Marine Utilities

Alkimos completes offshore structures and tunnels before riser connections

Published 6 October 2026 Publisher IMWO Region Asia Pacific Confidence Confirmed
Inside the Alkimos seawater intake pump station showing the two ocean tunnel portals and permanent pipework after tunnel excavation

Water Corporation, Western Australia; September 2026 Alkimos marine milestone release

Two distinct delivery fronts at Alkimos have crossed their physical-completion points. Jack-up barge Beverley installed both intake structures and the outfall diffuser before departing on 28 July, while the final tunnel boring machine reached the outfall structure in late August. Water Corporation now places permanent riser connections, inspections, surveys and commissioning checks ahead of first water in 2028.

Offshore installation and tunnelling have dated completion evidence

Water Corporation's current project page dates Beverley's departure to 28 July, Mary's intake arrival to May and Karli's outfall arrival to late August, then identifies riser connections as the next phase. Its 1 September release reports both tunnels and offshore structures complete, about 32,000 lining segments installed and the former marine exclusion zones removed. Transport WA's current public notice still gives both 500 m closure areas an end time of 6:00 PM on 31 October 2026, creating an access-record discrepancy that needs confirmation rather than an assumption about physical progress.

The connection gate still controls hydraulic readiness

Desalination intake and outfall systems only become operational when excavation, offshore structures, risers, mechanical connections and controls perform as one accepted circuit. At Alkimos, tunnel breakthrough and barge demobilisation remove major construction risks but do not demonstrate sealed connections, verified flow paths or compliant brine dispersion. The same distinction matters to suppliers and operators: heavy offshore installation demand has fallen away, while survey, diving, mechanical integration, electrical work, instrumentation, testing and commissioning remain tied to the 2028 first-water path.

Evidence conclusion

Public navigation records need formal reconciliation

Evidence now supports moving Alkimos beyond active tunnel excavation and major offshore installation. One public-record mismatch remains material: Water Corporation says marine exclusion zones were removed, while Transport WA still publishes closure notices through 31 October. That difference may reflect notice administration, residual maintenance-diving controls or a later access decision, but the available records do not settle it. Commissioning evidence should therefore start with permanent riser-connection records and closure reconciliation, then progress through inspection, survey, hydraulic testing, environmental compliance and integrated plant output before first water is treated as achieved.

Outstanding evidence

  • Permanent connection of the intake and outfall risers to both tunnels
  • Formal reconciliation of removed exclusion zones and Transport WA closure notices
  • Final marine inspections, surveys and maintenance-diving activity
  • Hydraulic, mechanical and environmental acceptance of the intake and outfall system
  • Integration with plant fit-out, power, transfer pipeline and 2028 first water

Related records 1

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