2.5
γ
0.5
V AVE C B
d 30cr = S f C S CV CT D
w
Equation 2-39
γ -γ
s w
K1 g D
where
d30CR = Critical d30 (i.e. minimum d30) size for stable riprap
Sf = Safety factor
CS = Coefficient of incipient failure
CV = vertical velocity coefficient
CT = coefficient for riprap thickness
D = local water depth
γw = unit weight of water
γs = unit weight of riprap
VAVE = average channel velocity
CB = bend correction for average velocity (VSS/VAVE)
K1 = Correction for side slope steepness
g = Acceleration of gravity
Required input data for simple riprap calculations are: average channel
velocity, depth at the toe of the riprap, channel width, side slope, bend radius,
bend angle, riprap specific weight, and whether the cross-section is trapezoidal or
natural.
Riprap Gradation Tables
Size and specific gravity of available riprap are needed for this calculation,
and the 13 standard riprap sizes shown in EM 1110-2-1601 are encoded into
SAM.hyd as shown in the Table 6. Calculations begin with the smallest size
stone and continue until a stable size is reached.
Quarry-Run Stone
A known riprap gradation table may be specified in SAM. This input is not
currently available in SAMwin This option is useful for quarry-run riprap where
the gradation is known. Up to 5 sizes of quarry run riprap can be encoded.
These gradations should be entered one size per record starting with the smallest
and ending with the largest size. When this information is present, riprap size
computations use the quarry run stone. When quarry run stone is prescribed,
those stone sizes are used in lieu of the gradation tables encoded in SAM.
31
Chapter 2
Theoretical Basis for SAM.hyd Calculations
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