SW5190201_15-INCH Riprap Outlet at FES 16_7/16/2019

User Input Data
Calculated Value
Reference Data
Designed By: Tom Harrell Date: 6/12/2019
Checked By: TH Date:
Company: DEI
Project Name: Cambridge Southeast
Project No.:
Site Location (City/Town) Raleigh
Culvert Id. FES 16
Total Drainage Area (acres) 1.98
.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 nun1 tailwater condition unless reliable flood stage elevations
show- oche lse_
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 7.5
Minimum/Maximum tailwater? Max TW (Fig. 8.06b)
Discharge (cfs) 10

Velocity (ft./s)
M
Step 2. Based on the tailwater conditions detr-miined in step 1, enter Figure
8_06a orFignre 8_D6b, and determine d5o riprap size and minituu m apron length
(L). The d., size is the median stone size iu a well -graded riprap 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
Figure 8.06a
Riprap d50, (ft.)
Minimum apron length, La (ft.)
Apron width at pipe outlet (ft.) 3.75
Apron shape
Apron width at outlet end (ft.) 9.25
Step 4. Deterirutke the inammu m stone diameter:
dr.. = 1.5 x d5D
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5. Deterinitke the apron thickness:
Apron thickness = 1.5 x dr,.
Maximum TW
Figure 8.06b
0.5
8
3.75
1.25
Maximum TW
0
Minimum TW Maximum TW
Apron Thickness(ft.) 1.125 0
Step 6. Fit the riprap apron to the site by niak ng it level for the ininim1un
length, La, from Figure 8_06a or Figure 8_0 b_ Extend the apron farther
do xnstreani and aloniz 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 receii-mg stream is straight_
Solve locations may require lining of the entire channel cross section to asstue
stability_
It may be necessary io increase the size of riprap Where protection of the
channel side slopes is necessary p pendky 8.05)_ 'Where overfalls exist at
pipe outlets or flows are a cessive, a phinge pool should be considered, see
page 8_06_8_