Callide Dam FAQ

Callide Dam Gates Project

Callide Dam, Biloela, Queensland

This maintenance project has been set up to investigate, repair and restore Callide Dam’s gates to address intermittent occurrences of vibration during their operation. This project will ensure ongoing dam safety and long-term water security.

Frequently asked questions

What is the issue with Callide Dam’s spillway gates?

Callide Dam’s six large spillway gates, which were installed in 1988, have only been required to operate on seven occasions.

The gates are an integral part of the Callide Dam operation system and allow flood flows from upstream to pass through the dam. The gates operate this way to protect the integrity of the dam structure from water rising above the full supply level and to maximise the amount of water stored in the dam.

During three of these occasions, Sunwater has observed vibrations of the spillway gates which could lead to operational issues with the gates.

What do you mean by ‘vibration’?

In this situation vibration refers to unexpected, rapid oscillating motion of the gates when they are releasing water during operation.

What is Sunwater doing to fix the vibrations?

Sunwater has undertaken a rigorous and robust series of investigations into the vibrations, in accordance with its well-established asset management and maintenance program.

Following completion of the dam safety review for Callide Dam in January 2019, further investigations were recommended including an independent Qualitative Risk Assessment of the spillway gate vibrations and computational fluid dynamics modelling work.

In September 2020 possible vibration mechanisms were again dismissed as possible triggers for the vibration. Sunwater then sought further technical advice on taking the gates out of service to mitigate the vibration risk and enable further detailed physical investigations.

Expert advice during a Comprehensive Risk Assessment of the dam in late 2020 led to Sunwater commencing the Callide Dam Gates Project in early 2021.

Why are the gate faces required to be removed from the spillway for inspection?

This project is the next logical stage in the process to find the root cause of the gate vibration and ensure the gates can operate safely. Removing the gates from service immediately eliminates any possible gate failure risk. It is also the fastest and most effective way to undertake additional testing. It will allow expert inspections and testing of the faces, gate arms and associated infrastructure that would otherwise be difficult or impossible to carry out with the gates still in place.

With dam storage levels around 51 per cent (21 per cent prior to implementing the temporary full supply level), and the dry season approaching, now is the ideal time to safely remove them for inspection and undertake restoration work.

How long is this work going to take and when will the gates be returned to service?

Sunwater is committed to restoring the gates to service as quickly as possible. Our target date for completion of these works is the end of 2021, prior to the wet season. Getting the gate faces off will give us the best chance to develop and implement a solution in this timeframe.

Why did you lower the dam’s full supply level?

Callide Dam’s full supply level was reduced in June 2021 to allow for safe access to infrastructure to complete maintenance works.

From the lodgement date of the 399B notice, the top of Callide Dam’s concrete spillway crest reflects the maximum height of the dam wall. Prior to issuing the notice, the top of the concrete spillway crest represented 41 per cent of the dam’s capacity, however, from the date of 399B notice and to prepare for the removal of the gates and when the gates are removed, Sunwater will refer to the top of the concrete spillway as the dam’s FSL of 100 per cent.

The temporary change was necessary for communicating accurately and consistently to the community and emergency bodies because in the instance of extreme weather events, the water level reaching 100 per cent must signal a forthcoming spill.

The below table explains the previous and current temporary full supply level of Callide Dam. The infographic on the Safety and emergency management page further explains this temporary change.

Previous supply level before project commencement Current as of June 2021Temporary full supply level as of week commencing 21 June 2021
Capacity: 100% (top of gates)Capacity: 21% (approximately)Capacity: 100% at top of spillway crest (was 41% with gates in place)
Volume: 136,300 MLVolume: 28,665 MLVolume: 55,380 ML

What does this change in full supply level mean for customers’ water allocations?

Based on historical inflows during the dry season, we expect the temporary full supply level to have little to no impact on the dam’s actual capacity and importantly, the change will have no impact on current announced allocations for Sunwater customers.

Water allocations are set for the year and cannot decrease as dam capacity levels reduce. Should inflows occur however, allocations can increase (to a maximum of 100 per cent).

Allocations for the 2021-22 water year were announced in July 2021 and are listed on the scheme page.

What if the works takes longer than expected and the gates are still out of service as we approach the wet season?

The project schedule will take into account a range of weather scenarios and will work closely with the dam’s operational team to prepare for these.

Is the dam unsafe?

There is currently no risk to the community of the dam gates failing as current dam water volumes are approximately 51 per cent (21 per cent prior to implementing the temporary full supply level) and well below the dam gates. With the dry season fast approaching, it is unlikely the gates will need to be operated before the gate faces are removed.
At Sunwater, we take our community safety obligations seriously. As dam operators, our focus throughout extreme weather events is to ensure our dams are managed safely and in accordance with operating procedures and emergency action plans.

In the unlikely event of a major rainfall inflow prior to the gate faces’ removal, Sunwater is confident that the operating changes it made in December 2019 and reflected in the dam’s Emergency Action Plan (EAP), provide ongoing procedural assurance that risks associated with operation of the dam are mitigated to the greatest degree possible.

How will you manage a significant weather event after you remove the gates from service?

The works will be undertaken during the dry season. With current dam water volumes at approximately 51 per cent (21 per cent prior to implementing the temporary full supply level) and well below the dam gates, the probability of the gates needing to be operated before or after the gate faces are removed is low.

As of the week commencing 21 June 2021, the top of the concrete spillway crest reflects the maximum height of the dam wall and will operate much like other Sunwater fixed crest dams such as Kroombit and Cania.

In the case of a significant weather event while the gates are off, once the storage level reaches the fixed crest, excess water flows over the spillway with no action necessary by the dam operator.

In accordance with dam safety regulations, the dam’s Spill Operations Manual and Emergency Action Plan is being updated to reflect the removal of the gates from service and temporary increase to storage, prior to their implementation, and communicated to stakeholders in advance.

How much will this work cost and how are the works being funded?

It is too early to provide costings, apart from the set-up of the project, as we are in the early stages of developing design recommendations for each work package within the project.

Some historic costs that Sunwater has incurred in relation to the Callide Dam gates vibration investigations have been absorbed by Sunwater and we did not charge the scheme.

Expenditure on refurbishment or replacement of assets is currently recovered through a scheme-level allowance. This enables customer charges to reflect a constant sum necessary to recoup the costs of asset refurbishment/replacement over a pre-determined period of time.
We will consult with our Callide Dam customers during our project planning process, including discussions on the cost/benefit considerations of implementing an additional temporary storage solution.

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