Environmental Engineering Reference
In-Depth Information
Table 2.3
C
faCTo
rs
Type of Pipe
C
Factor
Asbestos cement
140
Brass
140
Brick sewer
100
Cast iron
10 years old
20 years old
110
90
Ductile iron (cement lined)
140
Concrete or concrete lined
Smooth, steel forms
Wooden forms
Rough
140
120
110
Copper
140
Fire hose (rubber-lined)
135
Galvanized iron
120
Glass
140
Lead
130
Masonry conduit
130
Plastic
150
Steel
Coal-tar-enamel lined
New unlined
Riveted
150
140
110
Tin
130
Vitrified
120
Wood stave
120
Source:
Adapted from Lindeburg, M.R.,
Civil
engineering reference manual
,
4th ed., Professional Publications,
San Carlos, CA, 1986, p. 3-20.
Table 2.3). Generally, the
C
factor decreases by one with each year of
pipe age. Flow for a newly designed system is often calculated with a
C
factor of 100, based on averaging it over the life of the pipe system.
Note:
An alternative to calculating the Hazen-Williams formula, called
an
alignment chart
, has become quite popular for fieldwork. The align-
ment chart can be used with reasonable accuracy.
2.10.3.2.2 Slope
Slope
is defined as the head loss per foot. In open channels, where
the water flows by gravity, slope is the amount of incline of the pipe
and is calculated as feet of drop per foot of pipe length (ft/ft). Slope is
designed to be just enough to overcome frictional losses, so the velocity
remains constant, the water keeps flowing, and solids will not settle in
the conduit. In piped systems, where pressure loss for every foot of pipe
is experienced, slope is not provided by slanting the pipe but instead by
adding pressure to overcome friction.
