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

Runoff Reduction Fact SheetDisconnected PavementHow does Disconnected Pavement work?Impervious surfaces, such as those paved with regular asphalt or concrete, that convey stormwater to astorm drain system without allowing the water to flow over any impervious surface are considered“directly connected”. Compared to pervious areas, directly connected impervious surfaces contributeincreased runoff and associated pollutants to the downstream storm drain system. “Disconnection” ofimpervious surfaces can be achieved by sloping surfaces toward relatively small or narrow vegetated orporous areas where the water is filtered before entering the storm drain system, and/or infiltrated into theunderlying soils. Areas that can be disconnected include parking lots, driveways, sport courts, sidewalks,patios, courtyards, and roadways.Other names: Not directly connected pavement, divided sidewalks, separated sidewalks, bifurcated walk.Planning and Siting Considerations• Maximize the use of landscaping and natural areas that are planned for the site already. Designlandscaping to sit below adjacent impervious surfaces. The width of the vegetation needed isdependent on the area of contributing pavement; the ratio of impervious to pervious surfaceshould be 2:1 or less.• When draining pavement to open spaces, avoid environmentally-sensitive and protected wetlandsareas. These applications will not qualify for the runoff reduction credits discussed in this factsheet.• Check with the local permitting agency to determine if credit will be given for paved surfacesdraining to vegetated creek buffer areas.• Locate porous features in well drained soils (Types A or B) whenever possible. If porouspavement is used in C or D soils, an underdrain will be required.• Eliminate curbs and slope pavement to sheet flow into vegetation where possible. Where curbsare required for safety or other reasons, use curb cutouts to convey flow into the vegetation.• Maximize the use of Porous Pavement (as an alternative to conventional pavement) where it candouble as a disconnected conveyance zone. When draining an impervious area into porouspavement, refer to Porous Pavement Fact Sheet elsewhere in this chapter for planning and designrequirements.Suitable Land Use TypesResidential: Driveways, patios, and walkways can be disconnected. Also see Alternative Driveways FactSheet elsewhere in this chapter.Commercial: Plazas and courtyards, parking lots/stalls, overflow parking areas, some types of storageareas, walkways, and as entryway features. Not appropriate for retail gas outlets, auto maintenancebusinesses or locations where spills may occur.Industrial: Employee parking stalls, entryway, and pedestrian walk features. Not appropriate forprocessing/manufacturing areas involving extractive, chemical/petroleum, food, printing processes, andchemical storage areas.Roadways: Slope roadways to drain across vegetation or other porous surfaces.Parks and Open Space: Parking lots, park hardscape areas, pedestrian and bike trails, sports courts andplaygrounds. See notes above about draining to natural open spaces, environmentally-sensitive areas andcreek buffers.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsDP-2 May 2007