20050732 Ver 32_1st Submittal Documents to DWR.Boyd Devane_20150617

vJMCIQM&LEEEll
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
LETTER OF TRANSMITTAL
DATE: June 17, 2015
PROJECT NO: 2735 -0113 I TASK NO: EXP
RE: Briar Chapel - Phase 15 North
TRANSMITTAL NO: 1
PAGE 1 OF 1
WE ARE SENDING: ❑ Originals ® Prints ❑ Shop Drawings ❑ Samples
❑ Specifications ® Calculations ❑ Other -
Quantity Dwg Rev. Description Status
No.
1 Cover Letter Requesting Stormwater Management Plan Approval G
2 Stormwater Design Plans G
2 Narrative & Supporting Calculations G
2 BMP #23 Design Supplement G
2 BMP #23 O &M Agreement G
Issue Status Code: A. Preliminary B. Fabrication Only C. For Information D. Bid
E. Construction F. For Review & Comments G. For Approval H. See Remarks
REMARKS:
Boyd,
Please find the enclosed documents for your review and approval. Please let us know if you have any
questions or comments. Thank you.
Cc:
1730 Varsity Drive, Suite 500 Raleigh, NC 27606 919/233 -8091 Fax [phone]
McKIM & CREED, INC.
Signed
Gareth Avant, PE

�► CKA4 &CRE FT-rD E N G I N E E R 5
`;1�— ��11V14 1�EJ J 5U RVEY ©RS
P L A N N E R 5
June 17, 2015
Mr. Boyd Devane
512 N. Salisbury St.
Archdale Building - 9th floor
Raleigh, NC 27604
RE: Briar Chapel Phase 15 N
Mr. Devane,
Please find enclosed the plans, caclulations, supplement forms and operation and
maintenance agreements for the Phase 15 North subdivision at Briar Chapel.
This letter is to formally request approval of the stormwater management plan
for the enclosed plans in accordance with Water Quality Certification as issued
by the Division of Water Resources on January 11, 2008.
Please let me know if you have any questions on this. Thank you for your
assistance.
Sincerely,
McKIM & CREED, INC.
Venture IV Building 4�9 avm-3e—
S u i t e 500 Gareth Avant, PE
Project Engineer
1730 Voraity 6rire
Raleigh, NC 27606
919.233.8091
Fax [phone]
w ..mckimcreed.—m

Red triangles at the upper right hand corner indicate design comments
Please complete the yellow shaded items.
AVit—AA
NCDENR
Project name
Contact person
Phone number
Date
Drainage area number
Permit No.
(to be provided by DWQ)
r%
6 `C
STORMWATER 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.
919.233.8091
17- Jun -2015
1 - Wet Pond #23
II. DESIGN INFORMATION
Site Characteristics
Drainage area 754,858 ft2
Impervious area, post - development 338,602 ft2
% impervious 44.86 %
Design rainfall depth 1.0 in
Storage Volume: Non -SA Waters
Minimum volume required
Volume provided
Storage Volume: SA Waters
1.5" runoff volume
Pre - development 1 -yr, 24 -hr runoff
Post - development 1 -yr, 24 -hr runoff
Minimum volume required
Volume provided
Peak Flow Calculations
Is the pre /post control of the lyr 24hr storm peak flow required?
1 -yr, 24-hr rainfall depth
Rational C, pre - development
Rational C, post - development
Rainfall intensity: 1 -yr, 24 -hr storm
Pre - development 1 -yr, 24 -hr peak flow
Post - development 1 -yr, 24 -hr peak flow
Pre /Post 1 -yr, 24 -hr peak flow control
Elevations
Temporary pool elevation
Permanent pool elevation
SHWT elevation (approx. at the perm. pool elevation)
Top of 1 Oft vegetated shelf elevation
Bottom of 1 Oft vegetated shelf elevation
Sediment cleanout, top elevation (bottom of pond)
Sediment cleanout, bottom elevation
Sediment storage provided
Is there additional volume stored above the state - required temp. pool?
Elevation of the top of the additional volume
Briar Chapel - Phase 15N
Gareth Avant, PE
28,541 ft3 OK
29,861 ft3
OK, volume provided is equal to or in excess of volume required.
ft3
ft3
ft3
ft3
ft3
Y (Y or N)
3.0 in
0.40 (unitless)
0.68 (unitless)
0.13 in /hr OK
12.87 ft3 /sec
47.65 ft3 /sec
34.78 ft3
/sec
449.00 fmsl
447.50 fmsl
fmsl
448.00 fmsl
447.00 fmsl
Data not needed for calculation option #1, but OK if provided.
442.00 fmsl
441.00 fmsl
Data not needed for calculation option #1, but OK if provided.
1.00 ft
Y (Y or N)
449.0 fmsl
OK
Form SW401 -Wet Detention Basin- Rev.8- 9/17/09 Parts I. & II. Design Summary, Page 1 of 2

