Values of Runoff Coefficient (C) for Rational Formula

 

Land Use
C
Land Use
C
Business: 
   Downtown areas 
   Neighborhood areas 

0.70 - 0.95
0.50 - 0.70 
 Lawns: 
   Sandy soil, flat, 2% 
   Sandy soil, avg., 2-7% 
   Sandy soil, steep, 7% 
   Heavy soil, flat, 2% 
   Heavy soil, avg., 2-7% 
   Heavy soil, steep, 7%

0.05 - 0.10
0.10 - 0.15
0.15 - 0.20
0.13 - 0.17
0.18 - 0.22
0.25 - 0.35
Residential: 
   Single-family areas 
   Multi units, detached 
   Munti units, attached 
   Suburban

0.30 - 0.50
0.40 - 0.60
0.60 - 0.75
0.25 - 0.40 
 Agricultural land: 
  Bare packed soil 
   *Smooth 
   *Rough 
  Cultivated rows 
   *Heavy soil, no crop 
   *Heavy soil, with crop 
   *Sandy soil, no crop 
   *Sandy soil, with crop 
  Pasture 
   *Heavy soil 
   *Sandy soil 
  Woodlands


0.30 - 0.60
0.20 - 0.50

0.30 - 0.60
0.20 - 0.50
0.20 - 0.40
0.10 - 0.25 

0.15 - 0.45
0.05 - 0.25
0.05 - 0.25 
Industrial: 
   Light areas 
   Heavy areas

0.50 - 0.80
0.60 - 0.90 
 Streets: 
   Asphaltic 
   Concrete 
   Brick

0.70 - 0.95
0.80 - 0.95
0.70 - 0.85
Parks, cemeteries
0.10 - 0.25
 Unimproved areas
0.10 - 0.30
Playgrounds
0.20 - 0.35
 Drives and walks
0.75 - 0.85
Railroad yard areas
0.20 - 0.40
 Roofs
0.75 - 0.95

*Note:  The designer must use judgement to select the appropriate "C" value within the range.  Generally, larger areas with permeable soils, flat slopes and dense vegetation should have the lowest "C" values.  Smaller areas with dense soils, moderate to steep slopes, and sparse vegetation should assigned the highest "C" values.