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Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

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Run<strong>of</strong>f Reduction Fact SheetDisconnected Ro<strong>of</strong> DrainsDescriptionRo<strong>of</strong> drains can be disconnected from the storm drainsystem by directing the ro<strong>of</strong> run<strong>of</strong>f across vegetation orinto subsurface infiltration devices where it is filteredor infiltrates into the ground. The water may bedirected across lawns, through dense groundcover, intodevices such as a dispersal trench or dry well, ifacceptable to the permitting agency. Ro<strong>of</strong> run<strong>of</strong>f canalso be directed into vegetated swales and stormwaterplanters for stormwater quality treatment (see factsheets for these measures in Chapter 6).Consult a geotechnical engineer about site suitabilityand other design considerations.Source: <strong>City</strong> <strong>of</strong> PortlandSiting Considerations• Soils: Infiltration structures are generally suitable for Type A and B soils.• Depth to groundwater: For infiltration structures, minimum depth to groundwater table 10 feetbelow bottom <strong>of</strong> facility.• Setback: infiltration structures must be min. 20 feet from buildings (Smaller setback maybeallowed with geotechnical engineer approval, verify with local permitting agency).• Slope: up to 25%• Vegetation: sufficient vegetated area must be available for overland conveyance.Vector Considerations• Potential for mosquitoes due to standing water in vegetated features will be greatly reduced oreliminated if the feature is properly designed, constructed, and maintained to ensure completedrainage.Advantages• Takes advantage <strong>of</strong> existing/planned landscape areas; no additional space required.• Can reduce size <strong>of</strong> downstream stormwater quality treatment measures by reducing the volumerequired to treat.Limitations• Plant materials in landscaped areas receiving the run<strong>of</strong>f should be designed to withstandoccasional inundation.• Subsurface infiltration devices may eventually clog with sediment, requiring costlyreconstruction.• Soil permeability may limit applicability <strong>of</strong> subsurface infiltration structures.Maintenance Recommendations (Low 1 )• Irrigate and maintain vegetated areas to maintain infiltration and filtering capacity.• Periodically check for clogging <strong>of</strong> any subsurface pipes or infiltration systems (e.g., dry well) andrepair as needed.1 Compared to stormwater quality treatment control measures discussed in Chapter 6.<strong>Stormwater</strong> <strong>Quality</strong> <strong>Design</strong> <strong>Manual</strong> for the <strong>Sacramento</strong> and South Placer Regions<strong>May</strong> <strong>2007</strong>DRD-1

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