Dredging at the Port of Warrnambool

Warrnambool City Council is developing a 10-year dredging strategy for the Port of Warrnambool.

The Port of Warrnambool is owned by the Victorian Government which provides funding to support the port operations and maintenance.

Dredging is required to ensure sufficient water depth for the safe manoeuvring of boats in the port area and to help refract wave energy where boat launching and retrieval occurs.

Lady Bay is on a dynamic stretch of Victoria’s coastline with currents and storms constantly moving sand along the seabed and the shore.

Dredging is required to moderate the wave action around the port area and to ensure there is sufficient water depth for a wide range of boats.

Among the key considerations for the strategy is where to dispose of the 35,000 cubic metres of dredged sand, which is the proposed volume for removal in 2020 subject to funding.

Dredging will be undertaken in accordance with environmental approvals. 

There are four options:

Option 1. Disposal of dredged material in specially constructed retention ponds behind the dunes at Worm Bay. This is Council’s preferred option.

Option 2. Disposal of dredged material on to a wide stretch of Lady Bay beach from the Pavilion Café to Warrnambool Surf Life Saving Club (approx.) This would be about 20m wide and 1.5m deep.

Option 3. Hybrid which is a combination of options 1 and 2. Disposal of most material behind the dunes and some along the beach (up to 5,000 cubic metres of sand placed on the beach to help stabilise the dune face).

Option 4. Near-shore marine disposal of dredged material over a large area away from the port. This would create an artificial sand reef which would remain in place for a period of time before coastal action placed some material on the beach while a portion would be dispersed off-shore. 

Community feedback will help inform a decision on dredging and in evaluating each of the options Council, the Department of Environment, Land, Water and Planning and the Department of Transport will also consider:

• Environmental impacts
• Social impacts (such as visual and smell)
• Impact on recreational users of the Port and Lady Bay
• The potential return of material to the area that has been dredged
• Cost effectiveness
• Public safety (vehicle movements)
• Frequency of future dredging efforts

Advantages and disadvantages of each option

Option 1 – dredged material placed in retention ponds behind the dunes. Water drains from the sand back to the ocean, dredged sand can be used elsewhere

Advantages

• No risk of dredged material returning to the bay
• Sand kept in reserve to replenish the beach after storms
• Dredging ponds can be used again
• Beach remains accessible during eight-week dredging program
• Site is reclaimed land that has been used for disposal of dredged material for the past 90 years

Disadvantages

• Most expensive option due to double handling of material
• Does not directly replenish eroding dunes along Lady Bay
• Vegetation removal for ponds will have a visual impact when viewed from elevated building floors
• Odours from organic material breaking down will persist for some weeks

Option 2 – dredged material placed along Lady Bay beach to fortify dunes and create more beach area

Advantages

• Unlikely to have a significant impact on flora and fauna as sandy sediments settle quickly
• Replenishment or “nourishment” of beach would provide some protection against erosion
• May make the beach safer by with some stabilisation of slopes
• Would create more dry beach for recreational use

Disadvantages

• May initially be an unpleasant odour as organic material decomposes (not harmful and will dissipate quickly)
• Dredged material may return to the dredged area after high tides and rough seas
• Because of the above point a more frequent rate of maintenance dredging may be required
• There would be no access to parts of the beach while dredging is under way (approximately eight weeks)

Option 3  - Hybrid which is a combination of options 1 and 2. Disposal of most material behind the dunes and some along the beach (up to 5,000 cubic metres of sand placed on the beach to stabilise the dune face).

Advantages

• Creation of sand buffer on beach would provide modest protection against erosion of the foreshore
• Replenishment of beach could focus on more eroded sections
• This option retains material to augment the dune if erosion occurs 
• Lessened impact to pedestrian amenity during the campaign as the volume of sand being deposited on the beach is significantly reduced 

Disadvantages

• Vegetation removal for ponds will have a visual impact from an elevated viewing position
• Odours during dredging campaign will persist behind the dunes for longer than beach disposal options

Option 4 - near-shore marine disposal of dredged material.

Advantages

• Low impact on pedestrian amenity while dredging is under way
• Coastal processes will deliver sediment to the shoreline, similar to a natural process

Disadvantages

• More frequent dredging likely than if sand was completely removed from Lady Bay
• Coastal action and predicting sand movement is not an exact science

Indicate your preferred dredging option below - the survey closes on January 31, 2020.