Stormwater – helping to tackle Australia's water crisisWith reduced water supplies and a growing population, should Australians be letting stormwater go down the drain?
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Key textWater supplies in AustraliaWater is a big issue in Australia. There are water restrictions in most major cities, and climate change and recurrent droughts affect our agriculture industry. And it's easy to see why water is a big issue here. The average Australian uses 320 litres of water per day for domestic purposes. For overall per capita water usage, we are the third highest consumer in the OECD, only behind Canada and the United States. Irrigated agriculture uses nearly eight times more water than total household consumption. There are ever increasing pressures on our water supplies. Our population is growing – it's predicted to reach 25 million by 2032. And we will be very thirsty indeed, because the world will be a hotter place by then. Global warming is expected to decrease rainfall in Australia's 10 largest cities by an average of 15 percent by 2030. Perth will be worst affected, with a predicted 20 percent drop in the drop, and only Hobart can continue to expect healthy rainfalls. It's pretty clear that we need to make some changes to the way we use water. For Australia to effectively address the water crisis, a range of water management strategies need to be used. By signing the National Water Initiative (2004) Australian states and territories committed to more efficient water use, better water management and reuse of water. Desalination plants, recycled water and stormwater can all play a part in helping to tackle the water crisis. Already, the largest recycled water scheme in the southern hemisphere has been announced in Brisbane; desalination plants have been built or are currently being built in Perth, the Gold Coast, Sydney and Melbourne (Box 1: Australia's desalination situation); proposals for dam enlargements and the introduction of recycled water are being considered for Canberra, and a package of options which include desalination and stormwater reuse have been implemented in Adelaide. Every one of these cities is implementing water reuse in some form – a sign that the old model of letting our waste and stormwater run out to sea is no longer feasible. Tapping into stormwater Until recently, little attention has been paid to the reuse of stormwater. In most towns and cities, stormwater runs directly into a dedicated drainage system designed to carry the water away as quickly as possible into natural waterways or the ocean. In Australia, a significant volume of rainwater ends up as stormwater runoff. It is estimated in Sydney alone, 420 gigalitres of stormwater goes straight out to sea every year. That's the equivalent of almost the entire contents of Sydney Harbour. While it's tempting to think of all the ways wasted stormwater could be used, it's not as simple as directing stormwater drains into a dam. Firstly, suitable storage areas need to be established. In addition, stormwater runoff picks up all kinds of pollutants from our roads, driveways and footpaths – everything from garden clippings to detergents, sediment to paint, plastic bags and cigarette butts. These pollutants, in addition to the unnaturally high flows, can damage creeks and wetlands. Before stormwater can be safely used, the pollutants have to be removed (Box 2: Removal of pollutants from stormwater). The biofiltration approach One solution to the problem of pollutants in stormwater is to make stormwater systems more like natural waterways. When water flows through a creek or wetland, particulates and chemicals are filtered out by the aquatic ecosystem, cleansing the water. By retaining natural creeks in urban developments or creating vegetated waterways instead of large concrete stormwater channels, stormwater can be stripped of most of its offending pollutants. This approach is being adopted in several places around Australia. Cabbage Tree Creek, which flows into Moreton Bay in south-east Queensland, is one example of a waterway that has been rehabilitated through this approach. By installing a sedimentation pond and stormwater wetland to reduce nutrient and pollutant loads from stormwater runoff, the health of the creek's downstream ecosystem has been significantly improved. At Homebush, the Sydney Olympic Park was built to use recycled stormwater, which is filtered through the Millennium Wetlands, stored, and then used for water features, irrigation and toilet flushing, saving significant quantities of water. While in Melbourne, 'rain gardens' have been installed in new housing developments to filter stormwater runoff. These gardens are five metre square garden beds, filled with a sandy loam soil and water-loving plants, which filter the runoff as it passes through. The Wungong redevelopment in Western Australia will incorporate eucalypt-lined park avenues that serve as biofilters for its stormwater runoff, protecting the Wungong River from pollution. In Salisbury near Adelaide there is also research into treating stormwater to provide water which meets drinking quality requirements. CSIRO scientists have developed a method in which stormwater is treated by passing it through a reed bed; the water is then injected into a limestone aquifer via a well, where it is stored for twelve months. The water is then tested for its compliance with drinking water criteria and bottled.
