Will dredging affect the marine fauna and flora?
Flinders Ports is committed to limiting impact to marine fauna and flora during the Outer Harbor Channel Widening Project.
It is estimated four hectares of sparse seagrass will be removed directly from the dredge area. Indirect disturbance from dredging may impact approximately 158 hectares in a zone that follows the route of the Outer Harbor channel. Seagrass will be monitored before and after the project to measure impact.
Trained Marine Mammal Observers will work with the dredge team to monitor any mammals within 150m of the dredge equipment (caution zone). Works will delay or pause if marine mammals are spotted within 50m of the Backhoe Dredge and any sightings will be reported back to the Environment Protection Authority (EPA).
What measures are being taken to protect dolphins, whales and other marine mammals?
A trained Marine Mammal Observer will work with the dredge team to spot mammals and alert operators if the mammal comes within 150 metre of the dredge equipment. If the mammal moves within 50 metres of the Backhoe Dredge, dredge works will delay or pause until the mammal moves on.
Most large marine mammals, such as whales, seals, sharks and turtles, are deterred by the activity of the dredge vessel and tend not to go near it. In addition, whales are rarely sighted in the Gulf.
Dolphins are drawn to moving vessels, as they like to ride the ‘bow-waves’ these create. Everyday there are dozens of ships travelling in and out of the Outer Harbor port so movement of the dredge vessel, which will occur at a low speed, is not expected to cause any additional risks.
What investigations have been done to ensure the project does not affect marine life and other industries?
Flinders Ports conducted various environmental investigations to inform its Dredge Management Plan, Environmental Monitoring Program (EMP) and Pacific Oyster Mortality Syndrome (POMS) Management Plan, which aim to minimise impacts to the environment and any flow on effects to associated industries. These have helped determine the specific environmental measures put in place.
Some of the pre-dredge investigations and measures include:
- Survey of seagrass coverage and density
- Survey on the presence of Caulerpa taxifolia (a weed species)
- Quarantine risk assessment, quarantine inspection and invasive species inspection on all vessels prior to arriving in Australia
- Cleaning and conducting antifouling renewal on equipment
- Implementing a biofouling inspection and report by a third party
- Assessment on the dredge material placement area options, including surveys on the condition of the selected area
- Fitting vessels with GPS trackers utilising Automatic Identification System (AIS), including recordings of when and where the hopper doors are opened to deposit dredge material in the Dredge Material Placement Area
- Induction of trained Marine Mammal Observers to work as part of the dredge team to monitor marine mammal activities
- Conducting a noise impact assessment
- Investigation on contaminants in dredge material (material was identified as suitable for unconfined disposal at sea)
- Water quality assessment
- Preparation and implementation of an approved POMS Management Plan. This included survey on the presence of bivalves in dredge area, testing for presence of POMS, and removal or destruction of bivalves within the dredge area
In addition, further surveys on seagrass will be conducted for two years after the project is complete to track potential impact and recovery and determine if any necessary interventions are required.
How will the dredge works affect commercial fisheries?
The dredging will have no impact on commercial fisheries moving in and out of the Outer Harbor. There will be no change to the operations of the port. Dredging will be undertaken around operations. Flinders Ports doesn’t anticipate any impact to key fishery habitats or water quality in those areas. We have engaged with the fishing community and let them know that there may be a short-term, localised impact on fish stocks while the project is undertaken, but we don’t anticipate this will have any longer-term impact.
How will the water quality be tested?
Water quality will be monitored every 10 minutes during dredging at three sites – one site located north of the channel, one site to the south of the channel, and a background site located away from the dredging activity. Turbidity measurements adjacent the dredge area can then be compared to water quality at the background site. This will allow the project team to identify if elevated turbidity is the result of localised conditions i.e. wind, poor weather, or due to dredge activities.
Monitoring will measure turbidity (suspended sediments in water), Photosynthetically Active Radiation (to measure the light on the seafloor available to seagrass) and dissolved oxygen, pH, salinity and temperature.
Turbidity will be measured in Nephelometric Turbidity Units (NTU) which calculates suspended sediment in water. Should nominated limits be exceeded, as per the Dredging Licence conditions, the contractor will follow a set criteria for two levels – Alarm and Hold, and implement associated actions. For more information, see our environmental fact sheet.
If water quality reaches Alarm or Hold level, due to dredging activities, the following actions will occur:
- Alarm (2.8 NTU based on 15 day rolling median or 5.8 NTU based on 6 day rolling median) – Alter dredge methodology to reduce turbidity by changing location or direction of dredging and considering tidal currents, or altering the overflow regime to reduce fines spilt to water.
- Hold (5.8 based on 15 day rolling median or 15.8 NTU based on 6 day rolling median) – Crease dredging until turbidity falls back below specified limits, notify the Environment Protection Authority (EPA) and provide the EPA with a report on activity details and corrective action.
How will this affect recreational fishing in the area?
Recreational fishers will notice the dredge vessels in the area and be required to remain clear. The dredge will operate in and directly adjacent the shipping channel and swing basin. Recreational fishers should remain clear of that immediate area but no other restrictions will be implemented. Boat users should take note of important safety information including:
- Pass at 4 knots or less
- Pass on the side showing two diamonds during the day
- Pass on the side showing two green lights at night
- Do not approach within 100m of the dredge
- Pass to the stern of the vessels, including the survey vessel ‘Bay Lass’
- The vessels are restricted in their ability to manoeuvre
- Contact the dredge team using your boat radio on VHF Channel 12, if you’re unsure
What are the environmental risks being managed?
Management strategies have been developed for the key environmental risks associated with the dredge works. The main risks are:
- Potential impact to seagrass and water quality due to the generation of sediment plumes in the seawater
- Biosecurity risk of introduction of invasive marine species and spread of Pacific Oyster Mortality Syndrome (POMS)
- Vessel interactions with marine mammals
The Dredge Management Plan (DMP) outlines management actions for each risk, including objectives and performance measures which will be continuously reviewed and improved upon.