SWA000079_2020-11-23 SWM Report_20201124

United Rentals
914 Webb Road
Storm Water Management Report
and
Erosion Control Results
Rowan County, North Carolina
Initial Submittal: September 14, 2020
Resubmittal: November 23, 2020
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FREELAND and KAUFFMAN, Inc.
Engineers • Landscape Architects
209 West Stone Avenue
Greenville, South Carolina 29609
Tel: [phone]

INDEX
Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Pre-Development Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Runoff Curve Number Summary
Time of Concentration Summary
Rainfall Summary
Rate of Runoff Summary
USGS Quadmap
FEMA MAP
Rainfall Data
USDA Soil Survey Map, Legend and Soil Series Information
Pre-Development Drainage Map
TR-55 Pre-Development Calculations
Pre-Developed Area 1: 2, 10, and 100-year Hydrographs
Pre-Developed Area 2: 2, 10, and 100-year Hydrographs
Pre-Developed Area 3: 2, 10, and 100-year Hydrographs
Total Pre-Developed: 2, 10, and 100-year Hydrographs
III. Post-Development Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Runoff Curve Number Summary
Time of Concentration Summary
Rainfall Summary
Rate of Runoff Summary
Post-Developed Drainage Map
TR-55 Land-Use Curve Post-Development Calculations
Post-Developed Area 1 A: 2, 10, and 100-year Hydrographs
Post-Developed Area 1 B: 2, 10, and 100-year Hydrographs
Post-Developed Area 2A: 2, 10, and 100-year Hydrographs
Post-Developed Area 213: 2, 10, and 100-year Hydrographs
Post-Developed Area 3: 2, 10, and 100-year Hydrographs
IV. Detention Pond Design and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pond 1 Volume Calculations
Pond Report for Pond 1 with Stage/Storage Graph
Pond Report for Pond 1 with Stage/Discharge Graph
Pond 1 Section View
Pond 1 Front View
Pond 1 Routing: 2, 10, and 100-year Storm Event Hydrographs
Total Post-Developed Area 1: 2, 10, and 100-year Storm Event Hydrographs
Pond 2 Volume Calculations
Pond Report for Pond 2 with Stage/Storage Graph
Pond Report for Pond 2 with Stage/Discharge Graph
Pond 2 Section View
Pond 2 Front View
Pond 2 Routing: 2, 10, and 100-year Storm Event Hydrographs

Total Post-Developed Area 2: 2, 10,and 100-year Storm Event Hydrographs
Total Post-Developed: 2, 10, and 100-year Storm Event Hydrographs
V. Pipe Sizing Design and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stormdrain Model Report: 10-yr Storm Event
VI. Erosion and Sediment Control Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hydrograph Summary Re po rlydraflow Hydrographs Extension for Autodesk®Civil 3D@ by Autodesk, Inc.v2021
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 SCS Runoff 9.030 2 720 20,716 ------ ------ ------ PRE DEV 1
2 SCS Runoff 4.407 2 720 10,094 ------ ------ ------ PRE DEV 2
3 Combine 13.44 2 720 30,811 1,2 ------ ------ Total Pre Dev
5 SCS Runoff 8.149 2 716 16,538 ------ ------ ------ Post Dev 1A
6 Reservoir 1.001 2 736 16,188 5 777.47 7,270 Pond 1
7 SCS Runoff 2.920 2 720 6,846 ------ ------ ------ Post Dev 1B(By-Pass)
8 Combine 3.868 2 720 23,033 6,7 ------ ------ Total Post Area 1
10 SCS Runoff 3.165 2 716 6,424 ------ ------ ------ Post Dev 2A
11 Reservoir 0.828 2 724 6,419 10 783.31 2,091 Pond 2
12 SCS Runoff 3.295 2 716 6,659 ------ ------ ------ Post Dev 2B(By-Pass)
13 Combine 4.034 2 718 13,078 11, 12 ------ ------ Total Post Area 2
15 Combine 7.757 2 718 36,111 8, 13, ------ ------ Total Post Dev
2020-11-11.gpw Return Period: 2 Year Friday, 11 / 13/2020

Hydrograph Summary Re po r$ydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cuft) (ft) (cuft)
1 SCS Runoff 17.57 2 718 40,196 ------ ------ ------ PRE DEV 1
2 SCS Runoff 8.443 2 718 19,314 ------ ------ ------ PRE DEV 2
3 Combine 26.01 2 718 59,510 1,2 ------ ------ Total Pre Dev
5 SCS Runoff 13.81 2 716 28,577 ------ ------ ------ Post Dev 1A
6 Reservoir 1.272 2 744 28,226 5 778.16 13,285 Pond 1
7 SCS Runoff 6.260 2 720 14,329 ------ ------ ------ Post Dev I(By-Pass)
8 Combine 7.460 2 720 42,555 6,7 ------ ------ Total Post Area 1
10 SCS Runoff 5.364 2 716 11,101 ------ ------ ------ Post Dev 2A
11 Reservoir 2.453 2 722 11,095 10 783.64 3,458 Pond 2
12 SCS Runoff 5.748 2 716 11,789 ------ ------ ------ Post Dev 2B(By-Pass)
13 Combine 7.286 2 718 22,884 11, 12 ------ ------ Total Post Area 2
15 Combine 14.64 2 718 65,440 8, 13, ------ ------ Total Post Dev
2020-11-11.gpw Return Period: 10 Year Friday, 11 / 13/2020

Hydrograph Summary Re po rlydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021
Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph
No. type flow interval Peak volume hyd(s) elevation strge used Description
(origin) (cfs) (min) (min) (cult) (ft) (cuft)
1 SCS Runoff 32.10 2 718 74,057 ------ ------ ------ PRE DEV 1
2 SCS Runoff 15.23 2 718 35,219 ------ ------ ------ PRE DEV 2
3 Combine 47.33 2 718 109,276 1,2 ------ ------ Total Pre Dev
5 SCS Runoff 22.66 2 716 48,254 ------ ------ ------ Post Dev 1A
6 Reservoir 10.81 2 722 47,903 5 778.77 19,534 Pond 1
7 SCS Runoff 12.18 2 718 27,895 ------ ------ ------ Post Dev 1 B(By-Pass)
8 Combine 21.26 2 722 75,799 6,7 ------ ------ Total Post Area 1
10 SCS Runoff 8.803 2 716 18,745 ------ ------ ------ Post Dev 2A
11 Reservoir 5.354 2 722 18,739 10 784.01 4,949 Pond 2
12 SCS Runoff 9.630 2 716 20,276 ------ ------ ------ Post Dev 26(By-Pass)
13 Combine 14.26 2 718 39,015 11, 12 ------ ------ Total Post Area 2
15 Combine 32.94 2 720 114,813 8, 13, ------ ------ Total Post Dev
2020-11-11.gpw Return Period: 100 Year Friday, 11 / 13/2020

I. EXECUTIVE SUMMARY
This report details the storm water management system for the proposed United Rentals Store, located at
914 Webb Road, in Salisbury (Rowan County), North Carolina. The United Rentals site is not a portion of
a larger development, and it will be developed to retain an existing+/-6,532 square foot building, and will
include all associated parking areas, driveways, utilities, stormwater management system, and landscaping.
Runoff from the parcel currently discharges to both the east and west sides of the property and re-
combines in an un-named tributary of Town Creek before crossing under I-85. A proposed dry-detention
pond, located along the eastern side of the site, and a second dry-detention pond, located on the west
side of the site, will be used in combination to manage water quantity by being designed to fully
attenuating the 2, 10, and 100 year events to less than pre-developed rates while also providing freeboard
above the 100-year event.
Pre-Developed Analysis
Storm Event Pre-Developed Area 1 Pre-Developed Area 2 Total Pre-Developed
Peak Discharge Rate Peak Discharge Rate Peak Discharge Rate
2 year 9.03 cfs 4.41 cfs 13.44 cfs
10 year 17.57 cfs 8.44 cfs 26.01 cfs
100 year 32.10 cfs 15.23 cfs 47.33 cfs
Area 1 Point of Analysis Stormwater Pond Routing and Analysis
Storm Post-Dev. Area Post-Dev. Area 1 B Pond 1 Total Post-Dev. Area 1
Event 1 A Peak Flow Peak Flow (By-Pass) Flow Flow
2 year 8.15 cfs 2.92 cfs 1.00 cfs 3.87 cfs
10 year 13.81 cfs 6.26 cfs 1.27 cfs 7.46 cfs
100 year 22.66 cfs 12.18 cfs 10.81 cfs 21.26 cfs
Area 2 Point of Analysis Stormwater Pond Routing and Analysis
Storm Post-Dev. Area Past-Dev. Area 2B Pond 2 Total Post-Dev. Area 2
Event 2A Peak Flow Peak Flow (By-Pass) Flow Flow
2 year 3.17 cfs 3.30 cfs 0.83 cfs 4.03 cfs
10 year 5.36 cfs 5.75 cfs 2.45 cfs 7.29 cfs
100 year 8.93 cfs 9.63 cfs 5.43 cfs 14.36 cfs
Overall Stormwater Pond Routing and Analysis
Storm Pre-Dev. Pre-Dev. Total Pre- Post-Dev. Post-Dev. Total Post-
Event Area 1 Peak Area 2 Dev. Peak Area 1 Area 2 Dev. Flow
Flow Peak Flow Flow Peak Flow Peak
Flow
2 year 9.03 cfs 4.41 cfs 13.44 cfs 3.87 cfs 4.03 cfs 7.76 cfs
10 year 17.57 cfs 8.44 cfs 26.01 cfs 7.46 cfs 7.29 cfs 14.64 cfs
100 year 32.10 cfs 15.23 cfs 47.33 cfs 21.26 cfs 14.26 cfs 32.94 cfs

