Summer is on the way – well it certainly feels that way with Sydney last week experiencing the warmest August temperatures on record – and we haven’t even got to spring yet. And there’s a lot of talk of record high temperatures, low rainfall and more bushfires again this summer. But isn’t this how we always talk as winter comes to a close, our fear of drought and bushfire ever lurking? Well, if we do, these days there’s good reason – in the words of Bob Dylan, “The times they are a-changin’”.
The statistics tell the story. The last few years in Australia have been dry, particularly in the southeast. In Melbourne in each of the past three years only about 450 mm of rain fell in the city centre, down from the long-term average of about 650 mm. Last summer’s catastrophic Victorian bushfires were a harsh warning of things to come, say scientists, with climate change causing increased incidence of extreme weather events and an alarming decline in rainfall levels.
The Bureau of Meteorology predicts a decline in annual rainfall rates by up to 10 per cent in southern Australia by 2030 and by up to 20 per cent by 2050.
But just how much is being done to prepare for this decline in natural rainfall?
According to Professor Chris Walsh, Principal Research Fellow in the Department of Resource Management and Geography at the University of Melbourne, not nearly enough.
Walsh estimates that if Australians were to make use of stormwater harvesting methods such as retention ponds, rain gardens (which filtrate runoff back into the ground for reuse rather than it being directed to drains) and rainwater tanks, we could cut our water usage from the main storage supplies by up to half as well as greening and cooling our cities.
The economic benefits of stormwater harvesting include lower expenditure on flood mitigation infrastructure if more water is retained in the catchment. Another area of likely cost saving is on stormwater management for new housing developments.
“Before stormwater harvesting can be dismissed as ‘too expensive”, all of these benefits need to be costed, and this sort of economic analysis just hasn’t been done anywhere yet,” says Walsh. “ Certainly preliminary analyses that look at multiple benefits point to it being an economic as well as an environmental winner.”
In an average rainfall year in Melbourne, says Walsh, 80 to 90 per cent of that rainfall is allowed to run off into the stormwater drains and into the river system. Not only is this water wasted, untreated pollutants from runoff are causing enormous damage to waterways.
Governments, both state and federal, have resisted the harvesting of rainwater for re-use, opting instead for solutions such as desalination plants.
“The desalination fad is likely to be short lived,” says Walsh. “When the energy crisis really bites there will have to be a move to lower cost, low energy solutions that focus on reducing demand for water.”
Despite the resistance of government, Walsh is hopeful that they are starting to listen and are becoming more willing to fund other options including the harvesting of runoff from large commercial developments.
Large-scale desalination uses extremely large amounts of energy as well as specialised, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater.
The crunch will come when there is not enough renewable energy to power desalination plants, since under the Mandatory Renewable Energy Targets renewable power desalination must be largely powered by renewable energy sources. The Wonthaggi desalination plant in Victoria would need energy equivalent to the state’s existing combined wind and solar capacity (around 100 megawatts) to power it, says Walsh.
Government is still blind to sustainable solutions
“Part of the problem has been that water resource engineers tend to distrust dispersed solutions. And as politicians are advised by water resource engineers, this has created a certain blindness to the harvesting of stormwater,” says Walsh.
“But it really is the only hope we’ve got of sustainably adapting to declining water supplies and climate change. And if we don’t do this through numerous small scale projects we haven’t got a hope of saving our waterways and protecting species such as the Platypus, which is already at risk in several urban catchments of Melbourne.”
The reduction in demand for mains water when rainwater tanks and other solutions such as retention ponds are used is reflected in water usage figures from the National Water Commission.
Between 2003 and 2008 figures from the Commission show that demand for water from the mains supply in Brisbane (where rainwater tanks are mandated for all new developments) fell by 50 per cent.
In other states, where the take up of these solutions has been slower, there was still significant reduction; in Sydney demand fell by 29 per cent, Melbourne by 30 per cent, Perth 3 per cent and Adelaide 29 per cent.