As the drought situation in Australia worsens, there is increasing interest in tapping into existing sources of water, such as stormwater, which at the moment is just going down the drain – literally. There is ongoing research to make better use of the water that we have, in the hope of alleviating the ever-increasing strain on this precious natural resource. Related Nova topics: Population and environment - what's the connection?
Box 1: Australia's desalination situation'Water, water everywhere, nor any drop to drink' – the famous line from Coleridge's The Rime of the Ancient Mariner could be describing the world's water situation. Only three percent of the Earth's water is fresh water, and two-thirds of that is locked up in glaciers and polar ice caps. Seawater accounts for the remaining 97 percent of the planet's water.Australia is increasingly turning to desalination as a reliable additional water source that is independent of rainfall. Although desalination provides an almost limitless supply of drinking water from the ocean, the downsides of desalination are that it is expensive and requires a lot of electricity to run. Cities using desalination to boost their water supplies can expect significant increases in the cost of water. However, developing technology is bringing down the cost of desalination. The desalination plants being built in Australia use reverse osmosis technology. In reverse osmosis, sea water is forced at high pressure through a semipermeable membrane, allowing fresh water through while retaining dissolved salts on the other side. It takes a lot of energy to force sea water through these membranes and hence desalination uses a lot of electricity – which in Australia is generated from fossil fuels. This is being addressed by using renewable energy to power new desalination plants. The Kwinana desalination plant in Perth is powered by energy from the Emu Downs wind farm, while Sydney Water plans to buy green energy from accredited suppliers to power the Kurnell desalination plant. The Victorian desalination plant will be capable of providing around a third of Melbourne's annual water supply using renewable energy sources. In South Australia, plans have been announced for the construction of Australia's first solar-powered desalination plant near Port Augusta to bolster water supplies perilously dependent on the Murray-Darling River system. The plant will be constructed within a complex that will also house a commercial salt production facility which will harvest the excess salt generated from the desalination process. Desalination plants that discharge the concentrated salt water (or brine) are ideally sited where there are deep coastal waters and strong currents to disperse the discharge, which could otherwise affect coastal ecosystems. Related sites
Box 2: Removal of pollutants from stormwaterA number of methods have been developed to remove pollutants from stormwater. The processes involved in the treatment methods can be classified as physical, biological or chemical processes.Physical processes There are two general methods by which pollutants can be physically removed from stormwater. Sedimentation basins are designed to temporarily detain and reduce the flow of stormwater, which facilitates the settlement of sediments and other contaminants at the bottom of the basins. Basins are particularly effective in the removal of larger contaminants from stormwater, but are less effective in removing the smaller contaminants such as clay particles. The rate at which the sedimentation basins remove pollutants from the water is dependent on the flow of the water, the size of the sediments as well as the retention time of the stormwater in the basins. The second physical process used to remove pollutants from stormwater is filtration. Filtration involves the separation of materials from the stormwater by passing the water through a filter. This method is useful for the removal of suspended solids and pollutants bound to sediment in the water. However, the filtered materials accumulate in the filter and reduce the flow through the filter. Regular maintenance of the filter is required to retain the effectiveness of the filtration process. Biological processes Bacteria play an important role in wetlands and swales constructed as stormwater treatment systems by removing nitrogen, organic matter and dissolved metals. Under anaerobic conditions – conditions which are typical in sediments, where little or no oxygen is available – bacteria act as nitrogen-removing agents. They do this by converting nitrate (NO3) to nitrogen (N2). However, an excess of nitrogen from fertilisers and animal manure in stormwater can cause undesirable growth of bacteria, algae and plants. Bacteria and other micro-organisms also degrade organic matter like garden clippings suspended in the water by oxidation, releasing carbon dioxide gas. In addition, their role in converting sulfates to sulfides helps with removal of dissolved metals. Plants used in stormwater treatment can indirectly remove pollutants by promoting bacterial activity. They also take up metals and other nutrients from stormwater. Chemical processes Chemicals can be added to stormwater causing some of the pollutants dissolved in the water to become insoluble. For example, aluminium- and iron-containing chemicals can be added to make phosphorus compounds commonly found in commercial fertilisers insoluble in water. Alternatively, chemicals can be added to lower the pH of the water, making it more acidic, and reducing the solubility of some pollutants. The solids formed can generally be removed from the stormwater either by filtration or sedimentation.
