SW5190201_2018-12-14 30 Inch RCP Riprap Outlet_7/16/2019

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Designed By: T Harrell Date:
Checked By: Date:
Company: DEI
Project Name: Cambridge Southeast
Project No.: 16-154
Site Location (City/Town) Siler City
Culvert Id. FES #2
Total Drainage Area (acres) 5.9
.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 nunimum tailwater condition_
If it is greater than half the pipe diameter, it is classified maxlniuni condition_
Pipes that outlet onto Vvide flat areas -k ith no defined channel are assumed
to have a *fir-n num tailwater condition unless reliable flood stage elevations
show- otheise_
Outlet pipe diameter, Do (in.)
Tailwater depth (in.)
Minimum/Maximum tailwater?
Discharge (cfs) Q10
Velocity (ft./s)
091
12
Min TW (Fig. 8.06a)
14.91
8.7
Step 2. Based on the tailwater conditions deternuned in step 1, enter Figure
8_06a or Figure 8_D6b, and determine d5s riprap size and minituirn apron length
(L). The d_, size is the median stone size iu a well -graded riprap apron_
Step 3. Deterniine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end front the same figure used in Step 2_
Ji il1'YI',rn 772 hill
Figure 8.06a
Riprap d50, (ft.)
[QXN'7
Maximum TW
Figure 8.06b

Minimum apron length, La (ft.) 16
Apron width at pipe outlet (ft.) 7.5 7.5
Apron shape
Apron width at outlet end (ft.) 18.5 2.5
Step 4. Determine the ire-;tituum stone diameter:
d=1.5xd5D
Minimum TW
Max Stone Diameter, dmax (ft.) 1.125
Step 5. Deternutie the apron thicknesq=
Apron Thickness(ft.)
Apron thickness = 1.5 x dr,,.
Minimum TW
1.6875
Maximum TW
0
Maximum TW
0
,Step 6. Fit the riprap apron to the site by making it level for the n initmun
length, Ld, from Figure 8_06a 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 with the flow of the receii.-img stream_
Make any necessary alignment bends clear the pipe outlet so that the entrance
into the receil-ing stream is straight_
Solve locations may require lining of the entire channel cross section to asstue
stability -
It may be necessary to increase the size of ripr-ap where protection of the
chancel side slopes is necessary (Appendky 8.05)_ Where overfalls exist at
pipe outlets or flows are excessive, a phuige pool should be considered, see
page 8_06_8_

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