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

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

Last checked

15 July 2026

Coverage

Related sectors

Marine utilities is the primary work classification. Related sectors connect this record to adjacent marine delivery and market coverage.

Subject index

Related subjects

These subject pages bring together related projects, technical articles, reports, and evidence methods.

Project anatomy

Contract scope and delivery roles

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 evidence boundary
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.

Project timeline

Material developments

Dated events that changed scope, counterparties, delivery, commissioning or operating status.

Open this project in the Change Log

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.

Source

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.

Source

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.

Source

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.

Source

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.

Source

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.

Source

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.

Source

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.

Source

Evidence gap

What remains unverified

Outstanding evidence

  • 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

Reporting status

Construction, confirmed confidence

Last checked 15 July 2026 across 9 cited sources. The dated timeline above carries the project events.

Last checked 15 July 2026 Cited sources 9

Sources and related records

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Source collections

Project sources 9