20050732 Ver 22_Stormwater Info_20110719

?NICIQM&CREED
TO: NCDENR - DWQ 401 Unit
512 N Salisbury Street
Archdale Building -911, Floor
Raleigh, NC 27604
ATTENTION: Ms. Annette Lucas
WE ARE SENDING: ? Originals
? Specifications
?s-o?3a vaa
LETTER OF TRANSMITTAL
DATE: July 15, 2011
PROJECT NO: 2735-0073 TASK NO: EXP
RE: Briar Chapel - Phase 6 South Subdivision
Plans
TRANSMITTAL NO: 1 PAGE I OF 1
® Prints ? Shop Drawings ? Samples
? Calculations ? Other -
Quantity Drawing No. Rev. I Description Status
2 Stormwater Design Plans C3.1-3.3, D4.1-D4.3 G
2 Narrative & Supporting Calculations G
2 Wet Detention Basin O&M Agreement (1 Original, 1 copy) G
2 BMP#9 Wet Detention Pond Design Supplement G
2 Impervious Surface Area Table G
Issue Status Code
REMARKS:
A. Preliminary
E. Construction
Annette,
Please find the enclosed documents for
comments. Thank you.
JUL 1 9 2
if you have any questions or
1730 Varsity Drive, Suite 500 Raleigh, NC 27606 919/233-8091 Fax [phone]
Cc: McKIM & CREED, INC.
F
Signed -
Grant M. Livengood, PE
B. Fabrication Only C. For Information D. Bid
F. For Review & Comments G. For Approval H. See Remarks
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
Wet Detention Basin Operation and Maintenance Agreement
I will keep a maintenance record on this BMP. This maintenance record will be kept in a
log in a known set location. Any deficient BMP elements noted in the inspection will be
corrected, repaired or replaced immediately. These deficiencies can affect the integrity
of structures, safety of the public, and the removal efficiency of the BMP.
The wet detention basin system is defined as the wet detention basin,
pretreatment including forebays and the vegetated filter if one is provided.
This system (check one):
? does ® does not incorporate a vegetated filter at the outlet.
This system (check one):
? does ® does not incorporate pretreatment other than a forebay.
Important maintenance procedures:
- Immediately after the wet detention basin is established, the plants on the
vegetated shelf and perimeter of the basin should be watered twice weekly if
needed, until the plants become established (commonly six weeks).
- No portion of the wet detention pond should be fertilized after the first initial
fertilization that is required to establish the plants on the vegetated shelf.
- Stable groundcover should be maintained in the drainage area to reduce the
sediment load to the wet detention basin.

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- If the basin must be drained for an emergency or to perform maintenance, the
flushing of sediment through the emergency drain should be minimized to the
maximum extent practical.
- Once a year, a dam safety expert should inspect the embankment.
After the wet detention pond is established, it should be inspected once a month and
within 24 hours after every storm event greater than 1.0 inches (or 1.5 inches if in a
Coastal County). Records of operation and maintenance should be kept in a known set
location and must be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element: Potential problem: How I will rernediate the problem:
The entire BMP Trash/debris is resent. Remove the trash/debris.
The perimeter of the wet Areas of bare soil and/or Regrade the soil if necessary to
detention basin erosive gullies have formed. remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Vegetation is too short or too Maintain vegetation at a height of
long. a roximatel six inches.
Form SW401-Wet Detention Basin O&M-Rev.4 Page 1 of 4
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element: Potential problem: How I will remediate the problem:
The inlet device: pipe or The pipe is clogged. Unclog the pipe. Dispose of the
swale sediment off-site.
The pipe is cracked or Replace the pipe.
otherwise damaged.
Erosion is occurring in the Regrade the swale if necessary to
swale. smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
The forebay Sediment has accumulated to Search for the source of the
a depth greater than the sediment and remedy the problem if
original design depth for possible. Remove the sediment and
sediment storage. dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Erosion has occurred. Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Weeds are present. Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The vegetated shelf Best professional practices Prune according to best professional
show that pruning is needed practices
to maintain optimal plant
health.
Plants are dead, diseased or Determine the source of the
dying. problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application to establish the
ground cover if a soil test indicates
it is necessary.
Weeds are present. Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
The main treatment area Sediment has accumulated to Search for the source of the
a depth greater than the sediment and remedy the problem if
original design sediment possible. Remove the sediment and
storage depth. dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Algal growth covers over Consult a professional to remove
50% of the area. and control the algal growth.
Cattails, phragmites or other Remove the plants by wiping them
invasive plants cover 50% of with pesticide (do not spray).
the basin surface.
Form SW401-Wet Detention Basin O&M-Rev.4 Page 2 of 4
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
BMP element: Potential problem: How I will remediate the problem:
The embankment Shrubs have started to grow Remove shrubs immediately.
on the embankment.
Evidence of muskrat or Use traps to remove muskrats and
beaver activity is present. consult a professional to remove
beavers.
A tree has started to grow on Consult a dam safety specialist to
the embankment. remove the tree.
An annual inspection by an Make all needed repairs.
appropriate professional
shows that the embankment
needs repair. if applicable)
The outlet device Clogging has occurred. Clean out the outlet device. Dispose
of the sediment off-site.
The outlet device is damaged Repair or replace the outlet device.
The receiving water Erosion or other signs of Contact the local NC Division of
damage have occurred at the Water Quality Regional Office, or
outlet. the 401 Oversight Unit at 919-733-
1786.
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.
When the permanent pool depth reads 4.50 feet in the main pond, the
sediment shall be removed.
When the permanent pool depth reads 4.50 feet in the forebay, the sediment
shall be removed.
BASIN DIAGRAM
ill in the blanks)
Permanent Pool Elevation 462.50
Sediment Removal t.458.000 Pe anen
---------V
Volume
Bottom Elevaft Mi
n.
Sediment
Storage
FOREBAY
Pool
--Sediment-Removal-Elevation-458.00- - -- Volume
Bottom Elevation 457.00 2 1-ft Mon
Sedimer
Storage
MAIN POND
Form SW401-Wet Detention Basin O&M-Rev.4 Page 3 of 4
Permit Number:
(to be provided by DWQ)
I acknowledge and agree by my signature below that I am responsible for the
performance of the 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.
Project name:Briar Chapel Subdivision, Phase 6 South
BMP drainage area number:# 9
Print name:Bill Mumford
Title:Assistant Vice President NNP-Briar Chapel LLC
Address: 16 Windy Knoll Circle, Chapel Hill NC 27516
Phone:[phone]
Signature:
c?
Date: -1- I Z - Zv
Note: The legally responsible party 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.
I, Gfo+r ' A- deffion
, a Notary Public for the State of
No" roLc, y , County of l Af 04f nb , do hereby certify that
_P111 YY U'Wm Wcl personally appeared before me this
day of fi,? ly ao and acknowledge the due execution of the
forgoing wet detention basin maintenance requirements. Witness my hand and official
seal,
SEAL
My commission expires 3? 0/1 a
Form SW401-Wet Detention Basin O&M-Rev.4 Page 4 of 4
uS-O13a- 1) 20,
401 NARRATIVE &
SUPPORTING CALCULATIONS
Briar Chapel Development
Phase 6 South
Chatham County, North Carolina
July 18, 2011
Prepared for
BRIAR CHAPEL'S
Newland COMMU M

