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Stormwater Runoff Coefficients: SCS curve number

cn impervious C to cn open space fair 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

Civil Engineeringmethod type: SCS curve number10 rowsPage 2 of 5
method typerecord idC max (dimensionless)descriptionland usereturn period yr (yr)standardsurface typeunit
SCS curve numbercn impervious C98Paved impervious surface, HSG Cimpervious2USDA-NRCS TR-55 Table 2-2apaveddimensionless
SCS curve numbercn impervious D98Paved impervious surface, HSG Dimpervious2USDA-NRCS TR-55 Table 2-2apaveddimensionless
SCS curve numbercn industrial A81Industrial — 72% impervious, HSG Aindustrial2USDA-NRCS TR-55 Table 2-2aindustrialdimensionless
SCS curve numbercn industrial B88Industrial — 72% impervious, HSG Bindustrial2USDA-NRCS TR-55 Table 2-2aindustrialdimensionless
SCS curve numbercn industrial C91Industrial — 72% impervious, HSG Cindustrial2USDA-NRCS TR-55 Table 2-2aindustrialdimensionless
SCS curve numbercn industrial D93Industrial — 72% impervious, HSG Dindustrial2USDA-NRCS TR-55 Table 2-2aindustrialdimensionless
SCS curve numbercn open space fair A49Open space/parks — fair cover (50–75% grass), HSG Aopen space2USDA-NRCS TR-55 Table 2-2afair coverdimensionless
SCS curve numbercn open space fair B69Open space/parks — fair cover (50–75% grass), HSG Bopen space2USDA-NRCS TR-55 Table 2-2afair coverdimensionless
SCS curve numbercn open space fair C79Open space/parks — fair cover (50–75% grass), HSG Copen space2USDA-NRCS TR-55 Table 2-2afair coverdimensionless
SCS curve numbercn open space fair D84Open space/parks — fair cover (50–75% grass), HSG Dopen space2USDA-NRCS TR-55 Table 2-2afair coverdimensionless

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