Bed Form Roughness Prediction is made using Brownlie's (1983) method. It
uses velocity, hydraulic radius, slope, particle specific
gravity, d50 and the geometric standard deviation of the
bed sediment mixture.
Cross Section Velocity is printed for comparison with the velocity criteria for
stable channel design.
Shear Stress
is printed for comparison with the boundary shear stress
criteria for stable channel design.
Riprap Size
can be requested. If the calculated bed shear stress is
greater than Shield's critical value, the program will
notify the user.
Effective Width, Depth and Velocity are calculated, printed, and written to an
input file for use in sediment transport calculations,
SAM.sed.
Equivalent Hydraulic Radius and n-Value are calculated and printed for each
subsection in the cross section after the normal depth
calculations are completed.
Also, there are two options for coding the cross section. Single or compound
channels can be prescribed by defining the bottom width and side slopes for
simple triangular, rectangular or trapezoidal shapes. For example, Figure 2.1A
shows a low flow channel, a normal flow channel, and a high flow berm.
Complex channels can be prescribed by defining the station and elevation
coordinates, as on X1 and GR records in HEC-2/HEC-6. Figure 2.1B shows a
typical complex cross section as an example of what could be coded in this
format.
Normal Depth Calculations
Normal depth is calculated using one of five uniform flow equations, or one
of five USDA Soil Conservation Service (SCS) equations for grass-lined
channels. Different equations may be used in different panels. An iterative
procedure is used to converge on the specified total discharge. Then a composite
Manning's roughness coefficient and the effective hydraulic parameters are
calculated for the cross section.
Manning Roughness Equation When the hydraulic roughness is prescribed as
n-values, the Manning equation is used to determine normal depth.
8
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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