The detention facilities area designed as dry detention ponds where volume is provided to
properly store and release each identified storm event. Staged concrete outlet structures in each
pond will regulate discharge from the facilities. While the ponds are not physically connected or
managed by a common outlet control device, the two facilities will detain runoff for both their
applicable drainage sub-basins and the overall site to less than pre-developed rates. This report
also discusses the erosion control measures planned for the proposed development. The
permanent detention ponds will serve as a temporary sediment basins for the duration of
construction.

H. PRE-DEVELOPMENT CONDITIONS
The proposed development is situated on a +/-18.23 acre tract of land in the northeast quadrant
the intersection of Interstate 85 and Webb road. There are no wetlands (jurisdictional or isolated)
within the development area. The current land use is partially developed for the purposes of
agriculture equipment sales. The property consists of woods, in good condition, grass, gravel and
impervious ground covers.
The total area of analysis can be broken down into two drainage sub-basins (a review of the Pre-
and Post-Development Drainage Maps will help to clarify this Basin setup).
The Predeveloped drainage areas for this project are as follows:
• Pre-Developed Area 1 comprises +/-4.59 acres on the east side of the site. Area 1 drains
via sheet flow, shallow concentrated flow, and channel flow towards an existing open
ended 36" pipe on the eastern side of the site.
• Pre-Developed Area 2 comprises +/-2.13 acres on the west side of the site. Area 2 drains
via sheet flow and shallow concentrated flow towards the drainage ditch along the east
side of I-85.
Runoff Calculations:
TR-55 (Win TR-55, Version 1.00.00): TR-55 is used to calculate only the Runoff Curve Number
and the Time of Concentration for each of the drainage basins in both the pre- and post-
development condition. TR-55 allows for several distinct land-use characteristics and runoff flow
properties to be considered.
Hydraflow Hydrographs (2004, Version 8.0.0.0): Hydraflow Hydrographs, a computer model
based on the SCS Method, is used to generate the pre-developed and post-developed runoff
hydrographs, using the runoff curve number and time of concentration values generated by TR-
55. Hydrographs also models the detention pond, the outlet structure, and provides the routing
for each storm event through the pond system.
A. Runoff Curve Number:
The site is first analyzed to determine all different types of land use. Each land use is assigned a
runoff curve number between 0 and 100. The more impervious a material is, the higher the
runoff curve number. For example, pavement is almost completely impervious, and has a runoff
curve number of 98. Soil type also factors into the curve number for each land use. From review
of the NRCS Web Soil Survey maps, soils on this property are identified as Chewacla loam 0%-2%
(Type B/D), Enon fine sandy loam 2%-8% (Type C), Enon fine sandy loam 8%-15% (Type C),

Sedgefiled fine sandy loam 1%-6% (Type C/D), Udorthents, loamy (Type C), and Vance sandy clay
loam 2%-8% (Type C) where the majority of the soils on the developed portion of the site being
Type C.
Pre-Developed Area 1
Open space, grass Woods, good Gravel: 0.83 Ac. Impervious: 0.13 Ac.
cover(good condition: 1.51 Ac.
condition): 2.12 Ac
CN = 74 ICN =70 CN =89 CN =98
Total Land Area =4.59 Acres
Weighted Runoff Curve Number=76
Pre-Developed Area 2
Open space, grass Gravel: 0.14 Ac. Impervious: 0.17 Ac.
cover (good
condition): 1.82 Ac
CN = 74 ICN =89 CN = 98
Total Land Area =2.13 Acres
Weighted Runoff Curve Number=77
B. Time of Concentration:
The time of concentration for the existing drainage basin is calculated by determining the path
that runoff takes from the farthest corner of the property to the discharge location. Runoff
assumes three separate flow characteristics when traversing a property, sheet flow, shallow
concentrated flow, and open-channel flow. Sheet flow defines typical overland flow over open
areas. Shallow concentrated flow is used for any overland flow over 100, assuming the flow has
concentrated somewhat. Open-channel flow describes flow through ditches and pipes. TR-55
calculates travel times for each type of flow, given certain parameters. These parameters include
slope, roughness, and velocity. Following are the individual components of the Time of
Concentration:
Pre-Developed Area 1
Sheet Flow Shallow Channel flow (85
0 00 feet at Concentrated feet at 4.00 Us
4.95% average flow (155 feet at
slope) short 6.90% average
grass slope), over
unpaved surface
Tc=6.66 min. Tc =0.60 min. Tc= 0.36 min.

Total Time of Concentration =7.62 minutes
Pre-Developed Area 2
Sheet Flow Shallow
(100 feet at Concentrated
3.5% average flow (190 feet at
slope) short 2.40% average
grass slope), over
unpaved surface
Tc=7.68 min. Tc = 1.26 min.
Total Time of Concentration =8.94 minutes
C. Rainfall
The 24-hour precipitation amounts for the site are per NOAA:
2-year storm event: 3.33 inches
10-year storm event: 4.85 inches
100-year storm event: 7.21 inches
D. Rate of Runoff
The above curve number and time of concentration are parameters used to determine rate of
runoff using the SCS hydrograph method. A hydrograph for the pre-development condition can
be generated showing rate of flow versus time. These hydrographs are included in this section,
Following are the computed rates of runoff for the drainage basin:
Pre-Developed Area 1
Storm Event Flow Rate, 0 (cfs)
2 year 9.03
10 year 17.57
100 year 32.10
Pre-Developed Area 2
Storm Event Flow Rate, 0 (cfs)
2 year 4.41
10 year 8.44
100 year 15.23

Total Pre-Developed
Storm Event Flow Rate, Q (cfs)
2 year 13.44
10 year 26.01
100 year 47.33

