20191657 Ver 1_3500 Regency Pkwy- SWM Report (Stamped)_20191204

Prepared exclusively for:
Town of Cary Planning Department
Stormwater Report
3500 Regency Pkwy
Cary, NC 27518
November 5, 2019
r'����jg'

Stormwater Report
Table of Contents
1) Narrative
2) Maps
a. Soils Map
3) Drainage Area Plans
a. Predevelopment
4) Calculations
a. OF Curves
b. Runoff
c. Time of Concentration
d. Hydraflow
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.

Stormwater Report
Narrative
Plan Preparer
American Tower
Patrick P. Barry, PE
3500 Regency Parkway
Cary, NC 27518
Introduction
American Tower
Nicholas R. Pirro, EIT
3500 Regency Parkway
Cary, NC 27518
This plan and report are to be implemented by the contractor during the culvert installation project
proposed by American Tower. The existing elliptical culvert is grossly undersized due to upstream
development activities and repeatedly overflows into the parking lot The Construction Drawings
and Report have been developed to minimize accelerated erosion and sedimentation both during
and after the proposed construction activities and to control the stormwater runoff. This report will
refer to the Drainage Area for the proposal. Planned earth disturbance activities include cutting,
filling, and grading the existing topography to install three new circular culverts. The total limit of
disturbance associated with this project is 0.13 acres.
Existing Site Conditions
The site consists of a commercial office building, asphalt parking lots, asphalt private road,
concrete sidewalks and woods.
Applicable Project Permitting Required
Local Zoning Permit, Building Permit, Stormwater Permit
Description of Erosion and Sedimentation Controls
Erosion and sedimentation controls to be used on site include silt fence, rock construction
entrance, infiltration basin with rip -rap spillway and a roadside ditch with erosion control blanket.
Landscaping
There is no proposed landscaping involved with this project, only vegetation clearing along banks
as shown in the Construction Drawings. All existing surrounding tree canopies shall remain.
Soils
The following soil's descriptions have been taken from the Soils map site at
https://websoilsurvey.sc.egov.usda.gov. The soils map is provided in Section 2 in this report.
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.
,0)

Stormwater Report
Floodplain, Wetlands and Waterways
Portions of the subject property are located within a special flood hazard zone. The project
location is within the 100-year floodplain according to FEMA FIRM community panel number
3720076200J, with an effective date of May 2, 2006. The project is not located within the Swift
Creek Floodway. There is an ephemeral stream located within the limits of the project as
delineated by Tower Engineering Professionals which is fed by a detention pond upstream. We
have treated the detention pond as an impervious surface because the water is kept at maximum
capacity for aesthetic reasons and to our knowledge is not intended for stormwater purposes.
Project Site Runoff
The Rational method has been used for determining flow rates for this project.
The Stormwater runoff rates are being utilized to size and design the proposed culverts for this
project due to the current culvert being undersized for the drainage area seen. It was found that
the flowrate for the 25-yr storm is 150.43 cfs. Using this flowrate, we proposed (3) 48" circular
HDPE culverts to be installed across the private road owned by American Tower Corporation to
replace the existing failing culvert which is to be removed and disposed properly offsite during
construction
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.

Stormwater Report
Maps
a. Soils Map
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.

0
Hydrologic Soil Group —Wake County, North Carolina
a
699950
699990 700030 700070
700110 700150 700190
35° 43' 51" N
n
F
_ Lr�LJ
Soil MaN may not he valiel at this scale.
35° 43' 42" N
699990 700030 700070
700110 700150 700190
b
Map Scale: 1:1,880 if printed on A landscape (11" x 8.5") sheet.
`
Meters
N 0 25 50 100
150
Feet
0 50 100 200 300
Map projection: Web Mercator Conermordinates: WGS84 Edge tics: UTM Zone 17N WGS84
USDA
Natural Resources
Web Soil Survey
Conservation Service
National Cooperative Soil Survey
700230 700270 700310
70MM 700270 700310
v
a
700350
35° 43' 51" N
35° 43' 42" N
700350
v
a
12/4/2018
Pagel of 4

