Coolmunda Dam Gates Variable Counterweight Refurbishment

Scope of work

The scope of works included:

• Detailed design including shop drawings, certification, and registration of lifting equipment for all temporary works required.
• Fabrication, supply, and construction of the construction lifting equipment to extract the variable counterweights.
• Fabrication, supply, and installation of sufficient temporary gate restraint systems to fully restrain 2 gates (4 radical arms), suitable for the left bank retaining wall of piers.
• Fabrication and supply of 4 new VCWs.
• Removal of 4 of the VCWs from Gates 1 and 2 VCW chambers and replacement with the new VCWs, plus removal and reinstatement of one VCW from Gate 3 VCW chamber 3L for access purposes.

Remedial works and inspections within the VCW chambers, including:

• Removal of the existing VCW guides in the VCW chambers and replacement with new guides.
• Upgrade of the VCW chamber drain slide valve.
• Inspection of the balance pipes between the VCW chambers on each gate.
• Testing and commissioning of Gates 1 and 2 with the 4 new VCWs during the works.
• Dismantling, inspection, and testing of the 4 existing VCWs.

Innovative custom lifting frame

Due to the complexity and risks associated with working on a near-full dam, collaboration and expertise were sought from Abergeldie to find a safe and reliable solution to inspect and replace the existing guard rails. Abergeldie engaged key subcontractors to help design, construct, and fabricate a custom lifting frame that could be assembled at the spillway using the existing gantry crane rails. The frame was hydraulically actuated, allowing it to manoeuvre onto each pier to remove variable counterweights (VCWs).

This custom lifting frame provided a multi-purpose solution for accessing the gate chambers and removing the VCWs and minimised working at heights risks by enabling single assembly in one location. The innovative design incorporated hydraulic rams that pushed a section of the frame onto the piers, facilitating the removal of the VCWs with enhanced safety and efficiency.

Safety precautions for high-risk work atop a live dam

Working at heights atop a live dam and spillway bridge while the dam was at full capacity, required meticulous planning and safety measures. Abergeldie, in collaboration with Sunwater, conducted detailed works planning, emergency flood response planning, and programming to ensure the safe operation of these high-risk tasks.

To ensure the team worked safely within live chambers, they secured themselves to lock boxes, adhered to a group isolation permit and underwent extensive training in Lock Out Tag Out (LOTO) procedures and emergency response. These precautions were essential for preparing the team to handle potential emergencies effectively in this challenging environment.

Stringent safety measures were implemented, including a comprehensive Vehicle Management Plan, confined space entry protocols, and emergency rescue plans, to ensure the safe execution of work in confined spaces and restricted areas. An Emergency Response and Evacuation Plan was in place, with continuous monitoring and thorough equipment inspections to maintain safe working conditions at heights.

Ensuring integrity of water supply

Sediment and erosion controls were installed along the site perimeter and key locations, as necessary. Prior to engagement, all plant and equipment underwent thorough cleaning procedures. Additionally, a hard barrier was implemented on the work vessel to prevent any materials from freely entering the river, ensuring the integrity of the water supply remained uncompromised.

A secure water supply for the community

Now completed, the refurbishment of the Coolmunda Dam Variable Counterweights ensures the ongoing reliability of the gates to manage outflows from the dam and support a secure supply of water to customers. To prioritise customer value, the project strategy involved initially replacing four VCWs and assessing the remaining 10 for longevity, rather than replacing them all outright. This approach, which utilised the custom lifting frame, proved cost-effective, with the equipment retained by Sunwater for future use, including potential emergency scenarios.