7910

• UCREFRP Catalog Number: 7910
• Author: Bovee, K. D. and R. T. Milhous.
• Title: Hydraulic Simulation In Instream Flow Studies
• USFW Year: 1978.
• USFW - Doc Type: Theory And Techniques, Instream Flow Information Paper No. 5.
• Copyright Material: NO

V = average velocity in a channel
C = Chezy constant (empirically derived for each channel).
R = hydraulic radius
S = Se, slope of the energy grade line
In 1889, an Irish engineer, Robert Manning presented a velocity
equation, known in its present form as the Manning equation:
V = 1.486 R2I3Se? (3)
n
where,
V = the mean velocity in the channel, in feet per second.
R = the hydraulic radius, in feet
S = slope of the energy grade line
ne= coefficient of roughness, referred to as Manning 's n.
The version'of the Manning equation given as equation 2, is in
English units. If metric measurements are input for R, the term 1.486
is omitted from the equation, and V will be given in metric equivalents
to R.
The discharge may be calculated using either of the above velocity
equations, and substituting for V in the continuity equation (equation
1). The Chezy equation for determining discharge becomes:
Q = C Rh Se A (4)
and the Manning equation may be expressed as:
Q = 1.486 R213Se? A (5)
n
The range in Manning's n reported by Henderson (1966) are:
Man-made channels
Concrete 0.012 - 0.0I4
Rubble set in concrete 0.017
Earth, smooth, no weeds 0.020
Earth, some stones and weeds 0.025
Natural river channels
Clean and straight. 0.025 - 0.030
Winding, with pools and shoals 0.033 - 0.040
Very weedy, winding and overgrown 0.075 - 0.150
Clean straight alluvial channels 0.031 K116
In the last expression, K is the size of bed material for which 75
r ~ percent of the bed material is smaller and 25 percent larger, measured
G