SW5190201_2019-02-21 15 Inch RCP Drwy Cul 4 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 #4
Total Drainage Area (acres) 0.4
,Step 1. Determine the tailwater depth front 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 mitumum tailwater condition_
Lfit is greater than half the pipe diameter, It is classified maxinmi condition_
Pipes that outlet onto -Wide flat areas with no defined channel are assumed
to ha-ve a n,;niinuni tailwater condition unless reliable flood stage elevations
sho,kv otherwise -
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 7.5
Minimum/Maximum tailwater? Max TW (Fig. 8.06b)
Discharge (cfs) Q10 1.27
Velocity (ft./s) 8.3
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
S_U6aorFigure 8_06h, and determine d50riprap size and mininnun apron length
(L). The d_, size is the median stone size iu a well -graded riprap apron_
Step 3. Determiine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end fron7 the same figure used im Step 2_
Minimum TW Maximum TW
Figure 8.06a Figure 8.06b
Riprap d50, (ft.) 0.5
Minimum apron length, La (ft.) 3
Apron width at pipe outlet (ft.) 3.75 3.75
Apron shape

Apron width at outlet end (ft.) 4.25 1.25
,Step 4. Determine the inaxirnum stone diameter:
drcax 1.5 x d5d
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5. Detemune the apron thickness -
Apron thickness = 1.5 x dr1 ,:
Apron Thickness(ft.)
Maximum TW
0
Minimum TW Maximum TW
1.125 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_