Smith_Crk_Ph2A_SW_Report_v1SMITH CREEK PARK PHASE 2A – SMITH CREEK PARK PRESERVE
STORMWATER MANAGEMENT REPORT
215 Lake Emerald Drive E, Wilmington, NC 28411
November 2023
8601 Six Forks Road, Suite 700
Raleigh, NC 27615
Phone: 919-878-9560
11/1/2023
Table of Contents
Page
Project Summary and Land Use Tables ....................................................................................................... 1
Appendix A: Drainage Area Maps
Appendix B: Ditch and Pipe Schedules
Appendix C: FHWA Hydraulic Toolbox Calculations for Ditches and Pipes
Appendix D: Pre versus Post Rational Method Calculations
Appendix E: NOAA Atlas 14 precipitation data
Appendix F: WinTR-55 Time of Concentration Calculations
1.0 Project Summary
North Parcel – Smith Creek Park
Existing Conditions (Pre-Project)
The existing Smith Creek Park north parcel site in Hanover County is currently considered a low-density
development (less than 24% built-upon area) per Stormwater Management Permit Number SW8
091003, latest revision dated March 8, 2011. Discharge from this site includes runoff from the buildings,
hardscapes, parking lot, streets, and sidewalks. Existing SCMs include three swales on the site and
runoff is discharged into an existing pond as well. The total impervious area draining from the site is
146,919 sq ft. The site has a permit area of 4,013,680 sq ft, of which 1,558,030 sq ft is surface water,
leaving the permit area for density as 2,455,650 sq ft.
Proposed Conditions
The Smith Creek Park Phase 2 project portion located adjacent on the south side of the existing
permitted area is adding an additional 5008 sq. ft. of impervious to the north parcel. As a result, the
percentage of impervious area will be increased, but will remain less than 12%. The parcel will remain a
low-density development and will retain the existing SCM comprised of an NCDOT borrow pit acquired
by the County. The project is designed for this new impervious area to sheet flow and minimize Table 1
below shows the drainage area land use between existing and proposed conditions. The total permitted
site area will remain the same.
Existing Conditions Proposed Conditions
Land Cover Area (sf)
Area
(ac) % Land Cover Area (sf)
Area
(ac) %
Existing Roof,
Pavement, Hardscape 146,919 3.37 5.98
Roof, Pavement,
Hardscape 151,927 3.49 6.19
Existing Open Space 2,308,731 53.00 94.02 Open Space 2,303,723 52.89 93.81
Total Site w/out Pond 2,455,650 56.37 Total Site w/out Pond 2,455,650 56.37
Table 1: North Parcel Land Use Tabulation
South Park – Smith Creek Park
Existing Conditions (Pre-Project)
The existing Smith Creek Park south parcel site in Hanover County is currently an undeveloped parcel
consisting of natural trails and mature trees - mostly Long Leaf pines. Proposed improvements include a
paved walking trail, driveway, parking, and a picnic shelter. The total impervious area draining from the
site is 725 square feet consisting of pavement at the Lake Emerald Drive and Tupelo Honey Drive. Please
see Appendix A for drainage area maps for pre- and post-project conditions.
Proposed Conditions
Proposed improvements include a paved walking trail, driveway, parking, and a picnic shelter. The total
parcel area is. Table 2 details the added impervious as part of Phase 2A improvements. The percentage
of impervious area is less than 12%. Please see Appendix D for Pre versus post stormwater discharge
results. The drainage infrastructure was kept to minimum to keep the primitive setting of the park and
minimize tree impacts. Pipes with rip rap outlet pads at drawings and ditches were used as needed to
Page 1
SMITH CREEK PARK PRESERVE SWM– NEW HANOVER COUNTY OCTOBER 2023
convey point discharges to pipes. The proposed pipe and ditch drainage schedules are shown in
Appendix B. Time of concentrations were capped at 30 minutes for POI 1 and POI 2. TR-55 time of
concentration calculations area included in Appendix E.