Hydrologic Soil Group —Wake County, North Carolina
MAP LEGEND
Area of Interest (AOI)
0
Area of Interest (AOI)
Soils
Soil Rating
Polygons
0
A
0
A/D
0
B
0
B/D
0
C
0
C/D
0
D
0
Not rated or not available
Soil Rating
Lines
r 0
A
r 0
A/D
B
r
B/D
N 0
C
r 0
C/D
r 0
D
r 0
Not rated or not available
Soil Rating
Points
0
A
0
A/D
0
B
0
B/D
❑ C
0 C/D
0 D
❑ Not rated or not available
Water Features
Streams and Canals
Transportation
— Rails
­0 Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
MAP INFORMATION
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Wake County, North Carolina
Survey Area Data: Version 17, Sep 10, 2018
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Apr 27, 2014—May
6, 2014
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
USDA Natural Resources Web Soil Survey 12/4/2018
Conservation Service National Cooperative Soil Survey Page 2 of 4

Hydrologic Soil Group —Wake County, North Carolina
Hydrologic Soil Group
Map unit symbol
Map unit name
Rating
Acres in AOI
Percent of AOI
AaA
Altavista fine sandy
loam, 0 to 4 percent
slopes, rarely flooded
C
5.0
26.8%
ChA
Chewacla and
Wehadkee soils, 0 to
2 percent slopes,
frequently flooded
B/D
11.4
61.1 %
Ur
Urban land
1.9
10.2%
W
Water
0.4
1.9%
Totals for Area of Interest
18.7
100.0%
USDA Natural Resources Web Soil Survey 12/4/2018
Conservation Service National Cooperative Soil Survey Page 3 of 4

Hydrologic Soil Group —Wake County, North Carolina
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long -duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink -swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff.- None Specified
Tie -break Rule: Higher
USDA Natural Resources Web Soil Survey 12/4/2018
Conservation Service National Cooperative Soil Survey Page 4 of 4

Stormwater Report
Drainage Area Plans
a. Predevelopment
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.

L
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ry
U)
a
U
J
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n
U
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0
N
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U
'Ajo
AMERICAN TOWER°
ATC TOWER SERVICES, INC.
3500 REGENCY PARKWAY
SUITE 1100
CARY, NC 27518
PHONE: [phone]
FAX: [phone]
THESE DRAWINGS AND/OR THE ACCOMPANYING
SPECIFICATION AS INSTRUMENTS OR SERVICE ARE THE
EXCLUSIVE PROPERTY OF AMERICAN TOWERS LLC. THEIR USE
AND PUBLICATION SHALL BE RESTRICTED TO THE ORIGINAL
SITE FOR WHICH THEY ARE PREPARED. ANY USE OR
DISCLOSURE OTHER THAN THAT WHICH RELATES TO
AMERICAN TOWERS LLC OR THE SPECIFIED CARRIER IS
STRICTLY PROHIBITED. TITLE TO THESE DOCUMENTS SHALL
REMAIN THE PROPERTY OF AMERICAN TOWERS LLC
WHETHER OR NOT THE PROJECT IS EXECUTED. NEITHER THE
ARCHITECT NOR THE ENGINEER WILL BE PROVIDING ON -SITE
CONSTRUCTION REVIEW OF THIS PROJECT. CONTRACTOR(S)
MUST VERIFY ALL DIMENSIONS AND ADVISE AMERICAN
TOWERS LLC OF ANY DISCREPANCIES. ANY PRIOR ISSUANCE
OF THIS DRAWING IS SUPERSEDED BY THE LATEST VERSION
ON FILE WITH AMERICAN TOWERS LLC.
REV. DESCRIPTION BY DATE
zA DRAINAGE AREA NRP 11/05/19
ATC SITE NUMBER:
3500
ATC SITE NAME:
3500 REGENCY
PARK
SITE ADDRESS:
3500 Regency Parkway
Cary, NC 27518
LICENSURE:
PRELIMINARY:
NOT FOR
CONSTRUCTION
DRAWN BY:
NRP
APPROVED BY:
KYLE FAUST
DATE DRAWN:
11/05/19
ATC JOB NO:
3500
SHEET TITLE:
DRAINAGE AREA PLAN
SHEET NUMBER:
REVISION NUMBER:
DA-PRE
0

