Stormwater Quality Design Manual (May 2007) - City of Sacramento ...
Stormwater Quality Design Manual (May 2007) - City of Sacramento ...
Stormwater Quality Design Manual (May 2007) - City of Sacramento ...
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Technical RequirementsGreen Ro<strong>of</strong>How does a Green Ro<strong>of</strong> work?Green ro<strong>of</strong>s reduce run<strong>of</strong>f volume and peak flow through severalmechanisms. When it rains, the green ro<strong>of</strong>’s foliage, growthmedium, and root uptake zone retain a substantial portion <strong>of</strong> thestormwater that would otherwise flow from the ro<strong>of</strong> to the stormdrain system. The retention volume depends on many factors,including rainfall amount, depth and composition <strong>of</strong> the growthmedium, and the type, diversity, and maturity <strong>of</strong> the vegetation.Some <strong>of</strong> the retained stormwater is released to the atmospherevia evaporation and transpiration (after uptake by plants). Theremainder slowly infiltrates through the growth medium to thero<strong>of</strong> underdrains and is discharged to the storm drain systemwith the volume and peak flow rate reduced.Green ro<strong>of</strong>s are a proventechnology and have beenused/tested in Europe forover 40 years. They aregaining recognition in the USfor the environmental,economic, and social benefitsthey provide. There are nownumerous applications in theSan Francisco/San Jose BayArea <strong>of</strong> California.Green ro<strong>of</strong>s improve run<strong>of</strong>f water quality through a variety <strong>of</strong> biological, physical, and chemicalprocesses within the plants and growth media. At the ro<strong>of</strong> surface, airborne particulate matter(encompassing a range <strong>of</strong> organic and inorganic compounds) is intercepted and taken up by plant foliage.When it rains, stormwater (and associated air pollutants) is retained within and filtered through the growthmedia and root uptake zone. Contaminants sorb to clay and organic matter within the growth media.Further pollutant removal is achieved by bioremediation and phytoremediation, carried out by bacteriaand fungi present within the root systems. Pollutant removal increases as the vegetation and root systemsmature.Other Names: Ecoro<strong>of</strong>, green ro<strong>of</strong>top, nature ro<strong>of</strong>s, vegetated ro<strong>of</strong> coversPlanning and Siting Considerations• Involve the landscape architect, licensed structural engineer and mechanical engineer early in thedesign process with the project architect, since architectural ro<strong>of</strong> style (pitch/slope,configuration), ro<strong>of</strong> structural requirements, building heating/cooling needs, vegetation selection,and irrigation needs go hand in hand.• Proper design and management <strong>of</strong> drainage is essential. Inadequate drainage may result in moreload that the ro<strong>of</strong> can sustain;plant mortality; and/ordegeneration <strong>of</strong> the growthmedium.• Choose plants suitable for thelocal climate and consideringdesired future irrigation. Checkwith the local permittingagency for recommended plantsand planting guides for greenro<strong>of</strong>s.• Consider designing the greenro<strong>of</strong> to serve as a greenspaceamenity accessible to buildingtenants and/or the generalpublic. This is particularlyimportant quality <strong>of</strong> life benefitin dense, downtown urban areaswhere space for parks andnatural areas is at a premium.Pedestrian Walkway on Stanford University Parking Garage Green ro<strong>of</strong>, PaloAlto, CA. <strong>Design</strong> by Rana Creek Living Architecture.<strong>Stormwater</strong> <strong>Quality</strong> <strong>Design</strong> <strong>Manual</strong> for the <strong>Sacramento</strong> and South Placer RegionsGR-2 <strong>May</strong> <strong>2007</strong>
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