SW3191203_Calcs_20191227

EROSION CONTROL
& STORMWATER MANAGEMENT
CALCULATIONS
For
TRINITY RIDGE SUBDIVISION
Trinity Church Rd
Union County NC
SEAL
- 20165
Kevin E. Herring
ENGINEERING
WOW SAw Road
0a0m, NC-VI29

STORMWATER NARRATIVE
Trinity Ridge Sect. 2 Subdivision is a proposed 9 lot residential development
located off SR 2166 (Trinity Church Rd) approximately 620 feet west of SR 2168
(Carl Belk Rd). The site is in the Yadkin River Basin and drains to Polecat Creek.
The site is in Union County Zoning District.
The development is proposed as "low density" with a maximum built upon area of
24%. The street cross -sections are shoulder and ditch. This combined with
natural swales leaving the site shall provide the required conveyances.
The maximum built upon area per lot shall not exceed 9,000 sf for all 9 lots.
TRINITY RIDGE SECT. 2 SUBDIVISION
LOW DENSITY Subdivision Project Type
24%
Max Allowable Built Upon Area (DF)
462,323 sf
Total Site Area (SA)
110,957 sf
Total Allowable Imp. Area (SA x DF)
9
Number of Lots
29,216 sf
Roadway Area
(24,972 sf of pavement within prop road R/W)
(2,900 sf of drive across lots 9 & 10) 20'x145'
(1,344 sf of drives in R/W) 12'x16'x7 lots
54 sf
Other Area (Cluster Mailbox Pad)
9,000* sf Max Built Upon Area Per Lot
Polecat Creek
Receiving Stream
13-49-1
Stream Index
C
Stream Class
Yadkin/Pee Dee
IRiver Basin
*9,000 sf of BUA per lot reflects a 23.85% BUA for development.

EROSION CONTROL
CALCULATIONS

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SEDIMENT TRAP & SKIMMER BASIN Scale 1" = 100'
DRAINAGE AREA

Job: Trinity Ridge Job No. Date 11/25/2019 Sheet
Subject: REVISED TEMPORARY SEDIMENT TRAPS
By KEH Chk By
TRAP
DRAINAGE
AREA
(Ac)
DISTURBED
AREA
(Ac)
Runoff
Coeff.
C
Tc
(min)
Intensity
1(10)
(in/hr)
10 YEAR
PEAK
Q(10) cfs
ST-1
0.85
0.30
0.60
5
7.76
3.95
COMPOSITE RUNOFF "C" BASED ON C(DIST)=0.60 & C(UN-DIST)=0.33
DISCHARGE DETERMINED USING RATIONAL METHOD (Q=CIA)
SEDIMENT
TRAP
SURFACE AREA (SF)
REQ'D DESIGN PROV'D
VOLUME (CF)
REQ'D PROV'D
TRAP ELEV'S
WEIR BOTTOM
DIMENSIONS
@ TOP OF WEIR
WEIR
LNTH (FT)
ST-1
1720
Q(10)
1800
1080
3600
649.5
647.0
30
X
60
X
2.5
4
SURFACE AREA REQUIRED (SQ FT)= Q-435 sf/ac
VOLUME REQUIRED (CU FT)= 3600 cubic feet (Area disturbed)
VOLUMES PROVIDED BASED ON 2:1 SIDE SLOPES OF TRAP

Job Name
Subject
TRINITY RIDGE SUBDIVSION
TEMP SKIMMER BASIN
DETERMINE REQUIRED TRAP DIMENSIONS
Job No
Date 11/29/2019 Sheet
By KEH Chk By
DISCHARGE
REQUIRED
DIMENSIONS
SURFACE AREA
SEDIMENT
DRAINAGE
DISTURBED
Q=CIA"
SURFACE AREA
@ TOP OF PRIMARY SPILLWAY
PROVIDED
BASIN
AREA (Ac)
AREA(Ac)
(cfs)
(325)Q(10) (sq ft)
W L D
(sq ft)
SB 1.64 0.90 6.36
2068
35 X 60 X 2
2100
SB Composite "C" = 0.90ac @ 0.6 + 0.74ac @ 0.35 = 1.64ac @ 0.49 (Use 0.50)
Where C= 0.50 (composite) 1= 7.76 in/hr, Tc= 5 min for
DETERMINE STORAGE CAPACITY (At Skimmer Crest)
SEDIMENT
BASIN
DISTURBED
AREA(Ac)
REQUIRED
STORAGE VOLUME
1800cf per Acre Dist
STORAGE VOLUME
PROVIDED
(cu ft)
SB
0.90
1620
3360
Storage Volume based on 2:1 Side Slopes of Basin
SKIMMER ORIFICE DIAMETER (Determined by Faircloth Method)
(10 year Storm)
Calculate Skimmer Size for FalrclothSkimmer(E)
Basin Volume in Cubic Feet 3,360 Cu_Ft Skimmer Size 1.5 Inch
Days to Drain' 3 Days Orifice Radius 0.6 Inch[es]
Orifice Diameter 1.2 Inch[es]
In NC: assurue 3 days to drain If no results maximum floxw rate for asingIeskimmer is exceeded. Morethan oneskimmer map be required.
I.-]PA:8 =1LTA l=1:10=1L4 &A:214RviTA '1
SEDIMENT
BASIN
DISCHARGE
Q=CIA"
(cfs)
FROM CHART 8.07c
Minimum Emergency Spillway
SEDIMENT BASIN ELEVATIONS
BOTTOM SKIMMER EMERGENCY MIN. TOP
OF BASIN CREST SPILLWAY OF DAM
Q (cfs)
WIDTH (ft)
STAGE (ft)
SB
6.36
10
8
0.68
641
643
643.5
645.18
641
643
643.5
645.5
CONSTRUCTED DIMENSIONS
@ TOP OF EMERGENCY SPILLWAY
W L D
SB 37 X 62 X 2.5
4960 Sf X 2.5
Referenced Tables and Charts from NC Erosion & Sediment Control Manual (unless otherwise noted)
Minimum
Actual