Permit No.
II. DESIGN INFORMATION
Surface Areas
Area, temporary pool 21,437 ft2
Area REQUIRED, permanent pool 16,909 ft2
SAIDA ratio 2.24 (unitless)
Area PROVIDED, permanent pool, Aperm_ pool 17,183 ft2 OK
Area, bottom of 1 Oft vegetated shelf, Abet shelf 14,194 ft2
Area, sediment cleanout, top elevation (bottom of pond), Abot_pond 7,260 ft2
Volumes
Volume, temporary pool
Volume, permanent pool, Vpsnpool
Volume, forebay (sum of forebays if more than one forebay)
Forebay % of permanent pool volume
SAIDA Table Data
Design TSS removal
Coastal SAIDA Table Used?
Mountain /Piedmont SAIDA Table Used?
SAIDA ratio
Average depth (used in SAIDA table):
Calculation option 1 used? (See Figure 10 -2b)
Volume, permanent pool, Vpertnyool
Area provided, permanent pool, Ape--,-i
Average depth calculated
Average depth used in SAIDA, deV, (Round to nearest 0.5ft)
Calculation option 2 used? (See Figure 10 -2b)
Area provided, permanent pool, Ape,m_poa
Area, bottom of 1 Oft vegetated shelf, Abet shelf
Area, sediment cleanout, top elevation (bottom of pond), Abot_p°nd
"Depth" (distance b/w bottom of 1Oft shelf and top of sediment)
Average depth calculated
Average depth used in SAIDA, deV, (Round to nearest 0.5ft)
Drawdown Calculations
Drawdown through orifice?
Diameter of orifice (if circular)
Area of orifice (if- non - circular)
Coefficient of discharge (CD)
Driving head (H °)
Drawdown through weir?
Weir type
Coefficient of discharge (CW)
Length of weir (L)
Driving head (H)
Pre - development 1 -yr, 24 -hr peak flow
Post - development 1 -yr, 24 -hr peak flow
Storage volume discharge rate (through discharge orifice or weir)
Storage volume drawdown time
Additional Information
Vegetated side slopes
Vegetated shelf slope
Vegetated shelf width
Length of flowpath to width ratio
Length to width ratio
Trash rack for overflow & orifice?
Freeboard provided
Vegetated filter provided?
Recorded drainage easement provided?
Capures all runoff at ultimate build -out?
Drain mechanism for maintenance or emergencies is:
Form SW401 -Wet Detention Basin- Rev.8- 9/17/09
29,861 ft3 OK
67,374 ft3
13,949 ft3
20.7% % OK
90 %
N (Y or N)
Y (Y or N)
2.24 (unitless)
Y (Y or N)
67,374 ft3
17,183 ft2
3.92 ft OK
4.0 ft OK
N (Y or N)
17,183 ft2
14,194 ft2
7,260 ft2
5.00 ft
ft
ft
Y (Y or N)
2.75 in
in
0.60 (unitless)
0.50 ft
N (Y or N)
(unitless)
(unitless)
ft
ft
11.52 ft3 /sec
38.95 ft3 /sec
0.09 ft3/sec
2.47 days OK, draws down in 2 -5 days.
(to be provided by DWQ)
3 :1 OK
10 :1 OK
10.0 ft OK
3 :1 OK
1.5 :1 OK
Y (Y or N) OK
1.5 ft OK
N (Y or N) OK
Y (Y or N) OK
Y (Y or N) OK
8" DIP with gate valve and /or pump provided by owner
Parts I. & II. Design Summary, Page 2 of 2

Permit No.
III. REQUIRED ITEMS CHECKLIST
(to be provided by DWQ)
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.lf a
requirement has not been met, attach justification.
Pagel Plan
Initials Sheet No.
GCA C3.3 -C3.7 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 D4.1 -D4.3 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 D4.1 -D4.3 3. Section view of the wet detention basin 0" = 20' or larger) showing:
Side slopes, 3:1 or lower,
Pretreatment and treatment areas, and
Inlet and outlet structures.
GCA C3.3 -C3.7 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 C3.3 -C3.7 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