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7/9/2020 Precipitation Frequency Data Server
NOAA Atlas 14,Volume 2,Version 3
Location name:Salisbury, North Carolina,USA* v '�
Latitude: 35.6004',Longitude: -80.5286'
Elevation:784.42 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
Average recurrence interval(years)
Duration ��7�����
1 2 5 10 25 50 100 200 500 1000
[��F-o.387 0.458 0.535 0.588 0.648 0.688 0.724 0.755 0.788 0.810
(0.357-0.420) (0.423-0.499) (0.492-0.581) (0.540-0.637) (0.592-0.701) (0.625-0.745) (0.654-0.785) (0.678-0.820) (0.701-0.858) (0.715-0.884)
10-min 0.619 0.733 0.856 0.940 1.03 1.10 1.15 1.20 1.25 1.28
(0.570-0.671) (0.676-0.797) (0.788-0.930) (0.863-1.02) (0.943-1.12) (0.996-1.19) (1.04-1.25) (1.08-1.30) (1.11-1.36) (1.13-1.39)
15-min 0.773 0.921 1.08 1.19 1.31 1.39 1.45 1.51 1.57 1.60
(0.713-0.839) (0.850-1.00) (0.996-1.18) (1.09-1.29) (1.20-1.42) (1.26-1.50) (1.31-1.58) (1.36-1.64)JL(1.40-1.71) (1.41-1.75)
F-�]inF-'--o6-7F--'.-27-7F1.54 1.72 1.94 2.09 2.23 2.35[ -�F-2.50 2.59
(0.978-1.1 5) (1.17-1.38) (1.42-1.67) (1.58-1.87) (1.77-2.10) (1.90-2.26) (2.01-2.41) (2.11-2.55) (2.22-2.72) (2.29-2.83)
F60-min 1.32 1.601.972.242.582.833.073.303.58 3.79
_ (1.22-1.43) (1.47-1.74) (1.82-2.14) (2.063 3) 1 (2_36-2.79) (2.57-3.07) (2.77-3.33) (2.96-3.58) (3.19-3.90) (3.34-4.13)
FT-hr 1.53 1.85 2.30 2.63 T 3.07 3.39 3.71 4.02 4.43 4.73
(1.40-1.66) (1.70-2.02) (2.11-2.51) (2.41-2.87) (2.79-3.34) (3.07-3.69) (3.34-4.04) (3.59-4.39) 2-5(3.90-4.84) (4.1 .18)
3-hr e 1 1.63 1.96 2.45 2.82 3.32 3.70 4.07 4.45 4.96 5.34
( .50-1 78) (1.81-2.15) (2.25-2.68) (2.58-3.07) (3.01-3.60) (3.34-4.02) (3.66-4.42) (3.96-4.84) (4.35-5.41) (4.63-5.84)
6-hr 1.97 2.37 2.96 3.42 4.04 4.52 5.00 5.49 6.16 667
(1.81-2.15) (2.19-2.60) (2.72-3.24) (3.13-3.73) (3.67-4.38)JU4.08 4.90) (4.48-5.43) (4.87-5.97) (5.39-6.70)jt 5.76-7.26)
F:�-:h:r]F-2.32 2.80 3.51 4.07 4.84 5.45 6.07 6.72 7.60 8.29
(2.14-2.53) (2.58-3.06) (3.23m3.83) (3.73-4.43) (4.40-5.25) (4.91-5.90) (5.43-6.56) (5.94-7.25) (6.61-8.20) (7.11-8.95) .1
�-h ]F-2-.76 3.33 4.18 4.85 5.76 6.48 7.21 7.97 8.99 9.80
(2.58-2.97) (3.11-3.58) (3.90-4.50) (4.52-5.21) (5.34-6.18) (6.00-6.95) (6.66-7.74) (7.34-8.55) (8.25-9.66) (8.96-10.5)
�-d:ay]F-3.2-'-7F--3.'-7-7F-4.-82-7F5.56 6.56 7.36 8.16 8.99 10.1 11.0
(3.00-3.44) (3.61-4.14) (4.50-5.15) (5.18-5.94) (6.10-7.01) (6.82-7.86) (7.55-8.72) (8.29-9.61) (9.28-10.8) (10.0-11.8)
[ 3-7day 3.42 4.10 5.08 5.86 6.90 7.73 8.57 9.43 10.6 11.5
(3.20-3.65) (3.844.39)1 (4.76-5.43)11 (5.47-6.25)I (6.42-7.37) (7.18-8.26) (7.94-9.16) (8.71-10.1) (9.75-11.4) (10.6-12.3)
4-day 3.62 4.34 5.35 6.15 7.24 ) ( 8.10 8.98 9.88 11.1 12.1
(3.40-3.86) (4.08-4.64) (5.01-5.72) (5.75-6.56) (6.74-7.73 7.53-8.65) (8.33-9.60) (9.13-10.6) (10.2-11.9) (11.1-12.9)
[�]7-4.18 4.98 6.06 6.92 8.09 9.01 9.95 10.9 12.2 13.3
(3.94-4.45) (4.70-5.31) (5.71-6.45) (6.50-7.36) (7.58-8.60) (8.43-9.58) (9.28-10.6) (10.2-11.6) (11.3-13.1) (12.2-14.2)
1y 4.77 5.67 6.81
0-da 7.70 8.90 9.84 10.8 11.7 13.0 14.0
(4.51-5.05) (5.36-6.00) (6.44-7.21) (7.28-8.15) (8.38-9.41) (9.24-10.4) (1 0.1-11.4) (11.0-12.4)J1 (12.1-13.8) (13.0-14.9)
[20-dayF-6.-41-7F-7.-5-7--T-8--93 10.0 11.5 12.6 13.7 14.9 16.4 17.6
(6.10-6.74 (7.20-7.95) 8.49-9.38) 9.50-10.5) 10.9-12.0) .9-13.2) (1 112.9-14.4 (14.0-15.7 (15.4-17.3) (16.5-18.6)
30-day 7.93 9.33 10.8 12.0 13.5 14.7 15.9 17.0 18.5 19.7
(7.57-8.31) (8.90-9.76) (1 0.3-11.3) (11.4-12.5) (1 2.9-14.2) (13.9-15.4) (15.0-16.6) (16.1-17.8) 014-19.5) (18.5-20.7)
��ai]F-9.-9-9--�F-ll-.-7-7F-13-.3-
14.6 16.3 17.5 18.7 19.9 21.4 7 F-22.6
(9.58-10.4) (11.2-12.2) (12.8-13.9) (14.0-15.2) (15.5-16.9) (16.7-18.3) (17.8-19.5) (18.9-20.8) (20.3-22.4) (21.3-23.7)
18.8
15.6
3.9
�-day]F 1111.9.4 1313-14.4 15.0-16.2 16t3-107.7 18.0-19.5 (19 3020.9 20 5�22.2 (21 6�3.6) 2324 5.3) 242526.5
i
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
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.6004&lon=-80.5286&data=depth&units=english&series=pds 1/4

7/9/2020 Precipitation Frequency Data Server
(D NOAA Atlas 14,Volume 2,Version 3
Location name: Salisbury, North Carolina, USA* � P
Latitude: 35.60040,Longitude: -80.5286'
Elevation:784.42 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/hour)1
Average recurrence interval(years)
Duration��� 17-25
1 2 5 10 25 50 100 200 500 1000
[���F-4.64-75.50 6.42 7.06 7.78 8.26 8.69IF 9.06 9.46 9.72
(4.28-5.04) (5.08-5.99) (5.90-6.97) (6.48-7.64) (7.10-8.41) (7.50-8.94) (7.85-9.42) (8.14-9.84) (8.41-10.3) (8.58-10.6)
10-min 3.71 4.40 5.14 5.64 6.19 6.58 6.91 7.18 7.48 7.66
3424 (4.06 4.78) (4.73-5.58) (5.18-6.11) (5.66-6.71) (5.98-7.12) (6.24-7.48) (6.45-7.79) (6.65-8.14) (6.75 8.35)
F-1 _5-mtn 3.09 3.68 4.33 4.76 5.24 5.55 5.82 6.04 6.28 6.41
(2.85-3.36) (3.40�.01) (3.98-4.71) (4.37-5.16) (4.78-5.67) (5.04-6.01) (5.26-6.30) (5.43-6.56) (5.58-6.83) (5.65 6.99)
4.18 4.45 4.70 4.99 5.19
[����]F-2.-l-2-7F--2.-54-�F-3.O-8-7F-3.-4-5-7F-3.-88
(1.96-2.30) (2.35-2.77) (2.83-3.34) (3.16-3.74) (3.54-4.20) (3.80-4.53) (4.03-4.83) (4.22-5.10) (4.44-5.44) (4.57-5.66)
�]F 1.32 1.60 1.97 2.24 2.58 2.83 3.07 3.30 358 3.79
(1.22-1.43) (1.47-1.74) (1.82-2.14) (2.06-2.43) (2.36-2.79) JL-(2 (2.77-3.33) (2.96-3.58) (3.19-3.90) (3.34-4.13)
2-hr 0.763 0.924 1.15 1.32 1.53 1.70 1.86 2.01 2.21 2.36
(0.702-0.832) (0.848-1.01) I 1.05-L25) (1.20-1.43) (1.39-1.67) (1.53-1.84) (1.67-2.02) (1.79-2.19) (1.95-2.42) (2.06-2.59)
3-h,:]F 0.541 0.654 0.817 ^0.940 �1.10 ( 1.23 ) ( 1.36 1.48 1.65 1.78
(0.498-0.591) 02(0.6 -0.715) (0.750=0.892) (0.860-1.02) (1.00-1.20) 1.11-1.34 1.22-1.47) (1.32-1.61) (1.45-1.80) (1.54-1.94)
�h, 0.329 0.396 0.495 0.571 0.674 0.755 0.836 0.917 1.03 1.11
(0.303-0.359) (0.365-0.433) (0.455.0.541) (0.523-0.622) (0.613-0.732) (0.682 0.819) (0.749 0.907) (0.814-0.996) (0.899-1.12) (0.962 1.21)
:h,]IF-0.193 0.232 0.291 ( 0.338 0.401 0.452 0.504 0.558 0.631 ) 0.688
(0.10.210) (78- 0.214-0.254) (0.268-0.318) 0.310-0.368) (0.365-0.436) (0.408-0.489) (0.451-0.545) (0.493-0.602) (0.549-0.681 (0.590-0.743)
24-hr 0.115 0.139 0.174 0.202 0.240 0.270 00300 0.332 0.375 0.408
(0.107-0.124) (0.130-0.149) (0.163-0.187) (0.188-0.217) (0.223 0.258) (0.250-0.290) (0.278-0.322) (0.306-0.356) (0.344-0.403) (0.373-0.439)
2-day 0.067 0.081 ) 0.100 0.116 0.137 0.153 0.170 0.187 0.210 0.229
( .062-0.072) (0.075-0.086 (0.094-0.107) (0.108-0.124) (0.127-0.146) (0.142-0.164) (0.157-0.182) (0.173-0.200) (0.193-0.225) (0.209-0.245)
[3-day]F-0.0-4-77F-0.0-57-­IF0.071 0.081 0.096 0.107 0.119 0.131 0.147 0.160
(0.044-0.051) (0.053-0.061) (0.066-0.075) (0.076-0.087) (0.089-0.102) (0.100-0.115) (0.110-0.127) (0.121-0.140) (0.135-0.158) (0.147-0.171)
F4-day 0.038 0.045 6.056 0.064 0.075 0.084 0.094 0.103 0.116 0126
(0.0354-040) (0.042-0.048) (0.052-0.060) (0.060-0.068) (0.070-0.081) (0.078-0.090) (0.087-0.900) (0.095-0.110) (0.107-0.124) (0.115 0.135)
7-day 0.025 0.030 0.036 0.041 0.048 ­IF 0.054 .0597F 0.065 0.073 0.079
(0.023-0.026) (0.028-0.032) (0.034-0.038) (0.039-0.044) (0.045-0.051) (0.050-0.057) (0.055-0.063) (0.060-0.069) (0.067-0.078) (0.073-0.084)
0-day 0.020 0.024 0.028 0.032 0.037 0.041 0.045 0.049 0.054 0.058
1
(0.019-0.021) (0.022-0.025) (0.027-0.030) (0.030-0.034) (0.035 0.039) (0.039-0.043) (0.042-0.048) (0.046-0.052) (0.051-0.058) (0.054-0.062)
0.037
0.
24
20-day 0.01 -0 014) (0.01 -0 017) 0.018-0 020 0.020-0.022 0.02 30 025 0.02 5 0 0028 0.0270-0 030 0.029-0.033 (0.032--0 036 (0.03 -0 039)
30-day 0.011 0.0137F 0.015 0.017 0.019 0.020 0.022 0.0247F 0.026 0.027
(0.011-0.012) (0.012-0.014) (0.014-0.016) (0.016-0.017) (0.018-0.020) (0.019-0.021) (0.021-0.023) (0.022-0.025) (0.024-0.027) (0.026-0.029)
45-day 0.009 0.011 0.012 0.014 0.015 0.016 0.017 0.018 0.020 0.021
(0.009-0.010) (0.010-0.011) (0.012-0.013) (0.013-0.014) (0.014-0.016) (0.015-0.017) (0.016-0.018) (0.018-0.019) (0.019-0.021) (0.020-0.022)
0.017
60-day 0.08-0 009 0.09-0 010 0.010--0 011) 0.01100 012 0.013-0 014 0.01 30 015) 0.014-0 015) 0.01 -0 016 (0.016--0 018 0.017--0 018
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 11
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
https://hdsc.nws.noaa.gov/hdse/pfds/pfds_printpage.htmI?Iat=35.6004&Ion=80.5286&data=intensity&units=english&series=pds 1/4

