2012-01-17_REVISION - M2005050 ‎(2)‎

• Permit No: M2005050
• IBM Index Class Name: REVISION
• Doc Date: 1/17/2012
• Doc Name: SPILLWAY DESIGN DISCUSSIONS
• From: TIM CAZIER
• To: JAMES PIERCE
• Media Type: D
• Archive: No

Wherever vegetative linings are proposed, a suitable temporary liner shall be provided. Separate
calculations should be provided showing sufficient capacity and adequate protection both before and
after establishment of the vegetation. Maximum shear stress and roughness coefficients for the
temporary liners should conform to Table 6 or the manufacturer's specifications. Wherever
manufacturer's specifications are used, they should be documented in the narrative. Table 8 provides
roughness coefficients for some commonly used temporary liners. Additional information on the design
and use of channel linings may be obtained from the Federal Highway Administration's Hydraulic
Engineering Circular No. 15 (April 1988). Copies of this publication may be obtained by contacting:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: [phone]
Publication No.: PB -86- 184 -835
TABLE 8
Manning's Roughness Coefficient ( "n ") for Commonly Used Temporary Channel Linings
The maximum permissible shear stresses for Riprap channel linings are given in Table 6. The value of
Manning's "n" used should be taken from Figure 3. Since the roughness coefficient varies significantly
with the size of the rock and the depth of flow, use of standard "n" values may result in undersizing of
the channel or of the riprap protection. NOTE: Due to the rapid increase in shear stress with
increasing bed slope, reno mattresses or gabions should be considered for gradients > 10%
(0.10 ft/ft).
TABLE 9
Riprap Gradation, Filter Blanket Requirements, Maximum Velocities
NSA No.
Manning's "n"
Dept Ranges
Lining Type
0 -0.5ft.
0 - 0.15 m
0.5 -2.0ft.
(0.15 - 0.61 m )
>2.0 ft
(>0.61 m
Jute Net
1 0.028
0.022
0.019
Curled Wood Mat
0.066
0.035
0.028
S nthetic Mat
0.036
0.025
0.021
The maximum permissible shear stresses for Riprap channel linings are given in Table 6. The value of
Manning's "n" used should be taken from Figure 3. Since the roughness coefficient varies significantly
with the size of the rock and the depth of flow, use of standard "n" values may result in undersizing of
the channel or of the riprap protection. NOTE: Due to the rapid increase in shear stress with
increasing bed slope, reno mattresses or gabions should be considered for gradients > 10%
(0.10 ft/ft).
TABLE 9
Riprap Gradation, Filter Blanket Requirements, Maximum Velocities
NSA No.
Graded Rock Size in
Filter Blanket Requirements`
VmaX
(ft/sec
Max.
dso*
Min.
Size NSA No.
Placement
Thickness
R -1
1.5
.75
No.8
FS -1
N/A
2.5
R -2
3
1.5
1
FS -1
N/A
4.5
R -3
6
3
2
FS -1
3
6.5
R -4
12
6
3
FS-2
4
9.0
R -5
18
9
5
FS -2
6
11.5
R -6
24
12
7
FS -3
8
13.0
R -7
30
15
12
FS -3
10
14.5
The d5o stone size is the size exceeded by 50% of the total weight of the tonnage shipped (i.e. 50%
by weight shall consist of pieces larger than the d50 stone size ").
"* This is a general standard. Soil conditions at each site should be analyzed to determine actual filter
size. A suitable woven or non -woven geotextile underlayment, used according to manufacturer's
recommendations, may be substituted for the filter stone.
363- 2134 -008 / April 15, 2000 / Page 24