Re-directing stormwater for Melbourne's benefit
Melbourne, rightly or wrongly, has a reputation for being a city where it always seems to rain. In some periods particularly in late winter and spring, Melbourne and Victoria for that matter certainly gets its fair share in what the weatherman would term as a "normal" year for those of us that reside in this fair city, we know that the amount of rainfall we experience is highly variable. Not too long ago, much of Australia including Melbourne suffering water shortages due to a stubbornly persistent drought , and as a result, many of our green spaces were left parched. Consequently the use and storage of our water reserves became front and centre of many people's day to day conversation.
So with Melbourne's increasing population through continued urban and suburban expansion, and an increasing value that the community is putting into open green space and urban waterways, it is essential that councils and relevant authorities maintain these community assets in a manner that utilises and protects our water supplies in a sustainable way. These days the increasingly and more commonly used technology to capture and re-direct storm water in an urban setting is Water Sensitive Urban Design (WSUD).
In recent years, Melbourne Water have made the incorporation of WSUD technologies mandatory as a condition of a town planning permit when new developments are planned. According to the Melbourne Water website, a typical WSUD system can generally be applied in a few different ways which include:
- Grassed or landscaped swales.
- Infiltration trenches and bio-retention systems.
- Gross pollutant traps (GPT), wetlands and sediment ponds.
- Rainwater tanks - stormwater harvesting and reuse.
- Grey water harvesting and reuse.
- Rain gardens, rooftop and urban gardens.
- Porous pavements.
- Aquifer recharge and reuse.
Further to this, the key principles of WSUD are as follows:
- Protecting Waterways - Protection of waterways within urban developments so they can be maintained as valuable community assets and support healthy aquatic ecosystems.
- Manage stormwater in the landscape - Passively manage stormwater rather than allowing it to all drain into waterways. By reducing the volume and frequency of stormwater releases, the quality of stormwater reaching our waterways increases. Also it is worth pointing out that stormwater will only pass through during a normal rain event. If there is a heavy down pour, the WSUD technologies are designed to be bypassed to assist in preventing localised flooding.
- Addition of benefits whilst reducing development costs - Provision of a range of benefits including alternate supply, improved amenity and safety and enhancing waterways and lakes. The inclusion of WSUD minimises the drainage infrastructure development costs by reducing pipe sizes and potentially erplacing other large scale reticulated water systems with local solutions.
A great example of how WSUD can be used in an established urban is the Darling Street Stormwater Harvesting Project, East Melbourne. The case study explains that stormwater is harvested using an innovative technique where water is collected from two nearby existing drains, then diverted through a GPT and sedimentation chamber before being stored in an underground storage tank. Once the water is in the tank, it is pumped out and conveyed into aboveground bio-filtration systems (see image below) for treatment, then is finally stored within another storage tank.
The treated water can then be used to irrigate nearby parks and streetscapes including Darling Square, Powlett Reserve and medians on Grey, Simpson, Powlett and Albert Streets. Total cost of the project was a touch over $1.7 million, and was the first of its kind to be implemented by the City of Melbourne. The implementation of this project is the only beginning of a much larger program where the council aims to construct 1-2 systems on various sites within the City of Melbourne municipality.
In addition to the Darling Street project and in a response to the lack of rainfall over the last decade, the Yarra City Council and Melbourne Water collaborated between 2010 and 2011 to construct a raingarden within the Edinburgh Gardens in Fitzroy North. Similar to the Darling Street project, the raingarden filters stormwater and collects it in an underground storage tank located in the northeast section of the park. The raingarden itself takes approximately 600sq m of the site of the demolished Ladies Bowling Club within the southern section of the park. It is estimated that the water collected from the raingarden will be able to supply 50% of the water requirements for the Edinburgh Gardens.
Both aforementioned projects highlight the benefits of capturing stormwater in two different settings, however both were similar as they were retrofitted into existing infrastructure. But what about rainwater harvesting in apartment developments? Well it is safe to say that a number of recent developments have either incorporated rainwater harvesting such as Roi apartments in Fitzroy North and the upcoming C3 apartments in Brunswick. These residential developments harvest stormwater by collecting water from the roof and channeling it through to storage tanks that were or will be installed between the ceiling of the underground car park and the ground surface. Water filtration in this setting is generally not required as the roof surface is quite clean relative to roadways and urban streetscapes, so the water is used directly onto garden beds or for toilet flushing following storage.
WSUD has been a great success so far where implemented. Key drivers for the success of these projects for both councils and developers generally revolves around the costs and outcome, so with increased implementation, community acceptance and understanding of the technologies, there is no doubt that WSUD will continue its rise as a cost effective and environmentally appealing feature in our streets and in our homes, because the next drought is only ever so far away.