SW8050431_COMPLIANCE_20051128

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO. SW�(i
DOC TYPE ❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYMMDD

STORMWATER DIVISION CODING SHEET
NCG PERMITS
PERMIT NO.
/v
DOC TYPE
❑ HISTORICAL FILE
❑ MONITORING REPORTS
DOC DATE
❑
YYYYMMDD

Permit No..S(,ti g V 3 /
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied far use as an original
DWQ Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a wet detention basin supplement for each basin,
design calculations, plans and specifications showing all basin and outlet structure details, and a fully executed
operation and maintenance agreement.
I. PROJECT INFORMATION (please complete the following information):
Project Name:
North Countv Road Retail
Contact Person: Brad Sedgwick, PE Phone Number:
For project with multiple basins, specify which basin this worksheet applies to:
Elevations
[phone]
1
Basin Bottom Elevation
93.5
ft.
(door of the basin)
Permanent Pool Elevation
98
ft.
(elevation of'the orifice)
Temporary Pool Elevation
99.11
ft.
(elevation of the discharge structure overflow)
Area
Permanent Pool Surface Area
1920
sq. ft.
(water surface area at the orifice elevation)
Drainage Area
1.38
ac.
(on -site and off -site drainage to the basin)
Impervious Area
0.73
ac.
(on -site and off -site drainage to the basin)
Volumes
Permanent Pool Volume
} _2639
cu. ft.
(combined volume of main basin andforebuv)
Temporary Pool Volume
2635
cu. ft.
(volume detained above the permanent pool)
Forebay Volume
564
cu. ft.
(approximately 20% of total volume)
Other parameters
SA/DA ' 3.15 (surface area to drainage area ratio from DWQ table)
Diameter of Orifice 0.75 in. (2 to 5 day temporary pool draw -down required)
Design Rainfall 1 in.
Design TSS Removal 2 85 % (minimum 85% required)
Norm: SWU-102 Rev. 3.99 Page 1 of 4

Permit Na.
(to be provided by DWQ)
q-ZZ -01S
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DWQ Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a wet detention basin supplement for each basin,
design calculations, plans and specifications showing all basin and outlet structure details, and a fully executed
operation and maintenance agreement.
I. PROJECT INFORMATION (please complete the following information):
Project Name: North Coun Road Retail
Contact Person: Brad Sedgwick, PE Phone Number: [phone]
For project with multiple basins, specify which basin this worksheet applies to: 1
Elevations
Basin Bottom Elevation
Permanent Pool Elevation
Temporary Pool Elevation
Area
Permanent Pool Surface Area
Drainage Area
Impervious Area
Volumes
Permanent Pool Volume
Temporary Pool Volume
Forebay Volume
Other parameters
SA/DA'
Diameter of Orifice
Design Rainfall
Design TSS Removal 2
93.5
ft.
(floor of the basin)
98
ft.
(elevation of the orifice)
100.3
ft.
(elevation of the discharge structure overflow)
2510
sq. ft.
(water surface area at the orifice elevation)
1.38
ac.
(on -site and off -site drainage to the basin)
0.73
ac.
(on -site and off -site drainage to the basin)
4172 cu. ft. (combined volume of main basin and forebay)
7351 cu. ft. (volume detained above the permanent pool)
834 cu. ft. (approximately 20% of total volume)
4.168 (surface area to drainage area ratio from DWQ table)
0.625 in. (2 to 5 day temporary pool draw -down required)
1 in.
90 % (minimum 85% required)
Form: SWU-102 Rev. 3.99 Page 1 of 4

f
Footnotes:
t When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
2 The requirement for a vegetative filter may be waived if the wet detention basin is designed to meet 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices manual
(N.C. Department of Environment, Health and Natural Resources, November 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
N/A
a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
b. The forebay volume is approximately equal to 20% of the basin volume.
c. The temporary pool controls runoff from the design storm event.
d. The temporary pool draws down in 2 to 5 days.
e. If required, a 30-foot vegetative filter is provided at the outlet (include non -erosive flow
calculations)
£ The basin length to width ratio is greater than 3:1.
g. The basin side slopes above the permanent pool are no steeper than 3:1.
h. A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
i. Vegetative cover above the permanent pool elevation is specified.
j. A trash rack or similar device is provided for both the overflow and orifice.
k. A recorded drainage easement is provided for each basin including access to nearest
right-of-way.
1. If the basin is used for sediment and erosion control during construction, clean out of
the basin is specified prior to use a wet detention basin.
Pump m. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including fore bays and the
vegetated filter if one is provided.
This system (check one) (X) does ( ) does not incorporate a vegetated filter at the outlet.
This system (check one) ( ) does (X) does not incorporate pretreatment other than a fore bay.
Form: SWU-102 Rev. 3.99 Page 2 of 4

