20050732 Ver 31_Stormwater Info_20150424

4
44F
TO NCDENR — Division of Water Resources
401 & Buffer Permitting Unit
512 N. Salisbury St.
Archdale Building - 9th floor
Raleigh, NC 27604
ATTENTION Mr. Boyd Devane
�a�Sa�3a vim/
LETTER OF TRANSMITTAL
DATE April 17, 2015
PROJECT NO 2735 -0113
TASK NO EXP
RE Briar Chapel — Boulder Point Extension
TRANSMITTAL NO 1
PAGE 1 OF 1
WE ARE SENDING: ❑ Originals ® Prints ❑ Shop Drawings ❑ Samples
❑ Specifications ® Calculations ❑ Other -
Quantity
Dwg
No.
Rev.
Description
Status
2
Stormwater Design Plans
G
2
Narrative & Supporting Calculations
G
2
BMP #20 Design Supplement
G
2
BMP #20 O &M Agreement (1 Original, 1 copy)
G
Issue Status Code
REMARKS:
A. Preliminary B. Fabrication Only C. For Information D. Bid
E. Construction F. For Review & Comments G. For Approval H. See Remarks
Boyd,
Please find the enclosed documents for your review. Please let us know if you have any questions or
comments. Thank you.
Cc:
LR 10
APR 2 4 2015 ;
1730 Varsity Dnve, Suite 500 Raleigh, NC 27606 919/233 -8091 Fax [phone]
McKIM & CREED, INC.
Signed
Gareth Avant, PE

Permit Number
(to be provided by DWQ)
O�O� wAT F9�G
NCDENR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
BIORETENTION CELL SUPPLEMENT
This form must be filled out, printed and submitted
The Required Items Checklist (Part Ill) must be printed, filled out and submitted along with all of the required information
1. PROJECT INFORMATION' ��
• ' "' `°
Protect name
Briar Chapel Development - Boulder Point Drive Extension
Contact name
Gareth Avant, PE
Phone number
919 233 8091
Date
April 17, 2015
Drainage area number
1 - BMP 420
II. DESIGN]NFORMATION_m,
Site Characteristics
2
Drainage area
173,190 ft
Impervious area
79,129 ft2
Percent Impervious
45.5% %
Design rainfall depth
10 Inch
Peak Flow Calculations
Is pre /post control of the 1 -yr, 24 -hr peak flow required?
Y (Y or N)
1 -yr, 24 -hr runoff depth
3 In
1 -yr, 24 -hr intensity
013 in /hr
Pre - development 1 -yr, 24 -hr peak flow
ft3 /sec
Post - development 1 -yr, 24 -hr peak flow
ft3 /sec
Pre /Post 1 -yr, 24 -hr peak control
ft3 /sec
Storage Volume: Non -SA Waters
Minimum volume required
6,6590 ft3
Volume provided
6,891.0 ft'
OK
Storage Volume: SA Waters
1.5" runoff volume
ft3
Pre - development 1 -yr, 24 -hr runoff
ft 3
Post - development 1 -yr, 24 -hr runoff
ft 3
Minimum volume required
0 ft,
Volume provided
ft,
Cell Dimensions
Ponding depth of water
12 inches
OK
Ponding depth of water
100 ft
Surface area of the top of the bioretention cell
7 453 0 ft2
OK
Length
100 ft
OK
Width
60 ft
OK
-or- Radius
ft
Media and Soils Summary
Drawdown time, ponded volume
12 hr
OK
Drawdown time, to 24 inches below surface
12 hr
OK
Drawdown time, total
24 hr
In -situ soil
Sod permeability
in /hr
Planting media soil
Soil permeability
455 in /hr
OK
Soil composition
% Sand (by volume)
87%
OK
% Fines (by volume)
10%
OK
Form SW401- Bioretention -Rev 8
June 25, 2010
I APR 4 015
L_ _
13UF,' - - "t: hi 1=�E f2hFi f -I iiy.,�
Parts I and II Design Summary, Page 1 of 3

% Organic (by volume)
Phosphorus Index (P- Index) of media
3% OK
Total 100%
10 (unitless) OK
Permit Number
(to be provided by DWQ)
Form SW401- Bioretention -Rev B
June 25, 2010 Parts I and 11 Design Summary, Page 2 of 3

Permit Number
(to be provided by DWO)
Basin Elevations
Temporary pool elevation
522 00 fmsl
Type of bioretention cell (answer "Y" to only one of the two following
questions)
OK
Is this a grassed cell?
Y (Y or N) OK
Is this a cell with trees /shrubs?
(Y or N)
Planting elevation (top of the mulch or grass sod layer)
521 fmsl
Depth of mulch
Inches
Bottom of the planting media soil
519 fmsl
Planting media depth
2 ft
Depth of washed sand below planting media soil
0 4 ft
Are underdrains being installed?
Y (Y or N)
How many clean out pipes are being installed?
12
OK
What factor of safety is used for sizing the underdrains? (See
2
OK
BMP Manual Section 12 3 6)
Additional distance between the bottom of the planting media and
1 ft
the bottom of the cell to account for underdrains
Bottom of the cell required
517.6 fmsl
SHWT elevation
fmsl
Distance from bottom to SHWT
517 6 ft
OK
Internal Water Storage Zone (IWS)
Does the design include IWS
N
(Y or N)
Elevation of the top of the upturned elbow
fmsl
Separation of IWS and Surface
521 ft
Planting Plan
Number of tree species
0
Number of shrub species
Number of herbaceous groundcover species
Additional Information
Does volume in excess of the design volume bypass the
Y
(Y or N)
OK
bioretention cell?
Does volume in excess of the design volume flow evenly distributed
N
(Y or N)
Excess volume must pass through filter.
through a vegetated filter?
What is the length of the vegetated filter?
ft
Does the design use a level spreader to evenly distribute flow?
(Y or N)
Is the BMP located at least 30 feet from surface waters (50 feet if
Y
(Y or N)
OK
SA waters)?
Is the BMP located at least 100 feet from water supply wells?
Y
(Y or N)
OK
Are the vegetated side slopes equal to or less than 3 1?
Y
(Y or N)
OK
Is the BMP located in a proposed drainage easement with access
Y
(Y or N)
OK
to a public Right of Way (ROW)?
Inlet velocity (from treatment system)
>2 ft/sec
Insufficient inlet velocity unless energy dissipating devices are being
used
Is the area surrounding the cell likely to undergo development in the
N
(Y or N)
OK
future?
Are the slopes draining to the bioretention cell greater than 20 %?
N
(Y or N)
OK
Is the drainage area permanently stabilized?
Y
(Y or N)
OK
Pretreatment Used
(Indicate Type Used with an "X" in the shaded cell)
Gravel and grass
(8'inches gravel followed by 3 -5 ft of grass)
Grassed swale
OK
Forebay
X
Other
Form SW401- Bioretention -Rev 8
June 25, 2010 Parts I and 11 Design Summary, Page 3 of 3

