Cressbrook Dam Safety Upgrade: Overcoming Complex Challenges for Long-Term Water Security

Cressbrook Dam Safety Upgrade: Overcoming Complex Challenges for Long-Term Water Security

Cressbrook Dam Safety Upgrade: Overcoming Complex Challenges for Long-Term Water Security

The Cressbrook Dam Safety Improvement Project is a significant infrastructure upgrade aimed at enhancing the structural integrity and operational safety of Cressbrook Dam. This ~$300m project involves strengthening the dam wall, upgrading and widening the cast-in-situ concrete spillway, and improving monitoring and emergency response systems. These upgrades will help secure the long-term reliability of the water supply and ensure downstream community safety.

Bellwether Consulting Services was engaged as the owner’s estimator to develop an independent reference estimate for the concept design in collaboration with the design team. More specially, this scope involved:

  • Developing the Target Outturn Cost (TOC) and supporting the client in reviewing and assessing cost estimates and construction programs submitted by the D&C consortia.
  • Providing constructability advice to improve feasibility and risk management.
  • Assessing variation claims and construction programs during project delivery to maintain budget and schedule integrity.

One of the most complex aspects of the project is the widening of the cast-in-situ concrete spillway by 20m into the rock wall of the left-hand embankment. This presents several constructability challenges, including:

  • Rock Excavation & Stability: Extensive rock excavation is required to make space for the widened spillway. Careful blasting or controlled rock-breaking techniques must be used to prevent excessive vibrations that could impact the integrity of the existing dam structure.
  • Complex Formwork & Reinforcement: The scale of the widened spillway necessitates large-scale formwork and reinforcement placement, ensuring seamless integration with the existing structure while managing the challenges of working within a confined rock face.
  • Concrete Placement & Curing: Given the scale and environmental conditions, precise planning for concrete pouring, temperature control, and curing is required to ensure structural integrity and minimise shrinkage or cracking.
  • Access & Logistics: Working within a steep, restricted site requires specialised access solutions, including temporary haul roads, cranes, and scaffolding, to facilitate safe and efficient construction.
  • Hydraulic Performance Considerations: The widened spillway must be designed and constructed to maintain effective water flow and avoid turbulence or erosion issues, ensuring long-term performance and safety.

To address these challenges, Bellwether’s constructability lead, Adrian Vesnaver, played a key role in risk mitigation by staging the spillway and dam wall construction over multiple dry seasons. This approach allowed:

  • Controlled excavation and concrete placement in stable conditions, reducing exposure to wet weather delays.
  • Progressive reinforcement of structural elements, ensuring phased completion with minimal disruption.
  • Ongoing risk assessment, adapting methodologies as required to maintain project safety and efficiency.

Key to the successful delivery of this project and some further wisdom from our team will be:

  • Precision in Rock Excavation & Concrete Integration: Careful coordination between geotechnical, structural, and construction teams ensured stability and seamless expansion.
  • Efficient Staging for Risk Management: Dry season construction minimised flood risk and allowed optimal work sequencing.
  • Advanced Planning for Logistics & Access: Specialised equipment and strategic material handling reduced construction complexity.
  • Continuous Constructability Review: Ongoing assessment ensured practical, cost-effective solutions were implemented.

Bellwether’s expertise in cost estimation, constructability assessment, and risk mitigation has been instrumental in the successful development of this challenging project. The strategic approach to spillway widening within the rock embankment ensures long-term structural integrity while maintaining construction efficiency, supporting Toowoomba Regional Council in delivering a safe and effective dam upgrade.

Further information on this project can be obtained here  https://www.tr.qld.gov.au/our-region/major-projects/water-waste/15534-cressbrook-dam-safety-improvement-project