Maintenance activities shall be performed as follows:
1. After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs
within 2 to 5 days as designed.
2. Repair eroded areas immediately; re -seed as necessary to maintain good vegetative cover, now
vegetative cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to
maintain proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed
of in an appropriate manner and shall be handled in a manner that will not adversely impact water
quality (i.e. stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate depth
reading and not readily penetrate into accumulated sediments.
3.375 Amu, q VC6
When the permanent pool depth reads .. feet in the main pond, the sediment shall be removed.
'3:3-75 AV0,70-05
When the permanent pool depth reads =PW feet in the fore bay, the sediment shall be removed.
BASIN DIAGRAM
Ull in the blanks)
Permanent Pool Elevation 98
Sediment RemovaKEL 94.63 1 75%
Sediment Removal Elevation 94.63 75%
-------------- k-
Bottom Elevation\ 93.5 1/25%
Bottom Elevation 93.5 25%
FOREBAY MAIN POND
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and fore bay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment
through the emergency drain shall be minimized to the maximum extent practical.
T. All components of the wet detention basin system shall be maintained in good working order.
Form: SWU-102 Rev. 3.99 Page 3 of 4

I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: TrennSy Eason
Title: President
Address 400 Carl Street, Wilmington, NC 28403
Phone [phone]
Signature ` / AL -., ,/ //M
Date � ,lr S r
Note: The legally responsible parry should not be a homeowners association unless more than 50% of the lots
have been sold and a resident of the subdivision has been named the president.
1, k � "i LA, •• a Notary Public for the State of N C— ,
County of tU 0 ".; . ✓ , do hereby certify that fps o
personally appeared before me this �_�_ day of `�, 20 C5, and acknowledge the due
execution of the foregoing wet detention basin maintenance requirements. Witness my hand and official seal,
`off?OIARy. �y
U8VY
VER
SEAL
My commission expires '553 -,
Form: SWU-102 Rev. 3.99 Page 4 of 4

WET DETENTION POND ANALYSIS
'FILE NAME: S:IWQSIPOND1050431.WK1
PROJECT * SVV8 050431 REVIEWER: L. Lewis
PROJECT NAME: North County Road Retail DATE: 28-Nov-05
Legend Builders
Receiving Stream: ;*less Creels Class: C SW
Drainage Basin: Cape Fear Index No. CPF17 18-74-62
Site Area 1.38 acres
Drainage Area 6,,11; a0 square feet Area in Acres 1.38
IMPERVIOUS AREAS
Buildings
Parking
SW
TOTAL
SURFACE AREA CALCULATION
11250.00 square feet
191 '10.00 square feet
1493.00 square feet
square feet
square feet
square feet
square feet
3185square feet
Rational C
Rational Cc= 0.09
% IMPERVIOUS
52.99%
SA/DA Ratio
4,17%
Des, Depth
4.5
Req. SA
2506 sf
TSS:
90
Prov. SA
"t`. sf
VOLUME CALCULATION
* place a "1" in the box if Rational is used
Rational ?*
FOREBAY
Des. Storm
1,100 inches
Perm. Pool Volume=
4172
Rv=
0.527
Req. Forebay Volume=
834.4
Bottom
93.5 assumed
Provided Volume=
834.00
Perm. Pool
I' i'98"0, assumed
Percent=
Design Pool
*100.3 assumed
Storage met @elev 98.77 assumed
Elevation Area
Inc. Vol. Acc. Vol.
Req. Volume
=T91 cf
98.00 2510.00
0.00
Vol. Prov. at DP
cf
101.00 4388.00
10347.00 10347.00
ORIFICE CALCULATION
Avg. Head =
1.14 ft
Q2 Area =
0.43
sq. inches
Flow Q2, cfs
0.015 cfs
Q5 Area =
0.17
sq. inches
Flow Q5, cfs
0.006 cfs
Orifice Area
0,31
sq. inches
No. of Orifices
iL 1
Q=
0.011
cfs
Diameter, inches
F 0 62 ,
weir H x W
in
x
in
Drawdown =
21cs
days
Surface Area @DP =
39150 sq. ft.
Falling Head Drawdown =
11.1 days
C� 3,371064815
L= -0.227
COMMENTS
Surface Area and Volume are within design Guidelines. Orifice is too large