Permit No
(to be provided by DWQ)
III. REQUIRED ITEMS CHECKLIST, ` - >� <;,�._•
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.
Page/ Plan
Initials
Sheet No.
GCA
C3.0
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.
GCA
D3.1
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.
GCA
D3.1
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.
GCA
N/A
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.
GCA
Calc Booklet
5 A table of elevations, areas, incremental volumes & accumulated volumes for overall pond and for forebay,
to verify volume provided.
GCA
C3 0
6. A construction sequence that shows how the wet detention basin will be protected from sediment until the
entire drainage area is stabilized.
GCA
Calc Booklet
7. The supporting calculations.
GCA
Included
8 A copy of the signed and notarized operation and maintenance (0 &M) agreement
GCA
N/A
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

RD F J
APR 2 4 2'015
DEW - Vv, TEt, RFSUUkG:_ S
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
Bioretention 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.
Important operation and maintenance procedures:
— Immediately after the bioretention cell is established, the plants will be watered
twice weekly if needed until the plants become established (commonly six
weeks).
— Snow, mulch or any other material will NEVER be piled on the surface of the
bioretention cell
— Heavy equipment will NEVER be driven over the bioretention cell.
— Special care will be taken to prevent sediment from entering the bioretention cell.
— Once a year, a soil test of the soil media will be conducted.
After the bioretenttron cell is established, I will inspect it 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 will be kept in a known set location
and will be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element:
Potential problems:
How I will remediate the problem:
The entire BMP
Trash /debris is present
Remove the trash /debris.
The perimeter of the
Areas of bare soil and /or
Regrade the soil if necessary to
bioretention cell
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.
The inlet device: pipe,
The pipe is clogged (if
Unclog the pipe. Dispose of the
stone verge or swale
applicable).
sediment off -site.
The pipe is cracked or
Replace the pipe.
otherwise damaged (if
applicable).
Erosion is occurring in the
Regrade the swale if necessary to
swale (if applicable).
smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
Stone verge is clogged or
Remove sediment and clogged
covered in sediment (if
stone and replace with clean stone.
a licable ).
Form SW401- Bioretention O &M -Rev.3 Page 1 of 4

BMP element:
Potential problems:
How I will remediate the problem:
The pretreatment area
Flow is bypassing
Regrade if necessary to route all
pretreatment area and /or
flow to the pretreahnent area.
ullies have formed.
Restabilize the area after grading.
Sediment has accumulated to
Search for the source of the
a depth greater than three
sediment and remedy the problem if
inches.
possible. Remove the sediment and
restabilize the pretreatment area.
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.
The bioretention cell:
Best professional practices
Prune according to best professional
vegetation
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.
Tree stakes /wires are present
Remove tree stake/ wires (which
six months after planting
can kill the tree if not removed).
The bioretention cell:
Mulch is breaking down or
Spot mulch if there are only random
soils and mulch
has floated away
void areas. Replace whole mulch
layer if necessary. Remove the
remaining much and replace with
triple shredded hard wood mulch at
a maximum depth of three inches.
Soils and /or mulch are
Determine the extent of the clogging
clogged with sediment.
- remove and replace either just the
top layers or the entire media as
needed. Dispose of the spoil in an
appropriate off -site location Use
triple shredded hard wood mulch at
a maximum depth of three inches.
Search for the source of the
sediment and remedy the problem if
possible
An annual soil test shows that
Dolomitic lime shall be applied as
pH has dropped or heavy
recommended per the soil test and
metals have accumulated in
toxic soils shall be removed,
the soil media.
disposed of properly and replaced
with new planting media.
Form SW401- Bioretention O &M -Rev.3 Page 2 of 4

