FLOOD03351

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Hydraulic Design of Flood Control Channels
• Date: 7/1/1991
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

EM 1110-2-1601
1 Jul 91

b, Friction losses,

(1) The importance that friction plays in the determi-
nation cf flow characteristics in channels cannot be over-
stressed. Three equations (Chezy's. Manning's. and
Darcy's) are in genetal use for the determination of losses
due to friction. These equations expressed as friction
slope Sf. i.e.. slope of the energy grade line. are

(a) Chezy:

S . v2
f -
COR

(2-1)

(b) Manning:

V2n2
Sf .
2.21R4/~

(2-2)

(c) Darcy:

S . fV2
f m<g

(2-3)

where

v = velocity

C = Chezy coefficient

f = Darcy-Weisbach resistance
coefficient

g = acceleration of gravity

The relation between the coefficients in these equations
can be expressed as

C . Rl/6 . 10.8
.l.. 4l:lb n-- fIn"

(2-4)

(2) When determining friction coefficients. it should
be recognized that the energy grade line and therefore the
friction coefficient include uniformly occumng turbulence
and eddy losses as well as the friction loss. Equivalent

2-2

roughness for the s:une reason. Special. locally occurring
turbulence and eddy losses are to be determined sepa-
rately as covered in hydr:wlic textbooks and elsewhere in
this manual.

c. Friction coefficients,

(1) The equations for using equivalent roughness to
determine friction coefficients (plate 3) are

(a) For hydraulically smooth channels

(5.2Rn)
C . 32.6 loglO t ~

(2-5)

(b) For hydraulically rough channels

C. 32.6 loglO (12/R)

(2-6)

where R" is the Reynolds number.

(2) For the channel surlace to be hydraulically
smooth. the equivalent roughness must be less than the
critical value given by paragraph 8-12 of Chow (1959).

kc . (* )(~)

(2-7)

where v is the kinematic viscosity of water.

(3) Most channels (including concrete.lined chan-
nels) with appreciable velocity are hydraulically rough.
Plates 4 and 5 are furnished as an aid for determining
friction coefficients from equivalent roughness. Irrigation
and power canals generally fall in the transition zone
shown in Plate 3.

(4) Table 2-1. extracted from HDC sheets 631 to
631-2, provides accepClble equivalent roughness values
for SlI3ight. concrete,lined channels.

(5) See Chapter 3 for friction coefflcients for riprap.

(6) Values of k for natural river channels usually
fall between 0.1 and 3,0 ft (see Table 8-1 of Chow