Hydrologic Soil Group—Rowan County,North Carolina
542600 542700 542600 542900 543000 543100
35°36 20"N 35°36 20"N
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542600 542700 542800 542900 543000 543100
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Map Scale:1:4,130 if printed on A portrait(8.5"x 11")sheet.
Meters
$ N 0 50 100 200 300 8
Feet
0 200 400 800 1 2000
Map projection:Web Mercator Comer coordinates:WGS84 Edge tics:UTM Zone 17N WGS84
USDA Natural Resources Web Soil Survey 6/8/2020
Conservation Service National Cooperative Soil Survey Page 1 of 4

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Hydrologic Soil Group—Rowan County,North Carolina
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOl Percent of AOl
ChA Chewacla loam,0 to 2 B/D 0.9 3.9%
percent slopes,
frequently flooded
EnB Enon fine sandy loam,2 C 14.7 64.6%
to 8 percent slopes
to 15 percent slopes
C — — 2.2 9.5%
EnC Enon fine sand loam,8
_edg y /D - 14.7%
SeB Sed efield fine sand C/D 3.4',
loam, 1 to 6 percent
slopes
Ud Udorthents,loamy C 1.3 5.5%
VnB2 Vance sandy clay loam, !C 0.41 1.7%
2 to 8 percent slopes, I
moderately eroded
Totals for Area of Interest 22.81 100.0%'
t1SDA Natural Resources Web Soil Survey 6/8/2020
r Conservation Service National Cooperative Soil Survey Page 3 of 4

Hydrologic Soil Group—Rowan 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 6/8/2020
Conservation Service National Cooperative Soil Survey Page 4 of 4

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WinTR-55 Current Data Description
--- Identification Data ---
User: BKS/CRD Date: 7/21/2020
Project: United Rentals Units: English
SubTitle: Salisbury, NC Areal Units: Acres
State: North Carolina
County: Rowan NOAA
Filename: H:\United Rentals\Salisbury NC\Documents\Stormwater\2020-07--16 Pre Dev.w55
--- Sub-Area Data ---
Name Description Reach Area(ac) RCN Tc
------------------------------------------------------------------------------
PRE DEV 1 Outlet 4.59 76 .127
PRE DEV 2 Outlet 2.13 77 .149
Total area: 6.72 (ac)
--- Storm Data --
Rainfall Depth by Rainfall Return Period
2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr
(in) (in) (in) (in) (in) (in) (in)
--------------------------------------------------------------------------------
3.33 4.18 4.85 5.76 6.48 7.21 2.76
Storm Data Source: User-provided custom storm data
Rainfall Distribution Type: Type II
Dimensionless Unit Hydrograph: <standard>
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:42:15 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Storm Data
Rainfall Depth by Rainfall Return Period
2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr
(in) (in) (in) (in) (in) (in) (in)
--------------------------------------------------------------------------------
3.33 4.18 4.85 5.76 6.48 7.21 2.76
Storm Data Source: User-provided custom storm data
Rainfall Distribution Type: Type II
Dimensionless Unit Hydrograph: <standard>
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:42:19 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Summary Table
Sub-Area Drainage Time of Curve Receiving Sub-Area
Identifier Area Concentration Number Reach Description
(ac) (hr)
--------------------------------------------------------------------------------
PRE DEV 1 4.59 0.127 76 Outlet
PRE DEV 2 2.13 0.149 77 Outlet
Total Area: 6.72 (ac)
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:42:24 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Time of Concentration Details
Sub-Area Flow Mannings's End Wetted Travel
Identifier/ Length Slope n Area Perimeter Velocity Time
(ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr)
--------------------------------------------------------------------------------
PRE DEV 1
SHEET 100 0.0495 0.150 0.111
SHALLOW 155 0.0690 0.050 0.010
CHANNEL 85 4.000 0.006
Time of Concentration .127
PRE DEV 2
SHEET 100 0.0350 0.150 0.128
SHALLOW 190 0.0240 0.050 0.021
Time of Concentration .149
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:42:29 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Land Use and Curve Number Details
Sub-Area Hydrologic Sub--Area Curve
Identifier Land Use Soil Area Number
Group (ac)
--------------------------------------------------------------------------------
PRE DEV 1 Open space; grass cover > 750 (good) C 2.12 74
Paved parking lots, roofs, driveways C .13 98
Gravel (w/ right-of-way) C .83 89
Woods (good) C 1.51 70
Total Area / Weighted Curve Number 4.59 76
PRE DEV 2 Open space; grass cover > 750 (good) C 1.82 74
Paved parking lots, roofs, driveways C .17 98
Gravel (w/ right-of-way) C .14 89
Total Area / Weighted Curve Number 2.13 77
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:42:33 AM

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 1
PRE DEV 1
Hydrograph type = SCS Runoff Peak discharge = 9.030 cfs
Storm frequency = 2 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 20,716 cult
Drainage area = 4.590 ac Curve number = 76
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 7.62 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 1
Q (cfs) Hyd. No. 1 --2 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 1

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 1
PRE DEV 1
Hydrograph type = SCS Runoff Peak discharge = 17.57 cfs
Storm frequency = 10 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 40,196 cuft
Drainage area = 4.590 ac Curve number = 76
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 7.62 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 1
Q (cfs) Hyd. No. 1 -- 10 Year Q (cfs)
18.00 18.00
15.00 15.00
12.00 12.00
9.00 9.00
6.00 6.00
3.00 3.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 1 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 1
PRE DEV 1
Hydrograph type = SCS Runoff Peak discharge = 32.10 cfs
Storm frequency = 100 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 74,057 cuft
Drainage area = 4.590 ac Curve number = 76
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 7.62 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 1
Q (cfs) Q (cfs)
Hyd. No. 1 -- 100 Year
35.00 35.00
30.00 30.00
25.00 25.00
10.00 10.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 1 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 2
PRE DEV 2
Hydrograph type = SCS Runoff Peak discharge = 4.407 cfs
Storm frequency = 2 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 10,094 cuft
Drainage area = 2.130 ac Curve number = 77
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 8.94 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 2
Q (cfs) Hyd. No. 2 --2 Year Q (cfs)
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hyd No. 2