BMP element:
Potential problems:
How I will remediate the problem:
The underdramn system
Clogging has occurred.
Wash out the underdram system.
(if applicable)
The drop inlet
Clogging has occurred.
Clean out the drop inlet Dispose of
the sediment off -site.
The drop inlet is damaged
Repair or replace the drop inlet.
The receiving water
Erosion or other signs of
Contact the NC Division of Water
damage have occurred at the
Quality 401 Oversight Unit at 919 -
outlet.
733 -1786.
Form SW401- Bioretention O &M -Rev.3 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 - Boulder Point Drive Extension
BMP drainage area number:I - Bioretention Area #20
Print name:Laurie Ford
Title: Vice President, Operations -
Address: 16 Windy Knoll Circle, Chapel Hill, NC 27516
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
1, Megom E. L; a Notary Public for the State of
MIDOh .QO W4\Ck County of DULdArrt do hereby certify that
- L Gttt.r -i a FOCC� - _ __ personally appeared before me this
day of kbC it , 2.016. and acknowledge the due execution of the
forgoing bioretention maintenance requirements. Witness my hand and official seal,
e- UO;
NpTAII V
d PUBOG
If coko
G
tuw
SEAL
M+yn c ate
My commission expires 1161/m --
Form SW401- Bioretention I &M -Rev. 2 Page 4 of 4

401 NARRATIVE &
SUPPORTING CALCULATIO
Briar Chapel Development
Boulder Point Drive Extension
Chatham County, North Carolina
April 17, 2015
Prepared for:
BRIAR. ZCHAPEC
Newland COMMUNITIES
NNP Briar Chapel, LLC
16 Windy Knoll Circle
Chapel Hill, North Carolina 27516
Prepared By:
MCIQM&CREED
1730 Varsity Drive, Suite 500
Raleigh, North Carolina 27606
Phone: [phone]
Fax: [phone]
M&C Project No. 02735 -0113
`�`"✓ DAN ��
7PR 4 20 15 I i
acQ��4�ssra��� ���y�`' -r
"kALw
0,30348 =
04/17/2015

PROJECT DESCRIPTON
The purpose of the project is to construct stormwater management and roadway infrastructure
to support future development within the western area of the Briar Chapel development.
Based on the conditions of the approved 401 Water Quality Certification, NCDENR -DWQ will
require runoff from the roads and impervious surfaces to be captured and treated for 85% TSS
removal before being discharged into existing stream buffers. To meet this requirement, the
runoff from the current and future development within the eastern portion of the project will be
captured and directed into Bioretention #20. The western portion of the site, due to its relatively
small impervious area will bypass all offsite drainage through the project area and direct runoff
generated from the new proposed development into a scour hole, where it will be dissipated
and directed offsite as diffuse flow. Future development from the extension of Boulder Point
Drive will be captured and directed to approved BMPs to the maximum extent practicable
Calculations for this new facility are included in this package.
SITE DESCRIPTION
The project area is approximately 3.59 acres of disturbed area located within Briar Chapel West
development area, of which 2.24 acres have already been permitted. This extension will begin
at the current intersection of Boulder Point Drive and Briar Chapel Parkway and extend Boulder
Point Drive by approximately 1,250 feet.
The site generally slopes away from 3 high areas; 1 located at the intersection of Briar Chapel
Parkway and current Boulder Point Drive, where the site drains towards the west; 1 located
about midway of the alignment, where the site drains in both directions; and another located at
the western end of the extension which drains towards the east. Additionally, the western side of
the project area has buffered streams that are tributary to Pokeberry Creek (WS -IV; NSW).
SOILS
According to the Chatham County Generalized Soil Survey, the soils located on the site are
classified as Wedowee sandy loam, 2 to 35 percent slopes (WeB, WeC, and WeE).
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.

BIORETENTION DESIGN
The goal of this bioretention area will be to remove 85% of the total suspended solids entering
from the surrounding impervious drainage area before discharging into the adjacent stream. To
obtain the goal of keeping the footprint as small as possible the temporary ponding depth for
the design is 12 ", which is the maximum desired as stated in the BMP Manual. Any runoff
exceeding the ponding depth will be discharged, via a riser structure and outlet pipe, directly
into the adjacent stream buffer at non - erosive velocities. Engineered bioretention media will not
be placed until the northern future development has been stabilized such that no damage to
the media can occur. Runoff exceeding ponding depth will still be discharged
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
permanent stormwater management devices and shall adhere to conditions agreed upon by
the executed Operation and Maintenance agreements. Any measure that fails to function as
intended shall be repaired immediately.

