Overview

The proposed action by the Department of Defence (Defence) involves the delivery of priority works required to upgrade and enhance the infrastructure on HMAS Stirling, Garden Island, Western Australia (WA), to meet the requirements of the rotating conventionally-armed, nuclear-powered submarines (SSNs) arriving from 2027.

HMAS Stirling is Defence’s existing submarine base.

The proposed action is the first component of the Australia, the United Kingdom (UK), and the United States (US) (AUKUS) Optimal Pathway activities to occur at HMAS Stirling, which were announced by the Australian Government in July 2023.

The proposed action involves upgrading the existing Diamantina Pier and the Armament Wharf, and increasing small craft berthing capacity within HMAS Stirling, to support the berthing and maintenance of the SSNs. The proposed maritime infrastructure works involve (Att 1: Environment and Heritage Assessment, Section 2, pg 6-16):

• Upgrading the berthing facilities arrangements of Diamantina Pier to provide safe berthing of up to three SSNs during operation and one SSN during maintenance activities
• Increasing the existing small vessel berthing capacity to provide safe berthing of support vessels, including force protection vessels, harbour tugs and dive boats within Careening Bay
• Upgrading the services and berthing facilities arrangements of the Armament Wharf to provide safe berthing for one SSN during the loading and unloading of explosive ordnance.

The proposed action also includes dredging of a limited area to increase the under-keel clearance for safe and reliable movement of the SSNs during berthing and departure operations at Diamantina Pier and the Armament Wharf.

Proposed action area

The proposed action areas include (Att 1: Environment and Heritage Assessment, Section 2, pg 6):

• Areas of the marine environment where construction and operation activities will be undertaken, including the movement of dredge material between dredging sites to the spoil grounds
• Parts of Diamantina Pier and the Armament Wharf affected by the proposed action Potential laydown areas located at Careening Bay and Sulphur Bay.

Disturbance footprint

The total disturbance footprint for the proposed action is approximately 6.62 ha (Att 1: Environment and Heritage Assessment, Section 2, pg 6):

• Diamantina Pier:
  • Piling – 0.09 ha
  • Dredge pocket - 0.38 ha
  • Dredge disposal target area - 1.5 ha 
• Careening Bay - Small craft wet berth – 0.14 ha 
• Armament Wharf:
  • Piling & dredge pocket - 1.45 ha 
  • Dredge disposal target area - 3.03 ha 
  • Wharf extension - 0.03 ha.

Avoidance areas

Avoidance areas are areas of recognised conservation value that have been considered in the siting of the proposed action and intentionally avoided. Avoidance areas will be protected from any direct impacts.

The marine avoidance areas at Careening Bay and the Armament Wharf (Att 1: Environment and Heritage Assessment, Figure 2.1 and Figure 2.2) are known seagrass meadows. The terrestrial avoidance area within Careening Bay is a known nesting site for the little penguin (Eudyptula minor). The terrestrial avoidance area at the Armament Wharf is a known nesting area for rainbow bee-eaters (Merops ornatus).

Timing and duration

The construction program is proposed to commence in April 2025 (Att 1: Environment and Heritage Assessment, Section 2.3, pg 14).

Dredging is proposed to be conducted and completed within the month of March 2026 to minimise potential impacts to the little penguin. Dredging is expected to take between two to four weeks in total across both Diamantina Pier and the Armament Wharf.

Piling and installation of fender panels and floating pontoons is proposed to commence in April 2025. Piling must not occur in two consecutive little penguin breeding seasons. Completion of all construction is expected by September 2026. Piling is expected to take approximately 50 working days for fender piles and another 10 working days for the pontoons.

Construction hours

Construction activities that exceed guidance for acceptable received noise levels at residential accommodation precincts will be limited to the hours of 7 am and 7 pm, Monday through to Saturday to minimise the potential for noise impacts on residential (worker) accommodation at HMAS Stirling.

Construction activities that generate minimal or no noise may occur at any time (i.e. 24 hours a day on any given day including Sundays).

There are further restrictions for piling and dredging works that have the potential to disturb marine fauna:

• Construction works(excluding active vessels)will commence a minimum of 30 minutes after sunrise and will cease 30 minutes before sunset
• Active vessels(including boats and barges) will commence a minimum of 60 minutes after sunrise and cease 60 minutes before sunset.

HMAS Stirling will continue to operate as normal (24 hours per day, seven days per week).

