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The following table shows SCS curve number values, according to the SCS method for runoff calculations. Please scroll down for a description of the soil groups.
SCS Curve Numbers (CN)
Description of Land Use Hydrologic Soil Group
A B C D
Paved parking lots, roofs, driveways 98 98 98 98
Streets and Roads
Paved with curbs and storm sewers 98 98 98 98
Gravel 76 85 89 91
Dirt 72 82 87 89
Cultivated (Agricultural Crop) Land
Without conservation treatment (no terraces) 72 81 88 91 With conservation treatment (terraces, contours) 62 71 78 81 Pasture or Range Land
Poor (<50% ground cover or heavily grazed) 68 79 86 89
Good (50-75% ground cover; Not heavily grazed) 39 61 74 80 Meadow (grass, no grazing, mowed for hay) 30 58 71 78
Brush (good, >75% ground cover) 30 48 65 73
Woods and Forests
Poor (small trees/brush destroyed by over-grazing or burning) 45 66 77 83 Fair (grazing but not burned; some brush) 36 60 73 79
Good (no grazing; brush covers ground) 30 55 70 77
Open Spaces (lawns, parks, golf courses, cemeteries, etc.) Fair (grass covers 50 – 75% of area) 49 69 79 84
Good (grass covers >75% of area) 39 61 74 80
Commercial and Business Districts (85% impervious) 89 92 94 95 Industrial Districts (72% impervious) 81 88 91 93
Residential Areas
1/8 acre lots, about 65% impervious 77 85 90 92
1/4 acre lots, about 38% impervious 61 75 83 87
1/2 acre lots, about 25% impervious 54 70 80 85
1 acre lots, about 20% impervious 51 68 79 84
Group A Soils: High infiltration (low runoff). Sand, loamy sand, or sandy loam. Infiltration rate > 0.3 in/hr when wet.
Group B Soils: Moderate infiltration (moderate runoff). Silt loam or loam. Infiltration rate 0.15 – 0.30 in/hr when wet.
Group C Soils: Low infiltration (moderate to high runoff). Sandy clay loam. Infiltration rate 0.05 – 0.150 in/hr when wet.
Group D Soils: Very low infiltration (high runoff). Clay loam, silty clay loam, sandy clay, silty clay, or clay. Infiltration rate 0 – 0.05 in/hr when wet.