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.
— 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 remediate the problem:
The entire BMP
Trash /debris is present.
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.
approximately 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:
The inlet device: pipe or The pipe is clogged
swale
The pipe is cracked or
otherwise damaged.
Erosion is occurring in the
swale.
The forebay Sediment has accumulated to
a depth greater than the
original design depth for
sediment storage.
The vegetated shelf
The main treatment area
Erosion has occurred.
Weeds are present.
Best professional practices
show that pruning is needed
to maintain optimal plant
health.
Plants are dead, diseased or
dying.
Weeds are present.
Sediment has accumulated to
a depth greater than the
original design sediment
storage depth.
Algal growth covers over
50% of the area.
Cattails, phragmites or other
invasive plants cover 50% of
the basin surface.
How I will remediate the problem:
Unclog the pipe. Dispose of the
sediment off -site.
Replace the pipe.
Regrade the swale if necessary to
smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
Search for the source of the
sediment and remedy the problem if
possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
Prune according to best professional
practices
Determine the source of the
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.
Remove the weeds, preferably by
hand. If pesticide is used, wipe it on
the plants rather than spraying.
Search for the source of the
sediment and remedy the problem if
possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Consult a professional to remove
and control the algal growth.
Remove the plants by wiping them
with pesticide (do not spray).
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
appropriate professional
shows that the embankment
needs repair. (if applicable)
Make all needed repairs.
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
(fill in the blanks)
V Permanent Poo] Elevation 447.50
Sediment Remova\0o
42.00 � Pe maven Poo]
---- - - - - -- - - -- Volume Sediment Removal Elevation 442.00 Volume
BottomElev441.00 # -ft Min. -------------------------------------- - -` - -- ------
Sediment Bottom Elevation 441.00 1 -ft n.
Storage Sediment
Storage
FOREBAY 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 - Phase 15 North
BMP drainage area manber:I - Wet Detention Pond #23
Print name:Laurie Ford
Title:Vice President, Operations
Address: 16 Windy Knoll Circle. Chapel Hill. NC 27516
Phone:[phone]
Signa
Dat� —� S
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, G, Leo" l7 6 wvko w . a Notary Public for the State of
/V County of A J-1 , do hereby certify that
L4 k'I C. F:;ra( personally appeared before me this
4
day of _J 'vt v% L , and acknowledge the due execution of the
forgoing wet detention basin maintenance requirements. Witness my hand and official
seal,
S
rAOTAR),
3 �
z UBLIG Cs
f r��yyHllICj1 j}1jS14``�`�ka
SEAL
My commission expires l � (0/ 11
Form SW401 -Wet Detention Basin O &M -Rev.4 Page 4 of 4

401 NARRATIVE &
SUPPORTING CALCULATIONS
Briar Chapel Development
Phase 15 North
Chatham County, North Carolina
June 17, 2015
Prepared for:
BRIAR_ V7CHAPEC
by
Newland COMMUNITIES
NNP Briar Chapel, LLC
16 Windy Knoll Circle
Chapel Hill, North Carolina 27516
Prepared By:
vJ MCKIM&CREED
1730 Varsity Drive, Suite 500
Raleigh, North Carolina 27606
Phone: [phone]
Fax: [phone]
M &C Project No. 02735-0113
O \A ... CARp''' %,
pFESS10,y4 -��'���
036348 06/ W2015
,, �iF. fpGINE.E�.•�Q -.�

PROJECT DESCRIPITON
The purpose of the project is to construct water, sewer and roadway infrastructure to support 50
residential lots in the Phase 15 North section of the overall Briar Chapel Development.
Based on the conditions of the approved 401 Water Quality Certification, NCDENR -DWR will
require runoff from the roads to be captured and treated for 85% TSS removal before being
discharged into existing stream buffers. To meet this requirement, the runoff from the general
area of all Phase 15 North construction will be directed to Wet Detention Pond #23.
Calculations for these new facilities are included in this package.
Upon completion of the project's construction, the proposed public roads will be turned over to
and maintained by NCDOT.
SITE DESCRIPTION
The project area is approximately 20.32 acres located within the BC West development area,
which is west of the intersection of Granite Mill Boulevard and Briar Chapel Parkway.
The site slopes away from a ridge located near the center of the project area, and drains to the
southeast and southwest and into adjacent buffered streams. Slopes on the site range from 5 to
greater than 20% in localized areas.
SOILS
According to the Chatham County Generalized Soil Survey, the soils located on the site are
classified as Helena sandy loam, 6 to 10 percent slopes (HeC); Wedowee sandy loam, 2 to 15
percent slopes (WeB, WeD); and Wedowee sandy loam, 15 to 35 percent slopes, bouldery
(WdC, WdE)
The following soil descriptions are associated with the soils found on the site:
HeC - Helena sandy loam soils are often found in piedmont uplands, along ridges and
drainageways. Permeability is slow and the soils are moderately well drained. Soils have
a high shrink /swell potential. The seasonal high water is perched at a depth of 1.5 to 2.5
feet.
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.
Wd (X) - Wedowee sandy loam, bouldery soils carry the same characteristics of Wedowee
We(X) soils, listed above, with the exception that large boulders are more commonly
found.

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 buffer. The calculations provided with this package include all projected
future drainage areas that might be captured by the pond. Treated runoff will be dissipated by
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
permanent stormwater management devices and shall adhere to conditions agreed upon by
the executed Operation and Maintenance agreements included with this submittal. Any
measure that fails to function as intended shall be repaired immediately.