Stormwater Report
Calculations
a. IN Curves
b. Runoff Coefficients
c. Time of Concentration
d. Hydraflow Calculations
Confidential and proprietary.
© 2015 by ATC I LLC. All rights reserved.

NOAA Atlas 14, Volume 2, Version 3
Location name: Cary, North Carolina, USA*�'°
Latitude: 35.7297*, Longitude:-78.7869°
Elevation: 331.7 ft**
*source: ESRI Maps
source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Duration
Average recurrence interval (years)
1
���
2
5
10
25
50
100
200
500
1000
0.406
0.475
0.546
0.607
0.669
0.716
0.757
0.793
0.832
0.864
5-min
(0.373-0.444)
(0.435-0.519)
(0.501-0.596)
(0.555-0.661)
(0.610-0.730)
(0.649-0.780)
(0.683-0.824)
(0.711-0.864)
(0.740-0.908)
(0.762-0.944)
0.649
0.760
0.875
0.970
1.07
1.14
1.20
1.26
1.32
1.36
10-min
(0.595-0.709)
(0.696-0.830)
(0.802-0.955)
(0.887-1.06)
(0.972-1.16)
1 (1.03-1.24)
1 (1.09-1.31)
1 (1.13-1.37) 11
(1.17-1.44) 11
(1.20-1.49)
0.811
0.956
1.11
1.23
1.35
1.44
1.52
1.59
1.66
1.71
15-min
(0.744-0.886)
(0.875-1.04) 1
1 (1.23-1.47)
(1.31-1.57)
1 (1.37-1.66)
1 (1.42-1.73) 11
(1.47-1.81) 11
(1.51-1.87)
1.11
1.32
1.57
1.78
2.00
2.17
2.33
2.47
2.64
2.77
30-min
(1.02-1.21)
(1.21-1.44)
(1.44-1.72)
(1.63-1.94) 11
(1.83-2.18)
1 (1.97-2.37)
1 (2.10-2.54)
1 (2.22-2.69) 11
(2.35-2.88) 11
(2.44-3.02)
1.39
1.66
2.02
2.32
2.67
2.95
3.21
3.46
3.78
4.04
60-min
(1.27-1.51)
(1.52-1.81)
(1.85-2.20)
(2.12-2.52)
(2.43-2.91)
(2.67-3.21)
(2.89-3.49)
(3.11-3.78)
(3.37-4.13)
(3.56-4.41)
1.62
1.94
2.38
2.76
3.23
3.61
3.97
4.34
4.82
5.21
2-hr
(1.48-1.78)
(1.77-2.13)
(2.17-2.62)
(2.50-3.04)
(2.91-3.54)
(3.24-3.96)
(3.54-4.36)
(3.85-4.76)
(4.23-5.28)
(4.54-5.71)
1.72
2.06
2.54
2.96
3.50
3.95
4.39
4.86
5.47
5.99
3-hr
(1.57-1.89)1
(1.88-2.26) 11
(2.31-2.80) 11
(2.69-3.26)
(3.16-3.84)
(3.54-4.33)
(3.91-4.81)
(4.29-5.31)
(4.78-5.99)
(5.18-6.57)
2.06
2.47
3.05
3.57
4.23
4.79
5.35
5.94
6.73
7.41
6-hr
(1.89-2.26) 1
1 (2.79-3.35) 1
(3.83-4.62)
(4.31-5.22)
(4.78-5.83)
(5.25-6.46)
(5.87-7.32)
(6.39-8.07)
2.43
2.92
3.62
4.25
5.08
5.79
