Candowie Reservoir – dam upgrade

Client: Westernport Water
Location: Victoria, Australia
Date: November 2010 – October 2011

Investigating and designing the upgrade of an existing dam and spillway to increase storage and flood capacity


Candowie Dam is a 17m high embankment dam in south-east Victoria, Australia. The reservoir and associated water treatment plant is owned and operated by Westernport Water and provides the primary source of drinking water for Philip Island and surrounds.

Westernport Water planned to upgrade Candowie Dam by raising the full supply level by 3 m and upgrading the spillway to pass the 1:100,000 AEP flood. The result of the upgrade works would be to nearly double the reservoir capacity and create a spillway capacity that meets current guidelines.


Entura was engaged by Westernport Water to undertake investigations, detailed design and documentation for the Candowie upgrade project. Entura provided geotechnical, dam design, structural engineering and mechanical design services for the project.

The embankment upgrade utilised a crest wall, as there was limited area to extend the dam downstream due to the treatment works facilities. The spillway upgrade was required to be staged to provide flood protection for the works.

Project innovations included the post-tensioning of the raised outlet tower. Due to the limited size of the tower, the anchors were designed to be installed external to the dry tower.

Entura undertook the detailed design and specification of the embankment upgrade, spillway upgrade, outlet tower upgrade (including new walkway), wash water tank upgrade, Grantville – Glen Alvie Road upgrade and reservoir perimeter works (including access road, saddle dams and fencing).

Following on from the completion of the detailed design and specification, Entura was able to assist the client with technical evaluation of the tenders received and providing design support throughout the construction period including hold point inspections, answering contractor queries and reviewing quality to ensure the works were completed to the design intent.


The project has been taken successfully through construction, commissioning of the works and the defects liability period.  Westernport Water has been delighted with the outcomes of the project that has delivered a cost effective increase in the reliable water supply whilst lowering the dam safety risks to the community.

Entura’s careful investigations and detailed design and ongoing support of Westernport Water through the construction phase have ensured that risks were minimised during the implementation. Our operational experience has delivered an asset that is safe to operate and that will be easy to maintain throughout its life.