Coastal aquifers are a significant source of water for industry, drinking, public open space and a range of other uses. In coastal aquifers, dense salty water from the ocean meets the fresh water flowing out to sea below the surface of the land. This zone naturally occurs and is called the seawater interface.
The seawater interface can move inland if rainfall and groundwater recharge decline, or too much groundwater is abstracted. To maximise groundwater use without risking aquifers going saline, we need to know more about the location and movement of the seawater interface in many coastal areas.
Statewide seawater interface investigations, funded by our flagship State Groundwater Investigation Program (SGIP), are improving monitoring networks and giving us a better understanding of the seawater interface in priority areas across the state. These investigations began in 2016 and are ongoing around Western Australia.
What we are doing for these investigations
Statewide seawater interface investigations provide information, science and evidence-based advice to enable coastal groundwater resources to be used to their full potential, without going saline. The projects:
- use a combination of drilling, groundwater sampling and downhole and ground-based geophysics to measure and monitor the seawater interface
- install appropriate seawater interface monitoring in priority groundwater areas across the state
- assess new methods to effectively and efficiently investigate and monitor seawater interfaces.
So far we have:
- completed or are finalising investigations in the Cockburn, Peel Coastal, Myalup, Bunbury, Busselton-Dunsborough and Esperance areas
- commenced investigations in the Broome area and planning in the La Grange area.
Key findings and how we are using the information
In the Cockburn area we have completed our assessment and have:
- mapped the location of the seawater interface
- used our new knowledge of the extent of the seawater interface to refine the seawater interface risk zone and local licensing rules in the Cockburn groundwater allocation plan
- through the monitoring so far, found that the seawater interface moves seasonally – inland in summer and receding during winter/spring
- continued to monitor the seawater interface to assess any inland progression from abstraction and climate change.
Find a summary of the Cockburn area results and available reports.
In the Esperance area, we have completed our assessment and have:
- identified the location of the seawater interface in the Superficial aquifer
- identified the extent of saltwater intrusion from the Lake Warden wetland systems, including Pink Lake and Warden Lake
- identified where saline upconing is a risk for abstraction
- identified areas where the saltwater interface has progressed further inland since 2017
- used our new knowledge to develop maps showing the location and depth to saltwater in the Superficial aquifer
- continued to monitor the saltwater interface to assess any inland progression from abstraction and climate change.
- Find a summary of the Esperance area results and available reports.
In the Peel Coastal area we have:
- found hypersaline groundwater related to Peel Inlet in the east of the area that may be a higher risk to resource condition than seawater (ongoing monitoring is required to determine if this hypersaline groundwater is mobile)
- captured preliminary monitoring and logged data to indicate the ocean-side seawater interface has moved inland (ongoing monitoring is required to confirm if this is seasonal or if there is persistent inland seawater interface movement).
Findings from these investigations will help us manage seawater intrusion risks as part of allocation planning and licensing in priority areas around the state.
Where to get more details
Find a summary of our results and available information in the Cockburn seawater interface project.
Find a summary of our results and available information in the Esperance seawater interface project.
The following bore completion reports for completed SWI drilling programs can be can be requested:
- Cockburn seawater interface project – Bore completion report, HR408 (DWER 2019)
- Peel seawater interface project – Bore completion report, HR409 (DWER 2020)
- Esperance seawater interface project – Bore completion report, HR418 (DWER 2020)
- Bunbury to Dunsborough seawater interface project – Bore completion report, HR428 (DWER 2023)
- Myalup seawater interface project – Bore completion report, HR440 (DWER 2024)
Priority assessment reports completed to date include:
- Cockburn seawater interface project – Priority area assessment, HR 443 (DWER 2024)
- Esperance seawater interface assessment, HR 437 (DWER 2025)
To request copies of the internal technical reports for these investigations, email groundwater.info@dwer.wa.gov.au.
Access data from the monitoring bores installed as part of this investigation at our Water Information Reporting portal.
Read more about our groundwater investigations across Western Australia.
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