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

Chapter 5Traditional asphalt and concrete pavement can be substituted with one of severaldifferent types of porous pavements, such as pervious concrete and pavers. Thedegree of permeability varies by type of material (for example, reinforced grasspavement is more pervious than cobblestone pavers), and the appropriate type to usedepends on anticipated traffic loads and uses. There are various examples ofpervious concrete, and many examples of pavers installed throughout theSacramento area. Alternative driveways are one design application which involvesreplacing all or a portion of a standard impervious driveway with pervious materialssuch as grass or pavers. Check with the local permitting agency for any restrictionsassociated with the use of porous pavements or alternative driveway designs.Instead of using conventional roofs, which generate a lot of runoff during a rainstorm, consider installing an “green roof”, also known as an “ecoroof.” The rooffunctions like a sponge, using several inches of soil and a top layer of vegetation tocapture and slow rainwater as it flows from the rooftop to the ground. The concepthas been popular in Europe for centuries, has become more common in the PacificNorthwest and Midwest (e.g., Chicago), and is gaining popularity in California.Various green roof installations have been completed since the late 1990s in the SanFrancisco Bay Area and more recently in southern California. See the references atthe end of this chapter for more information.Disconnect Impervious SurfacesIn conventional designs, runoff and associated pollutants from impervious surfaces(such as parking lots and roof tops) flow directly to a storm drain system . In otherwords, the impervious areas are “directly connected” to the storm drains. Imperviousareas can be “disconnected” when the runoff from the area is redirected to flow overlandscaping, into stormwater planters, or through pervious pavement. In theSacramento and Roseville areas, many projects are already constructed withdisconnected roof drains, but there have been no design standards published to dateabout what to do with the runoff, short of routing it through a splash block or downspoutextender to protect the building foundation. This chapter addresses that need.This chapter introduces several measures that involve disconnecting impervioussurfaces from the storm drain system:• Disconnected Pavement• Disconnected Roof DrainsPlant More Trees To Intercept StormwaterTrees intercept stormwater and can retain a significant amount of the captured wateron their leaves and branches, allowing for evaporation and dissipation of the energyof runoff. Their root structures absorb and uptake runoff and associated pollutants.The shade provided by trees keeps the ground under the trees cooler, therebyreducing the amount of heat gained in runoff as it flows over the surface and into thestorm drain. In turn, this helps keep stream temperatures cool and healthy for fishand other aquatic life.Stormwater Quality Design Manual for the Sacramento and South Placer Regions5-2 May 2007