Basin #1 Wet Detention Pond Calculations
NC DENR Retention Requirements
Objective: design a wet detention basin with the following characteristics. a permanent water pool depth between 3- and
6-feet, a surface area that meets TSS removal requirements (values set by NC DENR and included here), a forebay that
is approximately 20% of the total pond volume, a temporary water pool sized to detain the initial 1 inch of rainfall runoff, an
outlet device that drains the temporary water pool within 2-5 days, and a length -to -width ratio of approximately 3:1.
av
Step 1: Determine the surface area required for bi6va TSS removal
Post -Development Conditions
Total Drainage Area
Impervious Drainage Area
Impervious Cover
Elevation of Permanent Pool Surface
Depth of Permanent Pool
1.38 ACRE Value from CAD
0.73 ACRE Value from CAD
52 9% Impervious Covet --(Impervious Drainage
Area)/(Total Drainage Area)'100%
98.0 FT Value selected by designer
4.6 FT Value selected by designer
Elevation of Wet Detention Pond Bottom 93.5 FT (Bottom Elevation)=(Permanent Pool Surface
Elevation) -(Depth of Permanent Pool)
Approximate Pond Length 110 FT Value from CAD
Approximate Pond Width 40 FT Value from CAD
Len th:Width Ratio 3.1 Ratio=(Len th)/(Width):1
Required SAIDA Ratio for 90% TSS Removal 4.168 Value from chat. Reference: "90% TSS
— Removal
Required Permanent Pool Surface Area 2,506 SF Required Surface Area=(Required SA/DA
Ratio)*(Total Drainage Area)
Provided Permanent Pool Surface Area 2,510 SF Interpolated value from stage -storage
calculations
Step 2: Determine the 1-inch runoff elevation within the wet detention pond.
Runoff Coefficient, Rv 0,526 MIN Rv=0.05+0.009'(% Impervious)
Required 1" Runoff Volume (Volume of Temporary 2,635 CF 1"Runoff Volume=1 inch'Rv'1 foot/12
Pool) inch'(Total Drainage Area)
Value from stage -storage calculations
Volume Below Permanent Pool 4,172 CF (cumulative pond volume at permanent pool
elevation)
Total Volume at Overflow Elevation 7.351 CF
Total Volume to be Controlled=(Volume Below
F- - Overflow), _,-
1" Runoff Volume Elevation 99.003 FT Value is interpolation based upon stage -storage
values. See stage -storage calculations
RECEIVED
SEP 2 '2 2005
DWQ
nROJ # 5W F050 43(

SteD 3: Calculate the required forebav volume (f8-22% of total pond volume) and compare to the forebay volume provided.
Total Pond Volume
4,172 CF
Value from stage -storage calculations
Required Forebay Volume
834 CF
Forebay Volume= Total Pond Volume *20%
Provided Foralbay Volume
834 CF
Value from stage -storage calculations
(Provided Forebay Volume)/(Total Pond
Provided Forebay Volume -Total Pond Volume
20%
Volume)'100%
Step 4_ Verify that time required to drawdown the ?-inch runoff volume is within 2 to 5 da
Diameter of Proposed Low -flow Orifice
0.625
IN
Value chosen by designer
Overflow elevation
100.30
FT
Value chosen by designer
(Total Elevation Head Above Orifice)=(Weir
Total Elevation Head Above Orifice
2.30
FT
Elevation) -(Elevation of Permanent Pool
Surface)
(Average Elevation Head Above
Orrflce)=[(Storage Elevation at Required
Average Elevation Head Above Orifice
1.15
FT
Volume)+(Elevation of Permanent Pool
Surface)X-(Storage Elevation at Required
Volume)
Cd, Coefficient of Discharge
0.60
Value chosen by designer
O, Flowrate Through Low -flow Orifice
0.01
CFS
G?=7Cd'(P)-((ti,am�eter�of Orrflce) (? )ft/92
IDrawdown Time for 14nch Runoff 2.77 DAYS (Drawdown Time)=(1" Runoff Volume)1Q*(1

