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Stormwater Runoff Coefficients: SCS curve number
cn res 1 2ac C to cn res 1 8ac D
Rational Method runoff coefficients (C values) by land use/surface type and return period, plus SCS/NRCS curve numbers (CN) by hydrologic soil group (A/B/C/D) and land cover/condition — from ASCE MOP 77, FHWA HEC-22, USDA-NRCS TR-55, and NEH-630
| method type | record id | C max (dimensionless) | description | land use | return period yr (yr) | standard | surface type | unit |
|---|---|---|---|---|---|---|---|---|
| SCS curve number | cn res 1 2ac C | 80 | Residential 1/2-acre lots (25% impervious), HSG C | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 2 acre lot | dimensionless |
| SCS curve number | cn res 1 2ac D | 85 | Residential 1/2-acre lots (25% impervious), HSG D | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 2 acre lot | dimensionless |
| SCS curve number | cn res 1 4ac A | 61 | Residential 1/4-acre lots (38% impervious), HSG A | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 4 acre lot | dimensionless |
| SCS curve number | cn res 1 4ac B | 75 | Residential 1/4-acre lots (38% impervious), HSG B | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 4 acre lot | dimensionless |
| SCS curve number | cn res 1 4ac C | 83 | Residential 1/4-acre lots (38% impervious), HSG C | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 4 acre lot | dimensionless |
| SCS curve number | cn res 1 4ac D | 87 | Residential 1/4-acre lots (38% impervious), HSG D | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 4 acre lot | dimensionless |
| SCS curve number | cn res 1 8ac A | 77 | Residential 1/8-acre lots (65% impervious), HSG A | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 8 acre lot | dimensionless |
| SCS curve number | cn res 1 8ac B | 85 | Residential 1/8-acre lots (65% impervious), HSG B | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 8 acre lot | dimensionless |
| SCS curve number | cn res 1 8ac C | 90 | Residential 1/8-acre lots (65% impervious), HSG C | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 8 acre lot | dimensionless |
| SCS curve number | cn res 1 8ac D | 92 | Residential 1/8-acre lots (65% impervious), HSG D | residential | 2 | USDA-NRCS TR-55 Table 2-2a | 1 8 acre lot | dimensionless |
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