Sustainable Land Development Today - February 2009 - (Page 9)

Photo courtesy of Intrinsic Landscaping, Kurt Horvath growing season. In some respects, native landscape systems were self irrigating in that they had the ability to receive and cycle significant amounts of water as a result of nightly condensation. Water accumulated on the surfaces of plants, worked its way down into the root system, or was stored along the surface of various plants for use by other organisms. One of the benefits of integrated green infrastructure systems relates to their ability to restore opportunities for condensation and daily water cycling to be restored. Greenroof systems, whether integrated into new construction, or retrofitted into existing buildings, can provide multiple stormwater management, energy-savings, and life-cycle benefits. Whereas typical rooftops generate significant runoff, greenroofs can reduce rainwater runoff by 70 percent or more on an annual basis (Hoffman and Fabry 1998). Even a greenroof with only three to four inches of a light-weight, modified soil mix can regularly absorb many common rainfall events. Greenroofs not only consume rainwater for plant growth but transpire moisture back into the atmosphere. Throughout many portions of the country, every acre of urban greenroof equates approximately five to eight hundred thousand gallons of water annually that will never leave the roof system in the form of surface-water runoff. Due in large part to their regional stormwater management benefits, many municipalities in Europe and a few in North America offer stormwater reduction credits for greenroofs, or provide grants to facilitate their design and construction. Porous pavement systems can be designed to infiltrate virtually all of the precipitation that falls on the pavement, and in many applications, absorb significant volumes of runoff that are generated from surrounding impervious surfaces as well. Research indicates that new porous pavement applications can effectively absorb as much or more than 10 inches of precipitation per hour and that although the infiltration rate may damp off after several years, infiltration rates remain in the range of 2.5 to three inches per hour for the life cycle of the pavement system (Borgwardt 1994), (Smith 2001). When used in combination with other site bio-retention measures such as bio-swales, French drains, level spreaders, and dry wells, porous-pavement systems can have a significant positive influence on runoff reduction and waterquality enhancement, even in dense urban settings, and in environments with poorly drained, high-clay-content soils. Whole systems design solutions which act to integrate building and site functions based upon “green” design principles can generate multiple benefits including the incorporation of sustainable, water-resource management practices. The Blackberry Creek Future Alternatives Analysis (USEPA, IDNR, Kane Co., CDF, 2003) indicates that through proper design, even densely developed industrial, commercial/retail, corporate and institutional, or residential developments can result in the significant reduction of runoff and associated downstream flooding, site- and watershed-scale, water-quality enhancement, the restoration of stable baseflow hydrology to site and regional aquatic systems, and promote aquatic habitat improvements. Numerous studies that have explored the costs associated with conventional vs. sustainable develop- ment strategies also indicate that green development is cost effective, both in terms of capital-development costs, as well as the cost of long term goods and services at the community scale. More recently, the downstream cost benefits of green development have been explored and documented (Haugland, et al). Several highly-urban, mixed-use development projects in Europe and throughout the United States have demonstrated that, through the creative integration of architecture, building and site engineering, landscape architecture, and ecology, off-site, surface-water runoff discharge can be drastically reduced or eliminated (Dreiseitl, Grau, and Ludwig 2001). Such effective demonstration projects illustrate how rainwater can be collected, cleansed, recycled for heating and cooling as well as graywater use, and incorporated for esthetic uses within both the building and site. It is generally our opinion, that density of development is not the critical factor in the generation of runoff and associated water quality problems, but rather the amount of effective imperviousness that is the primary contributor of runoff. There is no doubt that a strong correlation exists between density and water quality degradation in urban environments that are subject to conventional development practices. It is quite possible, however, to effectively reduce or eliminate this problem even in the most urban environments through the incorporation of creative, water-resource management strategies. SLDT About the author: James Patchett, ASLA, LEED AP, is the founder and president of Conservation Design Forum, based in Elmhurst, Ill. He can be reached at JPatchett@cdfinc.com. www.SLDTonline.com 9 http://www.SLDTonline.com

Table of Contents Feed for the Digital Edition of Sustainable Land Development Today - February 2009

Sustainable Land Development Today - February 2009 Contents Our Voice Modern Flood Disasters Origin of the Sustainability Movement SLDI in Focus Calendar Build Smart Product Innovation Takeoff and Cost Management Industry News Products & Services Advertiser Index Editorial Board SLDT Resources Last Word

Sustainable Land Development Today - February 2009

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