Gravel Bed River Option
In this option SAM uses the Limerinos (1970) equation to calculate grain
roughness on the bed, the Manning equation to calculate roughness on the
channel side slope, and the Meyer-Peter and Muller (1948) equation to calculate
sediment transport.
To access this option the "Gravel Bed River" box in the Options area must be
checked. No extra input is required; the checkbox simply sends flag to the
program to make the gravel bed calculations.
Cowan Multiplier Option
This option is currently available only for gravel bed streams. To access this
option, the "Specify Cowan Multipliers" box in Options area of the Stable
Channel Design screen must be checked see Figure 6.17. It allows the user to
provide additional bed roughness that may be added to the grain bed roughness
using the Cowan (1956) method. The additional roughness may be added to
account for factors such as surface irregularities, variability in channel shape,
obstructions, vegetation and meandering.
ntotal = m (nbase + nadditional )
where
= the base n-value, input for the bed and channel side
nbase
slopes (input elsewhere on the screens)
nadditional = the addition for surface irregularities +
the addition for variation in channel cross section +
the addition for obstructions +
the addition for vegetation.
Suggested values for these additions can be found in Cowan (1956) and Chow
(1959).
Meandering is accounted for with a meandering coefficient, m; for a straight
channel the meandering coefficient is 1.0. Appropriate values for the
meandering coefficient and additions to the grain roughness n-value can be found
in Cowan (1956) and Chow (1959).
The n-value additions and the meandering coefficient can be input for the
design reach and/or the supply reach. See Appendix C, GB record.
Example input data
Test 8A is a data set that provides the parameters for calculating the stable
channel dimension, i.e., the GC and PF records, and asks SAM.hyd to calculate
115
Chapter 6
Input Requirements and Program Output for SAM.hyd
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