DITCH CALCULATIONS

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ROADSIDE DITCH DRAINAGE AREAS Scale 1" = 100'

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ROADSIDE DITCH DRAINAGE AREAS Scale 1" = 100'

Job Name Trinity Ridge Subdivision Job No.
Subject DIVERSION CHANNEL SUMMARY SHEET
Date 11/25/2019
By KEH
<4.5f/s <1.0' F Design
Sheet
Chk By
Diversion
Channel
Drainage
Area (Ac)
Average
Slope (%)
Bottom
Width(ft)
Side Slope
ft/ft
Velocity
ft/s
Flow
Depth (ft)
Depth for
Liner (ft)
Top Width
T (ft)
Temporary
Liner
Ditch
Type
RD-1(1.5%)
0.22
1.50
0.50
3.5
1.38
0.37
1.00
7.50
STRAW WITH NET
A
RD-2(1.0%)
1.09
1.00
0.50
3.5
1.78
0.76
1.50
11.00
STRAW WITH NET
B
RD-3(1.5%)
1.30
1.50
0.50
3.5
2.16
0.75
1.50
11.00
STRAW WITH NET
B
STRAW WITH NET" TO BE NAG S-75 OR EQUAL

Job Name Trinity Ridge Subdivision Job No. Date 11/25/2019 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL: RD-1(1.5%)
DRAINAGE AREA: 0.22
MAX SHEAR Td allowed: 1.45
AVERAGE SLOPE: 1.50 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 2.52 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER: STRAW WITH NET
*MANNINGS (n) of 0.065 used for design
DISCHARGE**
DEPTH
VELOCITY
Calculated Shear
Q (cfs)
d (ft)
v (f/s)
(Td) ****
0.66
0.37
0.98
0.35
Calculated shear of 0.35 is less than the Permissable Shear*** of 1.45
Therefore STRAW WITH NET can be used as a temporary liner for RD-1(1.5%)
`Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
O=CIA Where C= 0.5 1= 7.76 in/hr for channel design,Tc= 5.0 min
1= 6.07 in/hr for 2 year storm REF: NOAA Atlas 14 Data
"`Permissible Shear Stress Td obtained from Table 8.05g
""Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manuai (unless otherwise noted)

Job Name Trinity Ridge Subdivision Job No.
Subject ROADSIDE DITCHES
DETERMINE GRASS LINER
PROPOSED GRASS LINER: TALL FESCUE
Use Retardence Class D
Date 11/25/2019 Sheet
By KEH Chk By
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL: RD-1(1.5%
AVERAGE SLOPE:
1.50 %
MAX VELOCITY allowed:
4.50 feet/sec
MANNING'S (n) used:
0.045
MAX VR allowed:
2.2
DISCHARGE
FLOW
WETTED
CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA
AREA
PERIMETER
DEPTH FROUDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs)
(sq ft)
(ft)
(ft) No. Fr VR
0.36 3.5 0.5 1.38 0.84
0.61
3.07
0.26 0.54 0.28
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 1.38 feet/sec is less than permissable velocity of
VR CHECK
Calculated VR 0.28 is less than the maximum allowable VR of
Therefore TALL FESCUE can be used as a grass liner for RD-1(1.5%)
`Permissible Velocity Obtained from Table 8.05a
"VR = Velocity ` Hydraulic Radius = Velocity ` Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manuai (unless otherwise noted)
2.2
4.50 feet/sec

Job Name Trinity Ridge Subdivision Job No. Date 11/25/2019 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL: RD-2(1.0%)
DRAINAGE AREA: 1.09 Acres
MAX SHEAR Td allowed: 1.45
AVERAGE SLOPE: 1.00 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 3.27 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER: STRAW WITH NET
*MANNINGS (n) of 0.033 used for design
DISCHARGE**
DEPTH
VELOCITY
Calculated Shear
Q (cfs)
d (ft)
v (f/s)
(Td) ****
3.31
0.60
2.11
0.38
Calculated shear of 0.38 is less than the Permissable Shear*** of 1.45
Therefore STRAW WITH NET can be used as a temporary liner for RD-2(1.0%)
`Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
O=CIA Where C= 0.5 1= 7.76 in/hr for channel design,Tc= 5 min
1= 6.07 in/hr for 2 year storm REF: NOAA Atlas 14 Data
"`Permissible Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manuai (unless otherwise noted)

