Table 5a
U.S. Corps of Engineers (mild) Method Riprap Size Calculation
J:\11JOBS\113-82323 Bear Lodge Mine\Surface Water\H&H calculations\Bear Lodge Riprap Rev D.xlsm
Page 1 of 2
Golder Associates
1/14/2014
Riprap Channel Evaluation
Date:
12/6/13
Bear Lodge Mine
By:
AMS
PROJECT NO.:
113-82323
Chkd:
MBR
Apprvd:
RP
Reach Designation
Design
Flow
Q (cfs)
Normal
Flow Depth
d (ft)
Depth
Averaged
Velocity
V (ft/s)
Velocity
Distribution
Coefficient
C
V
Channel
Side Slopes
Correction
K
1
Calculated
Particle
Size
D
30
(ft)
Riprap
Size
D
50
(in)
Recommended
Riprap D
50
(inches)
BC DIV U
280.7
2.02
6.60
1.00
0.97
0.20
3.2
6.0
BC DIV L
370.7
2.35
7.17
1.00
0.97
0.24
3.8
6.0
USACE Paper EM 1110-2-1601, 6/30/94
Inputs below as determined in EM 1110-2-1601, 6/30/94
1.1
S
f
: Minimum safety factor of 1.1 for moderate debris impact
0.3
C
s
: Value of 0.30 for angular rock
165
γ
s:
Density of solids (pcf)
2.2
Cg: Gradation Coefficient (D
85
/D
15
)
2.0
T: Riprap Thickness (x D
50
)
0.910
C
T
: Correction for thickness > 1.5 * D
50
Note: A C
V
of 1.25 should be used downstream of concrete channels due to the
difference in velocity profiles
Riprap D50 determined as recommended in EM 1110-2-1601, 6/30/94
USACE Method
Riprap Calculations for Mild Riprap (Bed Slopes <2%)
5.2
1
30
−
=
gdK
V
dCCCS D
w s
w
T V s f
γ
γ
γ
3
1
15
85
30
50
=
D
DD D
