TABLE 1: URBAN RUNOFF COEFFICIENTS (1)
Type of Surface
Runoff Coefficient "C"
Type of Surface
Runoff Coefficient "C"
Asphalt
0.85
Concrete
0.90
Roof
0.90
Lawns (Sandy)
   Flat (0-2% Slope)
0.07
   Rolling (2-7% Slope)
0.12
   Steep (greater than 7%)
0.17
Lawns (Clay)
   Flat (0-2% Slope)
0.15
   Rolling (2-7% Slope)
0.20
   Steep (greater than 7%)
0.30
 
(1)   From HERPICC Stormwater Drainage Manual - Revised July 1994.