Author: Patrick Brown, Melbourne Water.
Greenvale Reservoir is Melbourne’s most urbanised large dam, only 20km north of the CBD and bound on three sides by residential development. Melbourne Water is currently in the planning phase for major dam safety upgrade works scheduled to commence construction early in 2014.
The dam was constructed in 1971 by the Melbourne and Metropolitan Board of Works to supply water to the city’s expanding urban boundary to the north and west. The structure is comprised of a 2.8km long earthfill and rockfill embankment with a clay core, 55m high at maximum section and impounding 27,500 ML of water. Built to the engineering standards of the time, the central section of the dam was designed with blanket filters and downstream chimney filters from foundation to 3m below full supply level. The lower ‘wing embankments’ were not fitted with downstream chimney filters but in some locations were constructed with blanket filters.
The north-west of Melbourne has been an important growth corridor for the city over the last 40 years, resulting in significant development downstream of the dam. A risk assessment conducted in 2009 showed Greenvale Reservoir did not satisfy modern dam safety risk guidelines, prompting Melbourne Water to undertake investigations and the development of a business case for remedial works.
The project includes an array of works, including:
- raising the main dam chimney filters to the top of the dam level,
- construction of a full height filter buttress in the wing embankments,
- construction of a secant pile filter wall to link the main dam and wing embankment chimney filters,
- upgrade works to the secondary spillway,
- stabilisation works to the lower right abutment, and
- road works in the adjacent park and intersection works at Somerton road.
The secant pile filter wall is a major feature of the works. The secant piles will link the main dam and wing embankment chimney filters, which despite being adjacent are not at the same slope within the embankment. A large diameter piling rig will excavate a column of material and replace with filter. This process is then repeated to intersect adjacent columns, thus creating a vertical wall of filters.
“The upgrade works will bring Greenvale Reservoir in line with current industry best practice,” said Bill Welsford, Melbourne Water’s Project Manager. “The project has been through a rigorous design process, including review from internationally acknowledged experts.”
The reservoir is required to be operational for the duration of the works; however a reduced water level will be imposed to reduce the dam safety risk.
Further information will appear in ANCOLD e’news as the project progresses. For further information please contact Bill Welsford, Patrick Brown or Mark Arnold from Melbourne Water.