Mundaring Weir Stage 2 Upgrade – Engineering and Detailed Design

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The Water Corporation of Western Australia engaged GHD to conduct the engineering design for an upgrade of the Mundaring Weir outlet works.

Since 1903, Mundaring Weir has supplied water to the goldfields and surrounding agricultural region. The dam wall is a mass concrete gravity structure, with the original intake tower designed and operated as a dry well tower, containing three DN600 water supply inlets and a DN760 scour inlet. The intake tower consisted of two DN610 water supply outlet pipes and a DN760 scour pipe, which connected through to the downstream toe of the dam, the scour pipe being decommissioned in 1995.

The dam wall and spillway level was raised by 9.75 metres between 1946 and 1951. During these works, two new high-level DN760 water supply outlets were constructed in a slot cut, through the original dam wall and located between the intake tower and the right abutment. In 2012, these works were refurbished following detailed design by GHD.

The minimum operating level is set, based on utilisation of previous outlet works. Consequently, there is 16.7 GL of storage below this minimum operating level.

Due to low rainfall and dam inflow, the unusable water stored at Mundaring Weir has become increasingly valuable. A reduction of the minimum operating level will provide a once-off benefit, allowing access to an additional 10 billion litres of water, together with a reduction in evaporation losses, saving 1.5 billion litres of water per year.

Our work involved:

  • Permanent decommissioning of the top and intermediate inlets in the tower
  • New structural steel liner within the intake tower
  • New DN900 inlet into the tower
  • Refurbishment of the bottom inlet to the tower
  • Installation of bulkhead gates on the two inlets to the tower
  • New DN1000 MSCL pipework downstream of the dam
  • New guard valve pit and scour release
  • New inspection access tunnel (portal and adit) into the lower drainage gallery
  • Upgrade of site security
  • Upgrade of dam safety instrumentation, including provision of seepage measurement

As part of the design and construct contract, Clough appointed GHD to undertake the detailed design.

We are proud to be part of the upgrade to the Mundaring Weir, which will help secure Western Australia’s water supply in the increasingly drying climate.