Precipitation Frequency Data Server Page 1 of 3
NOAA Atlas 14, Volume 2, Version 3
jr Location name: Chapel Hill, North Carolina, US*
Latitude: 35.8280 °, Longitude: - 79.1077° e NX
Elevation: 505ft* ?
* source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS -based point precipitation frequency estimates with 90% confidence intervals (in inches /hour)' 1
Average recurrence interval (years)
C 1 11 2 11 5 11 10 11 25 11 50 11 100 11 200 11 500 11 1000
5 -min (4. 59845) (5. 8$6.43) 1 (6.20-7.40) (6. 248.15) 1 (74418.93) (7.8769.48) (8.24-9.98) (8.54-10.4) (8.83-10.9) 1 10.3
(9.04 -11.2)
10 -min 3.98 4.69 5.42 5.96 6.52 6.92 7.27 7.55 7.87 8.09
(3.64 -4.35) (4.30 -5.14) 1 (4.96 -5.93) (5.45 -6.52) (5.93 -7.12) (6.27 -7.55) (6.55 -7.93) (6.77 -8.26) (6.98 -8.60) (7.12 -8.85)
15 -min (3. 333.62) (3. 094.31) 11 (4.1855.00) (4. 005.49) 1 (505156.02) (5. 966.37) (5.5216.68) (5. 936.94) (5.86'6022) 1 6.77
(5.96 -7.40)
30 -min (2. 822.48) (2. 972.97) 1 (z.97?3.55) (3. 363.98) 1 (37404.45) (3. 944.80) (4.23-5.12) (4.43-5.40) (4. 6?5.74) I 5.48
(4.82 -6.00)
60 -min (1. 0455) (1.56710.87) 1 (1.91.0828) (2.12732.59) 1 (242772.97) (2. 09825) (2.323.53) (3.13.43.79) (3. 574.12) (3. 204.38)
2 -hr 1(0.766-0.925)11 (0.928-1 .12)11 (1.142538) (1.31414.58) 1 (1.51-1.83) (1.6762.03) (182102.23) (1.96-2.42) (2.1442.67) 1 2.61
(2.27 -2.87)
1 3 -hr 11(0.544-0.655)11(0.660-0.792)11(0.814-0.979)11 0.595 0.720 0 (0.93803.13) 1 (1.921.32) (1.21-1.48) (1.33-1.63) (1.45-1.78) (1.60-2.00) 1 1.98
(1.71 -2.17)
1 6 -hr (0.329 -03 92) (0.398 0 474)1(0.49150 587) (0.56700 678)1(0.663-0.797)11(0.740-0.895)11(0.815-0.994)11(0.890-1 0 .10) (0.988'3.23) (1.07235)
1 12-hr 1 (0.194 -02 30) (0.234 0 278)1(0.290 -03 45) (0.3 630 402)1(0.39 40.476) (0.446 -0537) (0.495 0 601) (0.544 - 0.668) (0.609 04 62)1 62-0.
(0.662- 0.841)
24 -hr 0.123 0.148 0.186 0.215 11 0.254 0.285 11 0.317 0.350 11 0.395 0.431
(o.115- 0.131) (0.139 - 0.159) (0.174 - 0.198) (0.201 - 0.229) (0.237 - 0.272) (0.265 - 0.305) (0.294- 0.340) (0.323- 0.376) (0.363 - 0.425) (0.394- 0.464)
1 2 -day 0.072 077) (0.08100 093)1(0.100 -0 115) (0.1105, 0.3132)1(0.135- 0.5155) (0.15110.2174) (0.166 - 0.0193) (0.182, 02 12) (0.204 -0 239) (0.221? 0 260)
1 3-day 1 (0.0470 - 01054) (0.0570 - 0.1065)11(0.0700 0 080) (0.08100 092)1(0.095 -0. 09) (0.10510.122) (0.1106 0..135) (0.12710.8149) (0.102 -00. 67)1 54-0.
(0.154- 0.182)
1 4 -day 0.040 0.048 0.059 0.068 0.080 0.089 0.099 0.109 0.122 0.133
(o.038- 0.043) (0.045 - 0.051) (0.055 - 0.063) (0.063 - 0.073) (0.074 - 0.085) (0.083 - 0.096) (0.091- 0.106) (0.100 - 0.117) (0.112- 0.132) (0.121 - 0.144)
1 7 -day (0.02 5 0 028) (0.0 30 - 010 3 4)1(0.036 0 041) (0.04100 046)1(0.048 0 054) (0.00.057 0 061) (0.058 0 067) (0.064 0 074) (0.070100 083) (0.07070 -0 090)
1 10 -day 0.021 0.025 0.030 0.034 0.039 0.043 0.048 110,052 0.058 0.062
(0.020- 0.022) (0.024 - 0.027) (0.028 - 0.032) (0.032 - 0.036) (0.037 - 0.042) (0.041 - 0.046) (0.044- 0.051) (0.048-0.055)11(0.053-0.062)11(0.057-0.067)1
1 20-day 1 (0.01) 0 0 015) (0.0106 0 018)1(0.0109 0 021) (0.02100 023)1(0.0 400 027) (0.026-0.02 9) (0.028-0.032)11(0.031-0.035)11(0.034-0.039)11(0.036-0.042)1
1 30 -day (0.010100 012) (0.010.014 014)1(0.010 5 0 017) (0.01'70 019)1(0.0109 0 021) (0.020 0 023) (0.02 -0 025) (0.00.025 0 027) (0.026 0 029) (0.0270 -0 031)
1 45-day 1 (0.009 0 010) (0.010100 012)11(0.01' 3 0 014) (0.01400 015)1(0.015 0 017) (0.010700 018) (0.0108 0 020) (0.0109 0 021) (0.020 - 0.023)1 21-0. 0.010 (0.021- o.oza)
1 60 -day 0.009 0.010 0.012 0.013 110,014 0.015 0.016 0.017 0.018 0.019
(0.008-0.009)11(0.010-0.011)11(0.011-0.012)11(0.012-0.013 ) (0.013 - 0.015) (0.014 - 0.016) (0.015- 0.017) (0.016 - 0.018) (0.017- 0.019) (0.018 - 0.020)
t Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5 %. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
http: / /hdse.nws.noaa.gov/hdse /pfds /pfds printpage .html ?lat - 35.8280 &lon = - 79.1077 &data =... 9/2/2014

