Geoscience Reference
In-Depth Information
Table 12.2 Some values of C
Description of area
Runoff coefficients
Business
Downtown
0.70 to 0.95
Neighborhood
0.50 to 0.70
Residential
Single-family
0.30 to 0.50
Multi-units, detached
0.40 to 0.60
Multi-units, attached
0.60 to 0.75
Residential (suburban)
0.25 to 0.40
Apartment
0.50 to 0.70
Industrial
Light
0.50 to 0.80
Heavy
0.60 to 0.90
Parks, cemeteries
0.10 to 0.25
Playgrounds
0.20 to 0.35
Railroad yard
0.20 to 0.35
Unimproved
0.10 to 0.30
Pavement
Asphaltic and concrete
0.70 to 0.95
Brick
0.70 to 0.85
Roofs
0.75 to 0.95
Lawns, sandy soil
Flat, 2%
0.05 to 0.10
Average, 2% to 7%
0.10 to 0.15
Steep, 7%
0.15 to 0.20
Lawns, heavy soil
Flat, 2%
0.13 to 0.17
Average, 2% to 7%
0.18 to 0.22
Steep, 7%
0.25 to 0.35
(From ASCE and WPCF, 1982.)
equations are available for this purpose. The equation proposed by Kirpich (1940), on
the basis of Ramser's (1927) data, is often quoted; this can be expressed as follows
0.062
L
S
1
/
a
0
.
80
t
c
=
/
(12.21)
where
t
c
is in hours,
L
is the length of the main channel from the furthest divide to the
outlet in km, and
S
a
is the average (dimensionless) slope, that is the ratio of the fall of
the main channel from the divide to the outlet and its length. As an alternative for very
small catchments, the time of concentration can also be taken as the time to equilibrium
(6.20) obtained analytically by means of the kinematic wave method. For turbulent flow,
