Project Overview:
Gordonbrook Dam, built in 1942 and upgraded in 1987, serves as the primary water supply for the town of Kingaroy. Over time, significant flood events caused substantial damage to the downstream spillway channel, including concrete loss, undermining, severe erosion, and structural damage to shotcrete walls and drop structures. Interim emergency measures had been implemented, but long-term remediation was required to restore structural integrity and improve resilience.
South Burnett Regional Council engaged PCA to carry out permanent remediation works to stabilise the spillway and mitigate future flood risks, while preserving dam safety and operational continuity.
Challenges
- Extensive erosion and undermining from flood discharges
- Structural damage to spillway base, drop structures, and shotcrete walls
- Formation of erosion holes and loss of foundation support
- Need to work around legacy materials and previously damaged concrete
- Ensuring compatibility of new structures with existing spillway geometry
- Managing water runoff to prevent future damage
Remediation Solution
PCA implemented a comprehensive repair and stabilisation strategy that included:
- Cleaning previous repair areas and infilling erosion holes with concrete
- Anchoring repairs into existing foundations for structural security
- Casting reinforced concrete capping slabs over repaired sections
- Shotcreting perimeter areas to seal and strengthen the channel
- Removing deteriorated concrete from drop structures to sound rock
- Layered backfilling with large rock and high slump concrete in voids
- Recasting drop structures to match original profiles
- Constructing transition sections to blend repairs into the spillway flow path
To prevent further erosion above the damaged shotcrete wall, PCA regraded and battered the slope across a 95m section between Drop Structure No. 3 and upstream of No. 2. A surface-level drainage trench was also constructed to redirect runoff and prevent water ingress behind the repaired wall.
Outcome
- Restoration of full structural integrity to the downstream spillway
- Improved erosion resistance and future flood resilience
- Stabilised channel geometry and improved water flow management
- Long-term dam safety assurance for South Burnett Regional Council
- Delivered a compliant, durable solution aligned with legacy infrastructure
