Stormwater Runoff Coefficients: rational_C
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) | C min (dimensionless) | C typical (dimensionless) | description | land use | notes | return period yr (yr) | surface type | unit |
|---|---|---|---|---|---|---|---|---|---|---|
| rational_C | commercial_downtown | 0.95 | 0.7 | 0.85 | Commercial — downtown / CBD | commercial | Rooftops and paved surfaces dominate; nearly fully impervious | 10 | downtown | dimensionless |
| rational_C | commercial_downtown_100yr | 0.97 | 0.8 | 0.9 | Commercial CBD — 100-year return period | commercial | Adjusted C for 100-yr event; multiply 10-yr C by frequency factor ~1.10–1.25 per ASCE | 100 | downtown_100yr | dimensionless |
| rational_C | commercial_neighborhood | 0.75 | 0.5 | 0.65 | Commercial — neighborhood / strip mall | commercial | Parking lots with some landscaping; 60–75% impervious typical | 10 | neighborhood | dimensionless |
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