Victorian Desalination Project Green Roof
Location: Lower Powlett Road, Wonthaggi, Victoria
Completion date: 2012
Area: 26,000 m2 on a new building
The Victorian Desalination Project green roof is the largest in the southern hemisphere. It covers a number of buildings of the process plant, ranging in pitch from 3.5 to 20 degrees. The undulating slopes of the roof are designed to limit visibility of the industrial buildings from the surrounding public areas and link to the nearby coastal landscape.
The Victorian Desalination Plant provides for desalinated water to be delivered from the private sector to the State Government owned water authorities. The plant is capable of supplying up to 150 billion litres of water a year to Melbourne, Geelong and via other connections to South Gippsland towns.
The aesthetic focus of the project was to soften the visual impact of the process plant buildings. Several other objectives were also considered in design of the green roof, including, ecological restoration of the area, thermal performance of the building, minimising the noise impacts from the desalination process plant and protection of the roof from the harmful effects of solar radiation.
The Victorian Government’s private sector partner, AquaSure, consists of Suez Environnement, Degremont, Thiess and Macquare Capital Group. The Theiss Degremont Joint Venture was the design and construct contractor for AquaSure. The green roof design delivery was provided by ASPECT Studios, with technical design, installation and maintenance by Fytogreen.
Design and Components
With a saturated dead load of 143kg/m2 plus live load, the roof is designed for maintenance access only.
The building is a steel frame structure with a timber ply roof deck. Waterproofing layer is Sika Sarnafil. A foam resin developed by Fytogreen was used as an underlay, trapping water and nutrients and helping the plants to grow. The drainage layer is a 20 mm Atlantis® Flo-Cell™ with a Bidim® A14 geofabric to filter sediment run-off.
The extensive green roof substrate mix was provided by Fytogreen and installed to a depth of 80 mm. The majority of the roof was constructed on a slope of less than 15 degrees and did not require any sheer protection. However, about 650 m2 of the roof was installed on slopes greater than 15 degrees and Geoweb® Cellular Confinement System was used to stabilise the substrate and vegetation. The 150 mm deep Geoweb® cells were installed over four days, with anchoring tendons running through every second row of cells to secure the system in place.
Due to the strong winds to which the green roof is exposed, a system of stainless steel hold-down netting was required in the areas subjected to the highest wind speeds. These winds create a twin vortex effect where the combined lateral forces and vertical uplift would risk dislodging the substrate ballast layer. The primary function of the mesh was to mitigate the insurance risk during establishment when the mulch layer was exposed. As time goes on it is expected that the plants will ameliorate wind uplift.
A sub-soil irrigation system was designed for the green roof by Netafim™ and installed by Fytogreen. The automatic drip system includes a weather monitoring station to ensure irrigation frequency and volume is appropriate. Data is collected on the amount of rainfall and the level of evaporation. Water for irrigation is captured from a 3.7 ha collection area and stored in a 0.5 megalitre pond. In addition to the captured storm water, 600 litres of process sampling water per hour is available from the desalination process plant.
The Fytogreen design for the green roof was carefully considered to ensure consistency with the coastal character, and to meet the ecological objectives of the project. Species selection focused on plants that are locally indigenous to the area using seed that was collected within 40 km of the site.
Given the site’s exposure to the elements in a windy and temperate coastal environment, testing was undertaken prior to construction to ensure that the species chosen would thrive in the conditions. Fytogreen established a test roof on a nearby site in 2009 to determine which species would respond well to the wind and variable temperatures, and to test planting patterns that would enhance the health of the plants.
Plants are fertilised using Osmocote® low phosphorus 12 to 14-month controlled release fertiliser. Application rates are adjusted as deemed necessary.
Disphyma crassifolium ssp. clavellatum
Rhagodia candolleana ssp. Candolleana
Fytogreen has a five-year contract to carry out any maintenance required for the green roof. Given the high profile of the project and the community expectations around aesthetics, the contract specifies standards for maintenance. This includes a requirement that vegetation cover must be at least 95 per cent, with no more than five per cent weeds. Fytogreen visits the site as required, to ensure these maintenance obligations are met. Visual inspections of plant health are important to ensure irrigation and nutrient levels are adequate.
Results and reflections
The opportunity to develop an indigenous plant palette for such a large scale green roof has demonstrated the way the natural ecology evolves and responds to the site conditions and the development of microclimates as the vegetation matures.
Some of the initial planting stock struggled to survive the windy conditions on-site. However, Fytogreen anticipates that the existing vegetation will provide protection for new plants that grow from self-sown seed, allowing them to establish more strongly on the roof.
Fytogreen points out that the requirement for irrigation water should not be underestimated, and it is important to be mindful of the client’s expectations in terms of the roof’s appearance. The aesthetic value may become a higher priority than designing for minimum water use. Recovery of irrigation run-off enables 80 per cent of the water to be re-used and ensures that water sensitive design principles are maintained without compromising plant performance and appearance.
The vast size of the green roof planted with Australian natives leaves a positive impression with all visitors to the site.
The inclusion of the green roof on the Victorian Desalination Project was an inspired gesture that added to the acceptance of the project by the local community and the wider public. ASPECT Studios reflects that because this roof was constructed in the absence of a formed Australian green roof design standard it is a testament to the innovation and skill of the design and construction team. Initially viewed as a risk, the green roof has proven to be one of the most successful elements of this challenging project and represents the growth of the green roof industry in Victoria.