Wet Detention Pond #1 Calculations
Stage -Storage Calculations for Proposed Wet Detention Pond
determine the storage capacity and characteristics of the proposed wet detention pond.
Pond side slope above Permanent Pool 3
Planted shelf 2' below Permanent Pool 6
Side Slope below planted shelf 2
incremental and cumulative storage of the wet detention Dond per contour interval.
Stage/Storage Above Permanent Pool (Including Forebay)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
CF
98.0
2,510
0
0 Permanent Pool
99.0
2,745
2,628
2,628
99.0031
2,747
9
2,636 -Treatment Volume
99.2
3,000
566
3,202
99.3
3,066
303
3,505
100.0
4,230
2,554
6,059
101.0
4,766
4,498
10,557
Stage/Storage Total Pond (Including Forebay)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
(CF)
93.5
199
0
0 +•Pond Bottom
94.0
328
132
132
95.0
488
408
540
96.0
681
585
1,124
97.0
1,452
1,066
2,191
98.0
2,510
1,981
4,172 -Permanent Pool
99.0
2,745
2,098
6,270
100.0
4,230
3,370
9,640
101.0
4,766
4,498
14,138
Forebay Only (20% of Total Pond)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
(CF)
93.5
40
0
0 -Bottom Elev.
94.0
66
26
26
95.0
98
82
108
96.0
136
117
225
97.0
290
213
438
98.0
502
396
834 *-Forebay Volume

NCDENR
STORMWATER CALCULATIONS
AND SUPPORTING DATA
NORTH COUNTY ROAD RETAIL
Castle Hayne, NC
New Hanover County
March 28, 2005
Prepared for:
Legend Builders, Inc.
400 Carl Street
Wilmington, NC 28403
Prepared by:
JBS Consulting
7332 Cotesworth Dr.
Wilmington, NC 28405
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NORTH COUNTY ROAD RETAIL
Castle Hayne, NC
New Hanover County
March 28, 2005
Table of Contents
March 28, 2005
DESIGN NARRATIVE
Existing Site
Proposed Improvements
Post Developed Basin Maps
Post -Developed Stormwater Storage Calculations
1" Treatment Volume Calculations

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NORTH COUNTY ROAD RETAIL
Castle Hayne, NC
New Hanover County
March 28, 2005
DESIGN NARRATIVE
Existing Site
Legend Builders, Inc. is proposing the development of a retail shop on a 1.38 acre tract of land,
located in New Hanover County on the south side of North County Road. The property has
approximately 400 feet of frontage on North County Road, a developed commercial property is
to the east, an undeveloped commercial property is to the south and a residential subdivision is
to the west of the proposed site.
Fioure 1 - USGS
Because the existing vegetation on the undeveloped site is up of immature trees and under
story growth, it is apparent that the site has been cleared in the past. Longleaf pines, red oak,
black oak, post oak, hickory, dogwood and holly are native vegetations that would be typical in
this area.

The New Hanover SCS Soil
Survey indicates that the
property's soil is Norfork fine
sandy loam (No) Norfork fine
sandy loam is a well drained soil
with moderate to rapid
permeability of 2 to 6 inches per
hour, the high water table is 6
feet or greater below the
surface. No wetlands have been
identified on the property. The
property is located in a basin
that drains to Ness Creek, which
is within the Cape Fear River
Basin and is a classified C, SW.
The classification is dated
09/01/1974 and the index # is
18-74-62.
Proposed Improvements
The proposed development will
consist of a retail building, �-
paved access drives and
parking, the necessary utilities
and a stormwater management
system. Water services will be
provided to the site from an
existing water main on the south
side of North County Road, sewer services will be on -site septic The site will be accessed from
North County Road a two locations and a total of 28 parking spaces are provided to serve the
retail building. The proposed impervious areas will be 11,250 sq.ft. Of building, 19,111 sq.ft. of
drives and parking. 427 sq.ft. of concrete walk, and 1,066 sq.ft. of impervious area for the
dumpster pad, making the total built upon area 31,854 sq.ft., 53% of the 1.38 acre total
property area.
New Hanover County requires that the Storm water runoff from the developed site for the 2, 10
and 25-year storm event does not exceed the peak discharge from the same storm events prior
to development. New Hanover County also recommends and NCDENR requires that a BMP be
provided to remove stormwater pollutants (treatment). In order to meet the treatment and
attenuation requirement, the project's stormwater runoff will be captured in swales and
transported to a detention pond located toward the westerly property line. The swales not only
transport runoff but will also provide additional storage once the water elevation of the detention
pond reaches the swale elevations. The proposed detention pond's permanent pool elevation
is 98, the bottom elevation is 94 and the top elevation is 101.25. An overflow structure is
provided to discharge excess stormwater to an existing ditch at the westerly property line
through a 15" RCP. The overflow structure is configured to return the 1 " treatment volume of
2635 cu.ft. to the 98 permanent pool elevation in 2.77 days with the use of a 3/4" orifice set at
elevation 98. The 2, 10 and 25 year storms are controlled by the same overflow structure with a
0.51 foot wide weir slot set at elevation 100.30 and the 50 and 100 year storms are allowed to
discharge the overflow structure's top at elevation 101.00.