Precipitation Frequency Data Server Page 1 of 3
NOAA Atlas 14, Volume 2, Version 3
jr Location name: Chapel Hill, North Carolina, US*
Latitude: 35.8282 °, Longitude: - 79.1072° e NX
Elevation: 508ft* ?
* source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS -based point precipitation frequency estimates with 90% confidence intervals (in inches)'
PF graphical
http: / /hdse.nws.noaa.gov/hdse /pfds /pfds printpage .html ?lat - 35.8282 &lon = - 79.1072 &data =... 9/8/2014
Average recurrence interval (years)
C
1 11
2 11
5 11
10 11
25 11
50 11
100 11
200 11
500 11
1000 1
5 -min
--0
0.829
0.856
(0.3709 0 454)
(0.448 - 0536)1(0.51'7
617)
(0.5 860.1679)1(0.620
-0. 44) (0.656
- 0.4790)
(0.687 0 832)
(0.7102 0 868)
0 906)1
(0.753- 0.936)
53-0.
10 -min
0.663
0.782
0.904
0.994
1.09
1.15
11
1.21
11
1.26
11
1.31
1.35
1
(0.606 - 0.725)
(0.717 - 0.856)1(0.827-
0.989)
(0.908 -1.09)
(0.989 -1.19)
(1.05 -1.26)
(1.09 -1.32)
(1.13 -1.38)
(1.16 -1.43)
(1.19 -1.48)
15 -min
- 114.25)
1
1
1.69
(0.758 -0906)
(0.9098308)11
(1.05
(1.1521.37)
(1. 5318.50)
(1.32416.59)
(1.38513.67)
(1.4251.74)
(1.476580)
(1.49 -1.85)
30 -min
- 114.24)
1
1
2 7
(1.04
(1.25318.49)
(1. 9612.78)
(1.67$199)
(1.86-2.23)
(1. 92040)
(2.12.35 2.56)
(2.22-2.70)
(2. 362.87)
(2.41-3.00)
60 -min
1
1
(1. 0455)
(1. 67087)
(1.91.0828)
(2.12732.59)
(242772.97)
(2. 09825)
(2.323.53)
(3.13.43.79)
(3. 574.12)
(3. 204.38)
2 -hr
1
1
1
5.23
(1. 3018.85)
(1. 602.23)
(2.29-2.76)
(2.618816)
(3.02-3.67)
(3. 374.07)
(3.62-4.45)
(3.9144.84)
(4.2785.34)
(4.55 -5.75)
3 -hr
12.38) 11
1
1
5.94
(1.647197)
(1. 8-
(2.45-2.94)
(2. 203.39)
(3.28-3.96)
(3.6404.43)
(3.99-4.89)
(4.3495.36)
(4. 945.99)
(5.15 -6.52)
6 -hr
12.35)
1
1
(1.97-
(2. 852.84)
(2. 423.51)
(3. 074.06)
(3.9734.77)
(4.43-5.36)
(4.88-5.95)
(5.306.56)
(5. 27939)
(6. 948.10)
12 -hr
1
1
1
9.37
(2. 352.77)
(2.20635)
(3.49-4.16)
(4.054)
(4.78-5.73)
(5. 896.47)
(5. 6870.24)
(6. 548.05)
(7. 449.18)
(7.98 -10.1)
24 -hr
1
15.50)
1
1
1
10.3
(2. 693.15)
(3.345681)
(4.744.76)
(4. 2-
(5.68-6.52)
(6.37875.33)
(7. 608.16)
(7. 649.02)
(8.24 0.2)
(9.46 -11.1)
2 -day
14.44) 1
- 15.51)
1
(3.23-3.69)
(3. 9-
(4.82
(5. 396.34)
(6.49-7.46)
(7. 378.34)
(7.98-9.26)
(8.74-10.2)
(9.78-11 .5)
(10.6-12.5)
3 -day
1
1
1
(3.42-3.90)
(4,14.3869)
(5.0745.79)
(5.8126.66)
(6.8137.83)
(7. 818.76)
(8.3709.71)
(9.10790.7)
(103712.1)
(11.1 -1.1 -1 3.1)
4 -day
1
1
1
12.8
(3.6184.12)
(4.3304.94)
(5.3206.08)
(6. 956.98)
(7.1308.20)
(7.9359.17)
(8.76-10.2)
(9.60 - 141.2)
(10.77 2.6)
(11.6 -13.8)
7 -day
1
1
(4.1844.72)
(4. 825.63)
(6. 546.84)
(6. 937.81)
(8:859.12)
(8. 050.2)
(9.80 -15.2)
(10.7112.4)
(119313.9)
(129415.1)
10 -day
11
1
4.1)
1
14.9
(4. 605.36)
(5. 596.37)
(6. 8170.65)
(7. 518.65)
(8.82-10.0)
(9.73-11
(10 6112.2)
(11.6-13.3)
(12 8314.8)
(13.8 -16.0)
20 -day
11
1
1
(6. 8775.14)
(7.5398.42)
(8. 849.94)
(9.95-11 .2)
(114?12.8)
(125314.1)
(136415.4)
(14.7516.8)
(16.2718.7)
(17.4 -2.4 -2 0.1)
9.8
30 -day
(7.9438.85)
(9 0.4) 1
(10.8-12. 1)
(12.0- 3.4)
1 (13.5-15. 1)
(14.7516.5)
(15 86187.8)
(16 9$19.2)
(18.4-21 .0)
(19.5-22.4)
45 -day
11
1
1
(10.2-11 .2)
(11.9-13. 1)
(13 6415.0)
(14.9-16.5)
(16.6-18.4)
(17 9619.9)
(19.21621.3)
(20.3-22.8)
(21.9-24.7)
(23.1 -26.2)
.1 -2
60 -day
12.8
14.9
16.8
18.3
20.2
21.7
23.0
24.4
26.1
27.5
(12.2 -13.4)
(14.2 -15.6)
(16.1 -17.6)
(17.5 -19.2)
(19.3 -21.2)
(20.6 -22.7)
(21.9 -24.2)
(23.1 -25.7)
(24.7 -27.6)
(25.9 -29.0)
Precipitation
frequency (PF) estimates in
this table are based on frequency
analysis of partial duration
series (PDS).
Numbers in
parenthesis are PF estimates at lower and upper bounds of the 90% confidence
interval. The probability that precipitation frequency estimates (fore
given duration
and average recurrence interval) will be greater than the upper
bound (or less than the lower bound) is 5 %. Estimates at upper bounds are not
checked against
probable maximum precipitation (PMP) estimates and may be higher than currently valid
PMP values.
Please refer
to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
http: / /hdse.nws.noaa.gov/hdse /pfds /pfds printpage .html ?lat - 35.8282 &lon = - 79.1072 &data =... 9/8/2014

