Greenvale Dam Safety Upgrade

AGS/ANCOLD Joint Event

Mark Arnold, Stephen Chia and Elliot Hannan

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.

Mark Arnold Principal Dams Engineer / Manager, Headworks Enablement – Melbourne Water

Mark is a civil engineer with over 20 years experience in dam safety and general asset management with Melbourne Water. Mark has particular experience balancing risk across various asset portfolios with particular focus on dams, retarding basins and levee banks Mark was instrumental in Melbourne Water’s dams portfolio risk management journey from 2007 when he began managing the risk assessment process from an owners perspective. This then led into targeted investigations and both administrative and engineering risk mitigation solutions including temporary reservoir level restrictions and ultimately a major dam safety upgrade at Greenvale Dam. Mark has also been a leader in the application of risk based techniques over traditional asset management, particularly in dam surveillance and the development of the first ever safety case for a dam, again at Greenvale.

Stephen Chia Principal Geotechnical Engineer – Dams, AECOM

Stephen is a civil engineer with more than 10 years’ experience predominantly in civil/geotechnical engineering of embankment dams. Stephen has experience in civil design, geotechnical investigations, geotechnical characterisation, engineering analysis, risk assessments, and construction. Stephen has been involved in various roles on a number of dam safety upgrades. Some of these include Dartmouth Dam, Greenvale Dam, Tullaroop Dam, Rowallan Dam and Upper Yarra Dam. Stephen is currently Project Managing the Cardinia Dam Safety Upgrade detailed design project. Stephen was a project engineer for the Greenvale Reservoir Dam Safety Upgrade project and was involved with the review of original construction, slope stability analysis, civil design and preparation of IFT and IFC drawings.

Elliot Hannan Technical Director/Group Leader – Dams, GHD

Elliot is an accomplished leader in the dams and hydropower industry with over 20 years of experience in roles ranging from Technical Director of complex major projects to leading diverse teams of consulting engineers. Elliot is currently the Business Group Leader Dams & Tunnels at GHD and has recently completed his Masters of Engineering Science (Civil) at UNSW. During his career, he has acted in various roles on a number of dam safety upgrades, dam risk assessments and designs of new dams. Some of these include the Mole River Dam, Dungowan Dam, Nullinga Dam, Laanecoorie Dam Safety Upgrade, and numerous other dam and hydraulic structure designs and studies. Elliot is currently leading the designs of the new dams as part of the Borumba and Pioneer-Burdekin PHES projects in Queensland. Elliot was the Project Manager for the Greenvale Reservoir Dam Safety Upgrade Design and Construction project and the lead design representative on site during the construction phase of the project.

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