Existing Conditions Proposed Conditions
Land Cover Area (sf)
Area
(ac) % Land Cover Area (sf)
Area
(ac) %
Existing Roof,
Pavement, Hardscape 725 0.02 0.02
Roof, Pavement,
Hardscape 88,750 2.04 2.40
Existing Open Space 3,702,311 84.99 99.98 Open Space 3,614,286 82.97 97.60
Total Site 3,703,036 85.01 Total Site 3,703,036 85.01
Table 2: South Parcel Land Use Tabulation
Page 2
APPENDIX A:
Drainage Area Maps
ST
M
STM
ST
M
S
T
M
S
T
M
ST
M
STM
ST
M
ST
M
ST
M
100-YR
100-Y
R
1
0
0
-
Y
R
1
0
0
-
Y
R
100-Y
R
100-Y
R
100-YR
100
-
Y
R
100
-
Y
R
100-
Y
R
1
0
0
-
Y
R
10
0
-
Y
R
100-YR 1
0
0
-
Y
R
100-Y
R
100
-
Y
R
1
0
0
-
Y
R
100-YR
100-YR
10
0
-
Y
R
100-YR
100
-
Y
R
10
0
-
Y
R
100
-
Y
R
100
-
Y
R
POI 2
Development is
newer than most
recent contours.
Rear of parcels
contribute to DA
POI 1
10050 200
SCALE: 1" = 100' - 0"
0SMITH CREEK PARK PRESERVE PRE MAPPING
2 POIs
H/C
VAN
H/C
2%
2%
2%
2%
H/C
VAN
H/C
Ditch A
Ditch B
Pipe A
Pipe B Pipe A-1
Ditch A-2
Pipe A-2
Pipe C
Pipe B-1
Pipe B-2
Ditch C
Ditch A-1
Ditch A-0
ST
M
STM
ST
M
S
T
M
S
T
M
ST
M
STM
ST
M
ST
M
ST
M
100-YR
100-Y
R
1
0
0
-
Y
R
1
0
0
-
Y
R
100-Y
R
100-Y
R
100-YR
100
-
Y
R
100
-
Y
R
100-
Y
R
1
0
0
-
Y
R
10
0
-
Y
R
100-YR 1
0
0
-
Y
R
100-Y
R
100
-
Y
R
1
0
0
-
Y
R
100-YR
100-YR
10
0
-
Y
R
100-YR
100
-
Y
R
10
0
-
Y
R
100
-
Y
R
100
-
Y
R
POI 2
Development is
newer than most
recent contours.
Rear of parcels
contribute to DA
POI 1
10050 200
SCALE: 1" = 100' - 0"
0SMITH CREEK PARK PRESERVE POST MAPPING
APPENDIX B:
Ditch and Pipe Schedules
Sheet 1 of 2
Designed WTG Date
Checked Date
NO.AREA C CA SUM CA YR Tc I Q Q100 n LENGTH V Df DEPTH SLOPE T (lb/ft^2)LINER T ALLOWED REMARKS
A-0 0.69 0.17 0.12 0.12 25 15 7.36 0.85 1.009 0.015 198'4.278 0.257 1.00 0.0308 0.2346 SEE C-1.4 1.7500
A-1 4.89 0.17 0.83 0.83 25 15 7.36 6.08 7.149 0.015 225'3.128 0.805 1.50 0.0036 0.0858 SEE C-1.4 1.7500
A-2 6.99 0.17 1.19 1.19 25 15 7.36 8.64 10.22 0.015 65'5.245 0.741 1.50 0.0113 0.2478 SEE C-1.4 1.7500
A 0.72 0.47 0.34 0.34 25 5 10.9 3.72 4.365 0.015 427'2.878 0.656 1.00 0.0040 0.0777 SEE C-1.4 1.7500
B 0.69 0.39 0.27 0.27 25 5 10.9 2.91 3.471 0.015 326'4.647 0.457 1.00 0.0169 0.2285 SEE C-1.4 1.7500
C 0.31 0.09 0.03 0.03 25 15 7.36 0.2 0.24 0.015 334'1.886 0.188 1.00 0.0091 0.4541 SEE C-1.4 1.7500
New Hanover County
25 Year Drainage Chart
DITCHCONTRIBUTING AREA
Smith Creek Park Preserve
10/24/2023
DITCH SCHEDULE
RUNOFF
DMK 10/30/2023
Sheet 2 of 2
Date
Date
NO.AREA C CA SUM CA YR Tc I Q Q100 n LENGTH V DIA.MATERIAL SLOPE TIME (S)INV IN INV OUT TOP ELEV HGL IN HGL OUT REMARKS
A 5.58 0.17 0.95 0.95 25 15 7.36 6.93 8.158 0.015 42'7.406 18"HDPE 0.0199 5.67 36.35 35.52 39.04 38.15 36.00
A-1 6.99 0.17 1.19 1.19 25 15 7.36 8.64 10.22 0.015 2x30'5.115 2x15"HDPE 0.0104 5.87 35.07 34.76 37.03 36.55 35.50
A-2 7.82 0.18 1.41 1.41 25 15 7.36 10.09 12.11 0.015 2x22'5.223 2x18"HDPE 0.0097 4.21 34.31 34.10 36.96 35.71 34.77
B 7.98 0.14 1.12 1.12 25 30 5.46 5.96 7.362 0.015 29'3.896 18"HDPE 0.0044 7.44 31.13 31.01 33.89 32.79 31.51
