GHD Pty Ltd: The raingarden is to provide a sustainable source of treated stormwater for the parks mature trees and sporting fields in a way that added to the existing landscape character of the park and added interest for users. Melbourne has experienced drought conditions for a number of years now and this project was to replace the existing need for potable water being used to irrigate our parks and gardens. This raingarden is designed to remove 16,000 kg of annual total suspended solids per year of operation. It will also remove a further 160 kg of nutrients, phosphorus and nitrogen, through vegetation growth. This litter and pollutants would otherwise end up in Melbourne’s waterways. Filtered water is then collected into a 200KL underground storage tank, and used to irrigate existing trees within the Edinburgh Gardens; providing around 60% of their irrigation needs in a normal year. In a normal year, the raingarden is expected to reduce potable water use for irrigation by 4 ML per annum.
The project involved sourcing stormwater from the North Fitzroy Main Drain and diverting it to a newly designed terraced raingarden within the Edinburgh Gardens, with the treated water being harvested for storage and irrigation of the trees within the park and local precinct. The main components of the project were:
• Diversion pipe from North Fitzroy Main Drain with gross pollutant trap.
• Surcharge pit into 700 sq.m rain garden.
• Terraced raingarden with appropriate planting and filter media to treat stormwater.
• Overflow pit with underground pipe connected to 200 kilo-litre underground storage facility with pump to irrigation distribution.
As described above the majority of the works undertaken to achieve this were underground with the large raingarden providing the visual element. The main design features of the raingarden are:
• Filter media and appropriate plants that help to treat the stormwater through uptake of excessive nutrients and filtering fine sediments.
• Four large terraces that respond to the sites natural grade, therefore minimising the requirement for taller retaining walls and balustrade, allowing informal public interaction,
• Terrace walls that extend out into the landscape to create lawn ‘room’ areas for passive recreation. These areas will create elevated views over the raingarden and provide different spatial experience in this area of the park which is currently characterised by large unbroken lawn areas.
• The strong lines of the extended terrace walls is repeated in the bands of planting in response to the recent history of the site as the location for the Inner Circle Railway Line.
• A ‘zig zagging’ feature steel low flow channel, connected to the surcharge pit, that delivers water to all four terraces in rain events.
• New tree planting to provide shade and enclosure for new small lawn areas
• Continuously curved edge to reinforce line of new shared path and existing avenue planting
Name: Edinburgh Gardens Raingarden
Location: Edinburgh Gardens: St Georges Road- Fitzroy North, Melbourne, Australia
Design Year: 2010
Year of Construction: 2011-2012
Area: 700 m2
Design Company: GHD Pty Ltd
Clients: Melbourne Water in collaboration with City of Yarra
Image credits: all GHD owned