recipitation Frequency Data Server
http: // hdsc. nws. noaa .gov /cgi- bin/hdsc /buiIdout.perl ?type =ldf &units =us &s. .
POINT PRECIPITATION��"�
FREQUENCY ESTIMATES
9 FROM NOAA ATLAS 14 wo
CHAPEL HILL 2 W, NORTH CAROLINA (31 -1677) 35.9086 N 79.0794 W 462 feet
from'Precrprtation- Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3
G M Bonnet, D Martin, B Lm, T Parzybok, M Yekta, and D Riley
NOAA, National Weather Service, Saver Spring, Maryland, 2004
Extracted Wed Jan 202010
Confidence Limits Seasonality Location Maps Other Info. GIS data Maps r Docs Return to State Map
Precipitation Intensity Estimates (in /hr) j
ARI* ; 10 I 15 I 30 60 i 120 f3j j 10 [20 30 I t45 60
5 rmn I� hr �6 hrhr . 12 hr 24 hr 48 hr 44 day 7 dav� years)i� min I' min min min II "�" l����F�� - j
4.93 ! 3 94 13.28 ! 2.25 1.40 0.84 0.60 0.36 0.21 10.12 i 0.07 ' 0.04 0.03 ! 0.02 0.01 j 0.01 O.OI 0.01 j
;5.81 4.64 ,3.89 J2.69 1.69 11.01 ;0.72 !0.43 j0_25 J015 0.09 ;005 10.03 ;OA3 10.02 �OAI 0.01 10.01 j
;6.70 15.36 452_3.21 2.06 j 1.25 !089_0.53 �0.32�0.19 Ir X0.06 004 ;0.03 0.02 �0.02�0.01 0.01
10 7.38 ; 5.90 4.98 13.61 2.35 1.43 1.03 0.62 ( 0.37 0.22 10.12 ; 0.07 0.04 0.03 10.02 0.02 10.01 10.01
_25 8.1 l F6:476 5.46 j 4 04 2_69 L66 1.20 0.73 j 0_44 ! 0.25 0.15 0.08 O:OS 0.04 0.03 0_02 0:02 0.01
50 8.62 6.86 t 5 79 4.36 2.95 L85 1 34 u 0.82 0 `50 0.29 j 0.16 1009 0.06 ! 0.04 0_03 0.02 0_02 0.02
100 9 07 7 21 ' 6.07 .4.65 3.20 ! 2.02 148 10.91 0.56 0.0.18 1 0.10 10.06 10.05 0.03 (OA2 0.02 10.02 j
200 v 9.44 7 49 j 6.30 ` 4 90 7 3.44 2.20 , 1.63 1.01 1 0162 j 0.35 0_20 411_ 0.07 OAS l 0.03 0.03 1 0.02 J O 2 ji
500 9.85 7.79:6.54 5.21 3.73 2.43 1 82 L 14 ; 0 71 1[!.4O J 0 22 1 0_12 0 08 0.06 ' Oy04 11 0.03 i [070i]0.02
1000 10.19 8.02 6.71 5.43 3 96 262 1.98 1.24 0.78 0 43 0.24 0.13 j 0.08 0.06 ; 0.04 11 0.03 0.02 0 02
* These precipitation kequencyesbmates are based on a partial duration series ARI is the Average Recurrence Interval
Please refer to NOAAAflas 14 Document for more information NOTE Formatting forces estimates near zero to appear as zero
* Upper bound of the 90% confidence interval
E5, Precipitation Intensity Estimates (in /hr) _ ARI ** 10 15 30 60 120 3 6 12 24 48 4 7 10 ' 20 30 I 45 60
(yea[s)i min �� mini min hr - hr hr -� hr daY �Y [day �Y �Y �Y �Y
�' 5_39 1 4.31 : 3.59 2.46 1 53 KY-, 0_65- 0.39 , 0.23 0 13_, 0.08 0.04 O. K0.0 0.01 i 0.011 0.01 10 O l
6.36 5. 88J4.26'2.94 L85iL11 0.79 047 10.28 10.16 ;0.09_0.05 0.03 '003 ;002 ;0.01 10.01 ;001
7.31 5.86 4.94 3 51 2.25 1 1 37 0 97 0.58 .0 - 3 4 0.20 0 12 0.06 0.04 0.03 0.02 10 02 O.OI 110.01 1
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 j 0.02 0.01 i
25 8.83 7.04 5.95 ; 4.41_ 2.93 1 1.82 1.31 0.79 10.48 0.27 ' 0.16 0.09 ! 0.05 0.04 0.03 0.02 ' 0.�2 11 0.01 !
50 9.38 7.48 ; 6.31 4.75 3.22 2.02 1.47 0.89 10.54 1 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 j 0.34 0.19 0.11 0.07 , 0.05 .0.03 i 0.02 0.02 00 02 ii
200 10.32 8_18 6.88 5.35 3.75 2.41 1.78 1.09 � 0_67 0_3� 0.21 0.12 0.07 0_06_ 0_04 I 0 03 0.02 0 �2
500 1 0.78 ' 8.52 7.15 F--
.69 F--
.08 F--
.66 1.99 ; 1.23 F--
.76 0 43 0.24 0.13 0.08 0 06 0 04 i 0 03 I 0 02 10 02
1000 11.14 8.77 7.34 ; 5.94 4.34 2.87 12.16 1.36 0.85 0.46 ! 0.26 0.14 _09 0.07 i 0 04 1 0.03 I 0 02 l 0 02 i
*The upper bound ofthe confidence interval at 90% confidence level is the value which 5% of the simulated quantle values for a given frequencyare greater than
**These precipitation frequency estimates are based on a partial duration series ARI is the Average Recurrence Interval
Please refer to NOAAA las 14 Document for more information NOTE Formatting prevents estimates near zero to appear as zero
* Lower bound of the 90% confidence interval
Precipitation Intensity Estimates (in /hr)
ARI ** 5 10 60 120 3 6 12 24 i 48 4 77 10 20 30 II 4�5
fvears)I min min min I min ' min min hr hr hr hr i hr I day {Fd
ay I day I day I day I day II day
of 4 1/20/2010 8.55 AM