6.51
7.28
8.33
9.25
12-hr
(2.23-2.66) 11
(2.67-3.20) 11
(3.31-3.96) 1
(4.59-5.53)
(5.19-6.29)
(5.79-7.07)
(6.39-7.89)
(7.20-9.02)
(7.87-10.0)
2.88
3.47
4.36
5.06
6.02
6.78
7.55
8.35
9.45
10.3
24-hr
(2.67-3.10) 1
1 (4.06-4.70) 11
(4.70-5.45)
(5.56-6.48)
(6.25-7.29)
(6.95-8.13)
(7.66-9.00)
(8.63-10.2)
(9.38-11.1)
3.33
4.01
5.00
5.77
6.82
7.65
8.50
9.38
10.6
11.5
2{iay
(3.09-3.58) 11
(3.73-4.32) 11
(4.64-5.38)
(5.35-6.21)
(6.31-7.34)
(7.06-8.24)
(7.82-9.16)
(8.60-10.1)
(9.65-11.4)
(10.5-12.4)
3.52
4.23
5.25
6.05
7.14
8.01
8.89
9.79
11.0
12.0
3{iay
(3.28-3.78) 11
(3.94-4.55)
(4.89-5.64)
(5.62-6.49)
(6.61-7.67)
(7.39-8.59)
(8.18-9.55)
(8.99-10.5)
(10.1-11.9)
(10.9-12.9)
3.72
4.46
5.51
6.33
7.46
8.36
9.27
10.2
11.5
12.5
4{iay
(3.47-3.98)
(4.16-4.78)
(5.13-5.90)
(5.89-6.78)
(6.92-7.99)
(7.73-8.95)
(8.55-9.93)
(9.38-10.9)
(10.5-12.3)
(11.4-13.4)
4.30
5.14
6.26
7.15
8.38
9.35
10.3
11.4
12.7
13.8
7{iay
(4.03-4.60)
(4.81-5.49)
(5.86-6.68)
(6.68-7.63)
(7.80-8.94)
(8.68-9.97)
(9.57-11.0)
(10.5-12.1)
(11.7-13.7)
(12.7-14.8)
4.91
5.85
7.03
7.96
9.22
10.2
11.2
12.2
13.6
14.6
10-day
(4.61-5.24)
(5.48-6.23)
(6.59-7.50)
(7.45-8.48)
(8.60-9.82)
(9.50-10.9)
(10.4-11.9)
(11.3-13.0)
(12.5-14.5)
(13.4-15.7)
6.58
7.76
9.19
10.3
11.8
13.0
14.2
15.4
17.1
18.3
20-day
(6.18-7.01) 1
1 (8.62-9.78) 11
(9.66-11.0) 11
(11.0-12.6)
1 (12.1-13.9)
1 (13.2-15.1)
1 (14.3-16.5) 11
(15.8-18.2) 11
(16.9-19.6)
8.17
9.61
11.2
12.4
14.0
15.3
16.5
17.7
19.3
20.6
30-day
(7.69-8.68)1
(9.05-10.2) 1
1 (13.1-14.9)
1 (14.3-16.2)
1 (15.4-17.5)
1 (16.5-18.9) 11
(17.9-20.6) 11
(19.0-22.0)
10.4
12.2
14.0
15.4
17.1
18.5
19.8
21.1
22.8
24.1
45-day
(9.90-11.0)
(11.6-12.9)
(13.3-14.8)
(14.6-16.2)
(16.2-18.1)
1 (17.4-19.5)
1 (18.6-20.9)
1 (19.8-22.3) 11
(21.3-24.2) 11
(22.5-25.5)
12.5
14.6
16.5
18.0
19.9
21.3
22.7
24.1
25.8
27.1
60-day
(11.9-13.2)
(13.9-15.4)
(15.7-17.4)
(17.1-19.0)
(18.8-21.0)
(20.2-22.5)
(21.4-24.0)
(22.7-25.4)
(24.2-27.3)
(25.4-28.7)
Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical

