SWA000106_Design Calculations_20210621

Culvert Calculations
For
Pinewood Subdivision
CESI PROJECT NO. 210113.000
Client: Olde South Land, LLC
Client Representative: David Tibbals
P: 704.995.2808
david(a)charlottecommercialuartners.com
Preparer's Name: Kate Underwood, PhD, PE
CESI
NCBELS Corporate License Number C-0263
PO Box 268
Concord, NC 28026-0268
P.704.786.5404
F.704.786.7454
M.704.902.6169
[e-mail]
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05/25/2021

Flow Calculation
Recommended Runoff Coefficients
Applicable Areas
Description of Area
Runoff Coefficient
1
RE - max 1 du/ac
0.35
* Ref. Table 2-4
Character of Surface
Runoff Coefficient
2
Pavement
0.95
* Ref. Table 2-5
Area Calculations
Applicable Areas
(sf)
(ac)
1
5,737
0.132
2
89,414
2.053
Total
95,151
2.184
Calculated Runoff
0.39
Coefficient C =
Frequecy Factor for
1.10
25 Year Interval Cf =
* Ref. Table 2-6
Assumed Time
Concentration Tc = 5 (mins)
Ave Rainfall Intensity (i)
(duration equal to Tc) = 8 (in/hr)
* Ref Table 2-3
Q = 7.42 cfs
2.3.1 Rational Method
The Rational Method is an empiricalrunoff formula that has gained wide acceptance because of its
simple, intuitive treatment of peak storm runoff rates for small drainage basins. This method relates
runoff to rainfall intensity, surface area, and surface characteristics by the formula:
where:
Q = Cf CiA
(2-1)
Q — peak runoff rate, in cubic feet per second
Cf = frequency factor to adjust the runoff coefficient for less frequent, high
intensity storms
C = runoff coefficient
I average rainfall intensity, for a duration equal to the time of
concentration, in inches per hour
A — drainage area of the tributary to the point under consideration, in
acres
Adapted January 10, 2008 2-6 Technical Standards Manual

Stormwater Culvert Minimum RCP Diameter Calculation
For circular pipes flowing just full_ the Manning equation can be reformulated as-
QL 3. S
D = 16 [(4-2)
where:
D = Theoretical pipe diameter (in) for just -full flow.
Q = Discharge (cfs).
n = Manning roughness coefficient (dimensionless).
s = Longitudinal slope (Wft).
Q=
7.423
(FlowCalc)
n =
0.012
* Ref Table 7-3
s =
0.0448
(4.48% slope)
D = 11.57 (in) RCP minimum diameter
15" RCP > 11.57" RCP therefore use 15" RCP

References
Tables Utilized in Culvert Calculations
are in Reference to City of Concord
Stormwater Technical Manual

irks]
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8
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0.1
SECTION 2
STORMWATER RUNOFF
0.2 0.4 0.6 0.8 1 2 4 6 8 10
Duration -Hours
Figure 2-2 Intensity -Duration -Frequency Curves for Concord, NC
20
TABLE 2-3
ORDINATES OF THE iDF CURVES FOR CONCORD, NC
Duration
Return Period (years)
Hours
Minute
1
2
5
10
5o
1 (0)
0
5
4.80
5.66
6.60
7.26
8.00
8.52
898
10
3.83
4.54
5.29
5.81
6.39
6.79
7.13
15
3.19
3,80
4.46
4,90
5.39
5,72
6,01
30
2.19
2,62
3.17
3.55
3.99
4.31
4,60
1
1.36
1,65
2.03
2.31
2.66
2.92
3.17
2
0.79
0,96
1.19
1.36
1.59
1.75
1.92
3
0.56
0.68
0.85
0.98
1.15
1.29
1.42
6
0.34
0,41
0.51
0.59
0.70
0.79
0.87
12
020
0,24
0.31
0,35
0,42
0.48
4.53
24
i?. 1 3
0,14
0.18
0.21
0.25
0,28
fl. ; 1
ldnpted Januor 10.2068 2-5 Technical Slandards Manual

SECTION 2
STORMWATER RUNOFF
TABLE 24
RECOMMENDED RATIONAL METHOD RUNOFF COEFFICIENTS
FOR LAND USE
Runoff Coefficient
Description of Area
{t p to 10-Year Design Storm)
Business.
Downtown
0.70 to 0.95
Neighborhood
0.50 to 0.70
Residential
RE - maximum of 1 dulac
0AS
RL maximum of 2 dulac
0.45
RM-1 and RM-2 - maximum of du/ac
0.50
RV - maximum of 8 dulac
0.57
RC - maximum of 15 dulac
0.65
industrial:
Light
0.50 to 0.80
Heavy
0.60 to 0.90
Parks and Cemeteries
0.10 to 0.25
Playgrounds
0.20 to 0.40
Railroad Yard
0.20 to 0A
Unimproved
0.10 to 0.30
TABLE 2-5
SUGGESTED RATIONAL METHOD RUNOFF COEFFICIENTS
FOR SURFACE TYPES
Character of Surface
Runoff Coefficient
(Up to 10-Year Design Storm)
Pavement : Asphaltic and Concrete
0.95
Brick
0.85
Wooded
0.25
Packed gravel areas
0.55
Unpacked gravel areas
0.85
Driveways and Walkways
0.95
Roofs
0.95
Turf Slopes: Fiat, 0 Lo I percent
0.25
Average, 1 to 3 percent
0.35
Hilly, 3 to 1.0 percent
0.40
Steep, 10 percent +
0.45
Cultivated Ground: Flat, 0 to 1 percent
0.10
Average, 1 to 3 percent
0.20
Hilly, 3 to 10 percent
0.25
Steep, 10 percent
0.30
Adapted January la. 2008 2-8 Technical Standards Manual