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 2
PRE DEV 2
Hydrograph type = SCS Runoff Peak discharge = 8.443 cfs
Storm frequency = 10 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 19,314 cuft
Drainage area = 2.130 ac Curve number = 77
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 8.94 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 2
Q (cfs) Hyd. No. 2-- 10 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 2 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 2
PRE DEV 2
Hydrograph type = SCS Runoff Peak discharge = 15.23 cfs
Storm frequency = 100 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 35,219 cuft
Drainage area = 2.130 ac Curve number = 77
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 8.94 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
PRE DEV 2
Q (cfs) Hyd. No. 2 -- 100 Year Q (cfs)
18.00 18.00
15.00 15.00
12.00 12.00
It
9.00 9.00
6.00 6.00
3.00 3.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 2 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 3
Total Pre Dev
Hydrograph type = Combine Peak discharge = 13.44 cfs
Storm frequency = 2 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 30,811 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 6.720 ac
Total Pre Dev
Q (cfs) Q (cfs)
Hyd. No. 3--2 Year
14.00 14.00
12.00 12.00
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 3 Hyd No. 1 Hyd No. 2

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 3
Total Pre Dev
Hydrograph type = Combine Peak discharge = 26.01 cfs
Storm frequency = 10 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 59,510 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 6.720 ac
Total Pre Dev
Q (cfs) Hyd. No. 3 -- 10 Year Q (cfs)
28.00 28.00
24.00 24.00
20.00 20.00
16.00 16.00
12.00 12.00
8.00 8.00
4.00 4.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hyd No. 3 Hyd No. 1 Hyd No. 2

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 3DO by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 3
Total Pre Dev
Hydrograph type = Combine Peak discharge = 47.33 cfs
Storm frequency = 100 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 109,276 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 6.720 ac
Total Pre Dev
Q (cfs) Q (cfs)
Hyd. No. 3 -- 100 Year
50.00 50.00
40.00 40.00
30.00 30.00
20.00 20.00
10.00 10.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 3 Hyd No. 1 Hyd No. 2

III. POST-DEVELOPMENT CONDITIONS:
A dry-detention pond is proposed on the eastern side of the project site and a second dry-
detention pond is proposed on the west side. Outflow from the detention systems will flow into
existing conveyance channels before combining in an un-named tributary of Town Creek before
crossing under I-85.
The total area of analysis can be broken down into four separate drainage basins (a review of the
Pre-and Post-Development Drainage Maps will help to clarify this Basin setup).
• Post Development Area 1 A comprises+/-2.60 acres. Area 1 A drains via sheet flow and
shallow concentrated flow towards pond 1 in the eastern part of the site. From there, run-
off drains to an unnamed tributary of Town Creek which flows under Interstate 85 to
Town Creek.
• Post Development Area 1 B comprises+/-1.97 acres. Area 1 B drains via sheet flow and
shallow concentrated flow that bypasses pond 1. From there, run-off drains to an
unnamed tributary of Town Creek which flows under Interstate 85 to Town Creek.
• Post Development Area 2A comprises +/-4.59 acres. Area 2A drains via sheet flow and
shallow concentrated flow towards pond 2 in the western part of the site. From there,
run-off drains to an unnamed tributary of the Ashley River.
• Post Development Area 2B comprises+/-1.14 acres. Area 2B drains via sheet flow and
shallow concentrated flow towards the detention pond in the northern part of the site.
From there, run-off drains to an unnamed tributary of the Ashley River.
Slopes across the majority of the developed areas range between 1.0%and 6%. Stormwater from
the developed site flows naturally to one of the proposed stormwater ponds or flows off-site
directly.
Runoff Calculations:
Runoff calculations are performed for Post-Development Area.
A. Runoff Curve Number:
Post-Developed Area 1 A
Open space, grass Gravel: 1.05 Ac. Impervious: 0.54 Ac.
cover(good
condition): 1.01 Ac
CN = 74 I CN =89 CN =98
Total Land Area =2.60 Acres
Weighted Runoff Curve Number=85

Post-Developed Area 1 B
Open space, grass Woods, good
cover(good condition: 1.51 ac.
condition): 0.46 Ac
CN =74 CN = 70
Total Land Area = 1.97 Acres
Weighted Runoff Curve Number=71
Post-Developed Area 2A
Open space, grass Gravel: 0.53 Ac. Impervious: 0.1 1 Ac.
cover (good
condition): 0.37 Ac
CN =74 CN =89 CN =98
Total Land Area = 1.01 Acres
Weighted Runoff Curve Number=85
Post-Developed Area 2B
Open space, grass Gravel: 0.46 Ac. Impervious: 0.15 Ac.
cover(good
condition): 0.53 Ac
CN = 74 ICN =89 CN =98
Total Land Area = 1.14 Acres
Weighted Runoff Curve Number=83
B. Time of Concentration:
Post Development Area 1 A
Sheet Flow(57 Shallow concentrated Shallow Concentrated Channel Flow (50'
feet at 1.00% flow for 75' @ 1.00% Flow for 140' @ at average 5 feet
average slope) on paved surface 1.21% on unpaved per second)
smooth surface surface
Tc= 1.02 min. Tc=0.60 min. Tc = 1.32 min. Tc=0.18 min.
Total Time of Concentration =3.12 minutes + use 6 minutes

Post Development Area 1 B
Sheet Flow (45 feet at 4.50% Shallow concentrated Channel Flow (220' at
average slope) grass, dense flow for 130' @ 4.50% average 4.5 feet per
on unpaved surface second)
Tc = 5.34 min. Tc=0.66 min. Tc=0.84 min.
Total Time of Concentration = 6.84 minutes
Post Development Area 2A
Sheet Flow(100 feet at 2.00% Shallow concentrated Shallow Concentrated
average slope) smooth surface flow for 60' @ 2.00% Flow for 18' @
on paved surface 16.70% on unpaved
surface
Tc= 1.20 min. Tc=0.36 min. Tc=0.06 min.
Total Time of Concentration = 1.62 minutes + use 6 minutes
Post Development Area 2B
Sheet Flow (100 feet at 4.60% Shallow concentrated
average slope) smooth surface flow for 30' @ 33.30%
on unpaved surface
Tc =0.84 min. Tc=0.06 min.
Total Time of Concentration =0.90 minutes + use 6 minutes
C. Rainfall
The 24-hour precipitation amounts for the site are per NOAA:
2-year storm event: 3.33 inches
10-year storm event: 4.85 inches
100-year storm event: 7.21 inches
D. Rate of Runoff
From this information, a hydrograph can be generated showing rate of flow versus time. Post-
development hydrographs for each storm event are included in this section.
Post Development Area 1 A
Storm Event Flow Rate, 0 (cfs)
2 year 8.15
10 year 13.81
100 year 22.66

Post Development Area 1 B
Storm Event Flow Rate, Q (cfs)
2 year 2.92
10 year 6.26
100 year 12.18
Post Development Area 2A
Storm Event Flow Rate, Q (cfs)
2 year 3.17
10 year 5.36
100 year 8.80
Post Development Area 2B
Storm Event Flow Rate, Q (cfs)
2 year 3.30
10 year 5.75
100 year 9.63

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WinTR-55 Current Data Description
--- Identification Data ---
User: BKS/CRD Date: 7/21/2020
Project: United Rentals Units: English
SubTitle: Salisbury, NC Areal Units: Acres
State: North Carolina
County: Rowan NOAA
Filename: H:\United Rentals\Salisbury NC\Documents\Stormwater\2020-07-20 Post Dev.w55
--- Sub-Area Data ---
Name Description Reach Area(ac) RCN Tc
------------------------------------------------------------------------------
POST D lA Reach 1 2.6 85 0.1
POST D 1B Reach 1 1.97 71 .114
POST D 2A Reach 2 1.01 86 0.1
POST D 2B Reach 2 1.14 83 0.1
Total area: 6.72 (ac)
--- Storm Data --
Rainfall Depth by Rainfall Return Period
2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr
(in) (in) (in) (in) (in) (in) (in)
--------------------------------------------------------------------------------
3.33 4.18 4.85 5.76 6.48 7.21 2.76
Storm Data Source: User-provided custom storm data
Rainfall Distribution Type: Type II
Dimensionless Unit Hydrograph: <standard>
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:41:34 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Storm Data
Rainfall Depth by Rainfall Return Period
2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr
(in) (in) (in) (in) (in) (in) (in)
----------------------------------------------------------------------------------
3.33 4.18 4.85 5.76 6,48 7.21 2.76
Storm Data Source: User-provided custom storm data
Rainfall Distribution Type: Type II
Dimensionless Unit Hydrograph: <standard>
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:41:38 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Summary Table
Sub-Area Drainage Time of Curve Receiving Sub-Area
Identifier Area Concentration Number Reach Description
(ac) (hr)
--------------------------------------------------------------------------------
POST D lA 2.60 0.100 85 Reach 1
POST D 1B 1.97 0.114 71 Reach 1
POST D 2A 1.01 0.100 86 Reach 2
POST D 2B 1.14 0.100 83 Reach 2
Total Area: 6.72 (ac)
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:41:46 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Time of Concentration Details
Sub-Area Flow Mannings's End Wetted Travel
Identifier/ Length Slope n Area Perimeter Velocity Time
(ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr)
--------------------------------------------------------------------------------
POST D 1A
SHEET 57 0.0100 0.011 0.017
SHALLOW 75 0.0100 0.025 0.010
SHALLOW 140 0.0121 0.050 0.022
CHANNEL 50 5.000 0.003
Time of Concentration 0.1
POST D 1B
SHEET 45 0.0450 0.240 0.089
SHALLOW 130 0.0450 0.050 0.011
CHANNEL 220 4.500 0.014
Time of Concentration .114
POST D 2A
SHEET 100 0.0200 0.011 0.020
SHALLOW 60 0.0200 0.025 0.006
SHALLOW 18 0.1670 0.050 0.001
Time of Concentration 0.1
POST D 2B
SHEET 100 0.0116 0.011 0.025
SHALLOW 40 0.1000 0.050 0.002
Time of Concentration 0.1
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:41:53 AM

