2005 – Pykes Creek Reservoir; Upgrading the Outlet Works for a 95 year old Dam

Mike Taylor, Jonathan Jensen and Greg Branson

Pykes Creek Dam is a 33 m high, 22,120 ML embankment dam, 72 km west of Melbourne owned and operated by Southern Rural Water.

The outlet works include a 30 m high “wet” outlet tower near the upstream toe of the dam on the right
abutment with its lower half comprising a concrete lined shaft excavated in rock. A 1.5 m diameter
concrete lined tunnel extends 30 m upstream from the base of the tower to a reinforced concrete inlet structure.

The only controls upstream of the downstream toe of the dam comprised 2 guard gates located on the downstream side of the tower, operated manually by means of handwheels from the top of the tower.

Major deficiencies with the outlet works included:

• No facility to de-water the tower to maintain the gates located at the base of the tower. The
  gates had become partially inoperable as a result.
• The gates in any case were extremely laborious and time consuming to operate.
• No facility to inspect and maintain the upstream tunnel and inlet structure.
• No facility to select variable drawoff levels to control water quality and temperature for river
  releases.
• The access footbridge to the tower was structurally inadequate to safely accommodate loads for remedial works on the tower.

A major constraint in addressing these deficiencies was that any remedial works needed to be
undertaken without draining the reservoir or interfering with the releases required for downstream
consumers, including irrigators in Werribee and Bacchus Marsh.The paper describes how all of the deficiencies have been addressed with no interruption to supply, by means of a collaborative effort between the dam owner, the consulting engineer, and 5 separate contractors, with the dam owner playing a leading role.