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Q
NNP Briar Chapel, LLC
16 Windy Knoll Circle
Chapel Hill, North Carolina 27516
4. Prepared By:
4e,# MCKIM&CREED
1730 Varsity Drive, Suite 500
Raleigh, North Carolina 27606
Phone: [phone]
Fax: [phone]
M&C Project No. 02735-0073

PROJECT DESCRIPITON
' The purpose of the project is to continue development in planned residential areas within the
Briar Chapel masterplanned development. Phase 6 South will provide roadway, water and
' sewer infrastructure for 134 residential lots. All lots will have limited impervious surfaces based on
lot classification and size.
' Future public roadways are set at widths of 27' measured from back of curb to back of curb.
Each public road will contain a 2.5' curb and gutter section on each side. All private alleys will
be 15' wide and have been designed to be inverted crown in order direct water flow to the
center of the alley where it will be caught and piped to the main storm drainage system.
Based on the conditions of the approved 401 Water Quality Certification, NCDENR-DWQ will
require runoff from the roads to be captured and treated for 85% TSS removal before being
' discharged into the existing stream buffer. To meet this requirement, one wet detention pond
has been designed to remove 90% TSS and to hold the volume from the 1 inch storm and
discharge the peak runoff from the 1-year, 24-hour storm at a rate below the pre-development
peak discharge rate. The wet detention ponds has been designed based upon the guidelines in
' the most recent edition of the North Carolina Stormwater Best Management Practices Manual.
Upon completion of the project's construction, the proposed public roads will be turned over to
' and maintained by NCDOT.
SITE DESCRIPTION
' The existing site is an approximately 38 acre tract that is a part of the Briar Chapel development
in Chatham County, North Carolina. The site is along Briar Chapel Parkway approximately two
' miles west of its intersection with US 15-501.
Two existing streams are located on each side of the proposed denuded area. No stream areas
are to be impacted during these earth moving activities. Chatham County has determined that
' both streams will require 50' riparian buffers, as measured from the top of the bank. The lower
portion of the western stream requires a 100' buffer. Both streams are within the Cape Fear River
Basin and are tributaries to Pokeberry Creek (WS-IV; NSW).
The site generally slopes from northwest to southeast. The slopes in the site range from 5-20% in
localized areas.
' SOILS
According to the Chatham County Generalized Soil Survey, the soils located on the site are
' classified as Wedowee sandy loam, 2% to 15% slopes (WeB, WeB, WeD).
The following soil descriptions are associated with the soils found on the site:
' We(X) - Wedowee sandy loam soils are often found in piedmont uplands, along ridges
and side slopes. Permeability is moderate and the soils are well drained. Soils have a low
shrink/swell potential. The seasonal high water is generally more than 6.0 feet below the
' surface.
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WET DETENTION DESIGN
The wet detention pond on this site has been designed to remove 90% of the total suspended
solids entering from the surrounding impervious drainage areas before discharging into the
adjacent stream. Areas downstream of the ponds exceeded the new slope limitations required
by the BMP Manual for level spreaders and vegetated filter strips. Treated runoff will be
dissipated via a riprap outlet protection device before entering any stream buffers.
Design parameters were taken from the BMP manual and from DWQ's design supplement forms.
MAINTENANCE CONSIDERATIONS
The property owner shall be responsible for periodic inspection and maintenance of all
temporary erosion control measures devices. Any measure that fails to function as intended
shall be repaired immediately.
I recipitation Frequency Data Server
http://hdsc.nws.noaa.gov/cgi-bin/hdsc/buiIdout.perl?type=idf&units=us&s...
POINT PRECIPITATION
FREQUENCY ESTIMATES
FROM NOAA ATLAS 14
CHAPEL HILL 2 W, NORTH CAROLINA (31-1677) 35.9086 N 79.0794 W 462 feet
from "Precipitation-Frequency Atlas ot'the United States" NOAA Atlas 14, Volume 2, Version 3
G.M. Bonnin, D Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland, 2004
Extracted: Wed Jan 20 2010
Confidence Limits Seasonality Y Location Maps 11 Other Info. GIS data Maps Docs 1
t Return to State Map
Precipitation Intensity Estimates (in/hr)

F
=

5 min
F3" 60

F 0

3 hr hr 12 hr

24 hr 48 hr 4 day

7 day 20

? 30 45 60
(
)
4.93 rrun
3.94 mmm
3.28 2.25 m
m
1.40 mm
0.84 - -
0.60 0.36 0.21
0.12 0.07 0.04 da
0.03 0.02 da
0.01 a
d
0.01 da
0.01 da
0.01
I ` 5.81 4.64 3.89 2.69 1.69 1.01 0.72 0.43 0.25 0.15 0.09 0.05 0.03 0.03 0.02 0.01 0.01 0.01
F 5 6.70 5.36 4.52 3.21 2.06 1.25 0.89 0.53 0.32 0.19 0.11 0.06 0.04 0.03 0.02 0.02 0.01 0.01
10 7.38 5.90 4.98 3.61 2.35 1.43 1.03 0.62 0.37 0.22 0.12 0.07 0.04 0.03 0.02 0.02 0.01 0.01
25 11 6.46 5.46 4.04 2.69 1.66 1.20 0.73 0.44 0.25 0.15 0.08 0.05 0.04 0.03 0.02 0.02 0.01
50 8.62 6.86 5.79 4.36 2.95 1.85 1.34 0.82 0.50 0.29 0.16 0.09 0.06 0.04 0.03 0.02 0.02 0.02
F 100 9.07 7.21 6.07 4.65 3.20 2.02 1.48 0.91 0.56 0.32 0.18 0.10 0.06 0.05 0.03 0.02 0.02 0.02
200
F 9.44 7.49; 6.30 4.90 3.44 2.20 1.63 1.01 0.62 0.35 0.20 0.11 0.07 0.05 0.03 0.03 0.02 0.02
500 9.85 7.79 6.54 5.21 3.73 2.43 1.82 1.14 0.71 0.40 0.22 0.12 0.08 0.06 0.04 0.03 0.02 0.02
1000 ! 10.19 8.02 6.71 5.43 3.96 2.62 1.98 1.24 0.78 0.43 0.24 0.13 0.08 0.06 0.04 0.03 0.02 0.02
` These precipitation frequency esti mates are based on a partial duration series. ARI is the Average Recurrence Interval.
Please referto NOAAAffas 14 Documentfor more information. NOTE: Formatting forces estimates near zero to appearas xro.
* Upper bound of the 90% confidence interval
Precipitation Intensity Estimates (in/hr)
ARI** 5 10 F15 30 60 0 3
- l2 24
F 48 4 7
F l0 20
F 30 45 60
(Years) min min min min min hr h
hr hr hr day day day day day [
day day
( 5.39 4.31 3.59 2.46 ! 1.53 0.92 0.65 0.39 0.23 ! 0.13 0.08 0.04 0.03 0.02 0.01 0.01 0.01 0.01
I 2 6.36 5.08 4.26 2.94 1.85 1.1 1 0.79 0.47 0.28 0.16 0.09 0.05 0.03 0.03 0.02 0.01 0.01 0.01
7.31 5.86 4.94 3.51 2.25 1.37 0.97 0.58 0.34 0.20 0.12 0.06 0.04 0.03 0.02 0.02 0.01 0.01
F 10 8.06 6.44 5.43 3.94 2.56 1.57 1.12 0.68 0.40 0.23 0.13 ! 0.07 0.05 0.04 0.02 0.02 0.02 0.01
25 8.83 7.04 5.95 4.41 2.93 1.82 1.31 0.79 0.48 0.27 0.16 ! 0.09 0.05 0.04 0.03 0.02 0.02 0.01
50 9.38 7.48 6.31 4.75 3.22 2.02 1.47 0.89 0.54 0.31 0.17 0.10 0.06 0.05 0.03 0.02 0.02 0.02
100 9.89 7.85 6.62 5.07 3.49 2.22 1.62 0.99 0.60 0.34 0.19 0.11 0.07 0.05 0.03 0.02 0.02 0.02
200 10.32 8.18 6.88 5.35 3.75 2.41 1.78 1.09 0.67 0.38 0.21 0.12 0.07 0.06 0.04 0.03 0.02 0.02
500
F 10.78 8.52 7.15 5.69 4.08 2.66 1.99 1.23 0.76 0.43 0.24 0.13 0.08 0.06 0.04
. 0.0
3
0. 02 0.02
1 1000 111.14 18.77 17.34 15.94 14.34 12.87 2.16 1.36 0.85 0.46 0.26 0.14 0.09 0.07 0.04 0.03 0.02 0.02
The upper bound ofthe confidence interval at 90% confidence level is the value which 5%ofthe simulated quanfile values fora given frequencyare greater than.
"These precipitation kequencyestimates are based on a partial duration series. ARI is the Average Recurrence Interval.
Please refer to NOAA Atlas 14 Document for more information. NOTE: Formatting prevents estimates near zero to appear as zero.
Lower bound of the 90%o confidence interval
Precipitation Intensity Estimates (in/hr)
5 10 15 30 60 120 3 6 l2 24 48 4 7 10 20 30 45 60
(yews)min min min min min min hr hr hr hr hr day [day day day day day day
1 of4
1/20/2010 8:55 AM
I recipitation Frequency Data Server