BKS/CRD United Rentals
Salisbury, NC
Rowan NOAA County, North Carolina
Sub-Area Land Use and Curve Number Details
Sub-Area Hydrologic Sub-Area Curve
Identifier Land Use Soil Area Number
Group (ac)
--------------------------------------------------------------------------------
POST D IA Open space; grass cover > 75% (good) C 1.01 74
Paved parking lots, roofs, driveways C .54 98
Gravel (w/ right-of-way) C 1.05 89
Total Area / Weighted Curve Number 2.6 85
POST D 1B Open space; grass cover > 75% (good) C .46 74
Woods (good) C 1.51 70
Total Area / Weighted Curve Number 1.97 71
POST D 2A Open space; grass cover > 75% (good) C .3 74
Paved parking lots, roofs, driveways C .11 98
Gravel (w/ right-of-way) C .6 89
Total Area / Weighted Curve Number 1.01 86
POST D 2B Open space; grass cover > 75% (good) C .53 74
Paved parking lots, roofs, driveways C .15 98
Gravel (w/ right-of-way) C .46 89
Total Area / Weighted Curve Number 1.14 83
WinTR-55, Version 1.00.10 Page 1 7/21/2020 9:41:58 AM

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 5
Post Dev 1A
Hydrograph type = SCS Runoff Peak discharge = 8.149 cfs
Storm frequency = 2 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 16,538 cuft
Drainage area = 2.600 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1 A
Q (cfs) Hyd. No. 5 --2 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440
Hyd No. 5 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 31DO by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 5
Post Dev 1 A
Hydrograph type = SCS Runoff Peak discharge = 13.81 cfs
Storm frequency = 10 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 28,577 cuft
Drainage area = 2.600 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (TO = 6.00 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1 A
Q (cfs) Hyd. No. 5 -- 10 Year Q (cfs)
14.00 14.00
12.00 12.00
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320
Hyd No. 5 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 5
Post Dev 1 A
Hydrograph type = SCS Runoff Peak discharge = 22.66 cfs
Storm frequency = 100 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 48,254 cuft
Drainage area = 2.600 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1A
Q (cfs) Hyd. No. 5-- 100 Year Q (cfs)
24.00 24.00
20.00 20.00
16.00 16.00
12.00 12.00
8.00 8.00
4.00 4.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Hyd No. 5 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 3DO by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 7
Post Dev 1 B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 2.920 cfs
Storm frequency = 2 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 6,846 cuft
Drainage area = 1.970 ac Curve number = 71
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.80 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1 B (By-Pass)
Q (cfs) Hyd. No. 7 --2 Year Q (cfs)
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 7 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension forAutodesk®Civil 3D@ by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 7
Post Dev 1 B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 6.260 cfs
Storm frequency = 10 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 14,329 cuft
Drainage area = 1.970 ac Curve number = 71
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.80 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1 B (By-Pass)
Q (cfs) Hyd. No. 7-- 10 Year Q (cfs)
7.00 7.00
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 7 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 7
Post Dev 1 B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 12.18 cfs
Storm frequency = 100 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 27,895 cuft
Drainage area = 1.970 ac Curve number = 71
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.80 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 1 B (By-Pass)
Q (cfs) Hyd. No. 7 -- 100 Year Q (cfs)
14.00 14.00
12.00 12.00
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 7 Time(min)

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 10
Post Dev 2A
Hydrograph type = SCS Runoff Peak discharge = 3.165 cfs
Storm frequency = 2 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 6,424 cuft
Drainage area = 1.010 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2A
Q (cfs) Q (cfs)
Hyd. No. 10--2 Year
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440
Time(min)
Hyd No. 10

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk(@ Civil 3DO by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 10
Post Dev 2A
Hydrograph type = SCS Runoff Peak discharge = 5.364 cfs
Storm frequency = 10 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 11,101 cult
Drainage area = 1.010 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2A
Q (cfs) Hyd. No. 10 -- 10 Year Q (cfs)
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320
Time(min)
Hyd No. 10

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 3DO by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 10
Post Dev 2A
Hydrograph type = SCS Runoff Peak discharge = 8.803 cfs
Storm frequency = 100 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 18,745 cuft
Drainage area = 1.010 ac Curve number = 85
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2A
Q (cfs) Hyd. No. 10 -- 100 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Time(min)
Hyd No. 10

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 31DO by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 12
Post Dev 2B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 3.295 cfs
Storm frequency = 2 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 6,659 cuft
Drainage area = 1.140 ac Curve number = 83
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 3.33 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2B (By-Pass)
Q (cfs) Hyd. No. 12 --2 Year Q (cfs)
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440
Time(min)
Hyd No. 12

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday,11 /13/2020
Hyd. No. 12
Post Dev 2B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 5.748 cfs
Storm frequency = 10 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 11,789 cuft
Drainage area = 1.140 ac Curve number = 83
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 4.85 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2B (By-Pass)
Q (cfs) Hyd. No. 12 -- 10 Year Q (cfs)
6.00 6.00
4.00 4.00
3.00 3.00
----------------
0 120 240 360 480 600 720 840 960 1080 1200 1320
Time(min)
Hyd No. 12

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 12
Post Dev 2B (By-Pass)
Hydrograph type = SCS Runoff Peak discharge = 9.630 cfs
Storm frequency = 100 yrs Time to peak = 716 min
Time interval = 2 min Hyd. volume = 20,276 cuft
Drainage area = 1.140 ac Curve number = 83
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 6.00 min
Total precip. = 7.21 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
Post Dev 2B (By-Pass)
Q (cfs) Q (cfs)
Hyd. No. 12 -- 100 Year
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200
Time(min)
Hyd No. 12

IV. DETENTION POND DESIGN AND RESULTS
Following are the results of the drainage study for this project. The overall post-development
discharge rate is represented by the outflow from the combined dry-detention ponds.
The stormwater management ponds for the site are designed to store and release all storm events
up to, and including, the 100-year storm. The ponds have been designed to ensure the 2, 10, and
100-year storm events have been fully attenuated to less than their pre-development flow rates.
Freeboard has been provided from the top of the 100-year storm event and the top of each pond,
as can be seen in the Flow Rate Summary Tables below. Water quality is required for this site and
a sand filter will be used.
Dry-detention pond 1, as can be seen outlined on the grading plan, will have a bottom elevation at
776.10' and a top elevation of 780.00'. The outlet structure will send the first 16,886 cf(2-year
runoff) through a 6" orifice set at 776.10'. The riser has a 0.50' weir set at elevation 777.55,
(right above the 2-year storm elevation) to control the outflow in the riser structure along with the
top of the riser structure set at elevation 778.50'. This pond will also have a sand filter that is 2.5'
in depth. See calculations below.
Dry-detention pond 2, as can be seen outlined on the grading plan, will have a bottom elevation at
782.30' and a top elevation of 785.00'. The outlet structure will send the first 6,424 cf(2-year
runoff) through a 6" orifice set at 782.30'. The riser has a 2.75, weir set at elevation 783.35,
(right above the 2-year storm elevation) to control the outflow in the riser structure along with the
top of the riser structure set at elevation 785.00'. See calculations below.
Each stormwater pond's discharge will be regulated by a 5-foot x 5-foot square concrete riser.
The top of the concrete riser will serve as the primary spillway.
The staged outlet structure is designed using the pond modeling software Hydraflow Hydrographs
2004 (included in this section). Hydrographs are generated showing the actual routing of the
design storm events through the detention pond. These hydrographs are included in this section.
The detention ponds routing and analysis are summarized as follows:

