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

Runoff Reduction Fact SheetDisconnected Roof DrainsDescriptionRoof drains can be disconnected from the storm drainsystem by directing the roof runoff 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. Roof runoff 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: City of 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 of 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 of existing/planned landscape areas; no additional space required.• Can reduce size of downstream stormwater quality treatment measures by reducing the volumerequired to treat.Limitations• Plant materials in landscaped areas receiving the runoff should be designed to withstandoccasional inundation.• Subsurface infiltration devices may eventually clog with sediment, requiring costlyreconstruction.• Soil permeability may limit applicability of subsurface infiltration structures.Maintenance Recommendations (Low 1 )• Irrigate and maintain vegetated areas to maintain infiltration and filtering capacity.• Periodically check for clogging of 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.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007DRD-1