1

L.
http: //hdsc.nws.noaa.gov/cgi-bin/hdsc/bui 1 dout.perl?type=pf&units=us&se...
;' POINT PRECIPITATION'
FREQUENCY ESTIMATES
FROM NOAA ATLAS 14
CHAPEL HILL 2 W, NORTH CAROLINA (31-1677) 35.9086 N 79.0794 W 462 feet
from'Precipilation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2. Version 3
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yckta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland, 2004
Extracte : Tue Jan 1
10
Confidence Limits , Seasonality Location Maps ?j Other Info. GIS data Maps Docs Return to State Map
Precipitation Frequency Estimates (inches)

ARI* 5 10 15 30
60 120 [Lhr
6 hr

12 hr
20 30 45 60
24 hr 48 hr 4 day 7 day F 10
(years)
I mm min
0.41 0.66 mm
0.82 mm rn m
1.12 1.40 1.68 -
1.79 2.15
2.54 y
2.96 3.46 3.87 4.44 5.05 6.76 8.39 10.69 12.84
F 2 0.48 0.77 0.97 1.34 1.69 2.02 2.16 2.59 3.06 3.58 4.17 4.64 5.30 6.00 ' 7.97 9.88 12.52 14.97
0.56 0.89 1.13 1.60 2.06 2.49 2.66 3.20 3.80 4.47 5.17 5.71 6.44 7.21 9.41 11.47 14.32 16.89
10 0.61 0.98 1.25 1.80 2.35 2.87 3.08 3.71 4.44 5.17 5.95 6.54 7.34 8.15 10.56 12.72 15.72 18.37
25 0.68 1.08 1.36 2.02 2.69 3.33 3.61 4.37 5.28 6.11 6.99 7.68 8.57 9.42 12.11 14.36 17.55 20.28
F 50 0.72 1.14 1.45 2.18 2.95 3.70 4.04 4.92 5.99 6.86 7.81 8.57 9.54 10.43 13.34 15.62 18.95 21.72

F 100
_
0.76 1.20
1.52
2.33 3.20 4.05
4.46 5.47
6.71
7.62 8.64 9.49 10.53 11.44 14.57 16.87 20.31 23.11
200 0.79 1.25 1.57 2.45 3.44 4.40 4.89 6.03 7.47 8.41 9.49 10.44 11.56 12.47 15.83 18.12 21.67 24.46
F 500 0.82 1.30 1.64 2.60 3.73 4.86 5.46 6.80 8.53 9.50 10.66 11.73F12 96 13.87 17.55 19.80 23.46 26.21
1000 0.85 1.34 1.68 2.72 3.96 5.23 5.93 7.44 9.43 10.35 11.58 12.76 14.06 14.97 18.89 21.09 24.83 27.53,
`These precipitation frequencyestmates are based on a partial duration series. ARI is the Average Recurrence Interval.
Please referto NOAAAfIas 14 Documentfor more information. NOTE: Formatting forces estimates near zero to appearas zgro.
10 0.67 1.07 1.36 1.97 2.56 3.14 3.37 4.05 4.83 5.51 6.36 6.99 7.82 8.66 1 1.1713.41 16.51 19.25
25 0.74 1.17 1.49 2.20 2.93 3.64 3.94 4.76 5.73 6.54 7.47 8.22 9.14 10.02 12.82 15.15 18.44 21.26
50 0.78 1.25 1.58 2.38 3.22 4.04 4.41 5.35 6.47 7.34 8.35 9.19 10.19 11.11 14.14 16.50 19.92 22.80
100 ! 0.82 1.31 1.66 2.53 ! 3.49 4.43 4.87 5.94 7.25 8.17 19.27 " 10.19 11.26 12.21 15.48 17.85 21.39 24.28
200 0.86 1.36 1.72 2.68 ! 3.75 4.82 5.34 6.56 8.06 9.03 10.19 11.22 12.3813.33 16.86 19.21 22.85 25.73
500 0.90 1.42 79
1. 2.84 4.08 5.32 5.96 7.39 9.20 110.21 11.47 12.65 13.91 1
4.86 18.72 21.04 24.81 27.63
F 1000 0.93 1.46 1.83 2.97 4.34 5.74 6.50 8.1 1 10.19 11.15 12.4913.7915.14 16.07 20.20 22.46 26.31 29.07
* Upper bound of the 90% confidence interval
Precipitation Frequency Estimates (inches)
ARI
? 30 60 120 3 6 12 24 48 4 7
5 10 m5
[ 10 20 30 45 60
(years) in
min mn min nun min hr hr hr hr hr day [day
i [. day day day day day
0.45 .0.72 0.90 1.23 1.53 ! 1.84 1.96 2.35 2.77 3.16 3.70 4.14 4.73 5.37 7.14 8.87 11.24 13.44
0.53 0.85 1.06 1.47 1.85 2.22 2.37 2.83 3.34 3.82 4.46 4.96 5.64 6.38 8.43 10.42 13.15 15.68
I 5 0.61 0.98 1.23 1.75 2.25 2.73 2.92 3.50 4.15 4.77 5.53 6.09 6.86 7.66 9.95 12.10 15.04 17.69
The upper bound ofthe confidence interval at 90%confidence level is the valuewhich 5%a ofthe simulated quantile values fora given frequencyare greater than.
" These precipitation frequency estimates are based on a partial duration series. ARI is the Average Recurrence Interval.
Please refer to NOAAAtIas 14 Document for more information. NOTE: Formatting prevents estimates near zero to appearas zero.
' >< Lower bound of the 90% confidence interval
Precipitation Frequency Estimates (inches)
[ARI *'S 10 15 30 60 120 3 6 l2 24 48 4 7 10 20 F30 45 60
ears) min min min min
I [ [ [
min min hr hr hr hr hr day day day day day day day
I of 4
1/19/2010 9:12 AM
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BMP #1 DESIGN

