Mount Bold Dam Safety Upgrade

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Mount Bold is an important storage for both natural inflow and water pumped from the River Murray, with a total capacity of around 46 billion litres. It was constructed between 1932 and 1938 and is approximately 25 kilometres south-east of Adelaide, within the Onkaparinga catchment in the southern Mount Lofty Ranges.

The surrounding reservoir reserve comprises more than 5,500 hectares of land, including three Trees for Life sites, and much native vegetation of conservation significance. More than 160 native animals call the reserve home, including the Southern Brown Bandicoot. The reserve is predominantly Stringy-Bark woodland, plus a Manna Gum woodland, swamps and creeks.

Mount Bold was designed and built as a water supply dam with the purpose to maximise storage levels as a critical and cost-effective source of supply to around 40% of metropolitan Adelaide. When the dam is not full, it can also provide limited flood protection downstream by opening the gates to release water in a controlled manner to absorb temporary flood water.

Dam safety upgrade project

Our state’s largest dam was identified for upgrade as part of standard process and responsibility to maintain our structures and assets in safe operating condition. We perform regular and extensive safety checks of the infrastructure, including annual engineering assessments. The dam remains safe on a day-to-day basis and there is no imminent risk of failure.

The dam safety project will align Mount Bold with the Australian National Committee on Large Dams’ (ANCOLD) updated guidelines that we follow to ensure best practice in the operation of our dams and reservoirs. The upgrade of Mount Bold will strengthen the dam structure against earthquakes and its capacity to safely pass any large flood events, while also providing improved flood protection to the downstream community.

Planning has been underway over the past several years including hydrology and geotechnical studies, flood modelling and development of options assessment.

Design options

Our current option (F2 displayed below) will include removal of the spillway gates and raising of the crest to create a primary spillway slot approximately 11.3 metres wide by three metres high. This will also provide an improved level of flood protection up to 1:100 annual exceedance probability (AEP) based on joint probability which means the dam is not always full, or 1:18 AEP if the dam is full at the start of a large rain event.

There is opportunity to include an additional flood attenuation design option as part of our dam safety project, however this depends on external funding as costs of increased flood mitigation works cannot be charged to SA Water customers.

Design options will not increase the maximum storage capacity (or FSL - full supply level) and we expect to confirm the design option as soon as possible during the concept design period.



Environmental impacts

Initial flora and fauna assessments have been undertaken to fully understand the complete and seasonable existence of species surrounding the construction footprint of the dam upgrade based on early concept designs.

Further surveys and assessments will be undertaken as part of environmental and planning approvals required for the project. We will also assess and balance environmental, cost and constructability requirements and implement strategies to minimise impacts including utilising existing footprints, revegetation planning and investigation of the use of a mini-hydro at the dam to offset energy costs.

Community involvement

We have been working with government agencies including the Department for Environment and Water (DEW), the Stormwater Management Authority (SMA) and local council to explore the additional flood attenuation design option and to source external funding required to deliver this option.

Engagement with key stakeholders has involved establishment of a community reference group in May 2020. We will continue engagement and consultation with the broader community as planning progresses through the concept, detailed design and construction phases of the project.

Our reservoir access team is also working to provide further opening of access to Mount Bold as part of our wider state government commitment to open reservoirs across South Australia for recreational use and enjoyment.

Next steps

Planning for this significant project continues and the project needs to follow a number of approval pathways and consideration to legislation such as ESCOSA, Cabinet and Public Works Committee, Planning and Infrastructure Act, Native Vegetation Act and EPBC Act, Aboriginal Heritage Act, Native Title Act, EPA Act, National Parks and Wildlife Act.

The procurement process recently commenced with expressions of interest for early contractor involvement contract released in December 2020. During concept design the engineering design services has been awarded to SMEC, and construction services has been awarded to Bardavcol and McConnell Dowell SRG and Leed Engineering Joint Venture.

Construction is currently expected to start in 2023 and will take approximately three and a half years.