'recipitation Frequency Data Server
http://hdsc.nws noaa.gov/cgi-bin/hdsc/buildout.perl?type=pf&Lmits=us&se ..
POINT PRECIPITATION
�FREQUENCY ESTIMATES &N
9 FROM NOAA ATLAS 14 410
CHAPEL HILL 2 W, NORTH CAROLINA (31-1677) 35.9086 N 79.0794 W 462 feet
from'? rec ilmitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3
GM BonnmD Martm,B Linj ParzybokMYckta, and D Riley
NOAA, National Weather Service, Silver Spring, Maryland, 2004
Extracted Tue Jan 19 2010
Confidence LirnitS nal=kyLocation Maps I Other Info I GIS data I Maps I Docs Return to State Map
P_ recipitation Frequency Estimates (inches)
F- F-
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24 hr 10 20 30 1 45 60
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[0 61 Fo98 ;[1�j F235 tKEal,71 F4 44 ff]F5 95 15:, F1056
:�5::-��] Fl- - 1 F-F-F-F-F-F-11-3�EF--
0 68 3 6 1 [�0:2:j FO: 3 3 3 [331E 4 3 7 5 2 8 6 11 6 99 17 68 8 57 9 42 1 14 36 K7 5:5� 20=28
_F L '[:::: - -
OF72- - E8: 2 9 5 :4:�[�O �43
I IF 14 E45: 4 04 F972E99: FC5 7 F5 F5:�62:: E893: 2 72
100 j - P�:F ff�K
F-1--j 1
FO 76 �33 IF320 4.05 14.46 4=7 K:71f: 619.49 4 1 0=5 3 11.44 4 57 6=87
0.79 1 2 [1.57 ] 2.45:JF344 14=40 4.89 6_03 F7 47 g=41 12 21.67 124.46:
E500 0.82: [1:30 1.64 2.60 3.73 5.46 6.80 8 53 9.50 10.66 1 1 73 12.96 [13.87 ] 17 55 19.80 133.461126.21
- - F--F-
=oo o Fo-8-5 34 68 � 72 3 9=6 5 23 � 93 44 �43 1 10=35 1=5 8 2=7 6 1 4=0 6 14.97 1 18.89 2 1 0=9 24.83 2 7=5 3
, FL- FL- F L
* These precipitation fireq uency esti mates are based on a partial duration series ARI is the Average Recurrence Interval
Please refer to NOAAAdas 14 Documentfor more information NOTE Formattmg forces estimates near zero to appearas 2ero
Upper bound of the 90% confidence interval
Precipitation Frequency Estimates (inches)
30 45
41 [ 4y 7y 1a) 0
30 60 IF�O 3 6 F7T24 day day d
ARI** �F5
h 12 h4
min hr hr
ini. 1� I * y Y
nun mint r r y y day (years) F.n [n.un nun nun j hr hr y day
24'113.44' day
F 4 72 ��[IT3 1.84 F, 96 F2 35 2�7P 16 F3 7o 14.14 4.73 8.87
7 i7i 4
- ��T F28 3 33 3 6 49 F=6 38 F
3 0 � 5 'F�O � 1 �4� 4 4 IF 6 1
_=2F�5 �F_ 222 4 F6 8 :4 [IT 2 FF75 F�6
F4
=53 - 6 86 766 9.95 1 � 2=1 0 1 5=0 4 K7 6=9
Fo-61 �1 2=3 Ff75 2�P 3 50 �=15F4 77 'IF6 09 IF F
7=3 9=2 F
�K Ff - 1 4.05 3
[JO= EIK7 36 �=97 F576 r,4:[3�7 4 =8 5 51 636 =8 F� 67 11.17 11�31 16.51 � �92
F _j
-F -
25 0.74 - 7 'F� 272 1 02 g��]T5 �5 F�
1 1.17 2 2 0 [��T F3 674 Fl 974 F(776F5 733 6 54 � =4 7 E47��O 474 2 26
TT9 F _8 F I
F-- F-- F- F- 10.19 - F- �� F- 19 - 22 80
OF78 F1 25 1.58 F404 F4 41 E35 6 47 7 34 8 35 19 19 11 11 1650 92 28
1785 2:1399j24.28
F o-1 9- Fl- 1221 [t�]F
F8 F927 1 26 F
Fo-82 1.3 -1 1[] 6=6 IF253 P9� F443 F48 7 F594 7=25 17
F- K-- [K F
86 jF
L3 6
_[I 77 68 3.75 4.82 534 56 8 6 903 J 10.19 1 12 27 1 :2T8 13=33 1=686'1=921 22.85 5 FH773
- - - - - 10.21 - - - 8=1
Fo -90 F, 4-2 E��]F2 84 jq��]F5 32 F596 F7 39 F9 2 0 EE 2=6 5 3=9 1 F14 86 ��F21 04 �4
6.50 -- I!-- IL-1-1 1 2 49 �=3 14 �=6 0 20 i[L2 =4 26.31 29=07
1000 FL-K11146 83 9 7 4.34 5.74 11 0 9 �=5 =1 79 �=5 07 6
-jF�l
The upper bound of the confidence interval at 90% confidence level is the value which 5% of the simulated quanule values for a given firequencyare greater than
These precipitation frequency estimates are based on a partial duration series ARI is the Average Recurrence Interval
Please refer to NOAAAllas 14 Document for more information NOTE Formatting prevents estimates near zero to appear as zero
* Lower bound of the 90% confidence interval
F_ -- nn-uuFPn recnip ita- t-
io- n 1
F
re
AR'**[ 510 ' � j F3��" l20 ' 3 6
(yas) min ! min nun _n_;I_m� F um r [ h
Estimates One
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45 ;1 60
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of 1/19/2010 9:12 AM

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BIORETENTION #20
DESIGN

BMP#20 SIZING CALCS
Project Name
Briar Chapel - Boulder Point Drive Extension
Project Number
02735 -0113
Date
April 17, 2015
3rd revision
2nd revision
1 st revision

Water Quality Pond Drainage Area Data
Project Briar Chapel - Boulder Point Drive Extension
Project No. 02735 -0113
Date April 17, 2015
Total site area 173,790 square feet = 3.99 acres
Impervious areas
Drama a area to and
Other Drainage Area
Existing
sf
Proposed
Change
[sf]
Existing
[sf ]
Proposed
sf
On -site buildings
0
0
0
0
0
On -site streets/ parking
0
75,361
75,361
0
0
On -site alleys
0
0
0
0
0
On -site sidewalks
0
0
0
0
0
On -site future (open space)
0
0
0
0
0
Off -site future development
0
0
0
0
0
5% Contin ncy
0
3,768
3,768
0
0
Total Impervious
0 1
79,129
1 79,129
0
0
Non-impervious areas
Drainage area to and
Other Drainage Area
Existing
Isf]
Proposed
[sf ]
Change
[sf ]
Existing
[sf ]
Proposed
sf
On -site grass/landscape
0
98,429
98,429
0
0
On -site woods
0
0
0
0
0
Other undeveloped
0
0
0
0
0
Total off -site non-impervious
0
0
0
0
0
Total non-impervious
0
98,429
98,429
0
0
Total Drainage Area
173,790
173,790
0
0
0
Percent Impervious
0.0
45.5
45.5
n/a
n/a
Notes:
2015.04.10.Wetland Sizing.xls
Site Drainage Area Data Page 2 of 13 Printed 4/17/2015 1:19 PM