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WATER QUALITY POND #9 CALCULATIONS
Project Name
Briar Chapel - Phase 6 S
Project Number
02735-0073
Date
July 8, 2011
3rd revision
2nd revision
1st revision

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Water Quality Pond Drainage Area Data
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011
Total site area 1,639,766 square feet =
37.64 acres
Drai nage area to and Other Drainage Area

Impervious areas Existing
s Proposed
s Change
s Existing
s Proposed
s
On-site buildings lots 0 473,100 473,100 0 0
On-site streets 0 188,789 188,789 0 0
On-site sidewalks 0 50,332 50,332 0 0
On-site future (open space) 0 20,000 20,000 0 0
Off-site buildings 0 42,500 42,500 0 0
Off-site streets 0 40,655 40,655 0 0
Off-site sidewalks 0 71489 7,489 0 0
Total Impervious 0 822,865 822,865 0 0
Drainage area to and Other Drainage Area

Non-impervious areas Existing
s Proposed
s Change
s Existing
s Proposed
s
On-site grass/landscape 0 785,984 785,984 0 0
On-site woods 1,639,768 30,917 -1,608,851 0 0
Other undeveloped 0 0 0 0 0
Total off-site non-impervious 0 0 0 0 0
Total non-impervious 1,639,768 816,901 -822,867 0 0
Total -Drainage Area 1,639,766 1,639,766 0 3,167,850 3,167,850
Percent Impervious 0.0 50.2 50.2 0.0 0.0
Notes:
2011.07.08.Wet Detention Pond #9.xls
Site Drainage Area Data Page 1 of 1
Printed 7/18/2011 9:26 AM

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Water Quality Pond Surface Area Calculations
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011
Total on-site drainage area to pond 1,639,766 square feet
Total impervious area in drainage area 822,865 square feet
Average water depth of basin at normal pool 3.5 feet
Location of site Chatham County
Site region Piedmont
% Impervious cover 50.2 percent
If the site is in a coastal area, will a vegetative filter be used? n/a
Surface Area/Drainage Area Ratios:
For a site in the Piedmont (85%) 1.9 percent
For a site in the Piedmont (90%) 2.8 percent
For a site in a Coastal County w/ Vegetative Filter 3.8 percent
For a site in a Coastal County w/out Vegetative Filter 5.0 percent

Required surface area of pond:
For a site in the Piedmont (85%) 31,170.0 square feet
For a site in the Piedmont (90%) 45,220.0 square feet
For a site in a Coastal County w/ Vegetative Filter 61,690.0 square feet
For a site in a Coastal County w/out Vegetative Filter 81,530.0 square feet
Notes:
2011.07.08.Wet Detention Pond #9.xls
Pond Surface Area Calcs
Page 1 of 1
Printed 7/18/2011 9:26 AM

Water Quality Pond Stormwater Runoff Volume Calculations
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011
Drainage area 1,639,766 square feet
Impervious area 822,865 square feet
Rainfall depth 1.00 inches
Percent Impervious 50.2 percent
R(v)=0.05+0.009*(Percent impervious)
Runoff coefficient - R(v) 0.50 in/in
Runoff volume=(Design rainfall)*(R(v))*(Drainage area)
Runoff volume 68,547.2 cubic feet
Notes:
2011.07.08.Wet Detention Pond #9.xls
Runoff Volume Calcs Page 1 of 1
Printed 7/18/2011 9:27 AM
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Water Quality Pond Volume Calculations
Stage-Storage Data for Pond - Temporary Pool
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011

Contour ID
Stage
Area
[s q. ft.
Area
acres Incremental
Area
[s q. ft. Incremental
Area
acres Incremental
volume
cu. ft Incremental
volume
acre-ft Cumulative
volume
cu. ft Cumulative
volume
acre-ft
462.5 0 46,957.0 1.078 46,957.0 1.1 0.0 0.0 0.0 0.0
463 0.5 51,331.0 1.178 4,374.0 0.1 24,572.0 0.6 24,572.0 0.6
463.9 1.4 53,758.0 1.234 2,427.0 0.1 47,290.0 1.1 71,862.0 1.6
464 1.5 54,030.0 1.240 272.0 0.0 5,389.4 0.1 77,251.5 1.2
465 2.5 56,787.0 1.304 2,757.0 0.1 55,408.5 1.3 132,660.0 1.4
466 3.5 59,599.0 1.368 2,812.0 0.1 58,193.0 1.3 190,853.0 2.6
467 4.5 62,468.0 1.434 2,869.0 0.1 61,033.5 1.4 251,886.5 2.7
468 5.5 65,394.0 1.501 2,926.0 0.1 63,931.0 1.5 315,817.5 2.9

2011.07.08.Wet Detention Pond #9.xls
Stage Storage (Temp Pool)
Page 1 of 1
Printed 7/18/2011 9:27 AM
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Water Quality Pond Volume Calculations
Stage-Storage Data for Pond - Permanent Pool
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011

Contour ID
Stage
Area
[s q. ft.
Area
acres Incremental
Area
[s q. ft. Incremental
Area
acres Incremental
volume
cu. ft Incremental
volume
acre-ft Cumulative
volume
cu. ft Cumulative
volume
acre-ft
457 0 22,273.0 0.511 22,273.0 0.5 0.0 0.0 0.0 0.0
458 1 25,689.0 0.590 3,416.0 0.1 23,981.0 0.6 23,981.0 0.6
459 2 29,243.0 0.671 3,554.0 0.1 27,466.0 0.6 51,447.0 1.2
460 3 32,937.0 0.756 3,694.0 0.1 31,090.0 0.7 82,537.0 1.3
461 4 36,771.0 0.844 3,834.0 0.1 34,854.0 0.8 117,391.0 1.5
462 5 40,741.0 0.935 3,970.0 0.1 38,756.0 0.9 156,147.0 1.7
462.5 5.5 46,957.0 1.078 6,216.0 0.1 21,924.5 0.5 178,071.5 1.4

2011.07.08.Wet Detention Pond #9.xls
Stage Storage (Perm Pool)
Page 1 of 1
Printed 7/18/2011 9:27 AM
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Water Quality Pond Volume Calculations
Stage-Storage Data for Pond - Forebays
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011

