Monitoring of the Impounded Supply
In 2021, leakage was identified in the Dannevirke impounded water supply, prompting detailed investigations, inspections and repair works.
Since then, Council has worked with engineers, geotechnical specialists and dam safety experts to assess the condition of the impounded supply and identify long-term solutions.
Current situation
Small pinholes identified in the liner were patched by divers, and the impounded supply has since stabilised. No new issues have been identified and there are no immediate risks at this time.
The impounded supply is stable and has remained stable following the repair work. While some seepage remains present, it is at a significantly reduced rate. This is expected as the design allows for some discharge from the system for naturally occurring groundwater; however, Council does not have the historical baseline data needed to definitively distinguish groundwater flows from any residual leakage.
What we can say with confidence is that the repair work substantially reduced flows, the reservoir remains stable, and ongoing monitoring indicates the supply is operating as intended. The focus is now on continued monitoring and management, rather than further repair works, while Council progresses additional resilience improvements to support the long-term security of Dannevirke’s water supply.
Ongoing monitoring
Council continues to closely monitor the condition of the impounded supply to make sure it continues to perform as expected.
Monitoring includes:
- Daily monitoring of the impounded supply.
- Regular inspections of the liner and repaired areas.
- Underwater drone inspections every six months.
- Monitoring for any changes to the repaired areas or other areas of the liner.
- Having plans and procedures in place should the condition of the impounded supply change.
This ongoing monitoring allows Council to identify any changes early and respond if required.
What happens next?
Monitoring of the impounded supply will continue, including six-monthly underwater drone inspections.
Council is also planning for additional treated water storage. This will provide greater resilience for Dannevirke’s water supply and provide an opportunity to undertake any future maintenance or repairs to the existing impounded supply if required.
Council will continue to provide updates if there are any significant changes to the condition or operation of the impounded supply.
In July 2021, leakage was identified from the liner of the Dannevirke Impounded Supply.
Following investigations, underwater inspections and advice from specialist engineers and dam safety experts, Council determined that the Impounded Supply remained structurally stable and was functioning as intended.
Three small pinholes identified in the liner were repaired, and monitoring following the repair work has shown a substantial reduction in the amount of water flowing from the system.
While some seepage remains, the Impounded Supply is stable and the level of seepage is significantly lower than it was before the repairs.
The impounded supply is stable and has remained stable following the repair work. While some seepage remains present, it is at a significantly reduced rate. This is expected as the design allows for some discharge from the system for naturally occurring groundwater; however, Council does not have the historical baseline data needed to definitively distinguish groundwater flows from any residual leakage.
What we can say with confidence is that the repair work substantially reduced flows, the Impounded Supply remains stable, and ongoing monitoring indicates it is operating as intended.
Council undertook geotechnical investigations and specialist assessments of the Impounded Supply, including underwater inspections of the liner.
Rather than emptying the Impounded Supply to undertake major repairs or replacement, specialist advice supported an approach of underwater assessment and targeted repairs while continuing to monitor the structure.
Three pinholes identified in the liner were patched. There are currently no additional holes that Council is aware of.
The repair work substantially reduced the amount of water flowing from the Impounded Supply. The supply has remained stable since the repairs, and ongoing monitoring continues.
Council also sought independent peer review of the approach. Specialist advice confirmed that while there are risks associated with the Impounded Supply, there are no immediate structural risks identified, and continued monitoring is appropriate.
The focus is now on continued monitoring and management of the Impounded Supply, rather than further repair works.
This includes:
- ongoing monitoring of outflows from the Impounded Supply
- underwater drone inspections of the liner every six months, and more frequently if required
- continued assessment of the condition and performance of the supply
- use of the submersible pump that has been designed and installed to enable treatment of the lower six metres of water.
At the same time, Council is progressing additional resilience improvements to support the long-term security of Dannevirke’s water supply.
Although the Impounded Supply is stable, Council is taking a precautionary approach to its operating level while ongoing monitoring, technical assessment and wider resilience planning continue.
The structural integrity of the Impounded Supply cannot be fully verified without removing the cover and liner, which would be a significant and costly undertaking. Council’s dam technical advisor has therefore recommended a cautious operating approach while further assessment is undertaken.
Council is also assessing the potential benefits and risks of different operating levels as part of its wider planning for Dannevirke’s water supply resilience. No decision has been made regarding any change to the current operating level.
Yes. The Impounded Supply continues to provide an important source of resilience for Dannevirke’s water supply.
It provides stored water that can be used during drought conditions or periods of adverse weather.
Other projects, including the planned raw water pre-treatment system, will provide additional resilience, but the Impounded Supply remains an important part of the overall water supply system.
Yes, the water continues to be safe to drink. Samples are taken every week from different locations across Dannevirke to be tested. Installing raw water pre-treatment will provide greater resilience during extreme weather conditions.
There are simple things households can do to prepare for periods of high demand or water shortages:
- have a plan for how your household would manage if water use needed to be reduced
- consider collecting and storing rainwater where practical
- look for ways to reduce water use in your everyday activities
- keep an eye on Council updates about water supply conditions and any water conservation measures.
Council will continue to provide information to the community if water conservation is needed.