Post Developed Basin Maps

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Basin #1 Wet Detention Pond Calculations
NC DENR Retention Requirements
Objective: design a wet detention basin with the following characteristics: a permanent water pool depth between 3- and
6-feet, a surface area that meets TSS removal requirements (values set by NC DENR and included here), a forebay that
is approximately 20% of the total pond volume, a temporary water pool sized to detain the initial I inch of rainfall runoff, an
outlet device that drains the temporary water pool within 2-5 days, and a length -to -width ratio of approximately 3:1.
Step 1: Determine the surface area required for 85% TSS removal
Post -Development Conditions
Total Drainage Area 1.38 ACRE
Impervious Drainage Area 0.73 ACRE
impervious Cover
52.9%
Value from CAD
Value from CAD
Impervious Cover --(Impervious Drainage
Area)!(Total Drainage Area)*100%
Elevation of Permanent Pool Surface
98.0
FT
Value selected by designer
Depth of Permanent Pool
4.5
FT
Value selected by designer
Elevation of Wet Detention Pond Bottom
93.5
FT
(Bottom Elevation)=(Permanent Pool Surface
Elevation) -(Depth of Permanent Pool)
Approximate Pond Length
300
FT
Value from CAD
Approximate Pond Width
100
FT
Value from CAD
Lenath:Width Ratio
3:1
Ratio=(Lenoth)/Midth):1
Required SAIDA Ratio fo 94% TSS Removal 3.150 Value from chart. Reference: "90% TSS
Removal
Required Surface Area=(Required SAIDA
Required Permanent Pool Surface Area 1,894 SF Ratio) *(Total Drainage Area)
Interpolated value from stage -storage
Provided Permanent Pool Surface Area (1,9201SF calculations
Stem 2: Determine the 1-inch runoff elevation within the wet detention pond.
Runoff Coefficient, Rv
0.526
INIIN
Rv=0.05+0.009*(% Impervious)
Required 1" Runoff Volume (Volume of Temporary
2,635
CF
1 "Runoff Volume=1 inch*Rv*1 foot/12
Pool)
inch*(Total Drainage Areal
Value from stage -storage calculations
Volume Below Permanent Pool
2,820
CIF
(cumulative pond volume at permanent pool
elevation)
Total Volume to be Controlled
2,635
CIF
Total Volume to be Controlled=(Volume Below
Total
Pool + 1" Runoff Volume
orage Elevation at Required Volume
F
99.1100
FT
Value is interpolation based upon stage -storage
values. See stage -storage calculations

Stec 3: Calculate the required forebav volume (18-22i6 of total oond volume) and compare to the forebav volume urovided
Total Pond Volume 2,820 CF Value from stage -storage calculations
Required Forebay Volume 564 CIF Forebay Volume=(Total Pond Volume)*20%
Provided Forebay Volume 564 CIF Value from stage -storage calculations
Provided Forebay Volume:Total Pond Volume 20%
(Provided Forebay Volume)/(Total Pond
Volume)*100
Step 4: Verifv that time required to drawdown the 1-inch runoff volume is within 2 to 5 days
Diameter of Proposed Low -flow Orifice
0.75
IN
Value chosen by designer
1" treatement volume elevation
99.11
FT
Value chosen by designer
(Total Elevation Head Above Orifice)=(Weir
Total Elevation Head Above Orifice
1.11
FT
Elevation) -(Elevation of Permanent Pool
Surface)
(Average Elevation Head Above
Orifice)=((Storage Elevation at Required
Average Elevation Head Above Orifice
0.56
FT
Volume)+(Elevation of Permanent Pool
Surface)X-(Storage Elevation at Required
Volume)
Cd, Coefficient of Discharge
0.60
Value chosen by designer
Q, Flowrate Through Low -flow Orifice
0.01
CFS
Q=Cd'(Pi)'((Diameter of Orifice A4) 11192
` (Drawdown Time)=(1 " Runoff Volume)/Q*(1
`Drawdown Time for 1-inch Runoff 2.77 DAYS

