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

Runoff Reduction Fact SheetDisconnected PavementVariationsTwo variations of disconnected pavement that qualify forrunoff reduction credits are discussed in this fact sheet: 1)Pavement draining to landscaping, and 2) pavement drainingto porous pavement.Pavement Draining to LandscapingVegetated areas used to disconnect impervious surfaces caninclude either uniformly graded formal landscape features ordensely vegetated open space/natural areas on the site. Theimpervious surface must sheet flow into and through thevegetated area to promote filtration and settling. Thesevegetated features differ from Vegetated Filter Strips (see factsheet in Chapter 6) as they collect runoff from very smallareas, more variability in dimension is allowed and they donot qualify as “treatment” techniques per Table 3-2 (Selection Matrix). Look for opportunities to use smallpockets of landscaping and strips of turf grass for this application. The ratio of impervious to pervioussurfaces must be 2:1 or less to qualify for the runoff reduction credits presented in this manual.Use of reinforced grass pavement (“grasscrete”) allows forpedestrian access without vegetation damage andreduces runoff through infiltration. Photo: AlamedaCountywide Clean Water Program.Curb cutouts deliver runoff from a parking lot to avegetated swale. Vegetation must be lower thanpavement to prevent clogging and sediment buildupat the curb. Photo: City of FremontExamples:Sidewalks – Establish a vegetated strip betweensidewalks and the curb and gutter system in the street toallow for infiltration and filtration of sidewalk runoff.Driveways – Slope residential driveways toward yardvegetation or divert flow from the driveway to the yardthrough a slotted trench or other approved means. Seethe Alternative Driveways Fact Sheet elsewhere in thischapter for more information.Plazas, patios and walkways – Consider constructingthese surfaces using porous pavement materials (seePorous Pavement fact sheet elsewhere in this chapter)to reduce imperviousness and reduce runoff. If that isnot possible, slope the impervious areas to sheet flowinto adjacent vegetated areas.Commercial parking lots – Parking lot landscape areas between stalls or at the lot perimeter (typicallyalready required by permitting agency codes) can be designed to double as stormwater quality controlmeasures. As a first choice, design these areas to treat and filter parking lot runoff by integratingvegetated swales or stormwater planters (see fact sheets for these measures in Chapter 6). For smallerlandscape pockets where it is infeasible to run the water through vegetated swales or stormwater planters,apply the disconnected pavement concept to reduce runoff. Grade the parking areas to drain to thesefeatures, with slotted curbs or curb cutouts to allow the runoff to flow into and through the vegetation (seephoto). This may help reduce the size of needed downstream treatment measures for the site.Pavement Draining to Porous PavementConsider replacing or combining conventional paved surfaces (concrete, asphalt) with porous pavedsurfaces to meet paving area requirements, in order to accept and infiltrate runoff from adjoiningimpervious surfaces. The porous pavement may be any of the variations described in the PorousPavement fact sheet presented elsewhere in this chapter.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007DP-3