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Home My WebLink AboutCHERRY STREET COTTAGES - PDP - PDP160041 - SUBMITTAL DOCUMENTS - ROUND 2 - STORMWATER-RELATED DOCUMENTS (15)Page 4 Runoff Coefficient vs. Watershed Imperviousness Based on Runoff Coefficient estimating equation published by Urbonas, et.al. (1990) & WEF (1998) Basic equation for NRCS Soil Types C & D: CCD = KCD + (0.858*i3 - 0.786*i2 + 0.774*i + 0.04) Basic equation for NRCS Soil Type A: CA = KA + (1.31*i3 - 1.44*i2 + 1.135*i - 0.12) in which use values for CA > 0 in which: i = Ia/100, imperviousness ratio Ia = watershed imperviousness in percent CA = Runoff Coefficient for NRCS Soil Type A KA = Correction factor for CA when the storm return period is greater than 2-years CCD = Runoff Coefficient for NRCS Soil Types C and D KCD = Correction factor for CCD when the storm return period is greater than 2-years NRCS Soil Types 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr C & D 0.00 [-0.10*i+0.11] [-0.18*i+0.21] [-0.28*i+0.33] [-0.33*i+0.40] [-0.39*i+0.46] A 0.00 [-0.08*i+0.09] [-0.14*i+0.17] [-0.19*i+0.24] [-0.22*i+0.28] [-0.25*i+0.32] Imperv. Ratio ( i) 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 0.00 0.04 0.15 0.25 0.37 0.44 0.50 -0.12 -0.03 0.05 0.12 0.16 0.20 0.05 0.08 0.18 0.28 0.39 0.46 0.52 -0.07 0.02 0.10 0.16 0.20 0.24 0.10 0.11 0.21 0.30 0.41 0.48 0.53 -0.02 0.06 0.14 0.20 0.24 0.28 0.15 0.14 0.24 0.32 0.43 0.49 0.54 0.02 0.10 0.17 0.23 0.27 0.30 0.20 0.17 0.26 0.34 0.44 0.50 0.55 0.06 0.13 0.20 0.26 0.30 0.33 0.25 0.20 0.28 0.36 0.46 0.52 0.56 0.09 0.16 0.23 0.29 0.32 0.35 0.30 0.22 0.30 0.38 0.47 0.53 0.57 0.13 0.19 0.25 0.31 0.34 0.37 0.35 0.25 0.33 0.40 0.48 0.54 0.57 0.16 0.22 0.28 0.33 0.36 0.39 0.40 0.28 0.35 0.42 0.50 0.55 0.58 0.19 0.25 0.30 0.35 0.38 0.41 0.45 0.31 0.37 0.44 0.51 0.56 0.59 0.22 0.27 0.33 0.37 0.40 0.43 0.50 0.34 0.40 0.46 0.53 0.57 0.60 0.25 0.30 0.35 0.40 0.42 0.45 0.55 0.37 0.43 0.48 0.55 0.59 0.62 0.29 0.33 0.38 0.42 0.45 0.47 0.60 0.41 0.46 0.51 0.57 0.61 0.63 0.33 0.37 0.41 0.45 0.47 0.50 0.65 0.45 0.49 0.54 0.59 0.63 0.65 0.37 0.41 0.45 0.49 0.51 0.53 0.70 0.49 0.53 0.57 0.62 0.66 0.68 0.42 0.45 0.49 0.53 0.54 0.56 0.75 0.54 0.58 0.62 0.66 0.69 0.71 0.47 0.50 0.54 0.57 0.59 0.61 0.80 0.60 0.63 0.66 0.70 0.73 0.74 0.54 0.56 0.60 0.63 0.64 0.66 0.85 0.66 0.68 0.71 0.75 0.78 0.79 0.61 0.63 0.66 0.69 0.70 0.72 0.90 0.73 0.75 0.77 0.80 0.83 0.83 0.69 0.71 0.73 0.76 0.77 0.79 0.95 0.80 0.82 0.84 0.87 0.89 0.89 0.78 0.80 0.82 0.84 0.85 0.86 1.00 0.89 0.90 0.92 0.94 0.96 0.96 0.89 0.90 0.92 0.94 0.95 0.96 Notes: For Type B Soils, use the average of coefficients CCD and CA. When the Runoff Coefficient in above table is < 0, use 0. When compositing the Runoff Coefficient for different soil types, use the table values above regardless if they are < 0. Type C and D NRCS Hydrologic Soil Groups Type A NRCS Hydrologic Soils Group Values of Runoff Coefficient CCD Values of Runoff Coefficient CA Storm Return Period Values of Correction Factors KCD & KA 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Runoff Coefficient Page 5 I. One-hr Precipitation Values for Metro Denver Area Return period in years 2 5 10 50 100 Depth in inches 0.93 1.35 1.61 2.20 2.60 II. Recommended Runoff Coefficients for Metro Denver Business: Commercial areas Neighborhood areas Residential: Single-family Multiunit (detached) Multiunit (attached) Half-acre lot or larger Apartments Industrial: Light areas Heavy areas Parks, cemeteries: Playgrounds: Schools: Railroad yard areas: Undeveloped areas: Historical Flow Analysis Greenbelts, agricultural Off-site flow analysis (when land use not defined) Streets: Paved Gravel (packed) Driveways and sidewalks: Roofs: Lawns, sandy soil Lawns, clayey soil *Refer to Figures RO-3 through RO-5 in Runoff Chapter of USDCM. Percent Imper- viousness Land Use or Surface Characteristics 95 85 * 60 75 * 80 80 90 5 10 50 15 2 45 0 0 100 40 90 90 Watershed Impervious Ratio Runoff Coefficient vs. Imperviousness NRCS Hydrologic Soils C & D 100-yr 25-yr 10-yr 5-yr 2-yr 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Runoff Coefficient Watershed Impervious Ratio Runoﬀ Coeﬃcient vs. Imperviousness NRCS Hydrologic Soil A 100-yr 25-yr 10-yr 5-yr 2-yr