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

Runoff Reduction Control Measure Fact SheetAlternative Driveway DesignDisconnected DrivewayConventional driveways are considered “directly connected” to the storm drain system becausestormwater runoff from the driveway enters the storm drain system directly. Driveways disconnectedfrom the storm drain system reduce runoff and provide incidental pollutant removal by passing runoffover an adjacent vegetated or otherwise porous surface that intercepts, infiltrates and filters the runoff.There are various design approaches: 1) slope the driveway to drain onto adjacent turf or groundcover, 2)install a slotted drain near the lower third of the driveway and discharge the drain to a landscaped area (ifthis is not considered a safety/tripping hazard), and 3) install grooves in the driveway pavement to helpdirect flow to the vegetated area. Some agencies may also allow an under sidewalk drain which connectsthe depressed landscape area adjacent to the driveway with the gutter/storm drain.Design Criteria: See Table AD-1 for design criteria.Shared DrivewayDriveways can be configured to provide access to two or more garages. Consult the local permittingagency to determine if this practice will be allowed for your project.Table AD-1. Design Criteria for Alternative DrivewaysAlso see Appendix D for information on calculating runoff reduction credits.Variation Design Parameter RequirementPerviousDrivewayHollywoodDrivewayDisconnectedDrivewaySharedDrivewayGeneralSubgrade drainGeneralPorous center stripIrrigationGeneralEdge of drivewayGeneralSee Porous Pavement Fact Sheet for specifications.Surface sloped to provide positive drainage away from building foundations.Required in C and D soils. Use a gravel trench or perforated pipe embedded ina 8-12-inch layer of crushed rock. Connect to storm drain (not sanitary sewer).Tracks 2.5 to 3.5 feet wide, separated by a porous center strip at least threefeet wide.Slope driveway toward center strip to promote drainage or install grooves tohelp direct flow into porous strip.Porous center strip groundcover, grass or drain rock.Groundcover, grass, drain rock or porous pavement.Consider irrigation for center strip vegetation.Design the driveway cross slope greater than the longitudinal slope so thatrunoff is directed across landscape.Size the adjacent landscape area to accommodate flow from the driveway.Water from driveway surface should flow an average of 8 feet overlandscaping prior to reaching the right of way.If a slotted drain is used, install it perpendicular to the flow path to direct flowinto vegetation, and provide removable grates for cleaning.If runoff flows across sidewalk, it must sheet flow and spread at least two feetwide to avoid concentrated flows.Must be approximately 3 inches above the vegetated area.Configurations vary, consult local permitting agency.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007AD-3