The Darling Street Stormwater Harvesting Project in East Melbourne

Background Information

The Darling Street Stormwater Harvesting project in East Melbourne is an innovative stormwater harvesting project that provides treated stormwater to irrigate neighbouring parks and tree medians.The capture, treatment and storage elements are located in Darling Street, a quiet residential street in East Melbourne. The catchment is 37 hectares of the well established inner Melbourne suburb compromising of residents, commercial offices and the Mercy Hospital.This project is an initiative derived from City of Melbourne’s ‘Total Watermark – City as Catchment’ strategy and addresses three of its main targets: water demand reduction, use of alternative water sources and stormwater quality improvement.The project took advantage of a local streetscape upgrade - including replacement of poor performing golden elms, modification of tree islands and resurfacing of roadway - to trial a new stormwater harvesting technology that requires infrastructure to be installed below ground.

Goals of the Initiative

The main objective of this project was to reduce potable water demand by providing an alternative water supply source for irrigation of local parks and tree medians. The harvesting capacity of the system was therefore sized to meet irrigation demand for the nominated streets and reserves within the precinct.

Other objectives included:

•keeping costs and spatial footprint of the system as low as possible.

•achieving environmental benefits through the reduction of runoff volumes entering downstream water bodies.

•delivering an enhanced public realm for the community.

The Darling Street Stormwater Harvesting Project provides a range of social, environmental and economical benefits and due to the success of the pilot project, the City of Melbourne is now delivering two more stormwater harvesting schemes. These will be the first of a suit of harvesting schemes envisaged for the municipality.

Parties and Partners to the Initiative and Resources Used for Implementation

Design Team

Concept development – City of Melbourne, Cardno (Civil) and LIS (Landscape) Detailed Design - Citywide or Cardno with City of Melbourne.

Funding Partners (Government)

City of Melbourne Melbourne Water - Living Rivers.The Victorian Government through the Stormwater and Urban Recycling Fund.

Contractors (Private)

Design, construct and operations contractor – Citywide.System design and head contractor - Biofilta Stormwater Solutions.Principle sub-contractor - Multipro Civil.

The resources used for implementing the initiative include: Total cost - $1,737,000 (including $100,000 for a two year monitoring program), with funding from:

•Melbourne Water - Living Rivers: $200,000

•Victorian Government - Stormwater and Urban Recycling Funding: $291,000

Innovation for the Initiative

The Darling Street Stormwater Harvesting Scheme is evolutionary as it’s a world first in combining a number of known stormwater treatment technologies into a single package. It also utilised pre-grown mature vegetation in the biofiltration beds. This can be verified by Biofilta (the technology provider) obtaining an international patent for the system. The Darling Street scheme has been a pilot project for the City of Melbourne and Biofilta.Darling Street is the pilot project for the City of Melbourne’s long term stormwater harvesting strategy, which aims to annually implement 1-2 systems on various sites within the municipality. The project took advantage of a local streetscape upgrade to trial a new stormwater harvesting technology that requires infrastructure to be installed below ground. The success of this pilot has resulted in two more similar projects being implemented throughout the municipality.The Darling Street Stormwater Harvesting Scheme combines a range of existing technologies in an innovative combination providing space efficient, cost effective, best practice treatment and reuse of stormwater. The scheme uses underground elements to reduce the surface footprint by 90 percent. By concentrating the treatment into a central location the capital and operational cost are greatly reduced from the typical raingardens approach. It also allows for reuse to occur by including a second tank after biofiltration.The treatment system diverts stormwater from two existing drains via GPT’s and a sedimentation chamber before storing the water in a primary tank. The water is then pumped onto the biofiltration beds in a timed and controlled manner. The pump cycle is timed to flood the beds to a depth of 100mm. The time between dosing the filter beds is determined seasonally by the rate of filtration and recovery of the beds. The process aims to maximise reuse water production while achieving best practice stormwater treatment. If reuse water is not used within the irrigation system the clean water can overflow from the reuse tank and discharge downstream of the diversion point. The system has been process optimised where it can be switched between a summer mode where reuse is maximised and treatment is halted when the reuse tank is full, and a winter mode when treatment continues regardless.The major new technology utilised in the scheme is the use of pre-grown plant cells. The plants are grown in a nursery for 6-9 months in the selected filter media and arrive on site in a mature state with a well established root matrix. This means that treatment is maximised within one to two months rather than the 12 months establishment time of standard tube stock planted systems.The system assets, value and condition have been registered in the city’s Asset management system and the "as built" plans have been loaded into our GIS Map system including Dial before you dig.The Darling Street scheme also took advantage of the depth needed to gain gravity flow to the primary tank. This allowed the reuse tank to be placed on top of the primary tank, further reducing the excavation requirement of the project. The reuse water is modelled to contribute 89 percent of the average annual irrigation demand for the neighbouring parks and medians.

