If the roughness height, k s , of the bank is known, then it can be used instead
of Manning's roughness coefficient to define bank roughness. The model uses
Strickler's equation to calculate the bank roughness coefficient
1
ns = 0.039 k s
6
where k s is the roughness height in feet.
Composite hydraulic parameters are partitioned in the manner proposed by
Einstein (1950),
A = Rb Pb + Rs Ps
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 (equal velocity method
of compositing).
Sediment transport for the gravel-bed option is calculated using the Meyer-
Peter Muller equation:
2
3
1
γ s -γ w
kr
γ
3
2
3
Rb S = 0.047 (γ s - γ w ) d m + 0.25 w
2
γw
gs
3
g
k′
γ
r
s
where:
k r = total bed roughness = 1
nb
1
k r′ = particle roughness =
′
nb
γ w = specific weight of water, lbs/ft3 or N/m3
γ s = specific weight of sediment
d m = median sediment size, ft or m
g s = sediment transport in lbs/sec-ft or N/sec-m
Rb = bed hydraulic radius in ft or m
and
40
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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