SW6210202_RIPRAP B_20210406

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Designed By: Steve Waldron Date: 8/17/2020
Checked By: Ryan Jones Date: 8/17/2020
Company: LOWE ENGINEERS
Project Name: SOF OPERATIONS FACILITY
Project No.: 19-0049
Site Location (City/Town) FT. BRAGG
Culvert Id. B
Total Drainage Area (acres) 1.38
Step 1. Determine the tall -water 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 mirumiuu tailvater 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 minimum tailwater condition unless reliable flood stage elevation%
show otherwise.
Outlet pipe diameter, Do (in.)
Tailwater depth (in.)
Minimum/Maximum tailwater?
Discharge (cfs)
Velocity (ft./s)
18
8
Min TW (Fig. 8.06a)
8.18
12.1
Step 2. Based on the tailwater conditions determined in step I. enter Figure
8.06a or Figure 8.06b, and determine d5o riprap size and minimum apron length
(L). The d5o 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 d50, (ft.) 0.5
Minimum apron length, La (ft.) 10
Apron width at pipe outlet (ft.) 4.5 4.5
Apron shape
Apron width at outlet end (ft.) 11.5 1.5
Step 4. Deternnune the maximum stone diameter=
dMX = I.5 X d..,o
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5. Deternune the apron thickness:
Apron Thickness(ft.)
Apron thickness = 1.5 x d„,,
Minimum TW
1.125
Maximum TW
0
Maximum TW
0
Step 6. Fit the riprap apron to the site by making it level for the nunimluu
length, La, from Figure 8.06a or Figure 8.06b. Extend the apron farther
do,xnstream and along channel banks until stability is assured_ Keep the
apron as straight as possible and align it with the flow of the receiving stream -
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
Some locations nnay require lining of the entire channel cross section to assure
stability.
It may be necessary to increase the size of riprap where protection of the
channel side slopes is necessary (Appendix 8.05). NA -`here overfalls exist at
pipe outlets or flows are excessive, a plunge pool should be considered, see
page 8.06.8.