Chichester Dam risk assessment and upgrades

Inspections and assessments

Hunter Water completes regular inspections of Chichester Dam, including:

• Daily visual inspections
• Inspections following an earthquake
• Intermediate (annual) inspections
• Satellite monitoring for any movement every two weeks
• Movement surveys every two years
• Comprehensive (five-yearly) inspections
• A five-yearly risk assessment
• A 15-yearly safety review

In 2023, we completed the five-yearly risk assessment and 15-yearly safety review. These assessments were finalised with input from an independent dam safety Expert Review Panel and submitted to the independent regulator, Dams Safety NSW in August 2023.

These assessment processes included using the latest engineering and scientific methods, some of which were not available for previous reviews. Because of this new technology, in 2023, for the first time, we were able to evaluate new risks and test for new scenarios.

The assessment report confirmed that Chichester Dam remains safe for day-to-day operations and continues to operate as it has for almost 100 years under normal conditions.

The risk assessment looked at how the dam could respond in a range of rare and extreme scenarios, such as extreme flooding and major earthquakes, which could lead to a dam failure. The main risk to the dam wall relates to very rare flooding. The cumulative result of the likelihood and consequence of all scenarios has been identified as being above the regulatory safety threshold determined under the Dams Safety Act 2015.

We are now planning and delivering upgrades for Chichester Dam to improve its long-term safety, especially during these rare and extreme events.

Report recommendations and next steps

We are now implementing the report recommendations which include:

• upgrading concrete on spillway aprons as detailed in the report recommendations
• increasing flushing frequency of pressure relief drains and further enhanced monitoring
• installing additional modern monitoring equipment
• hydrologic (converting rainfall to runoff) and hydraulic (flow / movement of water) modelling
• site surveys and geotechnical investigations, including boreholes to collect and test soil samples.

We will continue to be proactive in the planning and delivery of safety upgrades for our dams and enhance our emergency response plans and ‘disaster readiness’ for all foreseeable hazards that may compromise the safety of the dam.

Work completed to date

Since the completion and public release of the Risk Assessment in 2023, the following has been completed:

Review flood hydrology and consequence assessment

An expert hydrology consultant was engaged in October 2023 to complete the update of these assessments. The initial detailed modelling has recently been completed with draft plans available for discussion at community sessions.

Environmental Assessments

Approvals have been received from National Parks and Wildlife Services for completion of geophysical investigations on the north abutment of the dam, along with preliminary discussions of proposed borehole drilling sites to be completed following this work. These approvals were necessary due to the sensitive environment surrounding the dam.

Closure of Knowledge Gaps

A consultant was engaged in November 2024 to undertake required investigations to close knowledge gaps in areas requiring specific technical expertise that will enable progression to the design of upgrade works, including photogrammetry, bathymetric and seismic surveys, geophysical testing, geological mapping, landslide geomorphological and reservoir rim stability hazard mapping. Due to the need to undertake assessments of the dam wall itself, significant work is being undertaken to plan the logistics of providing access for drilling of boreholes, with testing scheduled to be undertaken in early 2026. Due to the location of some of the boreholes, the water level in the dam may be required to be reduced to safely access the aprons below the spillway. This will be dependent on the dam level at the time of the investigations. If the water level needs to be lowered to allow the assessment to be safely undertaken, Hunter Water will notify downstream property owners of a controlled release.

Emergency Planning

A full update to the Chichester Dam Safety Emergency Plan was completed in December 2024, which also included the lowering of the Amber and Red alert levels to align with the outcomes of the Risk Assessment. The reduction in alert levels provides additional time for downstream residents to evacuate if required. A practical emergency exercise involving NSW SES, NSW Police and Dungog Shire Council was completed on 26 November 2024. An additional theoretical exercise was completed in June 2025 to further refine the plan and to provide training to additional Hunter Water staff members that can be called upon during emergencies. The emergency exercise was successful.

This revised Dam Safety Emergency Plan was used by all agencies in January, April and May 2025, in response to the severe weather events. SES notifications followed the protocols outlined in the Emergency Plan. The Dam Safety Emergency Plan is a comprehensive coordination document used by multiple agencies to ensure an appropriate response to severe weather and potential dam failure. While the document itself is not designed to be publicly facing, Hunter Water will talk through the Plan at the upcoming community information sessions, and we intend on sharing an executive summary version.

Instrumentation review

A review of options to provide close to real-time monitoring of the ancient landslide on the north abutment is due for completion in late 2025. Installation of any needed equipment would be installed during geotechnical investigations.

Emergency Lighting Upgrade

A major upgrade of the lighting of the dam wall was completed in June 2025 to improve the effectiveness of monitoring the dam during emergency events overnight or in poor light.

Post-tensioned anchor testing

Routine 5-yearly anchor testing is scheduled to be completed in late 2025 and may require a temporary reduction of the dam water level. If the water level needs to be lowered to allow the assessment to be safely undertaken, Hunter Water will notify downstream property owners of a controlled release.

Survey monitoring

Routine 2-yearly survey monitoring of the dam wall and north abutment is scheduled to be completed in late 2025.

Apron 4 Crack Repair

Design of cover plates to protect the historic crack in spillway been completed and contractor engaged. Work should be completed in late 2025 or early 2026 when spillway flows reduce.

Flushing of foundation pressure relief drains

Pressure relief drains were flushed in December 2023 and will be flushed again towards the end of 2025.

Learn more

We are here to help and answer any questions you may have about the report. Please get in touch by emailing yourvoice@hunterwater.com.au or calling 1300 657 657.