Jurien Bay Boat Harbour water quality improvements

JBBH experiences seasonal water quality issues that are mostly caused by seagrass accumulating and decomposing in the boat harbour.

The decomposing seagrass reduces oxygen in the harbour water and creates a strong hydrogen sulphide odour and occasionally results in the death of a large number of fish. These issues usually occur in winter through to spring. 

Over the past decade, DoT has completed a comprehensive data collection and research program to better understand these events and develop an effective solution.

This program included coastal modelling and environmental studies, data collection, and several trials including:

• dredging
• trawling, and
• use of a bubble curtain to prevent seagrass entering the harbour and to oxygenate the water.

Modelling studies showed that adding a 170-metre breakwater extension to the northern breakwater would divert a large amount of seagrass from entering the harbour, significantly improving the water quality. 
The works will involve using trucks and earthmoving equipment to import and place rocks to construct the spur groyne.

This proposed structural modification may result in some periodic trapping of seagrass on the northern beach outside the harbour.

The JBBH entrance modification comprising a new 170 metres breakwater extension is proposed to be delivered by DoT over the next 4 years utilising State Government funding. Funding for the project was announced in April 2024.

DoT completes maintenance dredging campaigns at JBBH approximately every 2-3 years.

Maintenance dredging is the process undertaken to remove accumulated marine sand and seaweed to:

• restore navigable depths for vessels;
• provide ongoing access and operational use of the harbour
• remove decomposing seaweed and maintain harbour water quality; and,
• restore natural tidal flushing.

Offshore placement

For maintenance dredging campaigns completed prior to 2020, dredged material has been placed onshore in a designated area north of the harbour.

As a more sustainable solution, DoT is now returning the dredged material offshore into a natural seabed depression.  

DoT has secured environmental approvals for this offshore disposal location and the dredged material will be placed in this area during future maintenance dredging campaigns. 

Maintenance dredging campaigns will be monitored and managed as per environmental approval conditions and the Jurien Bay Boat Harbour Maintenance Dredging Long Term Monitoring and Management Plan.

Offshore disposal location