Mount Bold is an important storage for both natural inflow and water pumped from the River Murray, with a total capacity of around 46 billion litres. It was constructed between 1932 and 1938 and is approximately 25 kilometres south-east of Adelaide, within the Onkaparinga catchment in the southern Mount Lofty Ranges.

The surrounding reservoir reserve comprises more than 5,500 hectares of land, including three Trees for Life sites, and much native vegetation of conservation significance. More than 160 native animals call the reserve home, including the Southern Brown Bandicoot. The reserve is predominantly Stringy-Bark woodland, plus a Manna Gum woodland, swamps and creeks.

Mount Bold was designed and built as a water supply dam with the purpose to maximise storage levels as a critical and cost-effective source of supply to around 40% of metropolitan Adelaide. When the dam is not full, it can also provide limited flood protection downstream by opening the gates to release water in a controlled manner to absorb temporary flood water.

Dam safety upgrade project

Our state’s largest dam was identified for upgrade as part of standard process and responsibility to maintain our structures and assets in safe operating condition. We perform regular and extensive safety checks of the infrastructure, including annual engineering assessments. The dam remains safe on a day-to-day basis and there is no imminent risk of failure.

The dam safety project will align Mount Bold with the Australian National Committee on Large Dams’ (ANCOLD) updated guidelines that we follow to ensure best practice in the operation of our dams and reservoirs. The upgrade of Mount Bold will strengthen the dam structure against earthquakes and its capacity to safely pass any large flood events, while also providing improved flood protection to the downstream community.

Planning has been underway over the past several years including hydrology and geotechnical studies, flood modelling and development of options assessment.

Design options

Our current option (F2 displayed below) will include removal of the spillway gates and raising of the crest to create a primary spillway slot approximately 11.3 metres wide by three metres high. This will also provide an improved level of flood protection up to 1:100 annual exceedance probability (AEP) based on joint probability which means the dam is not always full, or 1:18 AEP if the dam is full at the start of a large rain event.

There is opportunity to include an additional flood attenuation design option as part of our dam safety project, however this depends on external funding as costs of increased flood mitigation works cannot be charged to SA Water customers.

Design options will not increase the maximum storage capacity (or FSL - full supply level) and we expect to confirm the design option as soon as possible during the concept design period.



Environmental impacts

Initial flora and fauna assessments have been undertaken to fully understand the complete and seasonable existence of species surrounding the construction footprint of the dam upgrade based on early concept designs.

Further surveys and assessments will be undertaken as part of environmental and planning approvals required for the project. We will also assess and balance environmental, cost and constructability requirements and implement strategies to minimise impacts including utilising existing footprints, revegetation planning and investigation of the use of a mini-hydro at the dam to offset energy costs.

Community involvement

We have been working with government agencies including the Department for Environment and Water (DEW), the Stormwater Management Authority (SMA) and local council to explore the additional flood attenuation design option and to source external funding required to deliver this option.

Engagement with key stakeholders has involved establishment of a community reference group in May 2020. We will continue engagement and consultation with the broader community as planning progresses through the concept, detailed design and construction phases of the project.

Our reservoir access team is also working to provide further opening of access to Mount Bold as part of our wider state government commitment to open reservoirs across South Australia for recreational use and enjoyment.

Next steps

Planning for this significant project continues and the project needs to follow a number of approval pathways and consideration to legislation such as ESCOSA, Cabinet and Public Works Committee, Planning and Infrastructure Act, Native Vegetation Act and EPBC Act, Aboriginal Heritage Act, Native Title Act, EPA Act, National Parks and Wildlife Act.

The procurement process recently commenced with expressions of interest for early contractor involvement contract released in December 2020. During concept design the engineering design services has been awarded to SMEC, and construction services has been awarded to Bardavcol and McConnell Dowell SRG and Leed Engineering Joint Venture.

Construction is currently expected to start in 2023 and will take approximately three and a half years.