SW4211201_Design Calculations (Riprap)_20220113

User Input Data
Calculated Value
Reference Data
)esigned By: CFO Date: 10/12/202'
checked By: HSR Date: 10/12/202'
,ompany:
project Name:
project No.:
Site Location (City/Town) Winston-Salem
Culvert Id. 0+34
Total Drainage Area (acres) 1.08
Step 1. Determine the tailwater depth from channel characteristics below the
pipe outlet for the design capacity of the pipe. If the tailwater depth is less
than half the outlet pipe diameter, it is classified minimum railwater condition.
If it is greater than half the pipe diameter, it is classified maximum. . condition.
Pipes that outlet onto wide flat areas with no defined channel are assumed
to have a min m m. tailwater condition unless reliable flood stage elevations
show otherwise.
Outlet pipe diameter, Do (in.) 18
Tailwater depth (in.) 1
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 4.37
Velocity (ft./s) 5
Step 2. Based on the tad—i- conditions determined m step 1. enter Figunc
8 06a or Figure 8.06b_ and determine d. riprap sin and minimum apron length
(La. The d� size is the median stone size in a well -graded nprap apron.
Step 3. Determine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end from the same figure used in Step 2.
Minimum TW Maximum TW
Figure 8.06a Figure 8.06b
Riprap d5g, (ft.) 0.67
Minimum apron length, La (ft.) 10
Apron width at pipe outlet (ft.) 4.5 4.5
Apron shape Trapezoid
Apron width at outlet end (ft.) 11.5 1.5
Step 4. Determine the maximu n stone diameter
d,,,t, = 1.5 x d.
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 1.005 0
Step 5. Determine the apron thickness:
Apron thickness = 1.5 x din„
Minimum TW Maximum TW
Apron Thickness(ft.) 1.5075 0
Step 6. Fit the nprap apron to the site by making it level for the minimum
length- Li, from Figure 8 O6a or Figure 8 06b_ Extend the apron farther
downstream and along channel banks until stability is assured_ Keep the
apron as straight as possible and align it mith the flow of the receiving stream.
.Make any necessary alignment beads near the pipe outlet so that the entrance
into the receiving stream is straight.
Some locations may require lining o£the entire channel cross section to assure
stability.
It may be necessary to increase the size of nprap where protection of the
channel side slopes is necessary (Appendix &05). Where overfalls exist at
pipe outlets or flows are excessive, a plunge pool should be considered. see
page 8.06.8_

User Input Data
Calculated Value
Reference Data
)esigned By: CFO Date: 10/12/202'
checked By: HSR Date: 10/12/202'
,ompany:
project Name:
project No.:
Site Location (City/Town) Winston-Salem
Culvert Id. 6+93
Total Drainage Area (acres) 1.08
Step 1. Determine the tailwater depth from channel characteristics below the
pipe outlet for the design capacity of the pipe. If the tailwater depth is less
than half the outlet pipe diameter, it is classified minimum railwater condition.
If it is greater than half the pipe diameter, it is classified maximum. . condition.
Pipes that outlet onto wide flat areas with no defined channel are assumed
to have a min m m. tailwater condition unless reliable flood stage elevations
show otherwise.
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 0.8
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 3.86
Velocity (ft./s) 3.5
Step 2. Based on the tarlwater conditions determined m step I. enter Figunc
8 06a or Figure 8.06b_ and determine d. riprap sin and minimum apron length
(La. The d� size is the median stone size in a well -graded nprap apron.
Step 3. Determine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end from the same figure used in Step 2.
Minimum TW Maximum TW
Figure 8.06a Figure 8.06b
Riprap d5g, (ft.) 0.67
Minimum apron length, La (ft.) 9
Apron width at pipe outlet (ft.) 3.75 3.75
Apron shape Trapezoid
Apron width at outlet end (ft.) 10.25 1.25
Step 4. Determine the maximu n stone diameter
d,,,t, = 1.5 x d.
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 1.005 0
Step 5. Determine the apron thickness:
Apron thickness = 1.5 x din„
Minimum TW Maximum TW
Apron Thickness(ft.) 1.5075 0
Step 6. Fit the nprap apron to the site by making it level for the minimum
length- Li, from Figure 8 O6a or Figure 8 06b_ Extend the apron farther
downstream and along channel banks until stability is assured_ Keep the
apron as straight as possible and align it mith the flow of the receiving stream.
.Make any necessary alignment beads near the pipe outlet so that the entrance 10
into the receiving stream is straight.
Some locations may require lining o£the entire channel cross section to assure
stability.
It may be necessary to increase the size of nprap where protection of the
channel side slopes is necessary (Appendix &05). Where overfalls exist at
pipe outlets or flows are excessive, a phmge pool should be considered. see
page 8.06.8_

Figure 8.06a: Design of outlet protection from a round pipe flowing full, minimum
tailwater condition (Tw<0.5 diameter)
3�
Outlet M - Do t La
I
pipe "
diameter {lam) � I
RO
tr ter
to I
r ok PP 60
ve
50
� p
s
j � f
.4
t f l
20
i, 2 . J� f� 4 I: y 3
777777
0 2 o
CL
ho
... ..k •'• 111
V = 1S .. ..
re5 I
0
20 50 LD0 200 500 1000
Discharge (f,31see)
Curves may not be extrapolated.
Flgura 8.G6a Dosign of outlet protectwn protection from a round pipe Flowing full. minimum tailwatat cordiSion (Tw < 0.5 darrati
Rrr.1. 93 & 06.b
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