Maps

fir` {i r 1 Y � J � J �, �• �
BRIAR,tHA4'EL OVERALL
PR.OPERTY_3 NDARY
�. 10
BC WEST N
5 ORAGE POTLO. `
r '
of w
< Dj
��frJ 11 : \ •l. •
�J
() V PHASE N \ /
I 8 �/
l_ +
J_
SRIA HA
NWT ,l
\ I \
i 4F
BC PHASE
SE
E
UR
0
If✓
i
1
r
I:

Web GK WeB
1 532 -� m
VV HeB UdC WeC''- W WeE
WeD eB
UdC WeB � W � W WeE
yaa VaB v HeB WeD
WeC VaB fy WeB a m WdC �� /L
n
WeC HeB WeB WeD WeD 1V1 vv
W WeB ¢ W
c) WdC WeC U
WdC HeB VaB — WeD Q �o
WdC WeC - VV
N /eC WeC WeB = WeC
VVeC
W � VaB WdE WeC VaB WeB wed �QG G) WeC WeE
WeE WdC � WeD W WeB WdC 1530 W. WeE WeD VaB
� m
WeB WeC - We WeB e� WeD WeD We[
m� - VVaC _
39 67 WeD e� VaB WeC 1721
35 °50'00„ WeC WdC QW � s 'D S�
WdC m WeE �s> i WeB
.
WeD
t
WeC WeB WeC s
WeE
WeD VaB WeC WeC ChA eD
eC VVeD
WdC WeC
WdC WeE VaB WeE
WeD
Di WdE WeE
Web m WeC ez WOC
WeD WdC Vr WeD m WeE S
3966-, WdC WeC Bennett W WeE
© m Mountain y
� WeB WeC WeC
WeB
HeC WeC VV
WeD � WeB n 4 We p -
WeC WeB UV elr N!
WeE UdC
WdE W� WdC
WdE
WdC) ChA, WdE HeB WeE
WeC WeC WeC WeE WeB
WeB WeB WeD /
W WeD WeD
asg6- A WeB .WeC m - WeE ^UdC-
1526 - v 1717 W
0
Q VaB t WeD WeC 0
W HeB C� WeE
WdE WeC VaB VaB �Cyi WeB
4 WdC
W WeC p WeE
WeD WeB GkD WeC
� m WeC
E WdE W VaB 528 Ja �� WeB (D WeB CrC
� m
ca WdC CD WeC WeB WeC WeE WeD W c CD
CD WeD
WeB W WeC HeB CrB
WdE
3964 4 \"