Contour ID
Stage
Area
[s q. ft.
Area
acres Incremental
Area
[s q. ft. Incremental
Area
acres Incremental
volume
cu. ft Incremental
volume
acre-ft Cumulative
volume
cu. ft Cumulative
volume
acre-ft
457 0 3,700.0 0.085 3,700.0 0.1 0.0 0.0 0.0 0.0
458 1 4,465.0 0.103 765.0 0.0 4,082.5 0.1 4,082.5 0.1
459 2 5,297.0 0.122 832.0 0.0 4,881.0 0.1 8,963.5 0.2
460 3 6,196.0 0.142 899.0 0.0 5,746.5 0.1 14,710.0 0.2
461 4 7,163.0 0.164 967.0 0.0 6,679.5 0.2 21,389.5 0.3
462 5 8,195.0 0.188 1,032.0 0.0 7,679.0 0.2 29,068.5 0.3
462.5 5.5 9,706.0 0.223 1,511.0 0.0 4,475.3 0.1 33,543.8 0.3

2011.07.08.Wet Detention Pond #9.xls
Stage Storage (Forebays)
Page 1 of 1
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Water Quality Basin Dewatering Time Calculations
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011
Maximum surface area of basin 53,758 square feet
Maximum head of water above dewatering hole 1.40 feet
Orifice coefficient 0.60
Diameter of each hole 5.0 inches
Number of holes 1
Cross sectional area of each hole = 0.136 square feet
Cross sectional area of each hole = 19.6 square inches

Cross sectional area of dewatering hole(s) = 0.136 square feet
Cross sectional area of dewatering hole(s) = 19.6 square inches

Dewatering time for basin = 53.8 hours
Dewatering time for basin = 2.24 days
Notes:
Water Quality Pond Summary Information
Project Briar Chapel - Phase 6 S
Project No. 02735-0073
Date July 8, 2011
Drainage area to pond 1,639,766 square feet = 37.64 acres
Impervious area in drainage area 822,865 square feet = 18.89 acres
Bottom of pond elevation 457.00 feet
Normal pool elevation 562.50 feet
Pond volume at normal pool 178,071 cubic feet
Required volume for design rainfall 68,547 cubic feet
Required surface area for pond 45,220 square feet
Volume provided for storage of design rainfall = 71,862 cubic feet at elevation 463.9
Surface area provided at normal pool 46,957 square feet
2011.07.08.Wet Detention Pond #9.xis
Summary Data Page 1 of 1 Printed 7/18/2011 9:27 AM
1S
Pre-Development
2S
Post-Development
3P
BMP #9
Subca Reach and Lin k
BMP #9 Type 11 24-hr 1-inch Rainfall=1.00"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 8
Summary for Pond 3P: BMP #9
Inflow Area = 37.644 ac, 50.18% Impervious, Inflow Depth = 0.20" for 1-inch event
Inflow = 7.99 cfs @ 12.10 hrs, Volume= 0.620 of
Outflow = 0.26 cfs @ 19.78 hrs, Volume= 0.422 af, Atten= 97%, Lag= 460.8 min
Primary = 0.26 cfs @ 19.78 hrs, Volume= 0.422 of
Secondary = 0.00 cfs @ 5.00 hrs, Volume= 0.000 of
Routing by Stor-Ind method, Time Span= 5.00-40.00 hrs, dt= 0.05 hrs
Peak Elev= 462.86' @ 19.78 hrs Surf.Area= 50,111 sf Storage= 17,499 cf
Plug-Flow detention time= 677.6 min calculated for 0.421 of (68% of inflow)
Center-of-Mass det. time= 554.1 min ( 1,452.1 - 898.0 )
T Volume Invert Avail.Storage Storage Description
' #1 462.50' 315,819 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
462.50 46,957 0 0
463.00 51,331 24,572 24,572
464.00 54,030 52,681 77,253
' 465.00 56,787 55,409 132,661
466.00 59,599 58,193 190,854
467.00 62,468 61,034 251,888
468.00 65,394 63,931 315,819
Device Routing Invert Outlet Devices
#1 Primary 459.25' 36.0" Round Culvert
L= 48.0' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 459.25'/459.00' S=0.0052'/' Cc= 0.900
n= 0.013
#2 Device 1 462.50' 5.0" Vert. Orifice/Grate C= 0.600
#3 Device 1 463.90' 90.0 deg x 5.0' long x 0.35' rise Sharp-Crested Vee/Trap Weir C=2.50
#4 Device 1 464.25' 60.0" x 60.0" Horiz. Orifice/Grate C= 0.600
Limited to weir flow at low heads
1 #5 Secondary 466.00' 60.0' long x 16.0' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
Primary OutFlow Max=0.26 cfs @ 19.78 hrs HW=462.86' (Free Discharge)
t-1=Culvert (Passes 0.26 cfs of 43.41 cfs potential flow)
2=Orifice/Grate (Orifice Controls 0.26 cfs @ 2.04 fps)
' 3=Sharp-Crested Vee/Trap Weir ( Controls 0.00 cfs)
-Orifice/Grate ( Controls 0.00 cfs)
Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=462.50' (Free Discharge)
' t-5=Broad-Crested Rectangular Weir ( Controls 0.00 cfs)
BMP #9 Type 11 24-hr 1-inch Rainfall=1.00"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 9
Pond 3P: BMP #9
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Time (hours)

BMP #9 Type 1124-hr 1-year Rainfall=2.96"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 6
Summary for Subcatchment 1S: Pre-Development
' Runoff = 18.96 cfs @ 12.28 hrs, Volume= 2.171 af, Depth= 0.69"
Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-40.00 hrs, dt= 0.05 hrs
Type II 24-hr 1-year Rainfall=2.96"
Area (sf) CN Description
1,639,776 70 Woods, Good, HSG C
1,639,776 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
30.0 Direct Entry,
Subcatchment 1S: Pre-Development
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Time (hours)
BMP #9 Type 11 24-hr 1-year Rainfall=2.96"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 13
Summary for Pond 3P: BMP #9
Inflow Area = 37.644 ac, 50.18% Impervious, Inflow Depth = 1.63" for 1-year event
Inflow = 78.69 cfs @ 12.07 hrs, Volume= 5.108 of
Outflow = 17.41 cfs @ 12.42 hrs, Volume= 4.181 af, Atten= 78%, Lag= 21.0 min
Primary = 17.41 cfs @ 12.42 hrs, Volume= 4.181 of
Secondary = 0.00 cfs @ 5.00 hrs, Volume= 0.000 of
Routing by Stor-Ind method, Time Span= 5.00-40.00 hrs, dt= 0.05 hrs
Peak Elev= 464.55' @ 12.42 hrs Surf.Area= 55,535 sf Storage= 107,166 cf
Plug-Flow detention time= 373.7 min calculated for 4.181 of (82% of inflow)
Center-of-Mass det. time= 295.2 min ( 1,126.4 - 831.2 )
Volume Invert Avail.Storage Storage Description
#1 462.50' 315,819 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
462.50 46,957 0 0
463.00 51,331 24,572 24,572
464.00 54,030 52,681 77,253
465.00 56,787 55,409 132,661
466.00 59,599 58,193 190,854
467.00 62,468 61,034 251,888
468.00 65,394 63,931 315,819
Device Routing Invert Outlet Devices
#1 Primary 459.25' 36.0" Round Culvert
L= 48.0' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 459.25'/459.00' S=0.0052'/' Cc= 0.900
n= 0.013
#2 Device 1 462.50' 5.0" Vert. Orifice/Grate C= 0.600
#3 Device 1 463.90' 90.0 deg x 5.0' long x 0.35' rise Sharp-Crested Vee/Trap Weir C=2.50
#4 Device 1 464.25' 60.0" x 60.0" Horiz. Orifice/Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary 466.00' 60.0' long x 16.0' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
Primary OutFlow Max=17.31 cfs @ 12.42 hrs HW=464.54' (Free Discharge)
t1=Culvert (Passes 17.31 cfs of 66.30 cfs potential flow)
2=Orifice/Grate (Orifice Controls 0.89 cfs @ 6.52 fps)
3=Sharp-Crested Vee/Trap Weir (Orifice Controls 5.95 cfs @ 3.18 fps)
-Orifice/Grate (Weir Controls 10.46 cfs @ 1.78 fps)
Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=462.50' (Free Discharge)
1-5=Broad-Crested Rectangular Weir (Controls 0.00 cfs)

it

BMP #9 Type 1124-hr 1-year Rainfall=2.96"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 14
Pond 3P: BMP #9
0
LL

