Water Journal : Water Journal August 2012
workshop report 48 AUGUST 2012 water Collaboration in Stormwater Harvesting Learning to move from theory to practice The Collaboration in Stormwater Harvesting Workshop took place at the Ozwater'12 Conference & Exhibition on May 9 in Sydney. This report, which encapsulates the background and motivation for the workshop, as well as the outcomes, has been prepared by Steven J Kenway (Consultant, UWSRA), Dr Brian S McIntosh (International WaterCentre), David Hamlyn-Harris (Director, Bligh Tanner Pty Ltd), Adrian Crocetti (Brisbane City Council), Simon Toze (CSIRO), Don Begbie (Director, UWSRA) and Sharon Biermann (UWSRA). Stormwater is a substantial and yet largely untapped urban water source. In South-East Queensland, 245--750GL/year of stormwater flows unused from cities, compared with 350GL of water used for urban purposes in 2010. Other cities are similar. However, embedding the constructive use of stormwater as a resource in Australia remains elusive. Many challenges exist and, as a consequence, stormwater runoff continues to have numerous negative ecological impacts, degrading streams and contributing to erosion and sediment loading, while water supplies for our cities are imported from elsewhere, incurring energy costs and the requirement for significant capital investment in pipe and pump infrastructure. At Ozwater'12, the Urban Water Security Research Alliance (UWSRA) and International WaterCentre (IWC) convened a "hands-on" workshop to promote learning across organisations and disciplines about how effective, environmentally beneficial, healthy and well-maintained stormwater harvesting schemes might be implemented within brownfield urban development. The workshop aimed to bridge the gap between theoretical goals and real solutions through peer-to-peer learning involving a process and materials conducive to learning -- building with Lego blocks. Workshop Presentations The workshop involved a series of short presentations followed by a hands-on design exercise. David Hamlyn-Harris of Bligh Tanner kicked off with a presentation emphasising the water supply engineering design objectives of stormwater harvesting, including: (i) maximising permissible use of stormwater within total water use goals; (ii) ensuring fit-for-purpose, efficient and cost-effective design (including diversion structures, storage, treatment systems and pipe lines); and (iii) constructability and integration into the development. Dr Simon Toze (CSIRO) then tackled health risk management. Stormwater-treatment levels are dictated by proposed water uses to address risks. Potable use of stormwater requires high levels of treatment; however, for non-potable water uses, non-treatment barriers could be appropriate. Stormwater regularly has elevated levels of Enterococci, greater than 500 coliform-forming units/100 mL in wet weather. Trace chemicals such as cadmium, nickel and lead are of less concern from a human health perspective, unless the water is to be used for potable purposes. Adrian Crocetti ran through what Brisbane City Council learnt from the Millennium Drought regarding how to create stormwater- harvesting systems with positive social and environmental outcomes. Opportunities identified included the need to design and construct "fit-for-purpose" rather than over-engineered systems. This can reduce the capital and operational expenditure. Assets can be revitalised by improving connectivity with the local community. Wet spaces can be transformed and bring people back to the water. Major challenges included: (i) keeping the cost per kilolitre under potable supplies (energy use is key); (ii) enabling integrated planning by stakeholder engagement at the design stage; (iii) lack of space, aesthetics and perceptions in the use of public space; and (iv) supplying "fit-for-purpose" water while ensuring public health and safety requirements. Finally, Dr Brian S McIntosh outlined some of the typical ecosystem impacts caused by urban stormwater, including increased frequency and peak velocity of flow events and larger total volumes of stormwater flows caused by increased impervious surfaces. Collectively the impact of typically higher levels of imperviousness in urban areas increases the "flashiness" (rapid response) of stormwater flows and these are usually more erosive, carrying greater sediment load, nutrients and other contaminants into urban creek systems, ultimately reducing biodiversity and overall species abundance and productivity. The challenge from an ecosystem health perspective is to develop urban designs that promote less flashy, more 'natural' (non-urbanised) hydrological responses to rainfall events. Hands-On Design Challenge After the presentations, the workshop participants split into four teams. Each team was tasked with designing a stormwater harvesting scheme for a brownfield site of approx 55ha. Housing for around 4,000 people was expected. Each team had 45 minutes to create a next-generation urban development incorporating extensive stormwater harvesting and management using nothing more than an A0 aerial photograph, an information pack characterising the site and "building materials" such as Lego blocks, pipe cleaners, pom-poms and pieces of foam (Figure 1). Figure 1. Team 3 tackles the challenge of designing a multi-benefit stormwater harvesting system. Designs were encouraged to be imaginative and innovative as well as practical and cost-effective. The assessment "criteria" to be reflected in their design included: • Maximising stormwater use; • Multiple urban space outcomes and benefits; • Identification and management of health risks and fit-for purpose treatment; and • Enhancement of ecological habitat and/or ensuring degradation has been minimised or avoided. Once completed, each team had five minutes to "sell" the desirable scheme features to the judges.
Water Journal September 2012-1
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