The runoff coefficients to be used in the rational method shall be those indicated
in tables 1 and 2. In lieu of providing average block calculations, the engineer for
the subdivision may use the table 7.19.3 as applicable. In addition, for any drainage
analysis performed using the SCS method, the designer shall select curve numbers in
accordance with Urban Hydrology for Small Watersheds Technical Release 55 (TR55) and
tables 7.19.4 and 7.19.5.
TABLE 1. RATIONAL METHOD RUNOFF COEFFICIENTS
Development/Subdivision Type
Runoff
Coefficient
Residential:
Single-family detached
0.30 to 0.50
Two-family (duplex)
0.40 to 0.60
Single-family and multifamily attached
0.60 to 0.75
Commercial, retail and office:
Downtown area
0.70 to 0.95
Neighborhood and outlying areas
0.50 to 0.70
Industrial:
Light industry
0.50 to 0.80
Heavy industry
0.60 to 0.90
Parks and cemeteries
0.10 to 0.25
Playgrounds
0.20 to 0.40
Railroad yard areas
0.20 to 0.40
Vacant, open space and unimproved areas
0.10 to 0.30
TABLE 2. RUNOFF COEFFICIENTS FOR AVERAGE BLOCK CALCULATIONS