M'.ill
25
c
t 20
4-
a
di
U
15
49
a
10
CL
a
i
30
25
c
s 20
a
m
a 15
A,
49
a
10
CL
a
Pas -based depth -duration -frequency (DDF) curves
Latitude: 35.7297', Longitude:-78-7869'
---------------------
I
t t Jr t L N N O r{4 N rq rq rq N rq N Alb N rV A q O O O Ln O
,1 r-I rn w � N rn v Ln
Duration
5 _ --
0
1 2 5 10 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14, VoIume 2, Version 3 Created (GMT): Tue Nov 5 14:34:34 2019
Back to Top
Maps & aerials
Small scale terrain
Average recurrence
mterva I
{years}
— 1
2
— 5
— 14
— 25
54
100
200
500
1000
Duration
— 6-min —
2-day
— 10-min —
3-day
15-min —
4-dmy
— 30-min —
7-day
— 60-min —
10-day
— 2fir —
20-day
— 3-hr —
30-day
— Sfir —
45-day
— 12-hr —
60-day
24-Mr

NOAA Atlas 14, Volume 2, Version 3
Location name: Cary, North Carolina, USA*�'°
Latitude: 35.7297*, Longitude:-78.7869°
Elevation: 331.7 ft**
*source: ESRI Maps
source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hourp
Duration
Average recurrence interval (years)
1
2
5
10
25
50
1 100
100
200
500
1000
4.87
5.70
6.55
7.28
8.03
8.59
9.08
9.52
9.98
10.4
5-min
(4.48-5.33) 11
(5.22-6.23)
(6.01-7.15) 11
(6.66-7.93) 11
(7.32-8.76)
1 (7.79-9.36)
1 (8.20-9.89)
1 (8.53-10.4)
1 (8.88-10.9)
1 (9.14-11.3)
3.89
4.56
5.25
5.82
6.40
6.84
7.22
7.54
7.90
8.17
10-min
(3.57-4.25) 11
(4.18-4.98)
1 (5.32-6.35) 11
(5.83-6.98)
1 (6.20-7.45)
1 (6.51-7.86)
1 (6.76-8.22)
1 (7.03-8.62)
1 (7.20-8.92)
3.24
3.82
4.42
4.91
5.41
5.77
6.08
6.34
6.63
6.83
15-min
(2.98-3.54) 11
(3.50-4.18) 1
1 (4.49-5.35) 11
(4.93-5.90)
1 (5.24-6.29)
1 (5.48-6.62)
1 (5.69-6.92)
1 (5.90-7.23)
1 (6.03-7.46)
2.22
2.64
3.14
3.56
4.01
4.35
4.66
4.94
5.27
5.53
30-min
(2.04-2.43)1
(2.42-2.88) 11
(2.88-3.43)
(3.25-3.88) 11
(3.65-4.37)
1 (3.94-4.74)
1 (4.20-5.07)
1 (4.43-5.38)
1 (4.69-5.75)
1 (4.88-6.04)
1.39
1.66
2.02
2.32
2.67
2.95
3.21
3.46
3.78
4.04
60-min
(1.27-1.51) 11
(1.52-1.81) 11
(1.85-2.20)
1 (2.43-2.91)
1 (2.67-3.21)
1 (2.89-3.49)
1 (3.11-3.78)
1 (3.37-4.13)
1 (3.56-4.41)
0.810
F 0.969
1.19
1.38
1.61
1.80
1.99
2.17
2.41
2.60
2-hr
(0.738-0.891)
(0.884-1.06)
(1.09-1.31) 11
(1.25-1.52) 11
(1.45-1.77)
1 (1.62-1.98)
1 (1.77-2.18)
1 (1.92-2.38)
1 (2.12-2.64)
1 (2.27-2.86)
0.571
0.684
0.846
0.987
1.17
1.32
1.46
1.62
1.82
2.00
3-hr
(0.522-0.628)
(0.625-0.754)
(0.771-0.931)
(0.896-1.09) 11
(1.05-1.28)
1 (1.18-1.44)
1 (1.30-1.60)
1 (1.43-1.77)
1 (1.59-2.00)
1 (1.73-2.19)
0.344
0.413
0.510
0.596
0.706
F 0.800
F 0.894
F 0.992
1.13
1.24
6-hr
(0.316-0.377)