78.69 cfs
Inflow Area=37.644 ac
- Peak Elev=464.55'
Storage=107,166 cf
® Inflow
Iv OUfflOW
0 Primary
Seconca,y
BMP #9 Type 11 24-hr 10-year Rainfall=5.17"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 18
Summary for Pond 3P: BMP #9
Inflow Area = 37.644 ac, 50.18% Impervious, Inflow Depth= 3.63" for 10-year event
Inflow = 171.91 cfs @ 12.07 hrs, Volume= 11.375 of
Outflow = 77.43 cfs @ 12.25 hrs, Volume= 10.406 af, Atten= 55%, Lag= 11.1 min
Primary = 77.43 cfs @ 12.25 hrs, Volume= 10.406 of
Secondary = 0.00 cfs @ 5.00 hrs, Volume= 0.000 of
Routing by Stor-Ind method, Time Span= 5.00-40.00 hrs, dt= 0.05 hrs
Peak Elev= 465.93'@ 12.25 hrs Surf.Area= 59,391 sf Storage= 186,452 cf
Plug-Flow detention time= 188.0 min calculated for 10.406 of (91 % of inflow)
Center-of-Mass det. time= 143.0 min ( 951.4 - 808.4 )
Volume Invert Avail.Storage Storage Description
#1 462.50' 315,819 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
462.50 46,957 0 0
463.00 51,331 24,572 24,572
464.00 54,030 52,681 77,253
465.00 56,787 55,409 132,661
466.00 59,599 58,193 190,854
467.00 62,468 61,034 251,888
468.00 65,394 63,931 315,819
Device Routing Invert Outlet Devices
#1 Primary 459.25' 36.0" Round Culvert
L= 48.0' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 459.25'/459.00' S=0.0052'/' Cc= 0.900
n= 0.013
#2 Device 1 462.50' 5.0" Vert. Orifice/Grate C= 0.600
#3 Device 1 463.90' 90.0 deg x 5.0' long x 0.35' rise Sharp-Crested Vee/Trap Weir C=2.50
#4 Device 1 464.25' 60.0" x 60.0" Horiz. Orifice/Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary 466.00' 60.0' long x 16.0' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
Primary OutFlow Max=77.42 cfs @ 12.25 hrs HW=465.92' (Free Discharge)
t-1=Culvert (Inlet Controls 77.42 cfs @ 10.95 fps)
2=Orifice/Grate (Passes < 1.18 cfs potential flow)
3=Sharp-Crested Vee/Trap Weir (Passes < 11.92 cfs potential flow)
-Orifice/Grate (Passes < 141.76 cfs potential flow)
Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=462.50' (Free Discharge)
t-5=Broad-Crested Rectangular Weir (Controls 0.00 cfs)

BMP #9 Type 11 24-hr 10-year Rainfall=5.17"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 19
1 ?
3
0
LL

iI

Pond 3P: BMP #9
Hydrograph
¦ Inflow
[- Outflow
? Primary
C Secondary

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Time (hours)
BMP #9 Type 11 24-hr 100-year Rainfall=7.62"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 23
Summary for Pond 3P: BMP #9
[82] Warning: Early inflow requires earlier time span
Inflow Area = 37.644 ac, 50.18% Impervious, Inflow Depth > 5.95" for 100-year event
Inflow = 276.19 cfs @ 12.06 hrs, Volume= 18.680 of
Outflow = 210.36 cfs @ 12.16 hrs, Volume= 17.689 af, Atten= 24%, Lag= 6.0 min
Primary = 84.14 cfs @ 12.16 hrs, Volume= 15.241 of
Secondary = 126.23 cfs @ 12.16 hrs, Volume= 2.448 of
Routing by Stor-Ind method, Time Span= 5.00-40.00 hrs, dt= 0.05 hrs
Peak Elev= 466.86'@ 12.16 hrs Surf.Area= 62,069 sf Storage= 243,224 cf
Plug-Flow detention time= 131.3 min calculated for 17.688 of (95% of inflow)
Center-of-Mass det. time= 100.5 min ( 895.8 - 795.3 )
Volume Invert Avail.Storage Storage Description
#1 462.50' 315,819 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
462.50 46,957 0 0
' 463.00 51,331 24,572 24,572
464.00 54,030 52,681 77,253
465.00 56,787 55,409 132,661
466.00 59,599 58,193 190,854
467.00 62,468 61,034 251,888
468.00 65,394 63,931 315,819
' Device Routing Invert Outlet Devices
#1 Primary 459.25' 36.0" Round Culvert
L= 48.0' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 459.25'/459.00' S=0.0052'/' Cc= 0.900
n= 0.013
#2 Device 1 462.50' 5.0" Vert. Orifice/Grate C= 0.600
#3 Device 1 463.90' 90.0 deg x 5.0' long x 0.35' rise Sharp-Crested Vee/Trap Weir C=2.50
' #4 Device 1 464.25' 60.0" x 60.0" Horiz. Orifice/Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary 466.00' 60.0' long x 16.0' breadth Broad-Crested Rectangular Weir
Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63
Primary OutFlow Max=84.01 cfs @ 12.16 hrs HW=466.84' (Free Discharge)
L1=Culvert (Inlet Controls 84.01 cfs @ 11.89 fps)
' 2=Orifice/Grate (Passes < 1.33 cfs potential flow)
3=Sharp-Crested Vee/Trap Weir (Passes < 14.59 cfs potential flow)
=Orifice/Grate (Passes < 193.84 cfs potential flow)
Secondary OutFlow Max=122.57 cfs @ 12.16 hrs HW=466.84' (Free Discharge)
t5=Broad-Crested Rectangular Weir (Weir Controls 122.57 cfs @ 2.42 fps)
1
1
BMP #9 Type 11 24-hr 100-year Rainfall=7.62"
Prepared by McKim & Creed Printed 7/18/2011
HydroCAD® 9.10 s/n 04927 @2010 HydroCAD Software Solutions LLC Page 24
Pond 3P: BMP #9
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Time (hours)

