Ditch the Kerb Given the cost of installing and maintaining urban stormwater infrastructure, why not outsource it to the most experienced expert- Mother Nature.
text Russell Fortmeyer images Courtesy McGregor Coxall, Bates Smart
Technology
Les Miserables would be a very different novel if it were to occur in a bioswa le, as opposed to festering in the streets and sewers of revolutionary Paris. Rotten infrastructure, decaying on a massive scale, is not an unfamiliar phenomenon to the contemporary urban Australian, as it certainly was not to Victor Hugo. Like many Western democracies, Australia is falling apart, in need of billions of infrastructure spending merely to maintain the status quo, yet still happy to sprawl into the bush on top of costly hidden infrastructure that begins its entropic demise the moment the first shovel of earth is dug. If sustainable design has often embraced the language of revolutions, albeit more the Velvet variety than the current Libyan tumult, it nonetheless requires an overturning of convention to rethink design from the ground up, perhaps a bit more literally in the case of low-impact site stormwater strategies. Adrian McGregor is a managing director of McGregor Coxall, a Sydney environmental design studio, and one of a few landscape architects trying to introduce, if not a revolution, a more passive approach to site storm water design in Australia. Instead of
installing ever larger concrete or clay pipes to deal with storm runoff from the endless impervious surfaces of cities, McGregor would like to see more emphasis placed on reclaiming existing waterways and drainage ecosystems, installing the man-made infrastructure to facilitate what already works in nature. McGregor Coxall developed a strategy it called the 'Ecological Engine' for its 2001 competition-winning masterplan for the Green Square Town Centre in Sydney (the other team members included Wiel Arets Architects and Turner + Associates Architects). The site, halfway between the CBD and the airport, is formerly industrial, with scant evidence that Sheas Stream flows beneath it through concrete channels, collecting runoff from a nearly 250 hectare catchment area. Cities have perfected engineering natural waterways into hidden pipes (and, in their absence, isn't it just so Australian to then name a bar after them, for example Sydney's own Tank Stream?). McGregor's 'Ecological Engine', further developed in a commissioned design from 2007, used Sheas Stream as its organising principle, drawing a 16 litre per second constant base flow from the stream's
polluted water out of a culvert, creating a linear axis to cut through the new town centre along the actual path of the stream, and then diverting it through a series of biofiltration cells embedded in public park landscape and urban plazas. Finally, the filtered water collects into holding tanks at the lower end of the site, where it can be used for non-potable water demands in the project. "Having an open plaza at the core of the project, we realised we'd have a lot of stormwater flows across the site that we could deal with using an urban stream," says McGregor. "It tells a story to the public about this larger existing ecology and it's definitely a nice feature of the park." The project's developers have a revised scheme, which was under consideration by the City of Sydney Council and New South Wales Government when this was written in May 2011, which alters the McGregor Coxall landscape plan to instead place retail buildings over the Sheas Stream path and eliminate any potential for reclaiming a surface waterway in the plaza. However, McGregor remained hopeful the government's own environmental commitments and extensive public consultation process wou ld ensure the original stream plan remained intact. If it gets built, the Green Square 'Ecological Engine' would represent a first for such approaches in Australia. The concept relies on dual systems, since the stream McGregor's team developed is sized to handle the base flow of Sheas Stream, but not the higher flows caused during storm events (those flows still rely on the underground concrete pipes). Surface runoff in the park and plaza will filter into the constructed wetlands of the urban stream, rather than be diverted. The wetlands filter all of this water naturally, with native plants removing contaminants from the water through a slow, steady process, as opposed to energy-intensive black water or grey wa ter treatment facilities that have found favour in Green Star projects. It has been demonstrated elsewhere that plants, given the time, can clean soil contaminated with toxins like hydrocarbons and glycol through similar phytoremediation processes. Constructed wetlands, although they may sometimes dry out during summer months, generall y occur along paths of regular flow. A bioswale, however, depends on intermittent flows. Bioswales are basically tricked-out versions of a natural system, a low point where water collects during a storm and slowly seeps into the ground or runs off in search of lower and lower points on its way to the sea. A well-designed bioswale has gently sloping sides that lead to a long basin, vegetated with native plants or grasses, that can slope longitudinall y from one to four percent. In some cases, swales can be this simple, while others can be lined with subsurface filter fabric and contain a washed rock base concealing a perforated pipe running the entire length, or lead to large bio-basins or to underground sand pits for better filtration. Water runs into the swale, filters down through soil
McGregor Coxall's Green Square Town Centre proposal.
