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 operating system and allow 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 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.

Investigations into the gate vibrations led to the initial option of removing the gates being the fastest way to undertake additional testing to understand and fix the cause of the vibration.

Through further technical investigations and exploration of engineering solutions, Sunwater identified a potential solution that allows the gates to remain in place.

Implementation of this potential solution is expected to be finalised in 2022, after the wet season.

How long is this work going to take and when will the gates be returned to normal operation

Sunwater is committed to restoring the gates to normal operation as quickly as possible and expects work to be completed in 2022, after the wet season

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

In June 2021, Sunwater temporarily reduced Callide Dam’s full supply and operational levels to allow for work to be completed as part of the Callide Dam Gates Project.

The top of the concrete spillway crest became the maximum height of the dam (100 per cent) and the temporary full supply level, and the operational level was set at 69 per cent.

As investigations and some of the work to resolve the gate vibration issue are now complete, the dam’s operating level has been increased to 94.1 per cent of the temporary full supply level.

This change took effect on 23 December 2021 and will allow for approximately 14,000 more megalitres to be stored in Callide Dam, should it receive further inflows this wet season.

In the instance of inflows and the storage reaching higher than 94.1 per cent, slow releases will be required to return the storage to the project operational level as soon as possible.

The FSL was required to temporarily change as, in the event of extreme weather events, 100 per cent capacity must represent when the water level reaches the top of the dam wall and is about to spill.

This recent change has not impacted the Callide Dam Emergency Action Plan and based on ‘fill and spill’ scenario mapping of historical Callide Dam data, between the months of December 2021 and May 2022, the probability of Callide Dam spilling remains low. We expect the temporary FSL will have little impact.

The table below 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.

Full supply level before project commencementTemporary full supply level as of week commencing 21 June 2021Temporary project operating level as at 23 December 2021
Capacity: 100% (top of
gates
Capacity: 100% at top of spillway crest (was 41% with gates in placeCapacity: 94.1%
Volume: 136,300 MLVolume: 55,382 MLVolume: 52,098 ML

Does this mean the dam’s reduced full supply level will continue over the wet season?

Yes, the current reduced full supply level at the spillway crest and the lower project operational level of 69 per cent will remain during these works.

In the event of inflows and the storage capacity reaching 69 per cent, releases will be made to maintain this level. Where possible, Sunwater will plan releases to maximise aquifer recharges for the Callide Valley Water Supply Scheme

Sunwater has a site demobilisation plan in place, if required, as we enter the wet season.

In 2022, after the potential solution is in place, the temporary reduced full supply and operational levels will then be returned to the pre-project level.

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

Based on ‘fill and spill’ scenario mapping of historical Callide Dam data, between the months of November 2021 and May 2022, the probability of Callide Dam spilling remains low and we expect 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.

Is the dam unsafe?

At Sunwater, ensuring the safety of communities downstream is a top priority. 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.

Callide Dam is safe and will be operated in accordance with an amended emergency action plan (EAP).

Sunwater is confident that the operating changes made as part of the recent project update in November 2021 provide ongoing procedural assurance that risks associated with operation of the dam are mitigated to the greatest degree possible.

How will you manage the dam during a significant weather event?

The top of the concrete spillway crest currently reflects the maximum height of the dam wall and will operate much like other Sunwater fixed crest dams.

If a weather event occurs and it is expected that water will reach the fixed spillway crest, Callide Dam’s gates will be manually and safely raised above the water level, eliminating risk of dam failure.

In accordance with dam safety regulations, the dam’s Spill Operations Manual and Emergency Action Plan has been updated to reflect the reduced full supply level.

The Local Disaster Management Group will undertake an exercise to ensure operational readiness in the case of a significant weather event occurring.

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

Some historic costs that have been incurred in relation to the Callide Dam gates intermittent 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.

To date, Sunwater has contributed $1 million in capital toward the project.

As the dam’s gates will remain in place while we work on the best possible solution for the vibrations, we expect there to be a reduction to the originally forecast project cost.


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