Clare Weir is situated outside of Burdekin Falls Dam and is the most critical piece of infrastructure attached to the Burdekin Haughton Water Supply Scheme (BHWSS). It provides the pumping pool for Tom Fenwick Pump Station (TFPS), which supplies up to 3,300ML/day into the BHWSS (via Haughton Main Channel). The weir itself is a concrete structure that incorporates an outlet works and fish lock on the right abutment. 150 hydraulically operated flap gates sit atop the weir’s fixed crest. A travelling gantry is used to carry out maintenance activities. The gantry runs along two rails, one on the upstream side of the weir and one on the downstream side. During the 2018 BHWSS annual shut-down, the weir storage was drained to a point the upstream rail was exposed (it is under water during normal operation). An inspection of the upstream rail identified some significant corrosion, to the point the rail has failed in some locations. This prevented the gantry from being used and placing maintenance works are on hold.
An options study looking at solutions for reinstating access to the weir for the gantry recommended like-for-like replacement of the approximately 400m long rail. As the upstream rail is submerged during normal operation, access to replace it requires the pumping pool be lowered below fixed crest. The only time the weir can be drained to a point providing access to the rail is during the BHWSS annual shut-down (two weeks typically in June).
Within this 2-week shut down the Weir had to be drained, repaired and refilled. To undertake the works Civil Plus mobilised to site prior to the draining of the Weir to prevent any delays to the work window.
This consisted of the following;
• Constructing a crane pad
• Mobilising and 80t crane
• Installing and placing two dumb barges into the weir for access
• Placing a 16t excavator on one of the barges to be used as a crane for removal and reinstatement of the weir rail
• Loading a barge with 150m of scaffold
• Mobilising Site Facilities
The work crew consisted of approximately 25 ground crew plus supervisory staff which were split into a day and night shift to allow a continual workflow for the shutdown period. This was a first for SunWater completing a project in this manner.
Works were completed in sections in the following manner;
1. Mobilise floating equipment
2. Install scaffold decking and walkway
3. Remove concrete encasement from around the rail by jack hammering
4. Remove rail
5. Clean rail trough
6. Repair any damage hold down bolts
7. Install new rail to the previous line and level
8. Grout new rail in
Consideration and implementation of control measures to the following safety risks were also undertaken;
• Estuarine Crocodiles
• Working on Water
• Extend shifts and worker fatigue
• Silca Dust
• Remote Work
• Managing weather events
Despite it taking longer than expected to drain the weir causing a late start and having an unexpected rain event upstream of the weir during the shutdown period the works were completed on time and without incident. The following positive feedback was received by Travis Richards from SunWater on completion of the project. "CivilPlus were engaged to undertake a challenging replacement of a rail for our Gantry Crane at the Clare Weir. The project was planned, coordinated and completed within a tight time frame and on budget despite the need to manage a number of challenging river conditions. The team continually engaged on their plans to vary work activities and continue to be productive. The team should also be commended on maintaining a positive attitude and morale within the team despite the challenges."