Obstacles and Solutions for Innovation

Parking loss and the impact of the irrigation housing were reduced to address concerns raised by residents during community consultation.

Outcomes and Assessments

Outcomes achieved are as follows:

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% cheaper than traditional Water Sensitive Urban Design (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 21.3ML/yr of reuse water at $2.02/kL. Potable water currently cost $2.31/kL and will rise to $2.50/kL by June 2012. With the infiltration trench reuse the reuse potential raises to 24ML/yr and the levelised cost reduces to $1.80/kL. 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 storage for irrigation, improved water supply to parks and gardens, and reduced flow of run-off into waterways.The scheme has attracted local, national and international attention since construction began. The City of Melbourne has conducted 11 site tours with over 300 attendees and presented on the system in numerous forums, including to international audiences. The site has also received news coverage, featured in a Clearwater training video, as part of CNN’s coverage of the Rio+20 Summit and a DPCD video on leadership in local government.Engagement and capacity building within councils operations has also been enhanced. By delivering the project through our civil infrastructure mechanisms rather than going to open tender both our staff and head contractors were involved in the development and delivery of the project. This has also meant that there is ongoing ownership and a willingness to address maintenance responsibilities in a proactive manner. There has also been unforeseen flow on effects from this project where maintenance tasks on other WSUD sites are now being resolved that were previously issues. At many levels the Darling Street Scheme has raised awareness and support throughout council and beyond. The City of Melbourne is delivering two more stormwater harvesting schemes following the Darling Street approach namely at Fitzroy gardens and at Birrarung Marr. These will be the first of a suit of harvesting schemes envisaged for the municipality.

Assessments are as follows:

Water quality is improved to the best practice 80/45/45 standard for TSS, TN and TP. Monitoring of the scheme is being undertaken by the University of Melbourne’s Centre for Pollution Identification and Management (CAPIM). Initial results have confirmed that these nutrient removal targets are being met. Heavy metals and E. coli are also being effectively removed. Sediment and oils are being trapped before the biofiltration beds which increases their efficacy in nutrient removal.The staged treatment train allows for each element to perform to the best of its ability with coarse pollutants being handled by the GPTs, down to the final stage of UV disinfection which kills off any remaining bacteria and viruses before irrigation. This approach, along with only irrigating at nights, all but eliminates any public health risks from using stormwater for spray irrigation. The modelling predicts an annual irrigation reuse of 21.3ML, being 89 percent of the modelled irrigation demand of 24ML per year. Greater reuse may be achieved through winter soil moisture recharge delivery methods which have not been determined to date but is an approach that the City of Melbourne is pursuing.

Methods Applied

There were a number of methods that were developed during the project that assisted the success of this project. These key lessons were largely focused around the construction, implementation and maintenance phases.

These include:

•Involving Council’s engineering and parks departments during the design process ensured asset management and design issues were in line with Council’s existing maintenance practices.

•When placing infrastructure underground it is important to obtain good services and geotechnical information including groundwater condition during the design phase.

•To ensure smooth operations of construction works, it was necessary to know site specific constraints and in particular material allowances including cut, fill and disposal.

•Minimising the chain of command for site direction during construction works was shown to improve communication.

•Using new technologies introduces new maintenance requirements. Appropriate maintenance personnel and training needs to be organised early on to ensure timely provision of training.

•As the project adopted an innovative approach and new technology to managing, treating and re-using stormwater in a developed urban setting, there was a lot of external and internal interest. This resulted in numerous requests to host informal site tours and has stimulated knowledge sharing with peers.