Job Name Trinity Ridge Subdivision Job No.
Subject ROADSIDE DITCHES
DETERMINE GRASS LINER
PROPOSED GRASS LINER: TALL FESCUE
Use Retardence Class D
Date 11/25/2019 Sheet
By KEH Chk By
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL: RD-2(1.0%
AVERAGE SLOPE:
1.00 %
MAX VELOCITY allowed:
4.50 feet/sec
MANNING'S (n) used:
0.045
MAX VR allowed:
2.2
1 d
b1
b
DISCHARGE
FLOW
WETTED
CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA
AREA
PERIMETER
DEPTH FROLIDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs)
(sq ft)
(ft)
(ft) No. Fr VR
0.76 3.5 0.5 1.78 4.24
2.38
6.01
0.55 0.49 0.71
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 1.78 feet/sec is less than permissable velocity of
VR CHECK
Calculated VR 0.71 is less than the maximum allowable VR of
Therefore TALL FESCUE can be used as a grass liner for RD-2(1.0%)
'Permissable Velocity Obtained from Table 8.05a
"VR = Velocity' Hydraulic Radius = Velocity' Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
2.2
4.50 feet/sec

Job Name Trinity Ridge Subdivision Job No. Date 11/25/2019 Sheet
Subject ROADSIDE DITCHES By KEH Chk By
DETERMINE TEMPORARY LINER
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Velocity is checked to see if Temporary Liner is required. If required, 2 year storm is used for design.
Shear Stress is then compared to Permissable Shear Stress allowed.
PROPOSED CHANNEL: RD-3(1.5%)
DRAINAGE AREA: 1.30 Acres
MAX SHEAR Td allowed: 1.45
AVERAGE SLOPE: 1.50 %
VELOCITY CHECK of Channel Design using Manning of 0.02 (Bare Earth)
Calculated VELOCITY of 3.97 is GREATER THAN 2 Feet per second
TEMPORARY LINER REQUIRED (USING 2 YEAR STORM FOR DESIGN)
PROPOSED LINER: STRAW WITH NET
*MANNINGS (n) of 0.033 used for design
DISCHARGE**
DEPTH
VELOCITY
Calculated Shear
Q (cfs)
d (ft)
v (f/s)
(Td) ****
3.94
0.59
2.57
0.56
Calculated shear of 0.56 is less than the Permissable Shear*** of 1.45
Therefore STRAW WITH NET can be used as a temporary liner for RD-3(1.5%)
`Mannings Coefficient obtained from Table 8.05e
**RATIONAL METHOD USED TO DETERMINE DISCHARGE
Q=CIA Where C= 0.5 1= 7.76 in/hr for channel design,Tc= 5 min
1= 6.07 in/hr for 2 year storm REF: NOAA Atlas 14 Data
"`Permissible Shear Stress Td obtained from Table 8.05g
****Td=yds Where T=Shear Stress(lb/sq ft), y=unit wt of water, (62.4lb/cubic ft), d=flow depth(ft), s=slope(ft/ft)
Tables From the NC Erosion & Sediment Control Manuai (unless otherwise noted)

Job Name Trinity Ridge Subdivision Job No.
Subject ROADSIDE DITCHES
DETERMINE GRASS LINER
PROPOSED GRASS LINER: TALL FESCUE
Use Retardence Class D
Date 11/25/2019 Sheet
By KEH Chk By
APPROACH: Channel Design calculated using NORMAL DEPTH procedure.
Calculated VELOCITY is compared to MAXIMUM VELOCITY allowed for liner.
Calculated VR is then compared to Fig. 8.05c to determine if design is within range for prop.RETARDENCE CLASS
PROPOSED CHANNEL: RD-3(1.5%
AVERAGE SLOPE:
1.50 %
MAX VELOCITY allowed:
4.50 feet/sec
MANNING'S (n) used:
0.045
MAX VR allowed:
2.2
1 d
M
b
DISCHARGE
FLOW
WETTED
CRITICAL
DEPTH Side Slope Bottom VELOCITY Q=CIA
AREA
PERIMETER
DEPTH FROLIDE
(d) ft ft/ft Width (ft) V (f/s) Q(10) (cfs)
(sq ft)
(ft)
(ft) No. Fr VR
0.75 3.5 0.5 2.16 5.03
2.32
5.94
0.59 0.60 0.85
FLOW IS SUBCRITICAL
VELOCITY CHECK
Calculated velocity of 2.16 feet/sec is less than permissable velocity of
VR CHECK
Calculated VR 0.85 is less than the maximum allowable VR of
Therefore TALL FESCUE can be used as a grass liner for RD-3(1.5%)
'Permissable Velocity Obtained from Table 8.05a
"VR = Velocity' Hydraulic Radius = Velocity' Flow Area/Wetted Perimeter
Tables From the NC Erosion & Sediment Control Manual (unless otherwise noted)
2.2
4.50 feet/sec

