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Port Phillip's water situation
The City of Port Phillip is bordered by water along its 10 kilometre coastline and also embraces the largest inner-suburban lake at Albert Park. Much of our city is reclaimed swampland and is subject to flooding.
But we still have a water problem. Our soils are sandy and porous so rain, when we get it, is not retained to provide ongoing nourishment to trees and other vegetation. Rain runs quickly off all the impervious surfaces common to a densely built inner-suburban area - concrete, bitumen and roofs.
We are forced to draw on our state's dwindling supplies of drinking water to keep parks as well as our gardens and ourselves alive.
Our city has been and remains the most densely-settled area of Victoria with 34.5 persons per hectare - ten times the Melbourne metropolitan average and rising. At the same time, we're under extraordinary development pressure both residentially and commercially. One of the side effects of this trend is the loss of valuable garden space to more impervious surfaces such as additional roofing, carparks, paths and patios. This leads to considerably more stormwater runoff. In fact, there can be up to two or three times as much runoff created, which could lead to problems for much of our infrastructure - sewers, drains, streets and utility hardware - which is ageing.
Our bayside location demands that we have a properly functioning drainage system. Like many municipalities, we've been living off the massive engineering works undertaken over a century ago but many of our drains are now reaching the end of their useful life. As a responsible local government, we have no alternative but to start a planned and necessarily costly refurbishment of our drainage system. A means of reducing the cost of improving stormwater infrastructure is to reuse rainwater where it falls. This can be achieved by untilising road runoff or water from other areas of the public realm. It can also be achieved by encouraging or requiring the on-site use of stormwater in the private realm.
The most effective method of achieving this is to harvest rainwater into a tank and re-use it for irrigation or toilet flushing. In multiunit apartments, because there is often an absence of extensive plantings, it is better to use the water for toilet flushing. This is obviously a worthy idea, but at some point you've got to walk the walk as well as talk the talk so with funding from Coast and Clean Seas, which in turn is funded by Environment Australia, council's Urban Design & Architecture unit established a demonstration project to show how practical examples will fulfill the theory.
Ormond Road Stormwater Retention
A seven-unit development at 48 Ormond Road in Elwood, owned by Boss Properties and built by Hickory Developments harvests rainwater on the roof into a stormwater retention system, comprising a 15,000 litre-tank and UV disenfection and then the water is used to flush toilets. The project was monitored over 12 months.
Scope of study
The objective of the monitoring project was to establish that as a consequence of a building type change from single detached residential to medium density development, there would be no addition to stormwater runoff volumes because the additional volumes would be utilised on site. The purpose of monitoring flow to stormwater is to learn how much is lost, whether the capacity of the tank is maximising captured volumes and whether the predicted water use for toilet flushing is accurate.
Monitoring equipment was installed to log:
- Total Rainwater registered 90,000 litres
- Total Water used by the toilet system 300,000 litres
- Total mains top up would be 210,000 litres
- Overflow volume to stormwater - none registered
- Daily usage varied from 900 to 2000 litres per day.
Project findings
The actual recorded volume of 90,000 is significantly less than the predicted volume calculated to be approximately 132,000 litres based on a collection area of 240 m2 with Elwood typically receiving 600mm of annual rainfall (Bureau of Meteorology website www.bom.gov.au/climate)
Some of the low registrations of water volume in the inlet pipes and to stormwater drain can be attributed to some design/installation faults with the monitoring equipment. In that, the positioning of meters in the pipe meant that light flows could not be detected.
Another finding of the monitoring regime was that the toilet flushing volume which was theoretically proposed for the development was significantly different to actual usage. Prior to the monitoring period, daily usage had been envisaged as 437 litres per day. Data supplied by the logger has shown that daily usage varied from 900 to 2000 litres per day. The large range in daily toilet flushing volumes is in part due to the range of occupation rates where there was half occupation to full occupation over the course of the monitoring period. Despite this, toilet flushing volumes were at four times greater than anticipated.
Demonstration projects like this are often trialing not only the sustainable design technologies but the monitoring equipment itself. As this was the case in the project, some trends in water collection and reuse were collected, but their accuracy is limited.
In this project, however, building a picture of trends was sufficient. It has enabled refinement of the design approach for future projects, refinement of monitoring equipment design and installation. The experience of the monitoring this project has highlighted an important issue that contributes to the success of monitoring demonstration projects. And that is the importance of bringing stakeholders together to discuss the objectives of the project. The subcontractors, who had a big impact on the installation and calibration of the equipment, were not regularly briefed on the project and this contributed to poor data generation in one instance and missed opportunity for maximising water harvesting in the tank in another instance.
Probably the greatest success of the project has been the contribution of the project to the formulation of Council policy. Water collection for toilet flushing is one of the principle strategies employed in council's Sustainable Design Strategy which was endorsed by council in 2002.
You can find out more information in the  Ormond Rd Stormwater Retention Project document.
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Rainwater tanks for domestic applications
The capacity to incorporate such large stormwater retention features into multiunit developments relies on thinking about how it can be done very early in the design process and building them in. Yet in houses, it is possible to install rainwater tanks any time and use the water for garden irrigation and other uses.
In fact, garden water accounts for 30 per cent of total water consumed at a typical residence. We're talking about drinkable water too, so a rainwater tank could be a valuable eco-friendly addition to any house. There are a host of other approaches to save water around the house.
The Savewater website at www.savewater.com.au features information on indoor and outdoor products that save mains water use. These include: washing machines and dishwashers, shower heads and tap ware, mulches and irrigation systems, watering devices, hoses, rainwater tanks for irrigation and toilet flushing, greywater accessories and treatment and pool covers. A brief summary of the company and their product range is listed, together with full contact details for sourcing more information about specific products, their water efficiency and also retail outlets. Where available, links to suppliers' web sites are also included.
Other information is also available from the Advice & Resources page on this website.
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Pervious pavement treatments
Another method of retaining stormwater within multi-unit developments and houses is to use pervious pavement treatments for driveways, carparks and paths rather than asphalt and concrete. Some simple examples include gravel or porous asphalt, which allows water to percolate through to the ground underneath.
Also available are the new Eco-pavers, which are a system of paving that enables infiltration through the spaces between pavers. These were used at Homebush Bay, the Olympic Village, which was constructed with sustainable design objectives in mind.
There are plenty of other ways in which pervious surfaces can be utilised, and their use is certainly becoming more important as stormwater management becomes a pressing issue to be addressed by local government.
The state planning provisions, ResCode 2000, reflects this concern with clauses that stipulate that 20 per cent of new residential developments be set aside for pervious surfaces. This is sometimes more difficult to achieve in areas like COPP where there are higher densities but applicants can discuss options for achieving the objectives of the clause with council planners.
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Water campaign
For more information on how the City of Port Phillip improves on its own water consumption, visit the Water Campaign page on this website.
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More information
For more information regarding water saving features and sustainable design, use eServices to ask us a question, request information or give us feedback online. If you prefer call ASSIST on (03) 9209 6777 or TTy (03) 9209 6713 and ask for Sustainable Design.
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