Water Quality Pond Stormwater Runoff Volume Calculations
Project
Project No
Date
Drainage area
Impervious area
Rainfall depth
Percent Impervious
Briar Chapel - Boulder Point Drive Extensic
02735 -0113
April 17, 2015
173,790 square feet
79,129 square feet
1.00 inches
45.5
percent
R(v) =0.05 +0.009 "(Percent impervious)
Runoff coefficient - R(v) 0.46 in /in
Runoff volume = (Design rainfall) *(R(v)) *(Drainage area)
Runoff volume 6,658.8 cubic feet
Notes:
2015.04.10.Wetland Sizing.xls
Runoff Volume Calcs Page 3 of 13 Printed 4/17/2015 1:19 PM

Water Quality Pond Volume Calculations
Stage - Storage Data for Pond - Temporary Pool
Project Briar Chapel - Boulder Point Drive Extension
Project No 02735 -0113
Date April 17, 2015
Contour ID
Stage
Area
[sq ft
Area
acres ]
Incremental
Area
[sq ft
Incremental
Area
acres
Incremental
volume
cu ft
Incremental
volume
acre -ft
Cumulative
volume
cu ft
Cumulative
volume
acre -ft
521
0
6,3290
0 145
6,3290
01
00
00
00
0.0
522
1
7,4530
0 171
7,4530
00
6,891 0
02
6,891 0
02
523
2
8,6300
0 198
8,6300
00
8,041 5
02
14,9325
03
524
3
9,8960
0 227
9,8960
00
9,2630
02
24,195 5
04
525
4
11,2530
0 258
11,2530
00
10,5745
02
34,7700
05
526
5
12,7060
0 292
12,7060
00
11,9795
03
46,7495
0.5
2015 04 10 Wetland Sizing.xls
Stage Storage (Temp Pool) Page 4 of 13 Printed 4/17/2015 1 19 PM

2015.04.14.Bioretention Type 1124 -hr 1 -Yr Rainfall = 2.96"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 1
Summary for Subcatchment 1S: Pre - Development
Runoff = 3.15 cfs @ 12.09 hrs, Volume= 0.203 af, Depth> 0.61"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 1 -Yr Rainfall= 2.96"
Area (sf) CN Description
173,790 70
173,790 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
15.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
■ Runotf
3 Type II 24 -hr
1 -Yr Rainfall- 2.96"
Runoff Area = 173,790 sf
Runoff Volume =0.203 of
2 Runoff Depth >0.61"
0
LL Tc =15.0 min
,1 A CN_70
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)

2015.04.14.13ioretention Type 1124 -hr 1 -Yr Rainfall= 2.96"
Prepared by McKim & Creed Printed 4/17/2015
HydroCAD® 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 2
Summary for Subcatchment 2S: Post - Development
Runoff = 8.97 cfs @ 12.02 hrs, Volume= 0.453 af, Depth> 1.36"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 1 -Yr Rainfall= 2.96"
Area (sf) CN Description
98,429
74 >75% Grass cover, Good, HSG C
75,361
98 Paved parking, HSG C
173,790
84 Weighted Average
98,429
56.64% Pervious Area
75,361
43.36% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
10.0 Direct Entry,
Subcatchment 2S: Post - Development
Hydrograph
1011 I ■Runoff
Type 11 24-hr
1 -Yr Rainfall- 2.96"
7 Runoff Area = 173,790 sf
6 - Runoff Volume =0.453 of
Runoff DepthA .36"
5-
Tc =10.0 min
U.
41 1 ® CN =84
K
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)

2015.04.14.Bioretention Type 1124 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADS 10 00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 3
Summary for Pond 3P: Biorention Pond
Inflow Area = 3.990 ac, 43.36% Impervious, Inflow Depth > 1.36" for 1 -Yr event
Inflow = 8.97 cfs @ 12.02 hrs, Volume= 0.453 of
Outflow = 2.22 cfs 9 12.24 hrs, Volume= 0.287 af, Atten= 75 %, Lag= 13.6 min
Primary = 2.22 cfs @ 12.24 hrs, Volume= 0.287 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 522.34'@ 12.24 hrs Surf.Area= 7,858 sf Storage= 9,522 cf .
Plug -Flow detention time= 136.9 min calculated for 0.286 of (63% of inflow)
Center -of -Mass det. time= 63.9 min ( 854.7 - 790.8 )
Volume Invert Avail.Storage Storage Description
#1 521.00' 46,750 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq -ft) (cubic -feet) (cubic -feet)
521.00 6,329 0 0
522.00 7,453 6,891 6,891
523.00 8,630 8,042 14,933
524.00 9,896 9,263 24,196
525.00 11,253 10,575 34,770
526.00 12,706 11,980 46,750
Device Routing Invert Outlet Devices
#1 Primary 517.23' 18.0" Round Pond Outlet
L= 110.4' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 517.23'/ 515.90' S=0.0120'/' Cc= 0.900
n= 0.013, Flow Area= 1.77 sf
#2 Device 1 522.00' 24.0" W x 3.0" H Vert. Water Quality X 2.00 C= 0.600
#3 Device 1 522.40' 24.0" W x 4.0" H Vert. Orifice /Grate X 2.00 C=0.600
#4 Device 1 523.50' 36.0" x 36.0" Horiz. Riser C= 0.600
Limited to weir flow at low heads
Primary OutFlow Max =2.22 cfs @ 12.24 hrs HW= 522.34' (Free Discharge)
L1 =Pond Outlet (Passes 2.22 cfs of 16.81 cfs potential flow)
2 =Water Quality (Orifice Controls 2.22 cfs @ 2.22 fps)
3 =Orifice /Grate ( Controls 0.00 cfs)
=Riser ( Controls 0.00 cfs)