(0.378-0.453)
(0.466-0.559)
(0.543-0.652)
(0.640-0.771)
(0.720-0.872)
(0.798-0.973)
(0.876-1.08)
(0.981-1.22)
(1.07-1.35)
0.202
0.242
0.300
0.353
0.421
0.480
0.540
0.604
0.691
0.767
12-hr
(0.185-0.221)
(0.222-0.265)
(0.274-0.329)
(0.321-0.386)
(0.381-0.459)
(0.431-0.522)
(0.480-0.587)
(0.531-0.655)
(0.598-0.749)
(0.653-0.832)
0.120
0.145
0.182
0.211
0.251
0.282
0.315
0.348
0.394
0.429
24-hr
(0.111-0.129)
(0.135-0.156)
(0.169-0.196)
(0.196-0.227)
(0.232-0.270)
(0.260-0.304)
(0.289-0.339)
(0.319-0.375)
(0.359-0.425)
(0.391-0.464)
0.069
0.083
0.104
0.120
0.142
0.159
0.177
0.195
0.220
0.239
2-day
(0.064-0.075)
(0.078-0.090)
(0.097-0.112)
(0.111-0.129)
(0.131-0.153)
(0.147-0.172)
(0.163-0.191)
(0.179-0.211)
(0.201-0.238)
(0.218-0.259)
0.049
0.059
0.073
0.084
0.099
0.111
0.123
0.136
0.153
0.167
3-day
(0.046-0.053)
(0.055-0.063)
(0.068-0.078)
(0.078-0.090)
(0.092-0.106)
(0.103-0.119)
(0.114-0.133)
(0.125-0.146)
(0.140-0.165)
(0.152-0.180)
0.039
0.046
0.057
0.066
0.078
0.087
0.097
0.106
0.120
0.130
4-day
(0.036-0.042)
(0.043-0.050)
(0.053-0.061)
(0.061-0.071)
(0.072-0.083)
(0.081-0.093)
(0.089-0.103)
(0.098-0.114)
(0.110-0.129)
(0.119-0.140)
0.026
0.031
0.037
0.043
0.050
0.056
0.062
0.068
0.076
0.082
7-day
(0.024-0.027)
(0.029-0.033)
(0.035-0.040)
(0.040-0.045)
(0.046-0.053)
(0.052-0.059)
(0.057-0.066)
(0.062-0.072)
(0.070-0.081)
(0.075-0.088)
0.020
0.024
0.029
0.033
0.038
0.043
0.047
0.051
0.057
0.061
10-day
(0.019-0.022)
(0.023-0.026)
(0.027-0.031)
(0.031-0.035)
(0.036-0.041)
(0.040-0.045)
(0.043-0.050)
(0.047-0.054)
(0.052-0.060)
(0.056-0.065)
0.014
0.016
0.019
0.021
0.025
0.027
0.030
0.032
0.036
0.038
20-day
(0.013-0.015)
(0.015-0.017)
(0.018-0.020)
(0.020-0.023)
(0.023-0.026)
(0.025-0.029)
(0.028-0.032)
(0.030-0.034)
(0.033-0.038)
(0.035-0.041)
0.011
0.013
0.016
0.017
0.019
0.021
0.023
0.025
0.027
0.029
30-day
(0.011-0.012)
(0.013-0.014)
(0.015-0.016)
(0.016-0.018)
(0.018-0.021)
(0.020-0.022)
(0.021-0.024)
(0.023-0.026)
(0.025-0.029)
(0.026-0.031)
0.010
0.011
0.013
0.014
0.016
0.017
0.018
0.020
0.021
0.022
45-day
(0.009-0.010)
(0.011-0.012)
(0.012-0.014)
(0.013-0.015)
(0.015-0.017)
(0.016-0.018)
(0.017-0.019)
(0.018-0.021)
(0.020-0.022)
(0.021-0.024)
0.009
0.010
0.011
0.013
0.014
0.015
0.016
0.017
0.018
0.019
60-day
(0.008-0.009)
(0.010-0.011)
(0.011-0.012)
(0.012-0.013)
(0.013-0.015)
(0.014-0.016)
(0.015-0.017)
(0.016-0.018)
(0.017-0.019)
(0.018-0.020)
Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical

