1
6
ns = 0.039 k s
Equation 2-49
where ks is the roughness height, in ft. For riprap, ks should be set equal to the
minimum design d90.
Composite hydraulic parameters are partitioned in the manner proposed by
Einstein (1950):
A = Rb Pb + Rs Ps
Equation 2-50
where:
A = total cross-sectional area
Pb = perimeter of the bed
Ps = perimeter of the side slopes
This method assumes that the average velocity for the total cross section is
representative of the average velocity in each subsection.
Concentration, C, in ppm, is calculated using the Brownlie sediment transport
equation, which is also a regression equation and is based on the same extensive
set of flume and field data used to develop his resistance equations. This
equation was chosen because of its compatibility with the resistance equations,
which are coupled with the sediment transport equation in the numerical solution:
-0.3301
C = 9022 ( F g - F go )1.978 S 0.6601 Rb
Equation 2-51
d 50
4.596 τ *o0.5293
F go =
Equation 2-52
0.1405
0.1606
σ
S
τ * o = 0.22 Y + 0.06 (10)-7.7 Y
Equation 2-53
where
37
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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