Stormwater Ponds Routing and Analysis
Pre-Developed Analysis
Storm Event Pre-Developed Area 1 Pre-Developed Area 2 Total Pre-Developed
Peak Discharge Rate Peak Discharge Rate Peak Discharge Rate
2 year 9.03 cfs 4.41 cfs 13.44 cfs
10 year 17.57 cfs 8.44 cfs 26.01 cfs
100 year 32.10 cfs 15.23 cfs 47.33 cfs
Area 1 Point of Analysis Stormwater Pond Routing and Analysis
Storm Post-Dev. Area Post-Dev. Area 1 B Pond 1 Total Post-Dev. Area 1
Event 1 A Peak Flow Peak Flow (By-Pass) Flow Flow
2 year 8.15 cfs 2.92 cfs 1.00 cfs 3.87 cfs
10 year 13.81 cfs 6.26 cfs 1.27 cfs 7.46 cfs
100 year 22.66 cfs 12.18 cfs 6.23 cfs 17.85 cfs
Area 2 Point of Analysis Stormwater Pond Routing and Analysis
Storm Post-Dev. Area Post-Dev. Area 2B Pond 2 Total Post-Dev. Area 2
Event 2A Peak Flow Peak Flow (By-Pass) Flow Flow
2 year 3.17 cfs 3.30 cfs 0.83 cfs 4.03 cfs
10 year 5.36 cfs 5.75 cfs 2.45 cfs 7.29 cfs
100 year 8.93 cfs 9.63 cfs 5.43 cfs 14.36 cfs
Overall Stormwater Pond Routing and Analysis
Storm Pre-Dev. Pre-Dev. Total Pre- Post-Dev. Post-Dev. Total Post-
Event Area 1 Peak Area 2 Dev. Peak Area 1 Area 2 Dev. Flow
Flow Peak Flow Flow Peak Flow Peak
Flow
2 year 9.03 cfs 4.41 cfs 13.44 cfs 3.87 cfs 4.03 cfs 7.76 cfs
10 year 17.57 cfs 8.44 cfs 26.01 cfs 7.46 cfs 7.29 cfs 14.64 cfs
100 year 32.10 cfs 15.23 cfs 47.33 cfs 17.85 cfs 14.26 cfs 31.62 cfs
As demonstrated in the above table, the combined discharges of the Bypass Area and Ponds are
both detained to less than the pre-developed rates in the 2, 10, and 100 year events are passed
through the riser structures without overtopping the ponds. Hydrograph discharge tables are
provided in this section, with each table displaying time vs flow rate for each pond.

Water Quality Calculations — Sand Filter
The stormwater pond on-site has been designed as a dry detention pond. There will also be a
sand filter with the dry detention pond to address water quality. The sand filter has been designed
based on requirements from the NCDEQ Stormwater Design Manual.
Rv=0.05 +0.009 (Imp%) Drainage Area =2.60 AC (21% Impervious)
Rv=0.05 +0.009 (21) BUA=0.54 AC
Rv=0.24
WQv= Rv x Drainage Area x 1"
WQv=0.24 x 2.60 ac x 43,560 ftz/ac x 1/12" x 1"
WQv=2,265 cf
WQV(ADJ)=WQV(0.75) =2,265 (0.75) = 1,698.75 cf
1,698.75 cf occurs at elevation 776.50, Rip-Rap berm height set at 777.10
Max head measured from top of the berm (777.10) to the top of the sand (776.10), 1.00ft.
WQVADJ _ 1699
�maxfilter = � 1.00
AS+AF AS+AF
To ensure water quality volume is contained, As + AF >_ 1699
Ha= average head 4 Ha = hmaxfilter
2
Ha= 0.50ft
Minimum sedimentation Basin Surface Area
As = (240 * Rv*AD) * RD
As =240 * 0.24 * 2.60 *1
As = 149.76 sf
The dry pond has an actual surface area of 12,324 sf based on contour data, which is larger than
the minimum required of 149.76 sf.
Minimum Area of Sand Filter
Df= Depth of Sand Filter
K= Coefficient of permeability for the sand filter bed = 3.5 ft/day
t=Time required to drain the water quality volume through the sand filter bed. Per NCDENR
Stormwater BMP Manual 40 hours used. (1.66 Days)
Ha =Average head
(WQV)(Df) (1699)(2.5)
Asandfilter= (k)(t)(ha+Df) (3.5)(1.66)(0.50+2.5) —243.7 sf 244 sf used

Ensure Water Quality Volume iis1 Contained:
(AF + As)*( hmaxfilter) > WQVAdj
(244+12,324) * 1.00 > 1698.75
12,568 > 1698.75
Sandfilters must completely drain within 40 hours required by DWQ. This is show by using the
244 sf sand filter area and the minimum sand filter area equation to show that t<_ 1.66 days (40
hours).
Asandfliter= (WQV)(Df)
(k)(t)(ha+D f)
244 = (1699)(2.5) t= 1.66 days --> 1.66 days <_ 1.66 days
(3.5)(t)(0.50+2.5)
Underdrain Sizing Calculations
Underdrain sizing is based on Stormwater Manual.
Flow rate through the soil media is determined from Darcy's Law and assuming maximum
ponding and complete saturation along the depth of the medium.
OH
Q =AK L
Where,A=flow area perpendicular to L (ft2)
K= hydraulic conductivity (3.5 ft/day)
L= Flow path length (ft)
H = hydraulic head
Q =244ft2 * 3.5ft/day* 2.s f t = 610 cf/day=0.007 cfs
3.5 f t
Using a factor of safety of 10
Q*10=0.007 cfs * 10 =0.70 cfs

The following equation is then used to determine the diameter of single pipe,
Q*n
Where,D = Diameter of single pipe (inches)
n = roughness factor(recommended to be 0.011)
s = internal slope (recommended to be 0.5%)
Q = underdrain design flow cfs
0.70*0.011
D = 16 ( 0.0050.5 )311=6.97 in
Using table 5-1 from Chapter A-5 in the NCDEQ Stormwater Design Manual below it is
determined that five (5) 4" pipes are needed for the sand filter. Perforations shall be 3/8-inch in
diameter and cleanouts shall be provided at all bends and pipe ends.
Table 5-1
Number of Pipes Re aired in the Underdrain
If D is less than # of 4" pipes If D is less than # of 6"pij2es
5.13 2 7.84 2
5.95 3 9.11 3
6.66 4 10.13 4
7.22 5
7.75 6
8.20 7

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 6
Pond 1
Hydrograph type = Reservoir Peak discharge = 1.001 cfs
Storm frequency = 2 yrs Time to peak = 736 min
Time interval = 2 min Hyd. volume = 16,188 cuft
Inflow hyd. No. = 5 - Post Dev 1A Max. Elevation = 777.47 ft
Reservoir name = Pond 1 Max. Storage = 7,270 cuft
Storage Indication method used.
Pond 1
Q (cfs) Hyd. No. 6--2 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 240 480 720 960 1200 1440 1680 1920
Time(min)
Hyd No. 6 Hyd No. 5 i_I 1 1 1_i_ Total storage used = 7,270 cult

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 6
Pond 1
Hydrograph type = Reservoir Peak discharge = 1.272 cfs
Storm frequency = 10 yrs Time to peak = 744 min
Time interval = 2 min Hyd. volume = 28,226 cuft
Inflow hyd. No. = 5 - Post Dev 1A Max. Elevation = 778.16 ft
Reservoir name = Pond 1 Max. Storage = 13,285 cuft
Storage Indication method used.
Pond 1
Q (cfs) Hyd. No. 6 -- 10 Year Q (cfs)
14.00 14.00
12.00 12.00
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800
Time(min)
Hyd No. 6 Hyd No. 5 i 1 1_i 1 1_ Total storage used = 13,285 cult

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 6
Pond 1
Hydrograph type = Reservoir Peak discharge = 10.81 cfs
Storm frequency = 100 yrs Time to peak = 722 min
Time interval = 2 min Hyd. volume = 47,903 cuft
Inflow hyd. No. = 5 - Post Dev 1A Max. Elevation = 778.77 ft
Reservoir name = Pond 1 Max. Storage = 19,534 cuft
Storage Indication method used.
Pond 1
Q (cfs) Q (cfs)
Hyd. No. 6-- 100 Year
24.00 24.00
20.00 20.00
16.00 16.00
12.00 12.00
8.00 8.00
4.00 4.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 6 Hyd No. 5 L 1 1.1 11 Total storage used = 19,534 cult

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 8
Total Post Area 1
Hydrograph type = Combine Peak discharge = 3.868 cfs
Storm frequency = 2 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 23,033 cult
Inflow hyds. = 6, 7 Contrib. drain. area = 1.970 ac
Total Post Area 1
Q (cfs) Hyd. No. 8 --2 Year Q (cfs)
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 8 Hyd No. 6 Hyd No. 7