B-1 1.92 0.09 0.17 0.17 25 15 7.36 1.27 1.486 0.015 30'4.387 15"HDPE 0.0162 6.84 35.45 34.97 38.12 36.11 35.30
B-2 1.06 0.09 0.1 0.10 25 15 7.36 0.7 0.82 0.015 29'4.161 15"HDPE 0.0227 6.97 31.96 31.31 34.53 32.43 31.63
C 20.61 0.09 1.85 1.85 25 30 5.46 10.46 12.22 0.015 2x33'6.329 2x15"HDPE 0.0161 5.21 28.34 27.82 31.11 30.11 28.63
New Hanover County
25 Year Drainage Chart
Smith Creek Park Preserve
Designed
Checked
WTG 10/24/2023
PIPE SCHEDULE
CONTRIBUTING AREA RUNOFF PIPE
DMK 10/30/2023
APPENDIX C:
Pipe and Ditch Calculations
(FHWA Hydraulic Toolbox)
Hydraulic Analysis Report
Project Data
Project Title: SMITH CREEK PARK
Designer: WTG
Project Date: October 2023
Project Units: U.S. Customary Units
Channel Analysis: Ditch A
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0040 ft/ft
Manning's n: 0.0150
Flow 3.7200 cfs
Result Parameters
Depth 0.6564 ft
Area of Flow 1.2925 ft^2
Wetted Perimeter 4.1513 ft
Hydraulic Radius 0.3113 ft
Average Velocity 2.8782 ft/s
Top Width 3.9382 ft
Froude Number: 0.8854
Critical Depth 0.6252 ft
Critical Velocity 3.1726 ft/s
Critical Slope: 0.0052 ft/ft
Critical Top Width 3.75 ft
Calculated Max Shear Stress 0.1638 lb/ft^2
Calculated Avg Shear Stress 0.0777 lb/ft^2
Channel Analysis: Ditch B
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0169 ft/ft
Manning's n: 0.0150
Flow 2.9100 cfs
Result Parameters
Depth 0.4569 ft
Area of Flow 0.6263 ft^2
Wetted Perimeter 2.8896 ft
Hydraulic Radius 0.2167 ft
Average Velocity 4.6467 ft/s
Top Width 2.7414 ft
Froude Number: 1.7133
Critical Depth 0.5667 ft
Critical Velocity 3.0205 ft/s
Critical Slope: 0.0054 ft/ft
Critical Top Width 3.40 ft
Calculated Max Shear Stress 0.4818 lb/ft^2
Calculated Avg Shear Stress 0.2285 lb/ft^2
Channel Analysis: Pipe A
Input Parameters
Channel Type: Circular
Pipe Diameter 1.50 ft
Longitudinal Slope: 0.0199 ft/ft
Manning's n: 0.0150
Flow 6.9300 cfs
Result Parameters
Depth 0.7848 ft
Area of Flow 0.9358 ft^2
Wetted Perimeter 2.4258 ft
Hydraulic Radius 0.3858 ft
Average Velocity 7.4056 ft/s
Top Width 1.4984 ft
Froude Number: 1.6514
Critical Depth 1.0188 ft
Critical Velocity 5.4227 ft/s
Critical Slope: 0.0090 ft/ft
Critical Top Width 1.40 ft
Calculated Max Shear Stress 0.9745 lb/ft^2
Calculated Avg Shear Stress 0.4790 lb/ft^2
Channel Analysis: Ditch A-0
Notes:
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0308 ft/ft
Manning's n: 0.0150
Flow 0.8500 cfs
Result Parameters
Depth 0.2573 ft
Area of Flow 0.1987 ft^2
Wetted Perimeter 1.6276 ft
Hydraulic Radius 0.1221 ft
Average Velocity 4.2783 ft/s
Top Width 1.5441 ft
Froude Number: 2.1019
Critical Depth 0.3464 ft
Critical Velocity 2.3615 ft/s
Critical Slope: 0.0063 ft/ft
Critical Top Width 2.08 ft
Calculated Max Shear Stress 0.4946 lb/ft^2
Calculated Avg Shear Stress 0.2346 lb/ft^2
Channel Analysis: Ditch A-1
Notes:
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0036 ft/ft
Manning's n: 0.0150
Flow 6.0800 cfs
Result Parameters
Depth 0.8049 ft
Area of Flow 1.9436 ft^2
Wetted Perimeter 5.0906 ft
Hydraulic Radius 0.3818 ft