STORM DRAINAGE
CALCULATIONS

Culvert P1
DA = 1.40ac
C = 0.60, Tc=5min
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STORM DRAINAGE - DRAINAGE AREAS Scale 1" = 100'

Job: Trinity Ridge Subdivision Job No. Date 11/29/2019 Sheet
Subject: Tc Calcs - New Street Culvert By KEH Chk By
DRAINAGE AREA = 4.5 acs
Segment ID:
Al
Surface description (table 3-12):
Pvmt
Manning's roughness coeff., n:
0.01
Flow length, L (total L<300') (ft):
50.00
2yr 24 hour rainfall, P (in):
3.58
NOAA Atlas 14
Land slope, s (ft/ft):
0.015
Tc= 0.007 (nL)10.8 1
0.01
hours
P^0.5 x s^0.4
Segment ID:
A2
Surface description (table 3-12):
Dense Grass
Manning's roughness coeff., n:
0.24
Flow length, L (total L<300') (ft):
50.00
2yr 24 hour rainfall, P (in):
3.58
NOAA Atlas 14
Land slope, s (ft/ft):
0.015
Tc= 0.007 (nL)10.8 1
0.14
hours
P^0.5 x s^0.4
SHALLOW CONCENTRATED FLOW
Segment ID:
B
Flow length, L (ft):
500.00
Watercourse slope, s (ft/ft):
0.036
Average velocity, V (fig3-5) (ft/s):
3.10
Tc= L / (3600xV) T
0.045
hours
CHANNEL FLOW
Segment ID:
C
Assume velocity, V (ft/s):
7.00
Flow length, L (ft):
0.00
Tc= L / (3600xV) T
0.000
hours
Total Tc path =
0.202
hours = 12.1 minutes
USE 10 minutes for Analysis

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8.03.28 Bev. 6/06

Job Name Trinity Ridge Job No. Date 11/29/2019 Sheet
Subject STORM DRAIN (RATIONAL METHOD) By KEH Chk By
STORM DESIGN YEAR: 25
DETERMINE DRAINAGE AREA ENTERING CULVERT
PIPE
Drain
Area (Ac)
Runoff
Coeff "C"
Calculated
Tc(min)
Used
Tc(min)
Storm
Design YR
NOAA
I (in/hr)
Frequency
Factor
Discharge
Q (cfs)
P1
1.40
0.50
5
5
25
8.59
1.10
6.6
P2
4.50
0.50
12
10
25
6.85
1.10
17.0
MATERIAL
Manning n
Concrete Box Culvert
0.015
Concrete Pipe
0.013
Corrugated Metal Pipe
0.024
Plastic Pipe
0.010
Smooth Steel Pipe
1 0.010
DETERMINE MINIMUM PIPE SIZE USING MANNING EQUATION
Drain
PIPE Area
Discharge
Q(25)
Manning's
n
# of
Lines
Slope
S (ft/ft)
Proposed
Size (in) HW/D
Velocity
(fps)
P1 1.40
7
0.013
1
0.0110
18 1.00
6.50
P2 4.50
17
0.013
1
0.0125
24 1.19
8.64

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-A
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WI = £ 1 9
#1=15"
/WI = £O
Lin HEADWATER DEPTH FOR
HIAa 'EFF%CALF■2a3 CONCRETE PIPE CULVERTS
pltV,it,j 6W,IC14 WITH rN L E T C O N T R M
OF Ay■�Lf RGA611 A&. 'cap
%-a2

MANNING'S EQUATION FOR PIPE FLOW
Project: Trinity Ridge Location: P1
By: Date:
Chk. Bv: Date:
Mannings Formula d
Q=(1.486/n )ARh113S' i2
R=A/P
A=cross sectional area
P=wetted perimeter
S=slope of channel
n=Manning's roughness coefficient
Wetted Hydraulic
Area,ft2 Perimeter, ft Radius, ft
1.01 2.52 0.40
Created by: Mike O'Shea
V=(1.49/n)Rh213S112
Q=V x A
Solution to Mannings Equation
velocity ft/s flow, cfs
6.50 6.56
mdo version 12.8.00
Clear Data
Entry Cells
INPUT
D=
18 inches
d=
10 inches
n=
0.013 mannings coeff
0=
167.2 degrees
S=
0.011 slope in/in
Mannina's n-values
PVC
0.01
PE (<9"dia)
0.015
PE (>12"dia)
0.02
PE(9-12"dia)
0.017
CMP
0.025
ADS N12
0.012
HCMP
0.023
Cone
0.013

MANNING'S EQUATION FOR PIPE FLOW
Project: Trinity Ridge Location: P2
By: Date:
Chk. Bv: Date:
Mannings Formula d
Q=(1.486/n )ARh213S' i2
R=A/P
A=cross sectional area
P=wetted perimeter
S=slope of channel
n=Manning's roughness coefficient
Wetted Hydraulic
Area,ft2 Perimeter, ft Radius, ft
1.97 3.55 0.56
Created by: Mike O'Shea
V=(1.49/n)Rh213S112
Q=V x A
Solution to Mannings Equation
velocity ft/s flow, cfs
8.64 17.06
mdo version 12.8.00
Clear Data
Entry Cells
INPUT
D=
24 inches
d=
14.44 inches
n=
0.013 mannings coeff
0=
156.5 degrees
S=
0.0125 slope in/in
Mannina's n-values
PVC
0.01
PE (<9"dia)
0.015
PE (>12"dia)
0.02
PE(9-12"dia)
0.017
CMP
0.025
ADS N12
0.012
HCMP
0.023
Cone
0.013