2015.04.14.Bioretention Type 1124 -hr 1 -Yr Rainfall= 2.96"
Prepared by McKim & Creed Printed 4/17/2015
HydroCAD® 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 4
N
V
3
O
U-
Pond 3P: Biorention Pond
Hydrograph
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
■ Inflow
■ Primary

2015.04.14.Bioretention Type Il 24 -hr 10 -Yr Rainfall= 5.17"
Prepared by McKim & Creed Printed 4/17/2015
HydroCAD® 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 5
Summary for Subcatchment 1 S: Pre - Development
Runoff = 10.96 cfs @ 12.08 hrs, Volume= 0.654 af, Depth> 1.97"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 10 -Yr Rainfall= 5.17"
Area (sf) CN Description
173,790 70
173,790 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
15.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
W
Type II 24 -hr
10- 10 -Yr Rainfall= 5.17"
9- Runoff Area= 173,790 sf
8 Runoff Volume =0.654 of
Runoff DepthA .97"
U. 6 Tc =15.0 min
5
CN =70
4
3
2
w
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
■ Runoff

2015.04.14.13ioretention Type 1124 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADOO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 6
Summary for Subcatchment 2S: Post - Development
Runoff = 20.32 cfs @ 12.01 hrs, Volume= 1.061 af, Depth> 3.19"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 10 -Yr Rainfall = 5.17"
Area (sf) CN Descriotion
98,429
74 >75% Grass cover, Good, HSG C
75,361
98 Paved parking, HSG C
173,790
84 Weighted Average
98,429
56.64% Pervious Area
75,361
43.36% Impervious Area
Tc Length Slope Velocity Capacity Description
min) (feet) (ft/ft) (ft/sec) (cfs)
10.0 Direct Entry,
Subcatchment 2S: Post - Development
Hydrograph
21 zoar as
20 Type II 24 -hr
18 10 -Yr Rainfall- 5.17"
1s Runoff Area = 173,790 sf
15
14 Runoff Volume =1.061 of
1Z Runoff DepthA.19"
3 1 Tc =10.0 min
LL ,0
8 CN =84
7
6
5 9
0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
❑ Runoff

2015.04.14.Bioretention Type 11 24 -hr 10 -Yr Rainfall =5.17"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADG 10 00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 7
Summary for Pond 3P: Biorention Pond
Inflow Area = 3.990 ac, 43.36% Impervious, Inflow Depth > 3.19" for 10 -Yr event
Inflow = 20.32 cfs @ 12.01 hrs, Volume= 1.061 of
Outflow = 10.71 cfs @ 12.13 hrs, Volume= 0.890 af, Atten= 47 %, Lag= 7.3 min
Primary = 10.71 cfs @ 12.13 hrs, Volume= 0.890 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 523.30'@ 12.13 hrs Surf.Area= 9,012 sf Storage= 17,591 cf
Plug -Flow detention time= 84.8 min calculated for 0.887 of (84% of inflow)
Center -of -Mass det. time= 38.2 min ( 810.3 - 772.1 )
Volume Invert Avail.Storage Storage Description
#1 521.00' 46,750 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq -ft) (cubic -feet) (cubic -feet)
521.00 6,329 0 0
52200 7,453 6,891 6,891
523.00 8,630 8,042 14,933
524.00 9,896 9,263 24,196
525.00 11,253 10,575 34,770
526.00 12,706 11,980 46,750
Device Routing Invert Outlet Devices
#1 Primary 517.23' 18.0" Round Pond Outlet
L= 110.4' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 517.23'/ 515.90' S=0.0120'/' Cc= 0.900
n= 0.013, Flow Area= 1.77 sf
#2 Device 1 522.00' 24.0" W x 3.0" H Vert. Water Quality X 2.00 C= 0.600
#3 Device 1 522.40' 24.0" W x 4.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4 Device 1 523.50' 36.0" x 36.0" Horiz. Riser C= 0.600
Limited to weir flow at low heads
Primary OutFlow Max =10.66 cfs @ 12.13 hrs HW= 523.29' (Free Discharge)
t-1 =Pond Outlet (Passes 10.66 cfs of 18.35 cfs potential flow)
2 =Water Quality (Orifice Controls 5.20 cfs @ 5.20 fps)
3= Orifice /Grate (Orifice Controls 5.46 cfs @ 4.09 fps)
=Riser ( Controls 0.00 cfs)

2015.04.14.Bioretention Type Il 24 -hr 10 -Yr Rainfall =5.17'
Prepared by McKim & Creed Printed 4/17/2015
HydroCADO 10.00 s/n 04927 0 2011 HydroCAD Software Solutions LLC Page 8
m
Z
3
0
LL
Pond 3P: Biorention Pond
Hydrograph
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
FE-1 nflow
■ Primary