3967
35° 50'00"
3966
3965

Wet Detention Pond #23
Design

WATER QUALITY POND #23 CALCULATIONS
Project Name
Briar Chapel - Phase 15 North
Project Number
02735 -0113
Date
June 17, 2015
3rd revision
2nd revision
1 st revision

Water Quality Pond Drainage Area Data
Project
Briar Chapel -
Phase 15 North
Project No.
02735 -0113
Date
June 17, 2015
Total site area
754,858
square feet =
17.33
acres
Drainage
area to pond
Other Drainage
Area
Existing
Proposed
Change
Existing
Proposed
Impervious areas
[sf]
[sf]
[sf]
[sf]
[sf]
On -site buildings (BUA)
0
183,700
183,700
0
0
On -site streets
0
103,720
103,720
0
0
On -site alleys
0
0
0
0
0
On -site sidewalks
0
20,400
20,400
0
0
On -site future (open space)
0
0
0
0
0
On -site future (Amenity)
0
0
0
0
0
Off -site future development
0
0
0
0
0
10% Contingency
0
30,782
30,782
0
0
Total Impervious
0
338,602
338,602
0
0
Drainage
area to pond
Other Drainage
Area
Existing
Proposed
Change
Existing
Proposed
Non - impervious areas
[sf]
[sf]
[sf]
[sf]
[sf]
On -site grass /landscape
0
298,394
298,394
0
0
On -site woods
754,858
117,862
- 636,996
0
0
Other undeveloped
0
0
0
0
0
Total off -site non - impervious
0
0
0
0
0
Total non - impervious
754,858
416,256
- 338,602
0
0
Total Drainage Area
754,858
754,858
0
Percent Impervious
I 0.0 I
44.9
I
44.9
na
I /
na
I /
Notes:
2015.06.01.Wet Detention Pond #23.xls
Site Drainage Area Data Page 2 of 18 Printed 6/23/2015 10:44 AM

Water Quality Pond Surface Area Calculations
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
Total on -site drainage area to pond 754,858
Total impervious area in drainage area 338,602
Average water depth of basin at normal pool
Location of site
Site region
% Impervious cover
Chatham County
Piedmont
44.9 percent
square feet
square feet
4.0 feet
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 %)
1.58 percent
For a site in the Piedmont (90 %)
2.24 percent
For a site in a Coastal County w/ Vegetative Filter
2.94 percent
For a site in a Coastal County w /out Vegetative Filter
3.89 percent
Required surface area of pond:
For a site in the Piedmont (85 %) 11,900.0 square feet
For a site in the Piedmont (90 %) 16,940.0 square feet
For a site in a Coastal County w/ Vegetative Filter 22,200.0 square feet
For a site in a Coastal County w /out Vegetative Filter 29,360.0 square feet
Notes:
2015.06.01.Wet Detention Pond #23.x1s
Pond Surface Area Calcs Page 3 of 18 Printed 6/23/2015 10:44 AM

Water Quality Pond Stormwater Runoff Volume Calculations
Project
Project No.
Date
Drainage area
Impervious area
Rainfall depth
Briar Chapel - Phase 15 North
02735 -0113
June 17, 2015
754,858 square feet
338,602 square feet
1.00 inches
Percent Impervious 44.9 percent
R(v)= 0.05 +0.009 *(Percent impervious)
Runoff coefficient - R(v) 0.14 in /in
Runoff volume = (Design rainfall) *(R(v)) *(Drainage area)
Runoff volume 28,540.4 cubic feet
Notes:
2015.06.01.Wet Detention Pond #23.xls
Runoff Volume Calcs Page 4 of 18 Printed 6/23/2015 10:44 AM

