At the Southern Seawater Desalination Plant in Binningup, Western Australia, critical offshore infrastructure plays a key role in ensuring a reliable supply of drinking water for the region, while supporting the protection of the surrounding marine environment.
One key component of the seawater intake system is the Stage 1 Transition Box, a buried concrete structure that connects two 1.6 m HDPE intake pipelines to the plant’s intake tunnel. Operating beneath the seabed in a challenging marine environment, this structure plays an important role in maintaining the integrity and reliability of the plant’s seawater intake system.
Following the identification of progressive structural degradation and sand ingress, Sacyr Agua worked closely with Water Corporation and specialist delivery partners to develop a low-impact remediation solution. The objective was clear: restore functionality and extend asset life without requiring full replacement of the structure.
Developed in collaboration with SEA Global, SF Design and Fremantle Commercial Diving, the solution involved the installation of a precision-machined modular HDPE lining system. Reinforced in key locations and grouted in place, it created a sealed, load-bearing internal flow path. Computational Fluid Dynamics (CFD) modelling, structural verification and full-scale dry and wet testing were used to validate the design ahead of offshore installation.
The project was delivered under demanding offshore conditions, including subsea construction, restricted access, limited weather windows and stringent environmental controls. Specialist diving teams installed more than 75 custom-machined HDPE components within the existing structure, restoring intake integrity while minimising disturbance to the surrounding marine environment.
“This was more than a repair – it was a coordinated effort across design, fabrication and marine execution,” said Paul Oosthuizen, Maintenance Manager at the Southern Seawater Alliance.
By rehabilitating the existing structure rather than replacing it, the project reduced seabed disturbance, minimised operational impacts and extended the service life of a critical element within the plant’s intake infrastructure.
Australian Water Award
In 2025, the Transition Box Remediation project received industry recognition through an Australian water sector award for innovation in marine infrastructure delivery.
