Table 5
U.S. Corps of Engineers (Steep) Method Riprap Size Calculation
J:\11JOBS\113-82323 Bear Lodge Mine\Surface Water\H&H calculations\Bear Lodge Riprap Rev D.xlsm
Page 2 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)
Unit Flow
(ft
2
/sec)
Flow
Concentration
Factor
Calculated
Particle
Size D
30
(ft)
Riprap
Size D
50
(inches)
Recommended
Riprap D
50
(inches)
WRF 1
299.8
1.34
12.48
1.25
0.55
8.5
9
WRF 2a
417.1
1.62
16.79
1.25
0.67
10.4
12
WRF 2b
417.1
1.62
16.79
1.25
0.67
10.4
12
WRF 3
556.8
1.90
21.66
1.25
0.79
12.3
12
WRF DIV W
36.6
0.44
3.24
1.25
0.38
6.0
9
PIT DIV S
48.5
0.74
5.69
1.25
0.60
9.4
12
PIT DIV N1
65.1
0.80
7.07
1.25
0.76
11.9
12
PIT DIV N2
101.2
1.07
8.21
1.25
0.58
9.0
9
PD-N
157.5
1.31
11.30
1.25
0.51
8.0
9
PD-S
70.4
0.65
5.89
1.25
0.54
8.5
9
* Reach HR-U is consumed by the Reserve Pit
USACE Paper EM 1110-2-1601, 6/30/94
Inputs below as determined in EM 1110-2-1601, 6/30/94
2.2
Cg: Gradation Coefficient (D
85
/D
15
)
Riprap D50 determined as recommended in EM 1110-2-1601, 6/30/94
1.25 Flow Concentration Factor (1.25 from USACE steep riprap method)
USACE Method
Riprap Calculations for Steep Riprap (Bed Slopes >2% but <20%)
31
32
555 .0
30
95.1
g
q S
D
=
3
1
15
85
30
50
=
D
DD D
