using negative values for TR/TMIN . CS = 0.30 is multiplied by CIFRSS when
TR/TMIN is negative -- the default for CIFRRS is 1.25 which yields CS = 0.375.
The vertical velocity distribution coefficient, CV , varies as a function of the
ratio of bend radius, R, to channel width, W. CV = 1.0 in straight channels, for
the inside of bends, and for bends where R/W is 26. The equation for CV
when R/W < 26 is:
R
= 1.283 - 0.2 log10
CV
W
The maximum value allowed for CV is 1.283. CV is determined in SAM
using either a calculated water-surface width or a water-surface width prescribed
on record RS, and a bend radius prescribed as variable on the RR record.
The side slope correction factor, K1 , is calculated by SAM from geometric
input and the empirical side slope correction graph in EM 1110-2-1601. The side
slope steepness angle is calculated for each panel. When the steepness is milder
than 1V:3H the side slope correction factor is 1.0. The steepest side slope
allowed is 1V:1.5H.
The bend correction factor, CB , which is the same as VSS / VAVE in EM 1110-
2-1601, is determined differently depending on whether the channel is a natural
channel or a trapezoidal channel. In SAM, a trapezoidal cross section is
identified by setting NTRAP on the RR record equal to 1. If no value is
assigned a natural channel is assumed. CB is calculated in SAM as a function of
the R/W ratio. For trapezoidal channels:
R
1.48 ≤ C B ≤ 0.82
C B = 1.71 - 0.78 log10
W
and for natural channels:
R
1.58 ≤ C B ≤ 0.90
= 1.74 - 0.52 log10
CB
W
NOTE: THESE DESCRIPTIONS AND CODING FOR CB REFLECT 1991
GUIDANCE.
When riprap calculations are made using known velocity and depth, care must
be taken in defining the input variables. Depth is the depth of water at the toe of
the riprap. SAM will adjust the depth to 0.8 D as prescribed in EM 1110-2-1601
(USACE 1991, 1994). If the local depth averaged velocity at 20 percent up-slope
102
Chapter 6
Input Requirements and Program Output for SAM.hyd
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