Activities
Further readingAustralasian Science September 2007, page 11 Natives oust pollutants Reports on study which showed native grasses assisted the remediation of polluted sites.
July 2007, page 36-38 30/50 vision (by Vaughan Beck) Examines the barriers to reaching a population of 30 million in Australia by 2050.
March 2006, pages 38-41 Stormwater pollution: Is it damaging urban waterways? (by Michael Barry) Explores the possible role of stormwater run-off in damaging urban waterways.
July 2004, pages 38-42 Water recycling options for the thirsty country (by John Radcliffe) Explores the potential of recycling water from three different sources.
Cosmos 6 June 2006 More people, less water: CSIRO examines future options Reports on study which examined how Australian cities would cope with increasing demands on water.
June 2006 The water crisis (by Sara Phillips) Explores Australia’s options to dealing with the water crisis.
Ecos No. 133, 2006, page 7 Wungong’s urban water master plan a pace-setter Looks into the plans for the Wungong redevelopment.
No. 130, 2006, page 15 Rain gardens buffer Melbourne’s waterways Looks at the installation of ‘rain gardens’ to filter stormwater in Melbourne.
No. 124, 2005, page 28-30 A Stirling idea (by Wendy Pyper) Reports on the development of a system which combines desalination with heating or cooling capacity.
No. 122, 2004, pages 8-10 The Aquadam (by Wendy Pyper) Explores a scheme for floating, self-powered desalination reservoirs.
No. 120, 2004, page 35 Stormwater drainage is reducing stream biodiversity (by Wendy Pyper) Reports on the damage to biodiversity due to increasing runoff into natural waterways.
No. 113, 2002, page 36 Being waterwise in spaceship suburbia (by Wendy Pyper) Explores waterwise urban developments.
No. 110, 2002, pages 28-30 Water alchemy (by Steve Davidson) Looks at the storage of urban stormwater in aquifers.
New Scientist 16 June 2007, page 5 Australia – not such a lucky country (by Tim Flannery) Looks at the effects of climate change on Australia.
16 June 2007, pages 8-11 Australia – the continent that ran dry (by Rachel Nowak) Looks at the water situation in Australia.
31 January 2007 Sydney faces soaring heat and vanishing rain Reports on weather predictions for Sydney in the future.
28 April 2001 Scenario 3 – population (by Debora MacKenzie) Explores a possible scenario in the world’s population in the 22nd century.
Scientific American 23 July 2008, pages 28-35 Facing the freshwater crisis (by Peter Rogers) Discusses the increasing demands for freshwater and possible solutions.
23 July 2008 Why don't we get our drinking water from the ocean by taking the salt out of seawater? (by Peter Gleick) Evaluates the use of desalination plants to supply water.
September 2007, pages 90-91 Fresh from the sea (by Mark Fischetti) Describes the desalination process.
Stormwater News Volume 1, Issue 5, 2002, page 3 A water management plan that sells while it works Looks at the planning and design features of the Lynbrook Estate development.
Volume 1, Issue 5, 2002, page 4 Improving Cabbage Tree Creek’s health Reports on improvements to the health of Cabbage Tree Creek.
Volume 1, Issue 1, 2000, page 4 Storming for gold Looks at the stormwater management system in place at Homebush.
Useful sitesEnvironment Protection Authority (Victoria, Australia)
Stormwater pollution (Essential facts, Melbourne Water)
Contains information on stormwater pollutants.
Stormwater pollution (Environment Protection Authority, South Australia)
Provides information on stormwater pollution and its impact on the environment.
Australian Broadcasting Corporation
Australian Government Department of the Environment, Water, Heritage and the Arts
The global water situation (savewater.com.au, Australia)
Contains information about the current global and Australian water situation.
National Water Initiative (National Water Commission, Australia)
The national initiative for water reform in Australia.
Glossarybiofiltration. Technique which uses natural living material to capture and filter out pollutants.gigalitre. One gigalitre is one thousand million litres. OECD. Organisation for Economic Co-operation and Development. stormwater. Any rain that falls on roofs or paved areas such as footpaths or roads.
External sites are not endorsed by the Australian Academy of Science. Posted June 2008. The Australian Foundation for Science is a supporter of Nova. This topic is sponsored by the Australian Research Council Linkage Learned Academies Special Project Grant.
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