is coastal inundation?

Flooding caused by the actions of the sea is coastal inundation. Flooding is the covering of normally dry land with a large amount of water. This can occur through effects of rainfall causing overland runoff or expanding of rivers, or via actions of the sea, including tides, waves, and storm surges, also known as king tides. Coastal inundation is generally temporary, but with climate change projections over longer timeframes, it will occur more often, for longer periods and can become permanent.

2. Why has this Statewide assessment been undertaken?

Understanding the extent and impacts of current and future inundation events is essential for state and local managers to strategically plan for and manage coastal inundation. The study has identified both state-wide strategic and location specific targeted actions to address inundation hazards.

The need for an inundation assessment was identified in the Assessment of Coastal Erosion Hotspots in Western Australia, and the inundation study has been funded and delivered through the CoastWA program in partnership with Department of Planning, Lands and Heritage (DPLH).

3. What did the assessment find?

The study examined the potential scale and extent of coastal inundation over the short to medium term across 45 coastal local government areas, identifying 23 specific at risk locations.

The most significant sites for coastal inundation management are at Bunbury and Busselton, with extreme susceptibility to coastal inundation identified at both. While both are actively managing existing risk through use of protective structures, exceptionally large events above typical design levels could overwhelm existing defences. The City of Busselton is currently undertaking detailed investigations into its coastal inundation management.

Carnarvon is also identified as having extreme susceptibility to coastal inundation due to its low elevation. The study recommends an economic review for Bunbury and Carnarvon to investigate in detail whether the current standard of protection is appropriate.

4. What are the main causes of inundation in WA?

Coastal inundation is typically caused by tropical cyclones in the North West and winter storms or cold fronts in South West. In the future sea level rise will raise water levels, the impacts of this will be felt during storm and cyclone events. Future higher water levels plus storm surge will lead to more frequent coastal inundation events with larger extents and depths.

5. Why is understanding the inundation threat important for coastal communities?

As the climate changes there will be impacts such as increased degradation of beaches, damage to existing coastal structures and increased frequency of inundation events that threaten private properties and public assets in high-risk areas. By understanding the threat we can proactively plan to minimise its impacts.

6. Who will use the assessment?

The study is designed to help local land managers plan, design and budget mitigation measures and seek Commonwealth and State funding. The report will also be used by the State Government to identify priority actions to strategically support management of inundation hazards.

7. How will the assessment help manage the inundation hazard?

The study identifies targeted actions for managing inundation hazards at 23 specific locations that will support and benefit future studies, works and local government Coastal Hazard Risk Management and Adaption Plans (CHRMAP’s). The information can also be used by local managers to secure funding through DoT’s Coastal Adaptation and Protection (CAP) Grants program, DPLH’s Coastal Management Plan Assistance Program (CMPAP) and the Commonwealth Disaster Ready Fund.

8. Where are the 23 specific locations?

The 23 specific locations and their assessed susceptibility to coastal inundation are shown on the map above. More detail on the area affected by inundation at each location is contained within the study and appendices, which contain a map that shows the extent of inundation at each site and information on the assets exposed to inundation hazards.

9. How will the recommendations be progressed?

The study has identified 13 locations where targeted works may alleviate inundation risk, however a closer analysis of each location is needed to understand the works required. DoT coastal engineers will work closely with local managers to scope individual studies through the CAP grant program, and then develop practical solutions for the land managers to seek funding opportunities.