SW5190201_2019-02-21 15 Inch RCP Drwy Cul 5 Riprap Outlet_7/16/2019

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Designed By: T Harrell Date: 2/25/2019
Checked By: D Blevins Date: 2/25/2019
Company: DEI
Project Name: Cambridge Southeast
Project No.: 16-154
Site Location (City/Town) Siler City
Culvert Id. Driveway Pipe #5
Total Drainage Area (acres) 0.29
Step 1. Determine the tailwater depth front channel characteristics below the
pipe outlet for the design capacity of the pipe_ If the tailw•ater depth is less
than half the outlet pipe diameter. it is classified minimum tailwater condition_
Lfit 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 mm- u- niiml tailw•ater condition unless reliable flood stage elevatiarrs
shoe otherwise_
Outlet pipe diameter, Do (in.)
Tailwater depth (in.)
Minimum/Maximum tailwater?
Discharge (cfs) Q10
Velocity (ft./s)
15
7.5
Max TW (Fig. 8.06b)
0.88
8.9
Step ?. Based on the tailwater conditions determined in step 1; enter Figure
8_46a or Figure 8_06b, and determine d50 riprap size and mininntm apron length
(L). The d, size is the median stone size in a well -graded riprap apron_
Step 3. Detemiine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end front the same figure used im Step 2_
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.)
Apron shape
Minimum TW
Figure 8.06a
0.33
3
3.75
Maximum TW
Figure 8.06b
3.75

Apron width at outlet end (ft.) 4.25 1.25
,Step 4. Determine the inaximum stone diameter:
drcax 1.5 x d5d
Minimum TW
Max Stone Diameter, dmax (ft.) 0.495
Step 5. Detemune the apron thickness -
Apron thickness = '1.5 x d,,. ,.
Apron Thickness(ft.)
Maximum TW
0
Minimum TW Maximum TW
0.7425 0
Step 6. Fit the riprap apron to the site by making it level for the rninimtun
length, L. , from Figure 8.06a or Figure 8.06b_ Extend the apron farther
downstream and along channel banks itntil stability is assured_ Keep the
apron as straight as possible and align it with the fio%v of the recen-1-ug stream_
Make any necessary alignment bends near the pipe outlet so that the entrance
into the recei7,-ing stream is straight_
Some locations may require lining of the entire channel cross section to assure
stabilitv_
It may be necessary to increase the size of riprap where protection of the
channel side slopes is necessary (Appendie 8.05_4'here a-erfalls exist at
pipe outlets or flows are excessive, a phinge pool should be considered, see
page 8.06.8_