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Incentivising stormwater management in cities and suburbs
The world’s populations are flocking to cities. In Australia, more than 90% of the population now live in cities and this is growing at a rate of 1.6% per year (ABS 2008). This growth has significant implications for the urban landscape. One of the greatest challenges for managing the changing urban landscape is dealing with water, particularly the excess stormwater runoff from increasingly impervious areas, transferred directly to streams through the expanding drainage network. Conventional stormwater management can lead to increases in stormwater volume of up to ten times, which leads to myriad impacts including flooding of houses, roads and infrastructure, degradation of stream channels and ecosystems, decreased replenishment of aquifers, and greater pollution of streams and bays. In Australia, the mechanisms currently employed to combat these impacts are failing to engender change. How can better stormwater management be incentivised to reduce these impacts?
Currently, the stormwater charge in Melbourne is charged irrespective of how much stormwater is generated by the property (as a fixed fee for residential, and based on property value for non-residential). The Victorian Government has, in its recent Water Plan, recognised that to complement existing provisions and regulations, stormwater management needs to be “improved by finding the best mix of legislative regulatory, financial and market-based incentives” (VicGov 2016). One possible solution could be to provide a financial incentive and simultaneously increase public awareness of the impacts of imperviousness, following the adage “if you can measure it, you can manage it”. Whilst true for drinking water, where smart meters are increasingly introduced to manage demand, could the same principles apply to stormwater runoff?
We examine a new approach to measure the impact of development on stormwater runoff through an imperviousness fee that would be calculated for each property, reflecting its impervious surfaces and the stormwater runoff it generates. Imperviousness fees have been introduced across Germany since the mid-1990s, following court rulings that deemed the previous charging approach as unfair, and implementing a “polluter pays” approach with an imperviousness fee. Four case studies are presented from different regions and cities of varying sizes (Hamburg, Munich, Dresden, and townships in the State of Baden-Wuerttemberg). Each application varies in the approach to implementation of the fee. Yet, a common thread is that post-implementation in all case studies observed improvements to their stormwater management situation, including reduced imperviousness, better data for modelling, and reduced flooding. For example, in the city of Munich, since 1995, over 4.5 Million square meters of imperviousness has been removed, resulting in a 3000 ML/year runoff reduction. In Baden-Wuerttemberg, within 2 years of the introduction of the fee, a qualitative survey found that 48% of townships perceived some decrease in imperviousness, with 11% reporting a high decrease. The reduction in imperviousness has been achieved through increasing pervious pavings, implementation of rainwater tanks, and green roofs.
What could the introduction of an imperviousness fee mean for Australian cities? Economically, the benefits could include reduced investment in drainage infrastructure, reduced potable water charges due to supply from rainwater tanks, and associated energy-savings from the cooling of green roofs, reducing energy demand during the summer period by up to 40% (Spala 2008). Stormwater control measures can reduce flooded areas by up to 40% for medium frequency events (Burns et al. 2015). Socially and environmentally, benefits include urban cooling, and amenity from increased watering of local parks (e.g. with the use of harvested stormwater). In flow-stressed waterways a reduction of current runoff can improve the ecology and geomorphology of streams, with improved water quality providing for healthier ecosystems and communities. Increased parks and healthy waterways have been found to increase nearby house prices by up to 5%, all of which can offset the initial increased cost to residents (Mekala 2015). This makes a strong business case for implementing an imperviousness fee in Australia.
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