Walsh concedes that some of this fall in demand was due to the introduction of water restrictions and public awareness of water use. But the Brisbane figures are particularly significant.
In Victoria the government has prevaricated for some time over including stormwater management in 5 Star building standards. Such a move would see similar falls in water demand to that of Queensland’s.
Current stormwater harvesting projects around the country are mainly demonstration projects. Walsh is involved in what he says is a world-first demonstration of restoring an urban creek by fixing up its biggest problem first: urban stormwater runoff.
The Little Stringybark Creek Project, a research program coordinated by The University of Melbourne and Monash University, involves working with local government, water authorities and residents to test the design and implementation of real, on-ground solutions. It will test how stormwater management can be improved in established suburbs, like Melbourne’s Mt Evelyn.
As part of the project, residents can apply for a grant to install harvesting systems such as rainwater gardens and tanks. A total of 55 properties funded through the project are expected to save over 5927,000 litres (or the equivalent of 2371 Olympic swimming pools) of mains water a year.
That also means that there will be five million litres less stormwater entering the local creek. In addition to the water savings, participating properties will each year prevent 14kg of nitrogen entering the creek. This is particularly good for the Yarra River and Port Phillip Bay, as nitrogen is a contributing factor in algal blooms.
The project is funded by Melbourne’s water supply companies, local government and the Victorian Government. Walsh hopes it will be one of many small to medium scale projects that encourage innovative and low cost water harvesting. Results and data collection from the project will be used to create a model for wider use.
Resistance can be overcome
Overcoming resistance from local councils to new solutions is also challenging, says Walsh. But a simple demonstration often does the trick. In the case of Mt Evelyn, the research team was able to demonstrate to the local council that it could harvest water from playing fields to water them instead of putting in a water bore.
“They needed three megalitres a year to maintain the fields and we showed them the buildings and roads surrounding these fields actually produce 11 megalitres – and that’s in a dry year.
“There is a general blindness to just how much water is out there. There is a super abundance of it and despite the fact there’s so much media coverage of increasing heat and reduced rainfall there’s resistance to looking at these simple solutions,” says Walsh.
But attitudes are changing.
One innovative project by Yarra Valley Water at Kalkallo Industrial Estate will harvest all stormwater runoff from the large greenfield commercial estate for reuse on the site, with the remainder pumped back into the main water supply.
It is this sort of project, if applied broadly around the country, that has the potential to make a major difference to water use as well as to the massive volumes of stormwater currently pouring into fragile waterways, says Walsh.
Another proposed project, Water Sensitive Cities, aims to harness the potential of stormwater to overcome water shortages, reduce urban heat island effects, and improve the landscape and liveability of Australian cities. Currently awaiting funding approval, the five-year research project proposes to develop a hybrid of decentralised and centralised water management solution, all directed at creating water sensitive cities.
The project team has been assembled by the Monash Sustainability Institute and includes researchers from Monash University, The University of Queensland, The University of Melbourne and EDAW Australia.
According to the project team, one of the reasons stormwater harvesting has not been adopted more broadly is a widely held perception that there is a lack of space for stormwater retention in the urban footprint.
“However this is based on a traditional view of urban design and landscapes.
Often, these schemes are inappropriately assessed in terms of their effectiveness as a sole or ‘silver bullet’ solution, whereas they form an integral part of a solution strategy incorporating a diversity of water sources,” says the team in its proposal fact sheet.
The team says there is also lack of understanding about sustainable technology options, implications for cities from climate change and the likely bene?ts of stormwater harvesting on urban micro-climate and water ecology as well as human health risks.
An important area for change, says Walsh, is reuse of treated sewage water.
“Governments have had a major aversion to recycling this water but this needs to change. It is a highly sustainable option and treatment processes are so good these days that the water that comes out is more pure than what is currently in our streams and dams,” says Walsh.
“If we are to effectively adapt to climate change the first priority should be reducing energy demand, not creating new energy intensive industries, particularly in the period when we should be building our renewable energy capacity.”
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