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 8
Total Post Area 1
Hydrograph type = Combine Peak discharge = 7.460 cfs
Storm frequency = 10 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 42,555 cuft
Inflow hyds. = 6, 7 Contrib. drain. area = 1.970 ac
Total Post Area 1
Q (cfs) Q (cfs)
Hyd. No. 8 -- 10 Year
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 8 Hyd No. 6 Hyd No. 7

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk@ Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 8
Total Post Area 1
Hydrograph type = Combine Peak discharge = 21.26 cfs
Storm frequency = 100 yrs Time to peak = 722 min
Time interval = 2 min Hyd. volume = 75,799 cuft
Inflow hyds. = 6, 7 Contrib. drain. area = 1.970 ac
Total Post Area 1
Q (cfs) Hyd. No. 8 -- 100 Year Q (cfs)
24.00 24.00
20.00 20.00
16.00 16.00
12.00 12.00
8.00 8.00
4.00 4.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 8 Hyd No. 6 Hyd No. 7

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 11
Pond 2
Hydrograph type = Reservoir Peak discharge = 0.828 cfs
Storm frequency = 2 yrs Time to peak = 724 min
Time interval = 2 min Hyd. volume = 6,419 cuft
Inflow hyd. No. = 10 - Post Dev 2A Max. Elevation = 783.31 ft
Reservoir name = Pond 2 Max. Storage = 2,091 cuft
Storage Indication method used.
Pond 2
Q (cfs) Hyd. No. 11 --2 Year Q(cfs)
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 11 Hyd No. 10 i_1 l I I.1 Total storage used = 2,091 cult

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 3DO by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 11
Pond 2
Hydrograph type = Reservoir Peak discharge = 2.453 cfs
Storm frequency = 10 yrs Time to peak = 722 min
Time interval = 2 min Hyd. volume = 11,095 cuft
Inflow hyd. No. = 10 - Post Dev 2A Max. Elevation = 783.64 ft
Reservoir name = Pond 2 Max. Storage = 3,458 cuft
Storage Indication method used.
Pond 2
Q (cfs) Hyd. No. 11 -- 10 Year Q (cfs)
6.00 6.00
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 11 Hyd No. 10 (_1_i_I_f Total storage used = 3,458 cuft

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 11
Pond 2
Hydrograph type = Reservoir Peak discharge = 5.354 cfs
Storm frequency = 100 yrs Time to peak = 722 min
Time interval = 2 min Hyd. volume = 18,739 cuft
Inflow hyd. No. = 10 - Post Dev 2A Max. Elevation = 784.01 ft
Reservoir name = Pond 2 Max. Storage = 4,949 cuft
Storage Indication method used.
Pond 2
Q (cfs) Hyd. No. 11 -- 100 Year Q (cfs)
10.00 10.00
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 11 Hyd No. 10 _L_1__1 1 1 Total storage used =4,949 cult

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D@ by Autodesk, Inc.v2021 Friday, 11 113/2020
Hyd. No. 13
Total Post Area 2
Hydrograph type = Combine Peak discharge = 4.034 cfs
Storm frequency = 2 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 13,078 cuft
Inflow hyds. = 11, 12 Contrib. drain. area = 1.140 ac
Total Post Area 2
Q (cfs) Hyd. No. 13--2 Year Q (cfs)
5.00 5.00
4.00 4.00
3.00 3.00
2.00 2.00
1.00 1.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 13 Hyd No. 11 Hyd No. 12

Hydrograph Report
Hydraf low Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 13
Total Post Area 2
Hydrograph type = Combine Peak discharge = 7.286 cfs
Storm frequency = 10 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 22,884 cuft
Inflow hyds. = 11, 12 Contrib. drain. area = 1.140 ac
Total Post Area 2
Q (cfs) Hyd. No. 13-- 10 Year Q (cfs)
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hyd No. 13 Hyd No. 11 Hyd No. 12

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 13
Total Post Area 2
Hydrograph type = Combine Peak discharge = 14.26 cfs
Storm frequency = 100 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 39,015 cuft
Inflow hyds. = 11, 12 Contrib. drain. area = 1.140 ac
Total Post Area 2
Q (cfs) Q (cfs)
Hyd. No. 13-- 100 Year
15.00 15.00
12.00 12.00
9.00 9.00
6.00 6.00
3.00 3.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 13 Hyd No. 11 Hyd No. 12

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 15
Total Post Dev
Hydrograph type = Combine Peak discharge = 7.757 cfs
Storm frequency = 2 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 36,111 cuft
Inflow hyds. = 8, 13 Contrib. drain. area = 0.000 ac
Total Post Dev
Q (cfs) Hyd. No. 15 --2 Year Q (cfs)
8.00 8.00
6.00 6.00
4.00 4.00
2.00 2.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 15 Hyd No. 8 Hyd No. 13

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk0 Civil 31DO by Autodesk, Inc.v2021 Friday, 11 /13/2020
Hyd. No. 15
Total Post Dev
Hydrograph type = Combine Peak discharge = 14.64 cfs
Storm frequency = 10 yrs Time to peak = 718 min
Time interval = 2 min Hyd. volume = 65,440 cuft
Inflow hyds. = 8, 13 Contrib. drain. area = 0.000 ac
Total Post Dev
Q (cfs) Hyd. No. 15-- 10 Year Q (cfs)
15.00 15.00
12.00 12.00
9.00 9.00
6.00 6.00
3.00 3.00
0.00 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 15 Hyd No. 8 Hyd No. 13

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk®Civil 3D®by Autodesk,Inc.v2021 Friday, 11 /13/2020
Hyd. No. 15
Total Post Dev
Hydrograph type = Combine Peak discharge = 32.94 cfs
Storm frequency = 100 yrs Time to peak = 720 min
Time interval = 2 min Hyd. volume = 114,813 cuft
Inflow hyds. = 8, 13 Contrib. drain. area = 0.000 ac
Total Post Dev
Q (cfs) Hyd. No. 15 -- 100 Year Q (cfs)
35.00 35.00
30.00 � 30.00
25.00 25.00
15.00 15.00
5.00 .._.m_.M..... ._,._ .. _ 5.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Time(min)
Hyd No. 15 Hyd No. 8 Hyd No. 13

V. Pipe Sizing Design and Results
Included in this report are the pipe sizing calculations for the on-site pipes and catch basins.
These are generated by the rational method and are based on the 10-year intensity for all storm
drain structures flowing to the pond. These calculations show the total flow for each pipe section,
velocity, hydraulic grade elevations, and spreads at each inlet. The flow, velocity, percent full, and
hydraulic grades have also been placed on the storm drain profile drawings.
It is noted that for certain pipes, these calculations show the "Total Flow (cfs)" exceeding the
listed "Capacity Full (cfs)." The Hydraflow Storm Sewers program calculates the "Capacity Full"
using the Manning's pipe equation for full flow. This equation assumes the slope of the Energy
Grade Line (EGL)to be equal to the slope of the pipe, and a flow depth equal to the diameter of
the pipe. For this project, the pipe sizes are minimized so that certain pipes are allowed to flow
under a surcharged condition. Surcharging a pipe places the Hydraulic Grade Line above the
crown of the pipe, builds up head on the flow through the pipes, and puts the pipes under
pressure. The HGL becomes steeper than the pipe inverts, and a flow greater than the full flow
capacity is observed. The Hydraflow Storm Sewers Version 8.0 User Manual explains this
phenomenon as a common and expected occurrence.

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VII. EROSION and SEDIMENT CONTROL
The following is a narrative of the sediment and erosion control devices to be used on the
proposed development to be constructed at 914 Webb Road. During land disturbance activities,
there will be approximately+/- 5.30 acres of total disturbance. Erosion and sedimentation
control for this project will be accomplished with a series of Best Management Practices (BMP's)
which are broken down into two construction phases.
During land disturbing activities on the subject site, the runoff will be controlled via a series of
sediment basins, inlet protection, check dams, silt fence, and stone construction entrance. The
sediment basins will be dewatered using Faircloth skimmers. The sediment basins will be
discharged with a reinforced concrete riser structure and will be converted to a permanent
stormwater pond. These items will be implemented per the NCDEQ erosion and sediment control
handbook and Rowan County requirements and maintained on a regular basis to insure their
proper operation.
Temporary seeding should be used throughout construction as needed, and all disturbed areas
should either receive stone base (for pavements) or permanent seeding as soon as each area is
complete. Permanent stabilization activities should not be delayed for the end of the project. Inlet
protection will be installed at storm drain inlets during all phases of construction, and check dams
will be employed as needed. Maintenance of the best management practices will continue until
final site stabilization can be achieved.
The SWPPP Plans and Details, which include a generalized sequence of construction, maintenance
notes, etc., can be found in the Site Development Plans, prepared by Freeland and Kauffman, Inc.