Construction activities

Site mobilisation and establishment of temporary facilities 

• Conduct Construction Environmental Management Plan (CEMP) inductions Install temporary signage and cordon off the avoidance areas
• Management and storage of materials and waste at designated laydown areas within the proposed action area or elsewhere within Stirling as agreed by the construction contractor and Stirling base management
• Implement environmental controls, mitigation and management measures as per the CEMP and
• Section 6, Att 1: Environment and Heritage Assessment (pg 63 - 76) Implement traffic management measures (vehicles and vessels)
• Establish a site compound and laydown areas within the proposed action area utilising existing hardstand facilities within the HMAS Stirling Careening Bay operation precinct and the Armament Wharf precinct.

Demolition of existing infrastructure

• Redundant fender frames will be dismantled and removed for disposal
• Pilings to be removed via vibration and/or cut at seabed where required, and removed for disposal 
• Disposal/recycling of steel piles off site.

Fender piling and installation

• Driven installation of tubular piles to design depth:
  • Piles will be installed from the deck of Diamantina Pier and the Armament Wharf
  • Piling is proposed to take approximately 10 weeks (50 working days), including Diamantina Pier, small craft berths and the Armament Wharf
• Assembly of fender frames from the existing Diamantina Pier deck.

Dredging and dredge disposal

• Design dredge volumes including over dredging allowance are: 
  • 6,500 m3 at Diamantina Pier
  • 13,000 m3 at the Armament Wharf
• Dredge spoil will be disposed of within the proposed action area at existing dredge spoil disposal sites:
  • The dredge disposal site within Careening Bay is approximately 380 m southeast of Diamantina Pier (Att 1: Environment and Heritage Assessment Figure 2.1).
  • The Armament Wharf dredge disposal site is approximately 480 m southeast of the wharf(Att 1: Environment and Heritage Assessment Figure 2.2).
• Dredging is proposed to be undertaken during March 2026 to avoid adverse impacts to the resident little penguin colony.
• Dredge spoil disposal will be conducted in accordance with the required Sea Dumping permit.

Small berth pontoon installation

• Driven installation of tubular piles to design depth, including: 
  • Piles will be installed from barge
  • Piling is proposed to take approximately two weeks (inclusive of both locations) 
• Assembly of pontoon Sections to each other and to restraint piles.

Armament Wharf extension and substation installation

• Driven installation of steel wharf piles to design depth:
  • Piles will be installed from the deck of the Armament Wharf
• Assembly of new deck and concrete pedestal to facilitate the construction of substation and low voltage switchroom.

Clean up/demobilisation

• Demobilise construction machinery and plant
• Remove the temporary construction compounds and temporary controls where they are no longer required
• Removal of any controls and signage. 

Operation and maintenance activities 

Diamantina Pier and the Armament Wharf berthing

The operational activities will be undertaken in accordance with Defence’s existing management controls and standard operating procedures for HMAS Stirling. The installation of the new fenders for SSN berthing does not introduce any new operational requirements or risks to those that are not already managed at HMAS Stirling. Measures in the Defence Operations Manual(OPSMAN 1) for Visits to Australia by Nuclear- Powered Warships will be implemented. Where additional environmental management measures are required that are related to the operation of the SSNs, these will be developed and managed by the Australian Submarine Agency, in concert with the US and UK submarine operators. Further information about the existing operational activities at Diamantina Pier and the Armament Wharf are provided in Section 2.4, pg 17, Att 1: Environment and Heritage Assessment.

Small craft wet berth

• Berthing of small vessels, including force protection vessels, dive boats and harbour tugs 
• Daily operation of small vessels during SSN presence at HMAS Stirling
• De-fouling of pier infrastructure including fender, frames and pilings to occur in accordance with current de-fouling protocols
• Minor in-water maintenance of vessels
• Continued day-to-day small boat maintenance and resupply activities

Project activities

Project activities that may have a director indirect impact on environmental values include:

• Construction activities:
  • Dredging and dredge disposal generating noise, vibration and turbidity and directly impacting:
    • Marine fauna and habitats, including but not limited to the little penguin
    • Seagrass
    • Water quality
  • Piling generating noise, vibration and turbidity and directly impacting:
    • Marine fauna and habitats, including but not limited to the little penguin
    • Seabirds
  • Construction lighting, indirectly impacting on:
    • Marine fauna and habitats, including but not limited to the little penguin
    • Seabirds
• Operational activities:
  • Small craft berthing generating noise, lighting and vessel movement impacting on: 
    • Marine fauna and habitats, including but not limited to the little penguin
    • Seabirds