Coastal management

Sea wrack (seaweed and seagrass) accumulation in Two Rocks is caused directly by the Two Rocks Marina which interrupts the alongshore movement of both sand and sea wrack. The beach immediately south of the Two Rocks Marina has experienced ongoing sea wrack accumulation since the construction of the marina, particularly during summer months, resulting in issues with beach usability, public safety and odour. This beach area falls outside of the City of Wanneroo managed land boundary, however a Section 91 licence for the use of Crown Land has been obtained to cover the 2021/22 summer period to enable the City to conduct works on this land during this time.
 
The Department of Transport (DoT) conducted an assessment of wrack accumulation for this location which confirmed excessive wrack accumulation during summer months and identified metocean conditions which resulted in the transport of the deposited wrack back into the ocean and away from the beach. The DoT Two Rocks Summer Wrack Accumulation Study (2020) can be found by clicking below:

Department of Transport - Two Rocks Summer Wrack Accumulation Study

The Sea Wrack Management Trial

In March 2022, the City, in consultation with the Two Rocks Yanchep Residents Association, conducted a Sea Wrack Management Trial which included the following:

• Regular beach monitoring to determine when the deposited sea wrack becomes an issue;
• Pushing of the deposited sea wrack back into the ocean using loaders on the beach during favourable weather conditions; and
• Deployment of GPS drifters into the water with the sea wrack to track sea wrack movements and confirm that the wrack is removed from the beach area.

Overall, it was concluded that the results of the trials did not justify the ongoing implementation of this methodology for sea wrack removal to the south of the Two Rocks Marina.

This project was partly funded by the State Government via the Department of Planning Lands and Heritage 2021/22 Coastwest Grant.

Next Steps

The City is currently assessing alternative sea wrack management options and have sought feedback from the community on a number of alternate management options via the Two Rocks Sea Wrack Management Community Survey which closed in late February 2023. Click to review a summary of community feedback. 

Following a review of community feedback and advice from the Department of Transport, the City plan to undertake another Sea Wrack Management Trial during a period of excess sea wrack accumulation. This Sea Wrack Management Trial will include the following sea wrack management methods:

• Development of a Sea Wrack Community Collection Point where community members can pick up sea wrack from the Two Rocks Marina for personal use as garden fertiliser or compost.
• Burial of excess sea wrack, that is not collected by the community, in front of the existing dune system to create a foredune. Burying sea wrack in front of the dune system will create a foredune and promote the growth of dune vegetation. This will improve biodiversity in the area and provide additional coastal protection.

Should you have any queries on management of sea wrack accumulation south of the Two Rocks Marina, please contact the City’s Specialist Coastal Engineer, Mr Rory Ellyard, on 9405 5883