function of bed-material grain size, channel-forming discharge, bed-material
sediment concentration, and bank composition.
0.5
Q
W = FB
Equation 2-41
FS
F B = 1.9
d 50
Equation 2-42
1
Q
D= FS 2
3
Equation 2-43
FB
0.875
FB
S=
Equation 2-44
0.125
C
3.63 g
1+
0.25
W
D
0.25
2,330
ν
where
W = channel width - ft
FB = bed factor
FS = side factor
Q = water discharge -cfs
d50 = median grain size of bed material - mm
D = depth - ft
S = slope
C = bed-material sediment concentration - in parts per million
g = acceleration of gravity - ft/sec2
υ = kinematic viscosity - ft2/sec
The results are true regime values only if Q is the channel forming discharge.
However, a width, depth and slope will be calculated for any discharge by these
equations.
Blench suggests that the following values be used for the side factor:
FS = 0.10 for friable banks
FS = 0.20 for silty, clay, loam banks
FS = 0.30 for tough clay banks
In order to calculate the Blench regime dimensions, the side factor, bed-
material sediment concentration, and the bed-material gradation should be input.
SAM.hyd sets default values for the Blench variables if none are specified: FS =
0.20, C = 0.0, and d50 = 0.25 mm.
34
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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