where
U* = gRS = boundary shear velocity
6.25 = empirical constant for fully rough flow
(2) The equation for rough flow may be obtained by substituting a variable,
Ar, for the constant, 6.25, and gRS for U*, and then combining with the Chezy
equation.
R
V
C
= Ar + 5.75 log10
=
Equation 2-8
ks
g
U*
R
C = g Ar + 5.75 log10
Equation 2-9
k
s
Ar g
R
C = 32.6 log10 10 32.6
Equation 2-10
k s
where Ar is the Iwagaki variable for rough flow. From Keulegan's study of
Bazin's data, the value of Ar was found to have a wide range, varying from 3.23
to 16.92. Keulegan used a mean value of 6.25 for Ar.
(3) The comparable form of the equation for smooth flow is
As g
g Rn
C = 32.6 log10 10 32.6
Equation 2-11
4C
where As is the Iwagaki variable for smooth flow.
(4) The roughness equation in the transition zone is a combination of the
equations for smooth and fully rough flow as follows:
4C
ks
C = - 32.6 log10
+
Equation 2-12
As g
Ar g
R 10 32.6
g Rn 10
32.6
13
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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