LOCATION: Chatham County, NC
Pond Name= BMP #9
Riser Outer Width = 6 ft
Riser Outer Length = 6 ft
Riser Inner Width = 5 ft
Riser Inner Length = 5 ft
Riser Height = 5.5 ft
Concrete Base Length = 8 ft
Concrete Base Width = 8 ft
Concrete Base Depth = 18 in
TE: 07/11/2011 DESIGNED BY: GCA
Riser Resisting Force =
Base Resisting Force =
Total Resisting Force =
Riser Buoyant Force =
Base Buoyant Force =
Total Buoyant Force =
Factor of Safety
9,075 lb
14,400 lb
23,475 lb
12,355 lb
5,990 lb
18,346 lb
1.28 Design Acceptable

1
C

1

DATE: 07/14/11 DESIGNED BY:

1
I GCA
PROJECT NAME: Briar Chapel Phase 6 S PROJECT NO: CHECKED BY
PROJECT LOCATION. Chatham County, NC 02735-0073 GIVIL
Storm Outlet Structure
Structure= BMP #9 Inlet FES #1 Q10/Qfull = 0.69
Size= 60 in VNfull = 1.073
Qio = 161.40 cfs V= 12.7 fps
Qfull = 232.55 cfs
Vfull = 11.84 fps
From Fig. 8.06.b.1: Zone = 5
From Fig. 8.06.b.2: D50 = 14 in
DMAx = 21 in
Riprap Class = 2
Apron Thickness = 36 in
Apron Length = 50.0 ft
s, r Apron Width = 3 x Dia = 15.0 ft
Storm Outlet Structure
Structure= BMP #9 Outlet Quo/Qfull = 1.61
Size= 36 in VNfull = MAX
Quo = 77.43 cfs V = 10.9 fps
Qfull = 48.02 cfs
Vfull = 6.79 fps
From Fig. 8.06.b.1: Zone = 6
From Fig. 8.06.b.2: D50 = 14 in
DMAx = 21 in
Riprap Class = 2
Apron Thickness = 36 in
` Apron Length = 30.0 ft
-
T Apron Width = 3 x Dia = 9.0 ft
`

1
7

I WET DETENTION BASIN SUPPLEMENT
i

I
' Permit No.
(to be provided by DWQ)
1

i
ATA OF WATF9
oz o?

_
?
_
_
NCDENR
' ST ORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be filled out, printed and submitted.
' The Required Items Checklist (Part 111) must be printed, filled out and submitted along with all of the required information.
I. PROJECT INFORMATION
Project name Briar Chapel Development - Phase 6 South
' Contact person Grant Livengood, PE
Phone number 919..233.8091
Date 8-Jul-2011
Drainage area number #9
'
11. DESIGN INFORMATION
Site Characteristics
Drainage area 1,639,766 ft2
' Impervious area, post-development 822,865 ft2
% impervious 50.18 %
Design rainfall depth 1.0 in
Storage Volume: Non-SA Waters
' Minimum volume required 68,547 ft3 OK
Volume provided 71,862 ft3
OK, volume provided is equal to or in excess of volume required.
' Storage Volume: SA Waters
1.5' runoff volume ft3
Pre-development 1-yr, 24-hr runoff ft3
Post-development 1-yr, 24-hr runoff ft3
' Minimum volume required ft3
Volume provided ft3
Peak Flow Calculations
' Is the pre/post control of the lyr 24hr storm peak flow req uired? Y (Y or N)
1-yr, 24-hr rainfall depth 3.0 in
Rational C, pre-development 0.40 (unitless)
Rational C, post-development 0.76 (unitless)
' Rainfall intensity: 1-yr, 24-hr storm 0.12 in/hr Insufficient. Check intensity calculation.
Pre-development 1-yr, 24-hr peak flow 18.96 ft3/sec
Post-development 1-yr, 24-hr peak flow 78.69 ft3/sec
Pre/Post 1-yr, 24-hr peak flow control 59.73 ft3/sec
' Elevations
Temporary pool elevation 463.90 fmsl
Permanent pool elevation 462.50 fmsl
SHWT elevation (approx. at the perm. pool elevation) fmsl
' Top of 1 Oft vegetated shelf elevation 463.00 fmsl
Bottom of 1Oft vegetated shelf elevation 462.00 fmsl Data not needed for calculation option #1, but OK if provided.
Sediment cleanout, top elevation (bottom of pond) 458.00 fmsl
Sediment cleanout, bottom elevation 457.00 fmsl Data not needed for calculation option #1, but OK if provided.
' Sediment storage provided 1.00 ft
Is there additional volume stored above the state-required temp. pool? N (Y or N)
' Elevation of the top of the additional volume fmsl
' Form SW401-Wet Detention Basin-Rev 8-9117/09 Parts I. & II. Design Summary, Page 1 of 2
Permit No
(to be provided by D WQ)
' 11, DESIGN INFORMATION
Surface Areas
Area, temporary pool 53,758 ft2
Area REQUIRED, permanent pool 45,913 ft2
' SAIDA ratio 2.80 (unitless)
Area PROVIDED, permanent pool, Ap rm_pwi 46,957 ft2 OK
Area, bottom of 10ft vegetated shelf, Ate, sheu 48,936 12
' Area, sediment cleanout, top elevation (bottom of pond), Abo, road 7,949 ftZ
Volumes
Volume, temporary pool 71,862 ft3 OK
Volume, permanent pool, Vcerm_p.i 178,072 ft3
' Volume, forebay (sum of forebays if more than one forebay) 33,544 13
Forebay % of permanent pool volume 18.8% % OK
' SAIDA Table Data
Design TSS removal
90 %
Coastal SAIDA Table Used? N (Y or N)
Mountain/Piedmont SAIDA Table Used? Y (Y or N)
' SAIDA ratio
Average depth (used in SAIDA table): 2.80 (unitless)
Calculation option 1 used? (See Figure 10-2b) Y (Y or N)
Volume, permanent pool, Vpem_pwl 178,072 ft3
Area provided, permanent pool, Amrm_p?i 46,957 ft2
' Average depth calculated 3.79 ft OK
Average depth used in SAIDA, day, (Round to nearest 0.5ft) 3.5 ft Insufficient. Check calculation.
Calculation option 2 used? (See Figure 10-2b) N (Y or N)
Area provided, permanent pool, A$,m_pool 46,957 12
Area, bottom of 1 Oft vegetated shelf, kt shell 48,936 ft2
Area, sediment cleanout, top elevation (bottom of pond), Ab,,_,,d 7,949 ft2
' "Depth" (distance b/w bottom of 1Oft shelf and top of sediment) 4.00 ft
Average depth calculated ft
Average depth used in SAIDA, day, (Round to nearest 0.5ft) ft
' Drawdown Calculations
Drawdown through orifice?
Y (Y or N)
Diameter of orifice (if circular) 5.00 in
Area of orifice (if-non-circular) in2
Coefficient of discharge (Cc)) 0.60 (unitless)
' Driving head (Ho) 0.47 ft
Drawdown through weir? N (Y or N)
Weir type (unitless)
Coefficient of discharge (C„,) (unitless)
' Length of weir (L) ft
Driving head (H) ft
Pre-development 1-yr, 24-hr peak flow 18.96 ft3/sec
Post-development 1-yr, 24-hr peak flow 78.69 ft3/sec
' Storage volume discharge rate (through discharge orifice or weir) 0.09 ft3/sec
Storage volume drawdown time 2.24 days OK, draws down in 2-5 days.
' Additional Information
Vegetated side slopes 3 :1 OK
Vegetated shelf slope 10 :1 OK
Vegetated shelf width 10.0 ft OK
' Length of flowpath to width ratio 3 :1 OK
Length to width ratio 1.5 :1 OK
Trash rack for overflow & orifice? Y (Y or N) OK
Freeboard provided 1.1 ft OK
' Vegetated filter provided? N (Y or N) OK
Recorded drainage easement provided? Y (Y or N) OK
Capures all runoff at ultimate build-out? Y (Y or N) OK
Drain mechanism for maintenance or emergencies is: 8" DIP with gate valve
' Form SW401-Wet Detention Basin-Rev 8-9/17/09 Parts I. & II. Design Summary, Page 2 of 2

