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Seqwater is investigating the upgrade of Lake MacDonald Dam as part of the dam improvement program to ensure compliance with the latest national guidelines into the future. Recent studies have identified several dam safety concerns including:

• Spillway discharge capacity, which is significantly less than required by current DEWS Acceptable Flood Capacity (AFC) Guidelines (2013); and
• Suboptimal dam design features including: inadequate filters; structural elements constructed on fill material, including the dam spillway; undersized structural elements; sand and alluvial lenses in the dam foundation that are potentially liquefiable; and, a spillway anchoring system with unknown corrosion protection.

Concept designs have been developed for the preferred upgrade options, being a new dam upstream or downstream of the existing dam, however, there were several uncertainties associated with the new dam that could not be defined without further investigation including:

• Ground conditions within the new dam foundation footprint;
• Spillway width based on dam foundation and PMF;
• Land approvals for the new dam upstream;
• Requirement for a fishway as part of the upgrade works;
• Operational impacts for the new dam downstream; and
• Flood diversion management and associated construction risk.

As a result, Seqwater is seeking tenders from experienced and qualified engineering service providers to further investigate, evaluate and select the preferred new dam option and then progress to preliminary (50%) design level.