Average Velocity 3.1282 ft/s
Top Width 4.8294 ft
Froude Number: 0.8690
Critical Depth 0.7609 ft
Critical Velocity 3.5002 ft/s
Critical Slope: 0.0049 ft/ft
Critical Top Width 4.57 ft
Calculated Max Shear Stress 0.1808 lb/ft^2
Calculated Avg Shear Stress 0.0858 lb/ft^2
Channel Analysis: Pipe A-1
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.25 ft
Longitudinal Slope: 0.0104 ft/ft
Manning's n: 0.0150
Flow 4.3200 cfs
Result Parameters
Depth 0.8127 ft
Area of Flow 0.8446 ft^2
Wetted Perimeter 2.3447 ft
Hydraulic Radius 0.3602 ft
Average Velocity 5.1148 ft/s
Top Width 1.1923 ft
Froude Number: 1.0710
Critical Depth 0.8423 ft
Critical Velocity 4.9112 ft/s
Critical Slope: 0.0094 ft/ft
Critical Top Width 1.17 ft
Calculated Max Shear Stress 0.5274 lb/ft^2
Calculated Avg Shear Stress 0.2338 lb/ft^2
Channel Analysis: Ditch A-2
Notes:
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0113 ft/ft
Manning's n: 0.0150
Flow 8.6400 cfs
Result Parameters
Depth 0.7410 ft
Area of Flow 1.6473 ft^2
Wetted Perimeter 4.6866 ft
Hydraulic Radius 0.3515 ft
Average Velocity 5.2450 ft/s
Top Width 4.4461 ft
Froude Number: 1.5185
Critical Depth 0.8758 ft
Critical Velocity 3.7550 ft/s
Critical Slope: 0.0046 ft/ft
Critical Top Width 5.25 ft
Calculated Max Shear Stress 0.5225 lb/ft^2
Calculated Avg Shear Stress 0.2478 lb/ft^2
Channel Analysis: Pipe A-2
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.50 ft
Longitudinal Slope: 0.0097 ft/ft
Manning's n: 0.0150
Flow 5.0450 cfs
Result Parameters
Depth 0.8049 ft
Area of Flow 0.9659 ft^2
Wetted Perimeter 2.4661 ft
Hydraulic Radius 0.3917 ft
Average Velocity 5.2232 ft/s
Top Width 1.4960 ft
Froude Number: 1.1455
Critical Depth 0.8643 ft
Critical Velocity 4.7852 ft/s
Critical Slope: 0.0077 ft/ft
Critical Top Width 1.48 ft
Calculated Max Shear Stress 0.4872 lb/ft^2
Calculated Avg Shear Stress 0.2371 lb/ft^2
Channel Analysis: Pipe B
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.50 ft
Longitudinal Slope: 0.0044 ft/ft
Manning's n: 0.0150
Flow 5.9600 cfs
Result Parameters
Depth 1.2121 ft
Area of Flow 1.5299 ft^2
Wetted Perimeter 3.3518 ft
Hydraulic Radius 0.4564 ft
Average Velocity 3.8957 ft/s
Top Width 1.1815 ft
Froude Number: 0.6033
Critical Depth 0.9426 ft
Critical Velocity 5.0970 ft/s
Critical Slope: 0.0083 ft/ft
Critical Top Width 1.45 ft
Calculated Max Shear Stress 0.3328 lb/ft^2
Calculated Avg Shear Stress 0.1253 lb/ft^2
Channel Analysis: Pipe B-1
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.25 ft
Longitudinal Slope: 0.0162 ft/ft
Manning's n: 0.0150
Flow 1.2700 cfs
Result Parameters
Depth 0.3573 ft
Area of Flow 0.2895 ft^2
Wetted Perimeter 1.4101 ft
Hydraulic Radius 0.2053 ft
Average Velocity 4.3873 ft/s
Top Width 1.1295 ft
Froude Number: 1.5273
Critical Depth 0.4446 ft
Critical Velocity 3.2455 ft/s
Critical Slope: 0.0070 ft/ft
Critical Top Width 1.20 ft
Calculated Max Shear Stress 0.3612 lb/ft^2
Calculated Avg Shear Stress 0.2075 lb/ft^2
Channel Analysis: Pipe B-2
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.25 ft