APRON
CALCULATIONS

Job: Trinity Ridge Job No.
Subject: Apron Calcs Al
APRON: Al (18" RCP)
Pipe Diameter, Do
18 Inches or
RECEIVING OUTLET (CHANNEL / SHEET FLOW):
Apron Length, L=
10 Feet (from Fig 8.06a)
Channel Width, b=
0.5 Feet
Side Slope, MA =
3 :1
H (2/3 Pipe Dia): =
1.0 Feet
Apron Width, W1 =
4.5 Feet (3 * Pipe Dia.)
Apron Width, W2 =
6.5 Feet
d5o Stone Size =
0.67 Feet (from Fig 8.06a) _
Apron Thickness, t=
18.1 inches
Outlet
W - Do + La
p1pe
diametern(,
LaAiiil
i
—►r
7 i water c 0.500
20
L=10'min
5 P1 10
Q(25) = 7cfs
Date 11/29/2019 Sheet
By KEH Chk By
1.5 Feet
CHANNEL
8 inches
20 50 100
Discharge (ft3lsec)
40
200 500
m
2
in
a
cG
cc
a
0
1 �
&0=8"
NCDOT
0 Class B
1000

Job: Trinity Ridge Job No. Date 11/29/2019 Sheet
Subject: Apron Calcs A2 By KEH Chk By
APRON: A2 (24" RCP)
Pipe Diameter, Do
24 Inches or
2 Feet
RECEIVING OUTLET (CHANNEL / SHEET FLOW):
SHEET FLOW
Apron Length, L=
12 Feet (from Fig 8.06a)
Channel Width, b=
0 Feet (Sheet Flow)
1 Tw
Side Slope, MA =
3 :1
H (2/3 Pipe Dia): =
1.3 Feet
*
�
Apron Width, W1 =
6 Feet (3 Pipe Dia.)
Apron Width, W2 =
14.0 Feet
dso Stone Size =
0.67 Feet (from Fig 8.06a) =
8 inches
Apron Thickness, t=
18.1 inches
Outlet M pp + La
9 _ _
pipe
diameter (Do)
a
80
T i water 0.500
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I
10
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SUPPORTING DATA

Table 2-4
Recommended Runoff Coefficient Values
Description of Area Runoff Coefredent IQ
Lawns
0.30
Wooded
0.25
Streets
0.95
Gravel Areas
0.65
Drives, walks, roofs
0.95
Bare soils
0.45
Residential (including streets):
Single-FamHy (Lot < 2U,C00 square feet - SF}
0.60
Single-Famlly (Lot> 20.000 square feet - SF}
0.50
Mufti-farnlly, Attached
0.70
Industrial,
Light areas
0.70
Heavy areas
0.80
Office Parks
0.75
Shopping Centers
0.80
Note: The above runoff coefficients are valid for 2-year to 10-year storm
frequencies
dryly. Coefficients must be accompanied with a CI factor when used for less frequent,
higher intensity storms.
Table 2-13
Roughness Coefficients (Manni;ng's n), far Sheet Flow
Surface Description
n
Smooth surfaces (concrete, asphalt
0.01 B
gravel, or bane sail
Fallow (no residue)
0.05
CuMvated Soils:
Residue Cower < 20%
0.06
Residue Cover s 20%
0.17
Grass:
Short grass pralrie
0.15
Dense grasses
0.24
Bermuda grass
0.41
Range (natural)
0.13
Woods'
Light underbrush
0.40
Dense underbrush
0.80
'The rr values are a composite of information by Engman (19M).
21ncludes species such as weeping lvegrass, bluegrass, buffalagrass_ blue gamma grass,
and native grass mixture.
'When selecting n, consider cover to a height of about 0.1 ft. This is the only earl of the plant
cover that w411 obstruct sheet flaw.
Source: MRCS. TR-55, Second Edrfiarr, .tune 1986

NOAA ATLAS 14
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WTN 9(We CONFIDENCE INTERVAL S AN❑ SUPPLEMENTARY INFORMATION
NOAAAIIas 14, Vol uMe 2, VefShon 3