1
0
1
Permit
(to be provided by DWQ)
111. REQUIRED ITEMS CHECKUST
Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been met, attach justification.
' Initials
GCA

0
1
1
P
Page/ Plan
Sheet No.
C3.1-3.3
GCA D4.1-D4.3
GCA D4.1-D4.3
GCA C3.1
1 GCA Calc Booklet
GCA C3.1

1?
GCA Calc Booklet
GCA Included
GCA Included
1. Plans (1" - 50' or larger) of the entire site showing:
Design at ultimate build-out,
Off-site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Basin dimensions,
Pretreatment system,
High flow bypass system,
Maintenance access,
Proposed drainage easement and public right of way (ROW),
Overflow device, and
Boundaries of drainage easement.
2. Partial plan (1" = 30' or larger) and details for the wet detention basin showing:
Outlet structure with trash rack or similar,
Maintenance access,
Permanent pool dimensions,
Forebay and main pond with hardened emergency spillway,
Basin cross-section,
Vegetation specification for planting shelf, and
Filter strip.
3. Section view of the wet detention basin (1" = 20' or larger) showing:
Side slopes, 3:1 or lower,
Pretreatment and treatment areas, and
Inlet and outlet structures.
4. If the basin is used for sediment and erosion control during construction, clean out of the basin is specified
on the plans prior to use as a wet detention basin.
5. A table of elevations, areas, incremental volumes & accumulated volumes for overall pond and for forebay,
to verify volume provided.
6. A construction sequence that shows how the wet detention basin will be protected from sediment until the
entire drainage area is stabilized.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
9. A copy of the deed restrictions (if required).
N/A 10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County
soil maps are not an acceptable source of soils information.
Form SW401-Wet Detention Basin-Rev.8-9/17/09 Part III. Required Items Checklist, Page 1 of 1

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IMPERVIOUS SURFACE AREA TABLE
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7/18/2011
Briar Chapel - Phase 6 South
Impervious Surface Area Table
Lot # Lot Type Impervious Surface Area (SF)
461 40' Lot 3,000
462 40' Lot 3,000
463 40' Lot 3,000
464 40' Lot 3,000
465 40' Lot 3,000
466 40' Lot 3,000
467 40' Lot 3,000
468 40' Lot 3,000
469 40' Lot 3,000
470 40' Lot 3,000
471 40' Lot 3,000
472 40' Lot 3,000
473 40' Lot 3,000
474 40' Lot 3,000
475 40' Lot 3,000
476 40' Lot 3,000
477 40' Lot 3,000
478 40' Lot 3,000
479 40' Lot 3,000
480 40' Lot 3,000
481 40' Lot 3,000
482 40' Lot 3,000
483 40' Lot 3,000
484 40' Lot 3,000
485 40' Lot 3,000
486 40' Lot 3,000
487 40' Lot 3,000
488 40' Lot 3,000
489 40' Lot 3,000
490 60' Lot 3,800
491 60' Lot 3,800
492 60' Lot 3,800
493 60' Lot 3,800
494 60' Lot 3,800
495 60' Lot 3,800
496 60' Lot 3,800
497 60' Lot 3,800
498 60' Lot 3,800
499 60' Lot 3,800
500 60' Lot 3,800
501 60' Lot 3,800
502 60' Lot 3,800
503 60' Lot 3,800
504 60' Lot 3,800
505 60' Lot 3,800
506 60' Lot 3,800
507 60' Lot 3,800
508 60' Lot 3,800
509 60' Lot 3,800
510 60' Lot 3,800
511 60' Lot 3,800
512 60' Lot 3,800
513 60' Lot 3,800
514 60' Lot 3,800
515 60' Lot 3,800
516 60' Lot 3,800
517 60' Lot 3,800
518 60' Lot 3,800
519 60' Lot 3,800
520 60' Lot 3,800
521 60' Lot 3,800
1 of 3
1
1
1
1
1
1
1
1
Briar Chapel - Phase 6 South
Impervious Surface Area Table
Lot # Lot Type Impervious Surface Area (SF)
522 60' Lot 3,800
523 60' Lot 3,800
524 60' Lot 3,800
525 60' Lot 3,800
526 60' Lot 3,800
527 60' Lot 3,800
528 60' Lot 3,800
529 60' Lot 3,800
530 60' Lot 3,800
531 60' Lot 3,800
532 60' Lot 3,800
533 60' Lot 3,800
534 60' Lot 3,800
535 60' Lot 3,800
536 60' Lot 3,800
537 60' Lot 3,800
538 60' Lot 3,800
539 60' Lot 3,800
540 60' Lot 3,800
541 50' Lot 3,500
542 50' Lot 3,500
543 50' Lot 3,500
544 50' Lot 3,500
545 50' Lot 3,500
546 50' Lot 3,500
547 50' Lot 3,500
548 50' Lot 3,500
549 50' Lot 3,500
550 50' Lot 3,500
551 50' Lot 3,500
552 50' Lot 3,500
553 50' Lot 3,500
554 50' Lot 3,500
555 50' Lot 3,500
556 50' Lot 3,500
557 50' Lot 3,500
558 50' Lot 3,500
559 50' Lot 3,500
560 50' Lot 3,500
561 50' Lot 3.500
562 50' Lot 3,500
563 50' Lot 3,500
564 50' Lot 3,500
565 50' Lot 3,500
566 50' Lot 3,500
567 50' Lot 3,500
568 50' Lot 3,500
569 50' Lot 3,500
570 50' Lot 3,500
571 50' Lot 3,500
572 50' Lot 3,500
573 50' Lot 3,500
574 50' Lot 3,500
575 50' Lot 3,500
576 50' Lot 3,500
577 50' Lot 3,500
578 50' Lot 3,500
579 50' Lot 3,500
580 50' Lot 3.500
581 50' Lot 3,500
582 50' Lot 3,500
2of3
7/18/2011
Briar Chapel - Phase 6 South
Impervious Surface Area Table
Lot # Lot Type Impervious Surface Area (SF)
583 50' Lot 3,500
584 60' Lot 3,800
585 60' Lot 3,800
586 60' Lot 3,800
587 60' Lot 3,800
588 60' Lot 3,800
589 60' Lot 3,800
590 60' Lot 3,800
591 60' Lot 3,800
592 60' Lot 3,800
593 60' Lot 3,800
594 60' Lot 3,800
Total Lot ISA 473,100
Roadways ISA 188,789
Sidewalks ISA 50,332
I Otal IsA /'Iz,zzl
Notes:
1. ISA = Impervious Surface Area (SF).
2. Total Lot Impervious Surface Area includes building footprint,
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