Maintenance dredging at Cockburn Sound

Fremantle Ports will undertake maintenance at Success Channel and Parmelia Channel in order to ensure safe shipping can occur in Cockburn Sound, WA.

In order to retain declared depths within these channels and maintain safe access for ships, Fremantle Ports will be undertaking a maintenance dredging campaign within the channels starting in late June.

This campaign will remove approximately 80,000m³ of sediment from five areas within the channels and forms part of the ongoing long-term maintenance dredging strategy referred to and approved by the Environmental Protection Authority (EPA) in 2007.

The RN Dredging Pty Ltd trailer suction hopper dredge Modi-R will be used for this maintenance dredging; this dredge is also contracted by Cockburn Cement Ltd (CCL).

The Modi-R has a state-of-the-art computerised navigational system.

Dredging overflow is discharged under the vessel and features a ‘green valve’, which reduces air discharged with overflow water, resulting in sediments and fines sinking to the seabed and reducing turbidity.

One maintenance dredging load will be undertaken every 24 hours, removing approximately 1,000m³ on every dredge path run.

The maintenance dredging will not be additional to CCL’s current dredging; instead, one trip to the CCL dredge area will be substituted with a maintenance site within the channels.

The maintenance dredging campaign will last for three to four months.

Dredged sediment will be deposited directly at the CCL wash-plant and used for the production of cement and lime, rather than being disposed of offshore.

A recent independent environmental assessment of the proposed maintenance dredging campaign determined that ‘… due to the length of time spent dredging each day and over the course of the campaign, maintenance dredging of the Success and Parmelia Channels represents a low risk of adverse impacts on the health of surrounding seagrass, habitats and fauna’​.​