Energy Slope Calculation
This option allows the energy slope to become the dependent variable in the
uniform flow equation:
S = f (Q, n,W, D, z)
Equation 2-35
The calculations are trial and error and convergence may be difficult. The
Brownlie n-value relationships may result in convergence failure due to the
discontinuity at the transition between lower and upper regime flow. SAM.hyd
prints a message to the output file when convergence fails.
Hydraulic Roughness Calculation
This option allows the n-value to become the dependent variable in the
uniform flow equation.
n = f (Q,W, D, z, S)
Equation 2-36
It is especially useful for calculating unknown roughness for one section of the
cross-section when roughness in known for other sections of the cross-section.
This calculation, like the other solutions of the uniform flow equation which
involve compositing, is trial and error. A simple solution of the Manning
equation for the total cross section is used to calculate the first trial roughness.
Roughness can be specified in some panels and calculated for others. If a
roughness in a panel is input, the program will convert it to a ks using the
Keulegan equation for fully rough flow unless the equation specified is Strickler.
However, only the Keulegan or Strickler equations can be used to calculate
roughness. If the program is asked to calculate roughness using the Manning's
equation option then it automatically uses the Strickler equation. If the program
is asked to calculate roughness using the Brownlie or Limerinos equation then
there is nothing to calculate because the roughness has been implicitly
determined by the bed gradation used. If the program is asked to calculate
roughness using the Grass equations then there is still nothing to calculate
because the roughness is again implicitly determined by the Grass equation
chosen.
NOTE: Limerinos, Brownlie and the Grass equations are not to be used with
negative roughness values because there is nothing to calculate -- the roughness
is implicitly determined by the bed gradation or the grass.
29
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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