The Challenge
This innovative stormwater harvesting project aims to resolve many design and maintenance issues that have hampered the Water Sensitive Urban Design (WSUD) industry, especially in space constrained inner urban areas.
Whilst this project is site specific it has a high degree of transferability and provides a good prototype for use in other sites and municipalities, providing good flexibility for variations in scale.
Some of the key drivers included:
- Providing a cost effective alternative to potable water for irrigation;
- Delivering stormwater projects in the inner urban areas that integrate well with the existing streetscape;
- Raising community awareness of the issues and confidence in technological solutions;
- Minimising resource use in the construction and maintenance of the system; and
- Remaining carbon neutral over the lifespan of the project.
The Project
Darling Street in East Melbourne has been identified as a prime location for stormwater harvesting for the purposes of reuse for landscape irrigation. The system diverts stormwater from existing drains in adjoining streets running perpendicular either side of Darling Street. The water is captured in an underground storage tank and then treated before being stored for reuse in the irrigation of neighbouring reserves and medians.
This is a centralised system to capture, treat and store stormwater for reuse, located at a low point on the catchment that is well integrated into the existing streetscape. The works involved the installation of diversions in the existing stormwater system, installation of Gross Pollutant Trap’s, underground tanks and pumps to facilitate water treatment and reuse, and central raised bio-filtration beds. The irrigation
pumps are connected to existing irrigation networks, which only require minor upgrading to utilise the treated stormwater in an efficient, safe, fit-for-purpose manner.
Based on these benefits, the project offers significant advantages over alternative practices, such as traditional drainage systems, and current bioretention practices such as raingardens. Improvements
on existing raingarden systems include more reliable and higher levels of filtering for pollutants, reduced land requirements, and storage of water for reuse in irrigation.
The design embodies many innovations, including reducing costs in capital outlay and implementation, and ongoing maintenance costs. It reduces risks associated with establishing bioretention basins, trip hazards, and maintenance of gross pollutants. Improved efficiency is expected from reduced land requirements, better filtering of pollutants and flexibility in scale. The project also provides an opportunity for mitigation against climate change, by allowing better control over stormwater flow to manage flash-flooding, and in the storage of water for use during drought conditions.
The Outcome
This project provides economic, social and environmental benefits. The economic benefits of this project include a more cost effective method for achieving stormwater quality targets that is up to 75 per cent cheaper than traditional WSUD approaches. The project also offers financial savings in ongoing maintenance costs estimated to be one tenth of traditional WSUD costs by shifting from a predominantly manual labour component to mechanised cleaning. A reduction in cost for the use of potable water for irrigation is also achieved as the levelised cost analysis puts the price of the 21.3 ML per year of reuse water at $2.32/kL. Potable water currently cost $2.31/kL and will rise to $2.50/kL by June 2012.
Surrounding areas of water demand identified include Darling Square, Powlett Reserve and medians in the Grey, Simpson, Powlett and Albert streets in East Melbourne. The modelled annual irrigation demand for these areas is 23.92 ML.
The social benefits include increased landscape amenity, greater community awareness and confidence in WSUD technological solutions, and mitigation of the Urban Heat Island effect.
Environmental benefits include substantial improvements in stormwater quality and reduced demand on Melbourne’s water storages for irrigation, improved water supply to parks and gardens, and reduced flow of run-off into waterways.
This system delivers on the three targets of water demand reduction, alternative water sources and stormwater quality improvements contained within the City of Melbourne’s Water Strategy Total Watermark – City as a Catchment
The Scheme was complete and opened in June 2012. The City of Melbourne is partnering with the Centre for Aquatic Pollution Identification and Management (CAPIM) based at University of Melbourne in a 24 months testing and monitoring period to determine whether the system is meeting its design goals and how to optimise the operations.
The City is also currently constructing two similar but larger stormwater harvesting scheme in Fitzroy Gardens and Birrarung Marr. These should be complete in November 2012 and October 2013 respectively.