Project record

Alkimos Seawater Desalination Plant marine tunnels and offshore structures

Participation
Not assessed
Project facts checked

First intake-to-tunnel connection complete; excavation towards the second riser continues

Project sources

Water Corporation's October update records the first permanent intake-to-tunnel connection complete and excavation towards the second intake riser. Both tunnel boring machines and their slurry and water-treatment support plants have been demobilised. Process-building fit-out and the wider water system continue towards planned first water in 2028.

Alkimos constructed tunnel lengths: 2.5 km intake and 4 km outfall. The October update records the first intake junction complete and excavation towards the second riser.

IMWO original Alkimos water-path diagram based on Water Corporation construction updates

Location

Australia / Asia Pacific

Segment

Marine utilities

Phase

Construction / Confirmed

Last checked

30 October 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 October owner update records the first intake connection complete, both tunnel boring machines off site and the associated slurry and water-treatment plants removed. It expects the reverse-osmosis building structure complete at the end of November, followed by membrane racks. First water remains planned for 2028. Earlier alliance programme dates remain in the original sustainability report.
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
The completed tunnel drives meet offshore intake and outfall structures through permanent riser connections. The owner reports the first intake-riser centre around 11 metres below the seabed and 10 centimetres from its planned target. Excavation now approaches the second intake riser; the completed permanent junctions will form the water paths used for marine-system testing.
Commercial evidence boundary
The prime alliance and major offshore installation scope are awarded and physically advanced. Remaining specialist demand sits in riser and tunnel connection, survey, inspection, mechanical and electrical integration, testing, commissioning and operations readiness. The 2028 path is an interface and acceptance programme rather than a new project-level EPC competition.

Project timeline

Material developments

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

Open this project in the Change Log

First permanent intake-to-tunnel connection completed

Water Corporation records the first intake junction complete and excavation towards the second riser, while both tunnel boring machines and their support plants have been demobilised. The reverse-osmosis structure is expected at the end of November before membrane-rack installation.

Source

Both tunnel drives reached the offshore structures

Water Corporation reports more than 6 km of tunnelling complete after Mary reached the intake in May and Karli reached the outfall in late August. Excavation and lining are complete, while permanent riser connections, inspections, surveys, system checks and accepted performance remain separate milestones.

Source

Beverley departed after installing the offshore structures

The project page records both intake structures and the outfall diffuser installed before the jack-up barge left Alkimos. Vessel demobilisation closes the main offshore installation campaign, but does not establish permanent tunnel connection, final marine acceptance or operating output.

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 lists Notices6665 and6666, issued17and10December2025 respectively, with two500m-radius closure areas beginning10December2025. The current listing retains their31October2026 endpoint.

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

  • Second intake-riser excavation and permanent connection
  • Remaining intake and outfall junctions and water-path checks
  • Latest Transport WA closure records and the owner's zone-removal statement
  • Reverse-osmosis building and membrane-rack installation
  • Integrated first-water programme across marine works, plant, power and transfer pipeline

Related reports

Related records 5

Reporting status

Project phase
Construction
Evidence confidence
Confirmed
Last checked
30 October 2026
Cited sources
11

Sources and related records

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Source collections

Project sources 11