Enlarged Cotter Dam – outlet works

Client: ACTEW
Location: Canberra, ACT, Australia
Date: November 2009 – December 2013

Designing the outlet works for a major dam enlargement project to secure a reliable water supply and protect against future drought.

Background

Severe drought through the 1990s and early 2000s led to major water restrictions in the Australian Capital Territory (ACT) that seriously affected households and industry. To secure a reliable water supply for the ACT and to address drought, climate change and variability, the 4 GL Cotter Dam reservoir was enlarged to increase capacity to around 78 GL – almost 20 times its previous size. The project involved the construction of a new dam downstream of the existing dam. In addition to providing resources for the dam design, Entura was the outlet works design sub-consultant.

Solution

Entura provided civil, mechanical and electrical design, procurement, and construction support services for the design and construction of the outlet works, which include a 65m-high intake tower with seven 1.0m-diameter intakes, each protected by a coarse and fine screen. A 1.5m vertical discharge pipe is provided through the base of the tower to the downstream outlet valves and water supply pipe.

Civil design included seismic analysis of the dry-well intake tower for construction and operational conditions, structural design of the intake tower and discharge pipe thrust analysis. Mechanical design included hydraulic modelling; discharge pipe design; intake, discharge and air valve specification; discharge works arrangement; stoplogs, screens and lifting frame; and dam gallery and intake tower ventilation. Electrical design included control system design, earthing, lighting and power systems.

During procurement and construction, Entura provided equipment and site inspections, expert technical advice, temporary construction design and constructability support. Entura ensured that equipment met design requirements and that the design enabled efficient construction.

Outcome

Entura’s design team worked closely with the client to develop designs that were both cost-effective and fit for purpose, responding to the requirements of the dam designer, constructor and the ultimate client. The outlet works were successfully constructed and commissioned, and the dam was opened in 2013. It is now playing a key role in securing the water supply for the region and protecting against future drought.

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