ARTICLE WATERWAY HEALTH AND URBAN DESIGN
The aim of the restoration is to return Little Stringybark Creek to something like this – a waterway in good condition with intact riparian vegetation and minimal erosion. Photo iStock.com/Akatjomar.
SNAPSHOT • A project in Melbourne on Little Stringybark Creek is providing an understanding of how urban infrastructure and design can affect natural waterways • Runoff from impervious areas connected via gutters, pipes and drains directly to a local waterway is highly destructive of its biology and ecology • Disconnecting this runoff with the use of rainwater tanks, raingardens, leaky tanks and infiltration trenches may allow degraded waterways to recover at least some of their biodiversity and ecological function • As a result of the project’s findings, Yarra Ranges Council has changed stormwater management in the existing urban areas of the creek, and is placing controls on the impacts of new development
Little Stringybark Creek, located 37 km from Melbourne, has an urban catchment of approximately 300 ha at its headwaters and a total catchment of about 800 ha. Development in the catchment is a mix of urban and semi-rural. The creek is the focus of a project that is providing an understanding of how urban infrastructure and design can affect natural waterways. Researchers from the University of Melbourne (Walsh et al 2012) have identified that if runoff from impervious areas is connected via gutters, pipes and drains directly to a local waterway, it is highly destructive of the biology and ecology of that waterway. Streams are extremely sensitive to even a tiny proportion (0.5 per cent) of directly connected impervious areas in their catchment. Conversely, if impervious areas are not connected, draining to bushland or gardens or the runoff is being used for household or landscape purposes, the impact is far less. Conventional practice has been to manage the level of contaminants in stormwater. This project shows there is a much stronger link between the area of directly connected impervious surfaces in a catchment and waterway health. The research has found that if impervious area runoff can be controlled, using rainwater tanks, raingardens, leaky tanks and infiltration trenches, then degraded waterways may be able to recover at least some of their biodiversity and ecological function.
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What is not immediately clear are the implications of these findings for irrigation from rainwater. On one hand, capturing runoff and using it for irrigation has multiple benefits; it increases the amount of groundwater flow to replicate historical baseflow for local waterways, it removes stormwater volume from the system and it creates new green spaces for cooling, amenity and even food. On the other hand, irrigation is not always a reliable use of collected water, e.g. in winter, and rainwater tanks should be connected to internal uses such as toilet flushing and hot water systems. In summer there may not be enough rainfall for irrigation, requiring relatively drought-tolerant planting.
Symptomatic of a larger issue Little Stringybark Creek also represents a more widespread urban problem. Infrastructure solutions that only consider one aspect of water management, such as draining water as quickly as possible from streets and buildings, can create unintended consequences in other parts of the urban system. A systems approach is needed for water cycle management that includes stormwater management in urban areas.
Restoration program A restoration program for the upper part of the Little Stringybark Creek was initiated in 2008 based on evidence showing that stormwater runoff causes severe ecological degradation in the following ways: • much more run-off is delivered more often, causing erosion and channel enlargement and destroying physical habitat • unfiltered runoff is typically of poor quality with high levels of nutrients, sediment and toxicants
