Project record

Alkimos Seawater Desalination Plant marine tunnels and offshore structures

Jack-up barge Beverley carrying out offshore intake and outfall construction for the Alkimos Seawater Desalination Plant

Water Corporation, Western Australia

Western Australia's Alkimos plant combines a 2.5 km seawater-intake tunnel, a 4 km brine-outfall tunnel, two offshore intake structures, four vertical risers, and a 130 m diffuser with the first 50 billion litres per year of desalination capacity. By July 2026 the intake tunnel and all offshore piling were complete, while the outfall tunnel and diffuser connection remained active.

Project signal

Construction in Australia

Track the handover from completed piling and intake tunnelling into outfall-TBM breakthrough, diffuser and riser connections, accepted marine-system testing, and integrated commissioning. The original annual-report programme placed tunnelling through July 2026 and marine construction through June 2026; the owner's July panel still had diffuser installation active, so current evidence must distinguish schedule movement from accepted completion. First water in 2028 still depends on convergence with the plant, power upgrades, and the Alkimos-to-Wanneroo transfer pipeline.

Current status Intake tunnel and offshore piling complete; outfall tunnel and diffuser installation remained active after the original June 2026 marine-work window Source confidence Confirmed

Location

Australia / Asia Pacific

Segment

Marine utilities

Status

Intake tunnel and offshore piling complete; outfall tunnel and diffuser installation remained active after the original June 2026 marine-work window / Confirmed

Evidence reviewed

15 July 2026

Controlled taxonomy

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Knowledge context

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Project anatomy

Scope, counterparties, and execution logic

Client / authority
Water Corporation, Western Australia
Delivery parties
Alkimos SeaWater Alliance, ACCIONA, Jacobs Group Australia
Contract route
Alliance design-build-operate-maintain delivery by Water Corporation, ACCIONA, and Jacobs, including ten years of operations and maintenance
Execution window
The alliance sustainability report dates construction from August 2024 to August 2027, tunnelling from July 2025 to July 2026, marine construction from November 2025 to June 2026, commissioning from August 2026 to June 2028, and operation from June 2028. The owner's July 2026 update still had outfall-diffuser installation active and its current public timeline allows marine tunnelling through late 2026; those later records supersede the original marine and tunnelling endpoints without proving a revised acceptance date.
Works package
A 50 GL/year Stage 1 seawater reverse-osmosis plant, scalable to 100 GL/year, with a 2.5 km intake tunnel, a 4 km outfall tunnel, two offshore intake structures, four vertical riser connections, a 130 m outfall diffuser with 20 ports, onshore process works, power upgrades, and a 33.5 km transfer pipeline to Wanneroo.
Marine interfaces
Two tunnel boring machines drive from shore beneath the dunes, reefs, and seabed to meet offshore risers. Jack-up and support barges install piled intake structures and the outfall diffuser, so survey control, vertical-shaft breakthrough, lifting, grouting, marine exclusion zones, fauna observation, and tunnel-to-structure acceptance share one critical interface.
Commercial read
The prime alliance and main marine scope are awarded. Specialist work remains in offshore installation, survey and positioning, tunnel and riser completion, environmental monitoring, mechanical integration, testing and operations readiness. The 2028 commissioning path, not a new project-level EPC competition, will determine the remaining delivery demand.
Next milestone
Confirm completion and acceptance of the outfall diffuser and 4 km outfall TBM drive, permanent tunnel-to-riser connections, closure of residual marine exclusion zones, then integrated intake, outfall, plant, power, transfer-pipeline, and first-water testing.

Material change register

What changed, when, and what it proves

Only source-bound events that alter phase, scope, counterparties, delivery, completion, commissioning, or acceptance are listed. A change can advance the record without proving the next gate.

Marine work continued beyond the original June window with diffuser installation still active

Water Corporation's July panel records all intake and outfall piling complete and the final outfall-diffuser installation phase under way. This advances the offshore package but also shows that the annual report's June 2026 marine-construction endpoint was not an acceptance date; diffuser placement, connection, testing and marine demobilisation remained open.

