Keeping stormwater in the catchment to save water and waterways

Although Australia has just come out of a 10-year drought, Melbourne itself “wasted” over three times as much water as would be generated by the new desalination plant, at the same time allowing this stormwater to pollute, erode and degrade our waterways.

The growth of cities leads to vast areas of vegetation being replaced by concrete and other impervious surfaces. Water falling on these surfaces can’t be absorbed into the soil. Instead it runs into stormwater drains that take it directly to the nearest stream or river, or to the sea. The frequent flushes of polluted stormwater, together with lower dry-weather flows, cause the loss of many species of animals and plants, and encourage the growth of nuisance and potentially toxic algae. Urban runoff also increases the size and frequency of large floods, which threatens both property and life.

Where once trees would have also absorbed the extra water from storms, their replacement with impervious surfaces such as roads and roofs, means that even small rainfall events cause erosion and pollution of waterways. Conversely, during dry weather, the loss of infiltration through porous soils, means that creeks are starved of precious ‘baseflows’, causing a further loss of biodiversity. Stormwater is the biggest threat to Melbourne’s waterways, including iconic species such as platypus.

Researchers at the University of Melbourne are conducting several integrated research programs, with the aim of developing a new approach to stormwater management; one which values stormwater as a resource and which prevents degradation to rivers and creeks.

Professor Fletcher, Associate Professor Chris Walsh and their team at the University of Melbourne are working on the Little Stringybark Creek Project, in collaboration with colleagues at Monash University, Melbourne Water, The Department of Sustainability and Environment, Yarra Valley Water and the Yarra Ranges Council, to trial this new approach to urban stormwater management in the suburb of Mount Evelyn (see www.urbanstreams.unimelb.edu.au). By using rainwater tanks and raingardens (a self-watering garden that receives runoff from a house roof, for example), they are demonstrating that urban stormwater can not only be a substantial water supply, but that using it improves urban amenity and protects streams from damage.

The Little Stringybark Creek project is the first of its type in the world, because it is testing novel ways of encouraging the public to become involved. For example, the research team ran a “Stormwater Auction”, where householders could bid to undertake projects on their property. At the same time, the research team is monitoring the flow, water quality and ecology of the creek, with the hope of seeing the return of sensitive species that have been lost from Little Stringybark Creek, but are found in nearby unurbanised creeks.

At the same time, the research team is monitoring how much water is saved by the use of rainwater tanks.

“This project shows that stormwater could actually be a rare win-win; by harvesting it, we provide our city with a ‘new’ water resource at the same time as helping to protect and restore our precious urban creeks”, Chris Walsh says.

In addition, they are working with the Green Infrastructure Research Group (http://www.landfood.unimelb.edu.au/green/), based at the University’s Burnley campus, to develop and test a range of new ‘green technologies’ for managing stormwater. These include green roofs and vegetated walls, passive irrigation systems and a range of techniques for infiltrating stormwater and restoring natural soil moisture in the urban landscape. These techniques have important benefits in helping to insulate buildings, also helping to cool the urban environment by restoring evapotranspiration.

Among the most exciting of these projects is the “Vegetable Raingarden” trial, which is testing whether self-watering vegetable gardens can help retain stormwater while boosting urban food production. The project is a collaboration between the University of Melbourne, Monash University and Melbourne Water. Demonstration days will be run to allow members of the public to inspect the garden and see how they could build such a system for themselves.

If the researchers get their way, stormwater will become a major part of the urban landscape in the future – helping to keep the urban landscape lush and green year round, and allowing Melbourne and other cities to restore its waterways as corridors of biodiversity throughout the city.

For more information:
Tim.fletcher@unimelb.edu.au
0407 517 662