Chichester Dam risk assessment report

The safety, health and wellbeing of our people and our community is Hunter Water’s highest priority. As part of our commitment as a responsible dam owner, Hunter Water has recently completed a five-yearly risk assessment to inform our 15-yearly safety review for the dam. 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.

What the five-yearly risk assessment and 15-yearly safety review involves

Hunter Water undertakes daily safety inspections of our dams.

In addition to these regular inspections, we conduct risk reviews at five-yearly intervals and major reviews at 15-yearly intervals, to ensure we are prepared for all foreseeable hazards that may compromise the safety of the dam. This is overseen by the independent regulator Dams Safety NSW and an independent dam safety Expert Review Panel.

In August 2023, Hunter Water finalised the five-yearly risk assessment to inform our 15-yearly safety review for Chichester Dam. The risk assessment considers two aspects, that is the likelihood of an event occurring and the consequence if it were to occur. Where the failure of a large dam is concerned, the likelihood is usually low, but the consequence is significant. Many ‘failure modes’ or different ways that the dam could feasibly fail (break), were considered during the five-yearly risk assessment.

The assessment is done through a combination of desktop analysis and detailed onsite investigations led by Hunter Water, with advice from an independent Expert Review Panel. They seek to apply modern engineering and scientific techniques to ensure our dams are managed to the highest possible standards.

Assessment report findings and next steps

The assessment report confirms 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 report also assesses how the dam responds to rare, very rare and extreme events, such as extreme flooding and major earthquakes. This new information helps us assess the risk that extreme events may pose to downstream communities and provides our engineers and independent expert review panel with new insights on the dams. The cumulative result of the likelihood and consequence of these events has been identified as being above the regulatory safety threshold in our recent five-yearly risk assessment.

Given the age of the dam, advances in dam technology over time, the impact of climate change and increased risk of extreme weather events, it is not unusual that a risk assessment of this nature has provided recommendations to ensure Hunter Water remains proactive in managing the safety of our dam. This is the first time that a risk assessment has been carried out in this particular way, under the new Dam Safety regulations and the risk assessment was informed by the latest scientific and engineering methods.

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.

Report recommendations and next steps

We are now actively working through the 2023 report recommendations over the coming months. These investigations and works 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.

Learn more

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