Wet Detention Pond #1 Calculations
Stage -Storage Calculations for Proposed Wet Detention Pond
determine the storage capacity and characteristics of the proposed wet detention pond.
Pond side slope above Permanent Pool 3
Planted shelf 2' below Permanent Pool 6
Side Slope below planted shelf 1.5
incremental and cumulative storage of the wet detention aond oer contour interval.
Stage/Storage Above Permanent Pool (Including Forebay)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
CF
98.0
1,920
0
0 Permanent Pool
99.0
2,745
2,333
2,333
99.1
2,808
278
2,610
99.1100
2,821
28
2,638 -Treatment Volume
99.3
2,943
548
3,186
100.0
4,230
3,488
5,820
101.0
8,699
6,465
12,285
Stage/Storage Total Pond (including Forebay)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
(CF)
93.5
117
0
0 Pond Bottom
94.0
191
77
77
95.0
283
237
314
96.0
393
338
652
97.0
1,012
703
1,354
98.0
1,920
1,466
2,820 -Permanent Pool
99.0
2,745
1,879
3,233
100.0
4,230
3,075
5,895
101.0
8,699
6,465
12,360
Forebay Only (20% of Total Pond)
Cumulative
Contour
Incremental
Volume, S
Contour
Area (SF)
Volume (CF)
(CF)
93.5
23
0
0 -Bottom Elev.
94.0
38
15
15
95.0
57
47
63
96.0
79
68
130
97.0
202
141
271
98.0
384
293
564 Forebay Volume

Wet Detention Pond Calculations
Reference: SAIDA Ratio for TSS Removal (NC DENR)
Surface Area/Drainage
Area for 85% TSS Removal with 30' Vegetative Filter (Coastal Counties)
Permanent Pool
Depth (ft)
Impervious
% 3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
10%
0.9
0.8
0.7
0.6
0.5
0.0
0.0
0.0
0.0
0.0
20%
1.7
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
30%
2.5
2.2
1.9
1.8
1.6
1.5
1.3
1.2
1.0
0.9
40%
3.4
3.0
2.6
2.4
2.1
1.9
1.6
1.4
1.1
1.0
50%
4.2
3.7
3.3
3.0
2.7
2.4
2.1
1.8
1.5
1.3
60%
5.0
4.5
3.8
3.5
3.2
2.9
2.6
2.3
2.0
1.6
70%
6.0
5.2
4.5
4.1
3.7
3.1
2.9
2.5
2.1
1.8
80%
6.8
6.0
5.2
4.7
4.2
3.7
3.2
2.7
2.2
2.0
90%
7.5
6.5
5.8
5.3
4.8
4.3
3.8
3.3
2.8
2.3
1 00%
8.2
7.4
6.8
6.2
5.6
5.0
4.4
3.8
3.2
2.6
Surface ArealDrainage
Area for 90% TSS
Removal without Vegetative Filter
(Coastal Counties)
Permanent Pool
Depth (ft)
Impervious
% 3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
1 0%
1.3
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
20%
2.4
2.0
1.8
1.7
1.5
1.4
1.2
1.0
0.9
0.6
30%
3.5
3.0
2.7
2.5
2.2
1.9
1.6
1.3
1.1
0.8
40%
4.5
4.0
3.5
3.1
2.8
2.5
2.1
1.8
1.4
1.1
50%
5.6
5.0
4.3
3.9
3.5
3.1
2.7
2.3
1.9
1.5
60%
7.0
6.0
5.3
4.8
4.3
3.9
3.4
2.9
2.4
1.9
70%
8.1
7.0
6.0
5.5
5.0
4.5
3.9
3.4
2.9
2.3
80%
9.4
8.0
7.0
6.4
5.7
5.2
4.6
4.0
3.4
2.8
90%
10.7
9.0
7.9
7.2
6.5
5.9
5.2
4.6
3.9
3.3
100%
12.0
10.0
8.8
8.1
7.3
6.6
5.8
5.1
4.3
3.6
Reference: "Stormwater Best Management Practices" by NCDENR DWQ Water Quality Section, April 1999