Fieldtrip: Greenvale Dam Safety Upgrade
AGS/ANCOLD Joint Event
For over 15 years Melbourne Water has managed its dams portfolio of 16 large water supply dams, over 250 retarding basins and numerous other weirs, lagoons and levee banks within a risk framework consistent with Regulatory expectations and industry good practice.
The first dams portfolio risk assessment of Melbourne Water’s major water storage dams was conducted from 2008 – 2011 and led to a series of subsequent targeted investigations, interim non-structural risk mitigation measures and ultimately a program of dam safety risk reduction capital works that continues today. Greenvale Reservoir is located approximately 20 km north west of Melbourne. It is an off-stream storage of approximately 27,000 ML, located within the upper catchment of the Moonee Ponds Creek and supplies potable water to the city of Melbourne.
Greenvale is classified as an Extreme Consequence Category storage in accordance with ANCOLD (2012). The dam was constructed from 1968 to 1972 with the embankment works completed in August 1970. The dam comprises four (4) embankments; a 40 m high Main Embankment, flanked by a West Wing and East Wing Embankment; and a separate Gully Embankment. The total length of the embankments is approximately 2750 m with a maximum height of approximately 51 m. The embankments are of earth-rockfill and earthfill design, with the filter provisions varying from embankment to embankment.
A 2008 Portfolio Risk Assessment of all Melbourne Water’s dams identified three key dam safety deficiencies for Greenvale Dam:
- Piping through the upper part of the Main Embankment (above the existing filters);
- Piping through the embankment for the wing embankment sections; and
- Retrogressive instability initiated within the foundation on the lower right abutment of the embankment (downstream of the dam).
From 2008 an operating level restriction was placed on Greenvale Dam in order to manage risk until more permanent engineering controls could be put in place. Given the importance of the reservoir within the water supply network and the difficulty of operating the storage with a 3m restriction on level, engineering works were prioritised above other dams. Between 2011 to 2015, Melbourne Water completed the detailed design and construction of Dam Safety Upgrade works to address identified dam safety deficiencies.
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