SECTION 2
STORMWATER RUNOFF
TABLE 2-5
FREQUENCY FACTORS FOR THE RATIONAL METHOD
Recurrence
Adjustment
Interval (years)
Factor, Cr
1 to 10
1.00
25
1.10
50
1.20
100
1.25
Rainfall Intensity,1
Rainfall intensity, i, is the average rate of rainfall in inches per how, intensity is selected on the
basis of design frequency of occurrence, a statistical parameter established by design criteria, and
time of concentration. Rainfall intensity can be determined for the 1-, 2-, 5-, 10-, 25-, 50-, and 100-
year return periods from Figure 2-2 and Table 2-3. Note that the total design storm depth (or
volume) is not used in the Rational Method. This method determines only the peak discharge rate
not the total runoff volume.
Travel Time, Tt
Travel time, T, is the time required for water to travel from one location to another in a watershed.
Tt is a component of time of concentration (.), which is the time for runoff to travel from the
hydraulically most distant point of the watershed to the point of design. T, is computed by summing
all the travel times for consecutive components of the drainage conveyance system. T, influences
the shape and peak of the runoff hydrograph. Urbanization usually decreases T., thereby increasing
the peak discharge; but T. can be increased as a result of (a) ponding behind small or inadequate
drainage systems, including storm drain inlets and road culverts; or (b) reduction of land slope
through grading.
T, is the sum ofT, values for the various consecutive flow segments.
where:
T, = TEl + Ta +. .. Tt.
T� = time of concentration, in minutes
m = number of flow segments
T, travel time, in minutes
(2-2)
Note: For application within the City, a minimum time of concentration of 5 minutes shall be used
for each area or sub area to which the Rational Method is applied.
Adapted January la. 2008 2-9 Technical Standards Manual

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Riprap

User Input Data
Calculated Value
Reference Data
Designed By: SAT Date: 04.19.2021
Checked By: KWU
Company: CESI
Project Name: Pinewood Subdivision
Project No.: 210113.000
Site Location (City/Town) Midland, NC
Culvert Id. FES-2
Step 1. Determine the taihw-ater depot fi-om 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 mi' in,um tallwater condition.
If it is greater than half the pipe diameter, it is classified maximtmi condition.
Pipes that outlet onto wide flat areas «71th no defined channel are assumed
to have a minimum tailwater condition unless reliable flood stage elevations
show otherwise.
Outlet pipe diameter, Do (in.) 15
Tailwater depth (in.) 0
Minimum/Maximum tailwater? Min TW (Fig. 8.06a)
Discharge (cfs) 7.42 See 10 year Hydraulic Gradeline Calculation
results
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
8.06a or Figure 8.06b, and determine d50 riprap size and minimum apron length
(L). The d50 size is the median stone size in 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 Maximum TW
Figure 8.06a Figure 8.06b
Riprap d50, (ft.)
0.4
Minimum apron length, La (ft.)
8
Apron width at pipe outlet (ft.)
3.75 3.75
Apron shape
Trapezoidal
Apron width at outlet end (ft.)
9 1
�r« a. Determine the inavainumm stone diameter:
d,aR = 1.5 x d,,o
Minimum TW Maximum TW
Max Stone Diameter, dmax (ft.) 0.6 0
Step 5. Determine the apron thickness:
CLASS SELCTION:
Apron thickness = I F, x d
Apron Thickness(ft.)
Minimum TW Maximum TW
0.9 0
B
RIP RAP CLASS
MINIMUM
MIDRANGE
MAXIMUM
A
2 IN
0.17 FT
4 IN
0.33 FT
6 IN 0.5 FT
B
5 IN
0.42 FT
8 IN
0.67 FT
12 IN 1 FT
1
5 IN
0.42 FT
10 IN
0.83 FT
17 IN 1.42 FT
2
1 9 IN
0.75 FT
14 IN
1.17 FT
23 IN 1.92 FT
Step 6. Fit the riprap apron to the site by making it level for the minimum
length, La, 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 receiving stream.
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
Some locations may 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), Where overfaUs exist at
pipe outlets or flows are excessive, a plunge pool should be considered, see
page 8.06.8.

30
Outlet IW • Do + La
pipe i
diameter (Ob)
La
F-
0
3 5 20 50 1D0 200 500 100U
7.42 -1 Discharge (ft3/sec)
Curves may not be extrapolated.
Figure 0.06a Design of outlet protection protection from around pipe flowing full. minimum tailwaier condition (Tw c 0.6 diameter).
Rev. 12 93 8.06.3