Hunter Water has completed a five year risk assessment of the Chichester Dam in New South Wales as part of its routine assessment program.
The Chichester Dam was built in the 1920s to serve the community and has continued to do so for hundreds of years. Over time the New South Wales water sector has continued to understand the conditions of the dam, especially under extreme environmental causes such as earthquake events and extreme floods.
The work and research being put into the Chichester Dam is helping to inform the Hunter Water 15-yearly safety review of the dam, ensuring that it continues to meet the standards of modern engineering and safety.
The five-yearly risk assessment, which has been sent to Dams Safety NSW, considers two main aspects: the likelihood of an event occurring and the consequences that could occur if an event were to happen.
Processes that are being used to see how the Chichester dam would respond in the case of rare and extreme conditions include modelling.
The modelling that has been constructed for the dam considers how it would hold if a severe event, larger than any experienced since the construction of the dam occurs.
Hunter Water Managing Director, Darren Cleary, said that the risk assessment identifies the aspects of the dam that require actions to ensure it can continue to safely operate.
“At the outset, I want to assure the Lower Hunter community that Chichester Dam is safe for normal, daily operations just as it has been for almost 100 years, and there is no immediate threat to community safety during regular conditions, nor to our drinking water supply.”
“We are following well-established processes to ensure we know that we possibly can keep Chichester Dam operating safely for many decades to come supplying drinking water to our community,” Mr Cleary said.
“Given the age of Chichester Dam, the impact of climate change, advances in dam technology over time and the appropriately thorough nature of the risk assessment, this finding is not unusual, and it is not unexpected that actions are needed to ensure the dam operates safely for many decades to come.”
“This is the first time we have carried out a risk assessment in this way, under the new Dam Safety regulations, and the latest scientific and engineering methods informed the risk assessment.
“These methods included detailed onsite geotechnical surveys and high-powered LiDAR to generate 3D ‘finite element modelling’ of the dam structure and foundation, helping to improve our understanding of different scenarios,”
“Hunter Water is actively working through the recommendations, and we have commenced interim works. We will continue investigations to determine the right options for long-term solutions so that the dam can continue to operate safely. Long term options could take between five and ten years from initial investigations to construction,” Mr Cleary said.
Interim works and construction investigations that Hunter Water suggest and have begun include the following:
- 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.
As the report findings relate to very rare conditions, Hunter Water is actively reassessing the existing Dam Safety Emergency Plan to ensure the community remains well prepared for such events.
Two community information sessions are being held for the local community which encourages individuals to find out more about the finding and recommendations of the Chichester Dam project.
“We are in direct contact this week with residents and property owners immediately downstream of Chichester Dam to ensure they are aware of the findings and update them on any changes to our Dam Safety Emergency Plan,” Mr Cleary said.
“We have invited them to two community drop-in information sessions we’re holding at the Bandon Grove School of Arts on Wednesday, 16 August and Saturday, 19 August.
“We encourage the local community to come along to find out more about the findings and recommendations and to ask the project team questions.”
The full report can be found here