2015.04.14.Bioretention Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 9
Summary for Subcatchment 1 S: Pre - Development
Runoff = 21.20 cfs @ 12.07 hrs, Volume= 1.268 af, Depth> 3.81"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 100 -Yr Rainfall= 7.62"
Area (sf) CN Description
173,790 70
173,790 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
15.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
23
22 zi.zo as
20 Type 11 24-hr
19 100 -Yr Rainfall= 7.62"
17. Runoff Area = 173,790 sf
16
15 Runoff Volume =1.268 of
14
12 Runoff DepthA.81"
11
u. 10 Tc =15.0 min
8 CN =70
7
4
3
2 %mom=
1
0-
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
■ Runoff

2015.04.14.13ioretention Type 1124 -hr 100 -Yr Rainfall = 7.62"
Prepared by McKim & Creed Printed 4/17/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Paoe 10
Summary for Subcatchment 2S: Post - Development
Runoff = 33.15 cfs @ 12.01 hrs, Volume= 1.784 af, Depth> 5.37"
Runoff by SCS TR -20 method, UH =SCS, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Type II 24 -hr 100 -Yr Rainfall= 7.62"
Area lsfl CN Descriotion
98,429
74 >75% Grass cover, Good, HSG C
75,361
98 Paved parking, HSG C
173,790
84 Weighted Average
98,429
56.64% Pervious Area
75,361
43.36% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) (ft/sec) (cfs)
10.0 Direct Entry,
Subcatchment 2S: Post - Development
Hydrograph
32- Type II 24-hr
30: 100 -Yr Rainfall= 7.62"
26 Runoff Area = 173,790 sf
2z' Runoff Volume =1.784 of
20 Runoff Depth >5.37"
0 18
LL 16 Tc =10.0 min
14- CN =84
8
6
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
■ Runoff

2015.04.14.Bioretention Type// 24 -hr 100 -Yr Rainfall = 762"
Prepared by McKim & Creed Printed 4/17/2015
HydroCAD® 10 00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Paoe 11
Summary for Pond 3P: Biorention Pond
[82] Warning: Early inflow requires earlier time span
Inflow Area = 3.990 ac, 43.36% Impervious, Inflow Depth > 5.37" for 100 -Yr event
Inflow = 33.15 cfs @ 12.01 hrs, Volume= 1.784 of
Outflow = 19.51 cfs @ 12.12 hrs, Volume= 1.609 af, Atten= 41 %, Lag= 6 4 min
Primary = 19.51 cfs @ 12.12 hrs, Volume= 1.609 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 524.06'@ 12.12 hrs Surf.Area= 9,974 sf Storage= 24,764 cf
Plug -Flow detention time= 69.0 min calculated for 1.608 of (90% of inflow)
Center -of -Mass det. time= 35.0 min ( 795.1 - 760.1 )
Volume Invert Avail.Storage Storage Description
#1 521.00' 46,750 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq -ft) (cubic -feet) (cubic -feet)
521.00 6,329 0 0
522.00 7,453 6,891 6,891
523.00 8,630 8,042 14,933
524.00 9,896 9,263 24,196
525.00 11,253 10,575 34,770
526.00 12,706 11,980 46,750
Device Routing Invert Outlet Devices
#1
Primary
517.23'
18.0" Round Pond Outlet
L= 110.4' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 517.23'/ 515.90' S=0.0120'/' Cc= 0.900
n= 0.013, Flow Area= 1.77 sf
#2
Device 1
522.00'
24.0" W x 3.0" H Vert. Water Quality X 2.00 C= 0.600
#3
Device 1
522.40'
24.0" W x 4.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4
Device 1
523.50'
36.0" x 36.0" Horiz. Riser C= 0.600
Limited to weir flow at low heads
Primary OutFlow Max =19.48 cfs @ 12.12 hrs HW= 524.04' (Free Discharge)
L1 =Pond Outlet (Barrel Controls 19.48 cfs @ 11.02 fps)
2 =Water Quality (Passes < 6.66 cfs potential flow)
3 =Orifice /Grate (Passes < 7.79 cfs potential flow)
=Riser (Passes < 15.57 cfs potential flow)

2015.04.14.Bioretention Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 4/17/2015
HydroCAD@ 10.00 s/n 04927 @2011 HydroCAD Software Solutions LLC Page 12
N
V
3
O
LL
Pond 3P: Biorention Pond
Hydrograph
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
FE-1 n-f I —ow
■ Primary

M riar hapel Boulder oint Extension
FPROJEC,T LOCATION: Chatham County, NC
TE: 04/17/2015
PR JE T N
02735 -0113
DESIGNED BY:
BSS
HE KED BY
GCA
Sorm Outlet Structure
Structure= HW -BPD -6
Q10/ Qfull =
0.62
Size= 18
in
V/Vfull =
1.05
Dia = 5.92
cfs
V =
5.6
fps
Qfull = 9.55
cfs
Vfull = 5.41
fps
From Fig. 8.06.b.1:
Zone
=
2
From Fig. 8.06.b.2:
D50
=
8
in
DMAx
=
12
in
Riprap Class
=
B
Apron Thickness
=
22
in
Apron Length
=
9.0
ft
Apron Width = 3 x Dia
=
5.0
ft
Storm Outlet Structure
Structure= HW- BPD -11
BMP #20 Outlet
Q10/ Qfull =
0.93
Size= 18
in
V /Vfull =
1.14
Qio = 10.71
cfs
V =
7.4
fps
Qfull = 11.54
cfs
Vfull = 6.53
fps
From Fig. 8.06.b.1:
Zone
=
2
From Fig. 8.06.b.2:
D50
=
8
in
DMAx
=
12
in
Riprap Class
=
B
Apron Thickness
=
22
in
Apron Length
=
9.0
ft
Apron Width = 3 x Dia
=
5.0
ft