PD5-based intensity -duration -frequency (IDF) curves
Latitude: 35.7297', Longitude:-78.7869'
1161616I6161
10.000
C
41
1.000
C
GJ
a-�
C
� 0.100
L
Ld
a 0.010
0 001
t t
Jr t
L
N
N r{4
N rq
rq
rq
N rq
O
N Alb
A q
O
O
O
Ln O
,1
r-I
rn
w
�
N
rn
v Ln
Duration
100.000
10.000
L
k
1.000
w
c
e
0.100
4.1
49
0.010
0.001 i 1 1 1 1 1 1 1 1 1
1 2 5 10 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14, Volume 2, Version 3 Created (GMT): Tue Nov 5 14:35:12 2019
Back to Top
Maps & aerials
Small scale terrain
Average recurrence
interval
{years}
— 1
2
— 5
— 14
— 25
54
100
200
500
1000
Duration
— 6-min —
2-day
— 14-min —
3-day
15-min —
4-dmy
— 3"in —
7-day
— 60-min —
10-day
— 2fir —
20-day
— 3-hr —
30-day
— Sfir —
45-day
— 12-hr —
60-day
24-Mr

3500 Regency Pkwy Cary, NC 27518 SWM Report
Post developed to Culvert
Soil
AREA
Group
COVER
CN
(ACRES)
CN*AREA
C
FOREST
0.16
13.50
2.16
C
MEADOW
0.26
5.60
1.46
C
IMPERVIOUS
0.97
40.40
39.19
59.50
42.80
USE C = 0.72

TR55 Tc Worksheet
Rational
<Name>
Description
A
Sheet Flow
Manning's n-value
= 0.240
Flow length (ft)
= 150.0
Two-year 24-hr precip. ((in))
= 3.47
Land slope (%)
= 2.00
Travel Time (min)
= 18.95
Shallow Concentrated Flow
Flow length (ft)
= 644.00
Watercourse slope (%)
= 4.58
Surface description
= Unpaved
Average velocity (ft/s)
= 3.45
Travel Time (min)
= 3.11
Channel Flow
R
0.011
0.0
0.00
0.00
+ 0.00
u
C
0.011
0.0
0.00
0.00
2065.00
0.00
1.90
0.00
Unpaved
Paved
2.22
0.00
+ 15.48 +
0.00
X sectional flow area ((sqft))
= 0.00
0.00
0.00
Wetted perimeter ((ft))
= 0.00
0.00
0.00
Channel slope (%)
= 0.00
0.00
0.00
Manning's n-value
= 0.015
0.015
0.015
Velocity (ft/s)
= 0.00
0.00
0.00
Flow length (ft)
= 0.0
0.0
0.0
Hydraflow Express by Intelisolve
Totals
= 18.95
= 18.58
Travel Time (min) = 0 + 0 + 0 = 0.00
Total Travel Time, Tc.............................................................................. 38.00 min