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The intake tunnel reached its offshore destination while the outfall drive remained incomplete

The owner's June panel records TBM Mary completing the 2.5 km intake drive in 196 days, all offshore piling complete and TBM Karli about 80% through the 4 km outfall drive. Intake-tunnel completion does not prove permanent riser connection, outfall completion, accepted diffuser performance, integrated testing or first water.

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Beverley mobilised for offshore intake and outfall installation

The Western Australian Government recorded arrival of the 78 m-leg jack-up barge with a 400 t crane for 24-hour installation of ocean intake and outfall structures. Vessel arrival and offshore activity establish mobilisation, not installed or accepted marine assets.

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Navigation closures established the offshore construction footprint

Transport WA issued two 500 m-radius closure notices for intake and outfall works beginning on 10 December 2025, identifying Beverley, Pilbara 400 SEMP, support tugs and work barges. A regulated marine work zone proves planned and authorised activity, not completed piling or structural acceptance.

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Both TBMs were assembled for the separate intake and outfall drives

Water Corporation announced that two more-than-four-metre-diameter TBMs would begin an 18-month programme beneath the seabed for a 2.5 km intake and 4 km outfall. Assembly and launch readiness do not prove tunnel advance, breakthrough, lining acceptance or offshore connection.

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Alliance reporting places the project into its construction phase

The alliance sustainability report dates construction from August 2024 and separates it from detailed design, tunnelling, marine construction, commissioning and operation. This is a programme phase boundary, not evidence that offshore works or tunnel excavation had started in August.

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Water Corporation selected the ACCIONA-Jacobs alliance for delivery and operation

Jacobs identified design, build, operation and maintenance scope with Water Corporation and ACCIONA, including separate 2.5 km intake and 4.1 km outfall tunnels. The appointment establishes delivery responsibility but not construction mobilisation or accepted marine output.

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Environmental approval established the controlled marine development envelope

EPA records Ministerial Statement 1207 approval for the plant and its marine components. Approval allows implementation under conditions; it is not an alliance award, notice to proceed, construction start or operating approval.

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Delivery watch

Evidence needed next

Confirm completion and acceptance of the outfall diffuser and 4 km outfall TBM drive, permanent tunnel-to-riser connections, closure of residual marine exclusion zones, then integrated intake, outfall, plant, power, transfer-pipeline, and first-water testing.

Decision watchpoints

  • Outfall diffuser installation, survey acceptance, and offshore marine demobilisation
  • Completion and breakthrough of the 4 km outfall tunnel after the original July 2026 programme point
  • Permanent tunnel-to-riser and intake-outfall mechanical connections
  • Marine fauna, underwater noise, water-quality, and seabed controls
  • Integrated first-water schedule across marine works, plant, power, and transfer pipeline

Related records 3

Project availability status

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Record control

Evidence reviewed date is not a project-event date.

IMWO changes phase, participants, scope, completion, or acceptance wording only when a dated source establishes the change. The review date records when the evidence set was checked; it does not claim that physical work changed on that date.

Evidence reviewed 15 July 2026 Sources in this record 9

Source record

EPA records environmental approval on 10 August 2023. Jacobs then identified its Water Corporation-ACCIONA alliance appointment on 19 April 2024, and the alliance sustainability report dates the construction phase from August 2024, tunnelling from July 2025, marine construction from November 2025, commissioning from August 2026, and operation from June 2028. Water Corporation's 15 July 2025 release records both TBMs assembled for the 2.5 km intake and 4 km outfall drives. Transport WA issued two closure notices on 9 December 2025 for marine construction beginning on 10 December. The Western Australian Government's 16 March 2026 record confirms Beverley mobilised to install the intake and outfall structures. Water Corporation's June panel records the 2.5 km intake TBM at its destination, the outfall drive about 80% complete, and all offshore piling complete; its July panel says diffuser installation remained the final offshore phase. The monthly panels do not state a day, so their public change dates retain month precision. The two intake structures, 130 m outfall diffuser with 20 ports, vertical risers and bored tunnels form one marine system. Piling, TBM completion, visible offshore structures, exclusion-zone expiry and first water remain separate from permanent connections, testing, owner acceptance, stable output and commercial operation.

Phase: construction. Evidence reviewed: 15 July 2026.

Project sources 9