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GREEN SQUARE HYDROLOGICAL SYSTEM
1. Storm water diversion from culvert I 2 . Biofiltration cells in urban stream I 3. Urban stream and pond system I 4. Filtered water holding tanks 5. Harvested roof water 16. Water feature circulation I 7. Non-potable water supply to buildings I 8. Filtered excess water to culvert
and rock, collects in this pipe and, in some cases, is fed into a finer filter and storage tank, while in others it may simply be fed directly into the city's stormwater system (bioswales tend to work better as filters for coarse or fine pollutants, whereas wetlands more effectively treat dissolved particles). Regardless, the swale itself slows this process by containing the water for a short duration, rather than fo rcing it all into the storm water system at once. Since volume largely dictates stormwater system design, a bioswale's delay tactic typically results in a sma ller stormwater system. In th e best of circumstances, often in suburban or semirural areas, the stormwater system can be avoided entirely. Extensive bioswales and permeable paving systems, which allow water to seep into the ground, were both deployed throughout the landscape of the Sydney Water faci lity in Potts Hill, completed in 2009. Designed by Bates Smart Architects, with Aspect Stud ios as landscape architect and Cardno as civil engineer, the suburban site and the client's institutional focus afforded an opportunity for an innovative carpark design.
Australia is falling apart, in need of billions of infrastructure spending merely to main tain the status quo, yet still happy to sprawl into the bush on top of costly hidden infrastructure.
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Instead of designing kerbs around all planters and landscape, which often creates a bathtub effect in carparks, the Sydney Water carpark's kerbless edges allows water to flow directly into bioswales.
as to why so few projects have innovatively addressed it at the building and urban scale. Mounting evidence implicates the design and construction industry. A 2006 University of New South Wales study found the bio-accumulation of toxic materials, notably copper and zinc, in Sydney Harbo ur likely accounted for a nearly 75 percent death rate in juvenile crustaceans who feed on contaminated seaweed. A recent study of the San Francisco Bay attributed nearly 60 percent of its toxic copper contamination levels to pipe corrosion, compared to 23 percent from wastewater treatment plants. Using solderless copper pipe systems or even alternatives like polyethylene can reduce or even eliminate this runoff. Such potential for contamination often restricts just how much a project may be able to give back to the environment, such as increasing the permeability of surfaces to allow more water into natural systems. McGregor Coxall considered this for the Green Square Town Centre. "We did include the proposition of aquifer recharge in one section, but there are major problems Instead of designing kerbs around all planters and landscape, which often creates a bathtub effect in carparks, where water collects and pools in the low areas around drains, the Sydney Water carpark's kerbless edges allows water to flow directly into bioswales. In more conventional secti ons, where kerbs were installed, pervious concrete pavers on both sides of the main roadway reduce stormwater flows. In addition, the bioswale, which runs along the north side of the building, acts as a buffer between the offices and the carpark, with a raised, planted bank providing both visual and practical separation from the carpark and the potential for heavy flows to infiltrate the building's perimeter. Slowing water's movement has significant benefits, particularly in reducing the contamination of stormwater that occurs during flood events (one of the reasons Green Star awards points to this effect in its Emissions category, which helped my Arup colleagues develop their 5 Star rating strategy for Sydney Water). Great quantities of water can all at once pull debris, or what are called 'suspended solids' in industry jargon, into the stream and, with this greater momentum, p ush masses of garbage into waterways, harbours or anywhere else stormwater systems typically discharge. Typically, the worst time to swim in an urban beach is right after a massive storm. This situation illustrates how tiny decisions, made at the scale of buildings, have massive environmental impacts when grouped together within a city. Australia's development of Water Sensitive Urban Design (WSUD) Treatment Measures substantially foc uses on stormwater, as well as all aspects of the water cycle, including its use and conservation. Most development plans (and Green Star) refer to two guidelines: the Urban Stormwater Best Practice Environmental Management Guidelines (CSIRO 1999) and Australian Runoff Quality, A Guide to Water Sensitive Urban Design (Engineers Australia, 2006). Both seek to reduce postdevelopment peak stormwater flows for 1-in-2-year storms and treat all stormwater leaving the site for 1-in-20-year storms. If Australia's water scarcity has resulted in much government attention to WSUD, particularly in Victoria, the question remains Technology
Sydney Water, Bates Smart/Aspect Studios. Photo: Tyro11e Bra11iga11
with aquifers around this area from leaching at toxic sites near the airport," says McGregor. "People are reluctant to engage with the aquifers, so yo u'd need a few years of investigation before you could make any decisions." That's often the problem with contamination - once you touch it, it belongs to you. But surely Sydney's post-industrial landscape, like those of cities everywhere, increasingly merits such investigation if we are to make best use of our existing infrastructure. Ditching the kerb, while not necessarily a revol utionary tactic, could be a good first step. ar
Russell Fortmeyer is a senio1路 consultant with the Sustainable Technologies Group in Arup's Los Angeles office. He writes frequently about architecture, technology and sustainability and is a former editor at Architectura l Record.