11/3/2019 Precipitation Frequency Data Server
NOAA Atlas 14, Volume 2, Version 3
Location name: Monroe, North Carolina, USA*'
Latitude: 34.83530, Longitude:-80.60610
Elevation: 659.78 ft**
%'04MR,
'source: ESRI Maps
" source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parcybok, 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
1
����������
2
5
10
25
50
100
200
500
1000
0.429
0.506
0.587
0.647
0.716
0.764
0.808
0.849
0.896
0.930
5-min
(0.395-0.466)
(0.465-0.551)
(0.538-0.639)
(0.593-0.702)
(0.653-0.776)
(0.694-0.828)
(0.730-0.876)
(0.763-0.921)
(0.798-0.974)
(0.822-1.01)
0.685
0.809
0.940
1.03
1.14
1.22
1.28
1.35
1.42
1.46
10-min
(0.631-0.744)
(0.744-0.882)
(0.862-1.02)
(0.948-1.12)
(1.04-1.24)
(1.11-1.32)
(1.16-1.39)
(1.21-1.46)
(1.26-1.54)
(1.30-1.60)
1.8
15-min
0.789-0 930
0.935-1.11
1.09 1929
1.20-1142
1.3241557
1.40-1 67
1.4761276
1.53 1084
1.59 1894
1.63 2400
1.17
1.41
1.69
1.90
2.14
2.32
2.49
2.64
2.84
2.98
30-min
1
( .08-1.27)
(1.29-1.53)
(1.55-1.84)
(1.74-2.06)
1 (2.25-2.70)
(2.38-2.87) 11
(2.53-3.09)
(2.63-3.24)
1.46
1.76
2.17
2.47
2.85
3.14
3.43
3.71
4.07
4.34
60-min
(1.35-1.59)
(1.62-1.92)
(1.99-2.36)
(2.26-2.68)
(2.60-3.09)
(2.86-3.41)
(3.10-3.71)j
1 (3.63-4.43)
(3.84-4.73)
1.68
2.03
2.52
2.89
3.37
3.74
4.12
4.49
4.98
5.35
2-hr
1
( .54-1.84)
(1.86-2.22)
(2.30-2.75)
(2.63-3.16)
(3.06-3.67)
(3.38-4.08)
(3.70-4.48 )
( 4.00-4.88 )
( 4.39-5.42 )
( 4.69-5.84 )
1.78
2.15
2.68
3.10
3.66
4.11
4.57
5.04
5.69
6.20
3-hr
1
( .63-1.96)
(1.97-2.37)
(2.45-2.95)
(2.82-3.40) 11
(3.31-4.01) 1
1 (4.47-5.49)
(4.97-6.21)
(5.37-6.78)
2.13
7 2.56
7 3.20
7 3.71
4.39
4.95
5.52
6.11
6.93
7.58
6-hr
(1.95-2.34)
(2.35-2.82)
(2.93-3.51)
(3.38-4.06)
(3.98-4.80)
(4.45-5.39)
(4.93-6.01)
(5.41-6.64)
(6.05-7.53)
(6.54-8.24)
2.50
2 3.0
3.79
4
5.26
5.96
6.69
7.45
8.53
9.41
12-hr
.40
(2 .30-2.74)
(2.77-3.32)
(3.47-4.15)
(4.01-4.82)
(4.77-5.75)
(5.36-6.50)
(5.95-7.28)
(6.56-8.11)
(7.39-9.28)
(8.04-10.2)
2.97
3.58
4.51
5.26
6.33
7.21
8.15
9.16
10.6
11.8
24-hr
(2.73-3.24)
(3.30-3.91)
(4.14-4.91)
(4.82-5.73)
(5.77-6.90)
(6.55-7.86)
(7.36-8.90) 11
(8.22-10.0) 11
(9.43-11.6)
( 10.4-13.0)
3.50
7 4.21
7 5.26
7 6.11
7.32
8.31
9.37
10.5
12.1
13.5
2iiay
(3.22-3.81)
(3.88-4.59)
(4.84-5.74)
(5.60-6.66)
1 (9.43-11.5) 1
1(11.8-14.9)1
3.71
7 4.46
7 5.54
7 6.41
7.65
8.67
9.74
10.9
12.5
13.9
3iiay
(3.43-4.03)
(4.12-4.84)
(5.11-6.02)
(5.90-6.97)
(7.01-8.32)
(7.91-9.43)
(8.84-10.6)
(9.81-11.9)
( 11.2-13.7 )
( 12.3-15.3)
3.92
4.70
5.82
6.72
7.98
9.02
10.1
11.3
13.0
14.4
4iiay
(3.64-4.25)
(4.36-5.10)
(5.38-6.31)
(6.20-7.28)
(7.34-8.66)
(8.26-9.80)
(9.21-11.0)
( 10.2-12.3 )
(11.6-14.2)
( 12.8-15.7)
4.54
7 5.42
7 6.61
7 7.57
8.92
10.0
11.2
12.3
14.1
15.6
7�ay
(4.24-4.88)
(5.06-5.83)
(6.16-7.11)
(7.05-8.14)
(8.27-9.60)
(9.24-10.8) 1
1(14.0-17.0)1
5.20
7 6.19
7
87
9.85
1.0 1
12.1
13.3
14.9
16.4
10-day
.46
.4
(4 .87-5.57)
(5.79-6.62)
(6.98-7.99)
(7.91-9.07) 11
(9.17-10.6) 11
(10.2-11.8) 1
1 (13.7-16.2)
(14.9-17.7)
6.97
8.23
9.73
10.9
12.6
13.9
15.2
16.5
18.4
19.8
20-day
(6.56-7.43)
(7.74-8.77)
(9.14-10.4)
(10.3-11.7) 11
(11.8-13.4) 11
(12.9-14.8)
1 (15.3-17.7) 11
(16.9-19.7)
(18.1-21.3)
8.56
10.1
11.7
13.0
14.8
16.1
17.4
18.7
20.5
21.8
30-day
(8.09-9.07)
(9.52-10.7)
(11.1-12.4)
(12.3-13.8) 11
(13.9-15.6) 1
1 (19.0-21.8)
(20.2-23.3)
10.7
12.6
14.4
15.9
17.7
19.2
20.6
21.9
23.7
25.0
45-day
(102-11.3)
11 (12.0-13.2)
11 (13.7-15.2)
11 (15.1-16.7) 1
1 (19.4-21.7)
(20.6-23.1)
(22.2-25.1)
(23.4-26.6)
12.8
15.0
17.0
18.6
20.6
22.1
23.5
24.9
28.1
60-day
=(258.2)
(122-13.4)
(14.3-15.7)
(16.2-17.8)
(17.7-19.4)
(19.5-21.5)
(20.9-23.1)
(22.3-24.7)
(23.5-26.2)
(26.3-29.6)
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=34.8353&Ion=-80.606l &data=depth&units=english&series=pds 1 /4