Hydrology Report
Hydraflow Express Extension for Autodesk0 AutoCADO Civil 3D0 by Autodesk, Inc.
Tuesday, Nov 5 2019
<Name>
Hydrograph type
= Rational
Peak discharge (cfs)
= 97.28
Storm frequency (yrs)
= 2
Time interval (min)
= 1
Drainage area (ac)
= 59.450
Runoff coeff. (C)
= 0.72
Rainfall Inten (in/hr)
= 2.273
Tc by TR55 (min)
= 38
OF Curve
= rainfall data.IDF
Rec limb factor
= 1.00
Q (cfs)
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0 00
Runoff Hydrograph
2-yr frequency
Hydrograph Volume = 221,808 (cult); 5.092 (acft)
Q (cfs)
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0 00
0 10 20 30 40 50 60 70 80
Time (min)
Runoff Hyd - Qp = 97.28 (cfs)

Hydrology Report
Hydraflow Express Extension for Autodesk0 AutoCADO Civil 3D0 by Autodesk, Inc.
Tuesday, Nov 5 2019
<Name>
Hydrograph type
= Rational
Peak discharge (cfs)
= 132.69
Storm frequency (yrs)
= 10
Time interval (min)
= 1
Drainage area (ac)
= 59.450
Runoff coeff. (C)
= 0.72
Rainfall Inten (in/hr)
= 3.100
Tc by TR55 (min)
= 38
OF Curve
= rainfall data.IDF
Rec limb factor
= 1.00
Q (cfs)
140.00
120.00
100.00
80.00
60.00
40.00
20.00
0 00
0 10 20 30
Runoff Hyd - Qp = 132.69 (cfs)
Hydrograph Volume = 302,536 (cult); 6.945 (acft)
Runoff Hydrograph
10-yr frequency
v vv 40 50 60 70 80
Time (min)

Hydrology Report
Hydraflow Express Extension for Autodesk0 AutoCADO Civil 3D0 by Autodesk, Inc.
Tuesday, Nov 5 2019
<Name>
Hydrograph type
= Rational
Peak discharge (cfs)
= 150.43
Storm frequency (yrs)
= 25
Time interval (min)
= 1
Drainage area (ac)
= 59.450
Runoff coeff. (C)
= 0.72
Rainfall Inten (in/hr)
= 3.514
Tc by TR55 (min)
= 38
OF Curve
= rainfall data.IDF
Rec limb factor
= 1.00
Q (cfs)
160.00
140.00
120.00
100.00
80.00
60.00
40.00
20.00
0 00
0 10 20 30
Runoff Hyd - Qp = 150.43 (cfs)
Hydrograph Volume = 342,978 (cult); 7.874 (acft)
Runoff Hydrograph
25-yr frequency
v vv 40 50 60 70 80
Time (min)

Culvert Report
Hydraflow Express Extension for Autodesk0 AutoCADO Civil 3D0 by Autodesk, Inc. Tuesday, Nov 5 2019
Proposed Culvert
Invert Elev Dn (ft)
= 320.89
Calculations
Pipe Length (ft)
= 65.00
Qmin (cfs)
= 150.43
Slope (%)
= 1.00
Qmax (cfs)
= 150.43
Invert Elev Up (ft)
= 321.54
Tailwater Elev (ft)
= (dc+D)/2
Rise (in)
= 48.0
Shape
= Circular
Highlighted
Span (in)
= 48.0
Qtotal (cfs)
= 150.43
No. Barrels
= 3
Qpipe (cfs)
= 150.43
n-Value
= 0.012
Qovertop (cfs)
= 0.00
Culvert Type
= Circular Culvert
Veloc Dn (ft/s)
= 4.86
Culvert Entrance
= Smooth tapered inlet throat
Veloc Up (ft/s)
= 7.36
Coeff. K,M,c,Y,k
= 0.534, 0.555, 0.0196, 0.9, 0.2
HGL Dn (ft)
= 323.95
HGL Up (ft)
= 323.67
Embankment
Hw Elev (ft)
= 324.67
Top Elevation (ft)
= 327.30
Hw/D (ft)
= 0.78
Top Width (ft)
= 25.00
Flow Regime
= Inlet Control
Crest Width (ft)
= 4.00
FF
FF k
-----------------
-----------------
i F F F • F k : i i F