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Raising Suma Park Dam Wall

Orange City Council has begun a major upgrade of the dam wall at Suma Park.

This page outlines the reasons behind the upgrade.

BACKGROUND

Dams in NSW are required meet a one in one million-year flood event, as prescribed by the NSW Dams Safety Committee.
Currently Suma Park Dam can only meet a one in 200-year flood event. Orange City Council is required to undertake work to improve the safety of this dam.
Over recent years, the Council has considered a number of approaches to addressing this issue and whether raising the dam wall could be considered as part of this work.
An additional benefit of this upgrade is improving water storage capacity in the catchment, while also providing water security for growing community needs and facilitating stormwater harvesting activities.
The City Council engaged Entura to undertake detailed design to meet the NSW Dams Safety Committee requirements. Entura was requested to undertake a detailed structural assessment of the dam to better determine the implications of raising the wall in association with the safety work.Suma Park Dam

This assessment has concluded that:

  • A 2-metre extension in the height of the wall should not be considered for Suma Park Dam due to the unacceptably high vertical and arch tensile stresses and potential unacceptable extent of cracking at the dam base
  • An increase in the range of up to one metre is the maximum which should be considered.
  • For an increase of up to one metre, the amount of land acquisition would be relatively minor, however it may still add some complexity to gaining approvals.
  • For the existing dam and an increase of up to one metre, stresses within the dam body are acceptable. However, there is a concern about potential cracking of the dam base with an increased full supply level and during an extreme flood.

At a meeting in November 2011, the City Council resolved to have a one metre dam wall rise considered in conjunction with the dam safety considerations. The detailed report the City Council considered at that meeting can be downloaded here.

Options for raising Suma Park Dam Wall [27.5KB]

The analysis shows that a one metre increase in the height of the Suma Park Dam is achievable, at a cost of around $4 million, bringing the total estimated project cost to $16 million. 

The cost per additional megalitre of secure yield (the annual amount of water that can be safely supplied) for this option is within the middle range of other alternatives considered by the Council. A one metre higher wall would increase dam storage capacity by 10 per cent and result in additional secure yield, estimated at between 100 and 200 megalitres. 

Detailed design and environmental assessment was undertaken to identify and mitigate risks and potential impacts. In addition to this, the City Council is implementing a dam warning system to alert downstream residents if water over the spillway reaches levels where dam failure may be a risk.

As part of the detailed environmental assessment to be undertaken as part of this project, an environmental flow regime was considered.

The City Council's meeting on 6 November 2012 decided to procced with the detailed design work and environmental assessment for a project to raise the height of the dam by 1 metre.

The Suma Park Wall Upgrade Report (6 November 2012) which was presented to that meeting, can be downloaded here.

You can also read an online article about the upgrade , and watch a short video.

 

 

 

COMMUNITY CONSULTATION

Summer Hill Creek Environmental Flow Study

An environmental flow study has begun that will assess the environment of Summer Hill Creek. This study was undertaken to inform the environmental assessment of the proposed Suma Park Dam Upgrade.

Suma Park Dam WallA change to the flows downstream of the dam has been identified as a potential impact from the raising of Suma Park Dam and is currently being studied to assess the ecological feasibility of the project. Mitigation measures such as the need for an environmental flow in Summer Hill Creek, downstream of the dam to where it joins the Macquarie River, are being considered to manage potential downstream impacts.

Environmental flows, arranged by extra releases of water from the dam, can ensure there's enough water to maintain the health of aquatic ecosystems, while meeting the demands of the community’s water users.

To ensure the environmental flow regime meets this balance, as much information as possible is sought to understand how Summer Hill Creek is used and how it is important to local residents, businesses and organisations. In addition, the influence of other major proposed regional water projects, such as Stormwater Harvesting Schemes and the Macquarie River Pipeline project will also be considered.

However, these projects and an assessment of their environmental impacts are separate to this study.

A community consultation has determined, through stakeholder consultation and scientific studies, how Summer Hill Creek is environmentally significant for stakeholders. The study will look at issues such as water quality, supply and river health. This will in turn help determine the size of potential environmental flows in Summer Hill Creek.

A workshop with key stakeholders and community representatives has been held and the report of the consultants was distributed to participants. Council has also answered the Frequently Asked Questions on the raising of Suma Park Dam wall.