11/3/2019 Precipitation Frequency Data Server
NOAA Atlas 14, Volume 2, Version 3
Location name: Monroe, North Carolina, USA*'
Latitude: 34.83530, Longitude:-80.60610
Elevation: 659.78 ft**
%'04MR,
'source: ESRI Maps
" source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parcybok, 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)
1
2
5
10
25
50
100
200
500
1000
5-min
5.15
6.07
(5.58-6.61)
7.04
(6.46-7.67)
7.76
(7.12-8.42)
8.59
(7.84-9.31)
9.17
1 (8.33-9.94)
9.70
1 (8.76-10.5)
10.2
1 (9.16-11.1)
10.8
1 (9.58-11.7)
11.2
1 (9.86-12.2)
4.11
4.85
5.64
6.21
6.85
7.30
7.70
8.08
8.50
8.78
10-min
(3.79-4.46)
(4.46-5.29)
(5.17-6.14)
(5.69-6.74)
(6.25-7.42)
1 (6.63-7.91)
1 (6.97-8.35)
1 (7.26-8.76)
1 (7.58-9.25)
1 (7.77-9.57)
15-min
3. 6 3?72
3.74 4743
4. 675.18
4. 0�5.68
5. 876.27
5. 0 6.68
5.874.04
6.161 7937
6. 617.76
6. 0 8501
2.35
2.81
3.38
3.79
4.28
4.64
4.97
5.29
5.68
5.95
30-min
1 (2.58-3.06) 11
(3.10-3.68) 11
(3.47-4.12)
(3.91-4.64)
(4.21-5.03)
(4.49-5.39)
1 (4.75-5.74)
1 (5.06-6.17)
1 (5.26-6.48)
1.46
1.76
2.17
2.47
2.85
3.14
3.43
3.71
4.07
4.34
60-min
(1.35-1.59) 1(1.62-1.92)
(1.99-2.36)
(2.26-2.68)
(2.60-3.09)
(2.86-3.41)
(3.10-3.71)
1 (3.33-4.02)
1 (3.63-4.43)
1 (3.84-4.73)
0.839
1.01
1.26
1.44
1.69
1.87
2.06
2.24
2.49
2.68
2-hr
(0.769-0.918)
(0.929-1.11) 11
(1.53-1.84)
(1.69-2.04)
1 (1.85-2.24)
1 (2.00-2.44)
1 (2.20-2.71)
1 (2.35-2.92)
0.593
0.716
0.893
1.03
1.22
1.37
1.52
1.68
1.89
2.07
3-hr
(0.542-0.653)
(0.654-0.788)
(0.815-0.982)
(0.938-1.13)
(1.10-1.34)
1 (1.23-1.50)
1 (1.36-1.66)
1 (1.49-1.83)
1 (1.66-2.07)
1 (1.79-2.26)
0.355
0.428
0.535
0.619
0.734
0.826
0.921
1.02
1.16
1.27
6-hr
(0.325-0.390)
(0.392-0.470)
(0.489-0.587)
(0.564-0.678)
(0.665-0.801)
(0.744-0.900)
(0.823-1.00)
(0.903-1.11)
1 (1.01-1.26)
1 (1.09-1.38)
0.208
0.251
0.314
0.365
0.437
0.495
0.555
0.618
0.708
0.781
12-hr
(0.191-0.228)
(0.230-0.276)
(0.288-0.345)
(0.333-0.400)
(0.396-0.477)
(0.444-0.540)
(0.494-0.605)
(0.544-0.673)
(0.613-0.770)
(0.667-0.850)
0.124
0.149
0.188
0.219
0.264
0.300
0.340
0.382
0.442
0.492
24-hr
(0.114-0.135)
(0.137-0.163)
(0.173-0.205)
(0.201-0.239)
(0.240-0.287)
(0.273-0.328)
(0.307-0.371)
(0.342-0.418)
(0.393-0.485)
(0.434-0.542)
0.073
0.088
0.110
0.127
0.152
0.173
0.195
0.219
0.253
0.280
2-day
(0.067-0.079)
(0.081-0.096)
(0.101-0.120)
(0.117-0.139)
(0.139-0.166)
(0.157-0.189)
(0.176-0.213)
(0.196-0.239)
(0.224-0.278)
(0.246-0.310)
0.052
0.062
0.077
0.089
0.106
0.120
0.135
0.151
0.174
0.193
3-day
(0.048-0.056)
(0.057-0.067)
(0.071-0.084)
(0.082-0.097)
(0.097-0.116)
(0.110-0.131)
(0.123-0.147)
(0.136-0.165)
(0.156-0.191)
(0.171-0.213)
0.041
0.049
0.061
0.070
0.083
0.094
0.105
0.117
0.135
0.150
4-day
(0.038-0.044)
(0.045-0.053)
(0.056-0.066)
(0.065-0.076)
(0.076-0.090)
(0.086-0.102)
(0.096-0.115)
(0.106-0.128)
(0.121-0.148)
(0.133-0.164)
0.027
0.032
0.039
0.045
0.053
0.060
0.066
0.073
0.084
0.093
7-day
(0.025-0.029)
(0.030-0.035)
(0.037-0.042)
(0.042-0.048)
(0.049-0.057)
(0.055-0.064)
(0.061-0.072)
(0.067-0.079)
(0.076-0.091)
(0.084-0.101)
0.022
0.026
0.031
0.035
0.041
0.046
0.050
0.055
0.062
0.068
10-day
(0.020-0.023)
(0.024-0.028)
(0.029-0.033)
(0.033-0.038)
(0.038-0.044)
(0.042-0.049)
(0.047-0.054)
(0.051-0.060)
(0.057-0.067)
(0.062-0.074)
0.015
0.017
0.020
0.023
0.026
0.029
0.032
0.034
0.038
0.041
20-day
(0.014-0.015)
(0.016-0.018)
(0.019-0.022)
(0.021-0.024)
(0.025-0.028)
(0.027-0.031)
(0.029-0.034)
(0.032-0.037)
(0.035-0.041)
(0.038-0.044)
0.012
0.014
0.016
0.018
0.021
0.022
0.024
0.026
0.028
0.030
30-day
(0.011-0.013)
(0.013-0.015)
(0.015-0.017)
(0.017-0.019)
(0.019-0.022)
(0.021-0.024)
(0.023-0.026)
(0.024-0.028)
(0.026-0.030)
(0.028-0.032)
0.010
0.012
0.013
0.015
0.016
0.018
0.019
0.020
0.022
0.023
45-day
(0.009-0.010)
(0.011-0.012)
(0.013-0.014)
(0.014-0.015)
(0.016-0.017)
(0.017-0.019)
(0.018-0.020)
(0.019-0.021)
(0.021-0.023)
(0.022-0.025)
0.009
0.010
0.012
0.013
0.014
0.015
0.016
0.017
0.019
0.019
60-day
(0.008-0.009)
(0.010-0.011)
(0.011-0.012)
(0.012-0.013)
(0.014-0.015)
(0.015-0.016)
(0.015-0.017)
(0.016-0.018)
(0.017-0.020)
(0.018-0.021)
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=34.8353&Ion=-80.606l &data= intensity&u nits=engl ish&series=pds 1 /4

