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Stormwater Runoff Coefficients: rational C
lawns clay flat to rail yards
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 | return period yr (yr) | standard | surface type | unit |
|---|---|---|---|---|---|---|---|---|---|---|
| rational C | lawns clay flat | 0.22 | 0.13 | 0.17 | Lawns — heavy clay, flat slope (< 2%) | pervious | 10 | ASCE MOP 77 Table 2-2 | lawn clay | dimensionless |
| rational C | lawns clay steep | 0.45 | 0.25 | 0.35 | Lawns — heavy clay, steep slope (> 7%) | pervious | 10 | ASCE MOP 77 Table 2-2 | lawn clay steep | dimensionless |
| rational C | lawns sandy avg | 0.2 | 0.1 | 0.15 | Lawns — sandy soil, average slope (2–7%) | pervious | 10 | ASCE MOP 77 Table 2-2 | lawn sandy avg | dimensionless |
| rational C | lawns sandy flat | 0.15 | 0.05 | 0.1 | Lawns — sandy soil, flat slope (< 2%) | pervious | 10 | ASCE MOP 77 Table 2-2 | lawn sandy | dimensionless |
| rational C | lawns sandy steep | 0.25 | 0.15 | 0.2 | Lawns — sandy soil, steep slope (> 7%) | pervious | 10 | ASCE MOP 77 Table 2-2 | lawn sandy steep | dimensionless |
| rational C | park cemetery | 0.35 | 0.1 | 0.2 | Parks, cemeteries, golf courses | parks | 10 | ASCE MOP 77 Table 2-2; TR-55 Table 2-2 | park cemetery | dimensionless |
| rational C | parking asphalt | 0.95 | 0.75 | 0.85 | Parking lots — paved (asphalt/concrete) | transportation | 10 | ASCE MOP 77 Table 2-2 | paved parking | dimensionless |
| rational C | pasture meadow | 0.3 | 0.1 | 0.2 | Pasture / meadow — good condition | agriculture | 10 | ASCE MOP 77 Table 2-2 | pasture | dimensionless |
| rational C | playgrounds | 0.4 | 0.2 | 0.3 | Playgrounds — grassed | parks | 10 | ASCE MOP 77 Table 2-2 | playground | dimensionless |
| rational C | rail yards | 0.45 | 0.2 | 0.35 | Railroad yard (ballast and gravel) | transportation | 10 | ASCE MOP 77 Table 2-2 | rail yard | dimensionless |
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