Conglomerate Dam upgrade

Client: TasWater
Location: Queenstown, Tasmania
Date: August–October 2013

Assessing, designing and overseeing leakage repairs, and considering options for longer term dam upgrades to ensure the safety of a critical source of treated water.

Background

Conglomerate Dam is the only source of treated water supply to Queenstown. The dam had a high probability of piping failure and was not constructed to modern design standards, which posed high risks to the client’s finances and reputation and to the broader community.

Seepage on the dam’s downstream face had been apparent since construction in 1971, but in 2013 the seepage increased significantly and a dam safety emergency was declared. Investigations found that the scour conduit, and possibly water supply conduit, through the embankment had multiple cracks.

Solution

Entura assessed options for and designed the leakage repair including analysis of hydraulics, pressure rating, soil load, access, alignment, size of pipes and access points. Entura investigated different technologies available for pipeline rehabilitation, ultimately selecting and designing slip lining of the scour and water supply conduits as well as sand filters around the conduits. Entura prepared technical specification and tender documents for the leakage repair work, and advised the client during the tender evaluation.

Entura supervised the leakage repair work and filter installation as an owner’s engineer. This involved developing pressure testing methodology for welded pipes and witnessing pressure tests, witnessing grout mix preparation and supervising grouting work, examining selected filters to confirm design requirements, supervising filter installation, undertaking commissioning inspection and providing expert advice on refilling the reservoir.

Entura also prepared an options assessment report which investigated a full dam upgrade and prepared a business case document, which was vital for securing funding for this upgrade work.

Outcome

With a clear understanding of the client’s priorities, Entura completed the options assessment as well as the detailed design well ahead of the agreed timeframe allowing TasWater to prepare the business case for undertaking leakage repairs. This was the first TasWater dam to use slip lining technology, which was implemented successfully and provides an example for future use at other dams within the client’s portfolio.

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