Warragamba Dam supplies up to 80% of Sydney’s water needs and is currently undergoing a range of major infrastructure upgrades. The outlet works upgrade is one of these projects. The outlet works of the dam were constructed in the 1950s and consisted of four 2100mm pipes with isolating gate valves and needle control valves feeding two large above ground pipelines running 27 kilometres east to Prospect Reservoir in Sydney’s western suburbs.
In the 1990s the then dam owner (Sydney Water) undertook a detailed and extensive risk analysis of the outlet works. The study resulted in a recommendation to remove the existing valves and replace them with a combination of emergency closure (guard) valves and isolating valves. Under the Sydney Catchment Authority (the present dam owner) work subsequently proceeded in 2004 as a design and construct contract with all aspects of construction and water supply risks identified. Stringent controls were developed and placed on work programs and pipeline shutdowns to ensure the safety of all involved and the integrity of the supply to Sydney.
The four outlets required eight large valves, which were manufactured in Germany and were required to meet stringent operational requirements.

At the time of writing three of the four outlets have been successfully upgraded and commissioned. Work has commenced on upgrading the fourth outlet, which is due for completion by the time of the conference, approximately 20 months ahead of schedule.
This paper discusses the project from the initiation of the risk analysis study, through the
consideration of options, development of the contract, and the supply, installation and commissioning of the large valves and pipe work. It highlights the role of risk assessment in selection of the preferred option and addresses some of the engineering challenges faced during the project.

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