535870 535930
34° 50' 10" N
�x
Hydrologic Soil Group —Union
County, North Carolina
(Trinity Ridge
Subdivision)
535990
:{
536050 536110
I
34° 49' 52" N
535870 535930 535990 536050 536110
Map Scale: 1:2,640 if printed on A portrait (8.5" x 11") sheet.
Meters
$ N 0 35 70 140 210
Feet
0 100 200 400 600
Map projection: Web Mercator Conermordinates: WGS84 Edge tics: UTM Zone 17N WGS84
USDA Natural Resources Web Soil Survey
Conservation Service National Cooperative Soil Survey
536170
536170
kD
536230
34° 50' 10" N
d
34° 49' 52" N
536230
11 /30/2019
Pagel of 4

Hydrologic Soil Group —Union County, North Carolina
(Trinity Ridge Subdivision)
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: Union County, North Carolina
Survey Area Data: Version 19, Sep 16, 2019
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jun 14, 2015—Feb 8,
2017
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 11/30/2019
Conservation Service National Cooperative Soil Survey Page 2 of 4

Hydrologic Soil Group —Union County, North Carolina
Trinity Ridge Subdivision
Hydrologic Soil Group
Map unit symbol
Map unit name
Rating
Acres in AOI
Percent of AOI
TbB2
Tarrus gravelly silty clay
loam, 2 to 8 percent
slopes, moderately
eroded
B
9.3
100.0%
Totals for Area of Interest
9.3
100.0%
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
USDA Natural Resources Web Soil Survey 11/30/2019
Conservation Service National Cooperative Soil Survey Page 3 of 4

Hydrologic Soil Group —Union County, North Carolina
Trinity Ridge Subdivision
Component Percent Cutoff.- None Specified
Tie -break Rule: Higher
USDA Natural Resources Web Soil Survey 11/30/2019
Conservation Service National Cooperative Soil Survey Page 4 of 4