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

Runoff Reduction Fact SheetDisconnected Roof DrainsTable DRD-2. Design Criteria for Disconnected Roof DrainsAlso see Appendix D for information on calculating runoff reduction credits.Variation/Parameter CriteriaSplash Block/Pop-up Drainage EmitterSurfaceSplash BlockSpreaderEmitter/pipeMinimum 2% positive slope away from building foundations for 4 feet minimum.Surface must be contoured to allow for sheet flow at least 5 feet wide. Must beplanted with erosion resistant vegetation (turf or dense groundcover). Ground coveruse limited to slopes less than 4%.Must be at least 24 inches long, 2 inches deep and 10-12 inches wide where itmeets the conveyance zone. Must weigh at least 10 pounds and be sloped awayfrom building.Where slope more than 8%, spreader required at end of splash block; spreadermust be drain rock, 24 inches long, 6 inches wide, and 8 inches deep, and level atsurface. Gravel may be placed below surface and covered with geotextile fabric, 4inches of soil and grass.Pipe must be at least 6 inches below the surface and a minimum of 4 inches indiameter (may not be suitable for large contributing roof areas). Emitter elevationmust be lower than the finished grade of the base of the downspout and the yarddrain (if used). Emitter must daylight no less than 5 feet from building (residentialonly).Travel Distance See Table DRD-1 and Appendix D.Dispersal Trench and Dry WellSoilsPretreatment SumpOverflowLoadingSurfaceDispersal Trench onlySetbackSoil type extending 3 feet from bottom of facility must have infiltration rate between0.52 inches per hour and 8.27 inches per hour. Soil may be amended to achieveinfiltration rate.Must be located a minimum of 5 feet from building. Must be labeled at surface“clean-out sump for dispersal trench or dry well”.Must be set on splash block.Must demonstrate that the appropriate loading tolerance is achieved for proposeduse of surface. Provide psi rating for structure/design.Minimum 2% positive slope away from building foundations (4 feet minimum) (perBuilding Code).Must be located a minimum of 20 feet from building. A smaller setback maybeallowed with geotechnical engineer approval.Configuration Must be installed parallel to site contours; must be a minimum of 2 feet wide and 18inches deep; must be a minimum of 8 feet long; must be lined with geotextile fabric(sides and top) and filled with drain rock.Surface LabelPerforated PipeSurface identification label may be required; check with the local permitting agency.Must be a minimum of 6 inches below grade.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007DRD-7