Western Harbour Tunnel, Sydney, NSW, Australia
Aurecon is transforming Sydney Harbour, replacing dredging with TBM tunnel engineering to deliver a faster, safer and more sustainable second harbour crossing.
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Aurecon was initially engaged by Seqwater to undertake an assessment of the flood damage that occurred at Borumba Dam during January 2011.
Borumba Dam is owned and operated by Seqwater and is primarily used to supply irrigation water by private pumping from Yabba Creek and the Mary River for local irrigation schemes and urban water supply for Gympie in Queensland.
The flood damage comprised slope instability at the left abutment, erosional damage in the stilling basin beside the spillway and at the toe of the dam, minor flooding of the Valve House, as well as material deposition in the downstream channel. It was established that Borumba Dam has a very unusual and complex spillway stilling basin system.
A side-channel overflow feeds into a spillway that is curved and super-elevated, with the left side of the spillway over 8 metres higher than the right side. This complex configuration posed challenges for the remediation design.
Numerous concept design options were discussed with Seqwater and the chosen options were taken into preliminary design.
Aurecon was subsequently appointed for the detailed design, which included an innovative reinforced rockfill approach, comprising rock riprap encased in reinforcing steel. The benefits of this approach included cost reductions, easier installation within an operating plunge pool environment as well as engineering advantages in terms of implementing a free-draining alternative to a hard facing scour protection.
During construction, Aurecon assisted Seqwater by providing construction supervision and works certification for the remediation.
The project has successfully provided remediation of the flood damaged infrastructure as well as a level of protection against future damage.
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