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

Runoff Reduction Credits for Disconnected PavementEfficiency multipliers were taken from Denver manual.Variation/ApplicationRunoff Reduction CreditsPavement Draining to LandscapingResidentialCommercialRunoff Reduction Credits can be obtained for disconnection of sidewalks (simplified inAppendix D-1, Form D-1b) and driveways (see Alternative Driveways Fact Sheet,simplified in Form D-1d).Runoff Reduction Credits can be obtained for use of landscaping to disconnect impervioussurfaces. Credit can apply to 100% of up to 1000 square feet of pavement draining to eachproperly designed vegetated area. (Source: Contra Costa Clean Water Program)Pavement Draining to Porous Pavement (Source: Denver)CommercialRunoff Reduction Credits can be obtained for disconnected impervious surfaces with theamount of credit dependent on the ratio of impervious surfaces to pervious surfaces. Morecredit is given for lower ratios. If the impervious surface area equals no more than half thearea of the porous surface, then credit is given for the entire impervious surface. As the ratioincreases above 0.5, the treatment provided is decreased resulting in a lower infiltrationfactor. Credit is not given for ratios above 2.0. Credit allowed for specificimpervious/pervious ratios are listed below:Impervious Area / Porous Area Ratio Efficiency Multiplier≤0.5 1.000.5 - 1.0 0.831.0 - 1.5 0.711.5 - 2.0 0.55The efficiency of the porous pavement in infiltrating sheet flow is dependent on the type ofpavement used. The following are the efficiency factors for different pavement types:Porous Pavement TypeEfficiency MultiplierModular Block Pavement 0.75Cobblestone Block Pavement 0.40Reinforced Grass Pavement 1.00Poured Porous Concrete Pavement 0.60Porous Gravel Pavement 0.75Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007 Appendix D-3 Page 2