Longitudinal Slope: 0.0227 ft/ft
Manning's n: 0.0150
Flow 0.7000 cfs
Result Parameters
Depth 0.2435 ft
Area of Flow 0.1682 ft^2
Wetted Perimeter 1.1427 ft
Hydraulic Radius 0.1472 ft
Average Velocity 4.1612 ft/s
Top Width 0.9901 ft
Froude Number: 1.7790
Critical Depth 0.3268 ft
Critical Velocity 2.7391 ft/s
Critical Slope: 0.0070 ft/ft
Critical Top Width 1.10 ft
Calculated Max Shear Stress 0.3449 lb/ft^2
Calculated Avg Shear Stress 0.2085 lb/ft^2
Channel Analysis: Ditch C
Notes:
Input Parameters
Channel Type: Triangular
Side Slope 1 (Z1): 3.0000 ft/ft
Side Slope 2 (Z2): 3.0000 ft/ft
Longitudinal Slope: 0.0091 ft/ft
Manning's n: 0.0150
Flow 0.2000 cfs
Result Parameters
Depth 0.1880 ft
Area of Flow 0.1060 ft^2
Wetted Perimeter 1.1890 ft
Hydraulic Radius 0.0892 ft
Average Velocity 1.8863 ft/s
Top Width 1.1280 ft
Froude Number: 1.0842
Critical Depth 0.1942 ft
Critical Velocity 1.7681 ft/s
Critical Slope: 0.0077 ft/ft
Critical Top Width 1.17 ft
Calculated Max Shear Stress 0.1068 lb/ft^2
Calculated Avg Shear Stress 0.0506 lb/ft^2
Channel Analysis: Pipe C
Notes:
Input Parameters
Channel Type: Circular
Pipe Diameter 1.25 ft
Longitudinal Slope: 0.0161 ft/ft
Manning's n: 0.0150
Flow 5.2300 cfs
Result Parameters
Depth 0.7974 ft
Area of Flow 0.8263 ft^2
Wetted Perimeter 2.3128 ft
Hydraulic Radius 0.3573 ft
Average Velocity 6.3294 ft/s
Top Width 1.2015 ft
Froude Number: 1.3450
Critical Depth 0.9271 ft
Critical Velocity 5.3587 ft/s
Critical Slope: 0.0108 ft/ft
Critical Top Width 1.09 ft
Calculated Max Shear Stress 0.8011 lb/ft^2
Calculated Avg Shear Stress 0.3589 lb/ft^2
APPENDIX D:
Rational Method Pre versus Post
Discharges at POIs
Smith Creek Park Preserve
Rational Method Computations
Study Point:
Computed By: WTG Date: 10/11/23
Checked By: Date:
1. Compute Rational Q:
Q = C*i*A where;
i = rainfall intensity*
A = Drainage area in acres
C = weighted C factor **
Hyd. Soil Grp. Land Use Area 2, 10-YR 25-YR
A Woods 2-6% 36.89 acres C = 0.25 0.25
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
A total = 36.89 acres
Therefore;
Weighted C2, 10 =0.25 where:(∑A*C)/∑A
Weighted C25 =0.25 where:(∑A*C)/∑A
i2=3.44 in/hr (TOC=30min)
i10=4.73 in/hr
i25=5.46 in/hr
Q2 =31.72 cfs
Q10 =43.62 cfs
Q25 =50.35 cfs
POI-1 PRE
Smith Creek Park Preserve
Rational Method Computations
Study Point:
Computed By: WTG Date: 10/11/23
Checked By: Date:
1. Compute Rational Q:
Q = C*i*A where;
i = rainfall intensity*
A = Drainage area in acres
C = weighted C factor **
Hyd. Soil Group Land Use Area 2, 10-YR 25-YR
A Woods 2-6% 36.47 acres C = 0.25 0.25
A Imper 2-6% = 0.42 acres C = 0.95 0.95
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
A total = 36.89 acres
Therefore;
Weighted C2, 10 =0.26 where:(∑A*C)/∑A
Weighted C25 =0.26 where:(∑A*C)/∑A
i2=3.44 in/hr (TOC=30min)
i10=4.73 in/hr
i25=5.46 in/hr
Q2 =32.73 cfs
Q10 =45.01 cfs
Q25 =51.96 cfs
POI-1 POST (Pipe C)
Smith Creek Park Preserve
Rational Method Computations
Study Point:
Computed By: WTG Date: 10/11/23
Checked By: Date:
1. Compute Rational Q:
Q = C*i*A where;
i = rainfall intensity*
A = Drainage area in acres
C = weighted C factor **
Hyd. Soil Grp. Land Use Area 2, 10-YR 25-YR
A Woods 2-6% 34.99 acres C = 0.25 0.25
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
acres C = 0 0
A total = 34.99 acres
Therefore;
Weighted C2, 10 =0.25 where:(∑A*C)/∑A
Weighted C25 =0.25 where:(∑A*C)/∑A
i2=4.98 in/hr (TOC=30min)
i10=6.53 in/hr
i25=7.36 in/hr
Q2 =43.56 cfs
Q10 =57.12 cfs
Q25 =64.38 cfs
POI-2 PRE
Smith Creek Park Preserve
Rational Method Computations
Study Point:
Computed By: WTG Date: 10/11/23
Checked By: Date:
1. Compute Rational Q:
Q = C*i*A where;
i = rainfall intensity*
A = Drainage area in acres
C = weighted C factor **
Hyd. Soil Grp. Land Use Area 2, 10-YR 25-YR
A Woods 2-6% 0.76 acres C = 0.25 0.25
A Imper 2-6% = 0.82 acres C = 0.95 0.95
A Woods 2-6% 13.72 acres C = 0.25 0.25
A Imper 2-6% = 0.78 acres C = 0.95 0.95
A Open space 2-6% = 1.35 acres C = 0.25 0.25
A Woods 2-6% 1.44 acres C = 0.25 0.25
A Open space 2-6% = 0.66 acres C = 0.25 0.25
A Open space 2-6% = 15.46 acres C = 0.25 0.25
A total = 34.99 acres
Therefore;
Weighted C2, 10 =0.28 where:(∑A*C)/∑A
Weighted C25 =0.28 where:(∑A*C)/∑A
i2=4.98 in/hr (TOC=30min)
i10=6.53 in/hr
i25=7.36 in/hr
Q2 =49.14 cfs
Q10 =64.43 cfs
Q25 =72.62 cfs
POI-2 POST (Pipe A-2, Pipe B, B-1, B-2)
APPENDIX E:
NOAA Atlas 14 Precipitation Data
APPENDIX F:
WinTR-55 Time of Concentration
Calculations
WTG Smith Creek Park
New Hanover NOAA-C 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)
--------------------------------------------------------------------------------
DITCH A-1
SHEET 100 0.0063 0.150 0.328
SHALLOW 536 0.0063 2 0.116
CHANNEL 775 3.400 0.063
Time of Concentration .507
========
DICTH A-0
SHEET 100 0.0100 0.400 0.597
SHALLOW 31 0.0100 2 0.005
CHANNEL 198 4.700 0.012
Time of Concentration .614
========
DITCH A
SHEET 28 0.0001 0.011 0.077
CHANNEL 426 4.000 0.030
Time of Concentration .107
========
DITCH B
SHEET 34 0.0590 0.150 0.057
CHANNEL 325 4.631 0.019
Time of Concentration 0.1
========
DITCH C
SHEET 88 0.0113 0.400 0.514
CHANNEL 333 2.000 0.046
Time of Concentration .56
========
PIPE A-2
SHEET 100 0.0113 0.400 0.569
SHALLOW 252 0.0113 2 0.041
Time of Concentration .61
========
PIPE B
SHEET 100 0.0082 0.400 0.647
SHALLOW 1113 0.0082 2 0.212
Time of Concentration .859
========
PIPE B-1
SHEET 100 0.0119 0.400 0.557
SHALLOW 277 0.0119 2 0.044
Time of Concentration .601
========
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WTG Smith Creek Park
New Hanover NOAA-C County, North Carolina
Sub-Area Time of Concentration Details (continued)
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)
--------------------------------------------------------------------------------
PIPE B-2
SHEET 100 0.0170 0.400 0.483
SHALLOW 428 0.0170 2 0.057
Time of Concentration .54
========
PIPE C
SHEET 100 0.0059 0.400 0.738
SHALLOW 1935 0.0059 2 0.434
Time of Concentration 1.172
========
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