Water Quality Pond Volume Calculations
Stage- Storage Data for Pond - Temporary Pool
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Temp Pool) Page 5 of 18 Printed 6/23/2015 10:44 AM
Incremental
Incremental
Incremental
Incremental
Cumulative
Cumulative
Contour ID
Stage
Area
Area
Area
Area
volume
volume
volume
volume
[sq. ft.]
[acres]
[sq. ft.]
[acres]
[cu. ft]
[acre -ft]
[cu. ft]
[acre -ft]
447.5
0
17,183.0
0.394
17,183.0
0.4
0.0
0.0
0.0
0.0
448
0.5
19,795.0
0.454
19,795.0
0.1
9,244.5
0.2
9,244.5
0.2
449
1.5
21,437.0
0.492
21,437.0
0.0
20,616.0
0.5
29,860.5
0.7
450
2.5
23,136.0
0.531
23,136.0
0.0
22,286.5
0.5
52,147.0
1.0
451
3.5
24,892.0
0.571
24,892.0
0.0
24,014.0
0.6
76,161.0
1.1
452
4.5
26,704.0
0.613
26,704.0
0.0
25,798.0
0.6
101,959.0
1.1
453
5.5
28,573.0
0.656
28,573.0
0.0
27,638.5
0.6
129,597.5
1.2
454
6.5
30,498.0
0.700
30,498.0
0.0
29,535.5
0.7
159,1310
1.3
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Temp Pool) Page 5 of 18 Printed 6/23/2015 10:44 AM

Water Quality Pond Volume Calculations
Stage- Storage Data for Pond - Permanent Pool
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Perm Pool) Page 6 of 18 Printed 6/23/2015 10:44 AM
Incremental
Incremental
Incremental
Incremental
Cumulative
Cumulative
Contour ID
Stage
Area
Area
Area
Area
volume
volume
volume
volume
[sq. ft.]
[acres]
[sq. ft.]
[acres]
[cu. ft]
[acre -ft]
[cu. ft]
[acre -ft]
441
0
6,124.0
0.141
6,124.0
0.1
0.0
0.0
0.0
0.0
442
1
7,260.0
0.167
1,136.0
0.0
6,692.0
0.2
6,692.0
0.2
443
2
8,481.0
0.195
1,221.0
0.0
7,870.5
0.2
14,562.5
0.3
444
3
9,793.0
0.225
1,312.0
0.0
9,137.0
0.2
23,699.5
0.4
445
4
11,186.0
0.257
1,393.0
0.0
10,489.5
0.2
34,189.0
0.5
446
5
12,651.0
0.290
1,465.0
0.0
11,918.5
0.3
46,107.5
0.5
447
6
14,194.0
0.326
1,543.0
0.0
13,422.5
0.3
59,530.0
0.6
447.5
6.5
17,183.0
0.394
2,989.0
0.1
7,844.3
0.2
67,374.3
0.5
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Perm Pool) Page 6 of 18 Printed 6/23/2015 10:44 AM

Water Quality Pond Volume Calculations
Stage- Storage Data for Pond - Forebays
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Forebays) Page 7 of 18 Printed 6/23/2015 10:44 AM
Incremental
Incremental
Incremental
Incremental
Cumulative
Cumulative
Contour ID
Stage
Area
Area
Area
Area
volume
volume
volume
volume
[sq. ft.]
[acres]
[sq. ft.]
[acres]
[cu. ft]
[acre -ft]
[cu. ft]
[acre -ft]
441
0
854.0
0.020
854.0
0.0
0.0
0.0
0.0
0.0
442
1
1,169.0
0.027
315.0
0.0
1,011.5
0.0
1,011.5
0.0
443
2
1,528.0
0.035
359.0
0.0
1,348.5
0.0
2,360.0
0.1
444
3
1,935.0
0.044
407.0
0.0
1,731.5
0.0
4,091.5
0.1
445
4
2,383.0
0.055
448.0
0.0
2,159.0
0.0
6,250.5
0.1
446
5
2,866.0
0.066
483.0
0.0
2,624.5
0.1
8,875.0
0.1
447
6
3,388.0
0.078
522.0
0.0
3,127.0
0.1
12,002.0
0.1
447.5
6.5
4,398.0
0.101
1,010.0
0.0
1,946.5
0.0
13,948.5
0.1
2015.06.01.Wet Detention Pond #23.x1s
Stage Storage (Forebays) Page 7 of 18 Printed 6/23/2015 10:44 AM

Water Quality Basin Dewatering Time Calculations
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
Water quality treatment volume
28,540
cubic feet
Total treatment volume
29,861
cubic feet
Maximum head of water above dewatering hole
1.50
feet
Driving head
0.50
feet
Orifice coefficient
0.60
Diameter of each hole
2.75
inches
Number of holes
1
Cross sectional area of each hole =
0.041
square feet
Cross sectional area of each hole =
5.9
square inches
Cross sectional area of dewatering hole(s) =
0.041
square feet
Cross sectional area of dewatering hole(s) =
5.9
square inches
Dewatering time for water quality volume =
2.36
days
56.7
hours
Dewatering time for total volume =
2.47
days
59.4
hours
Notes:
Dewatering time formula: t (days) = V / (Cd *A *Sgrt (2 *32.2 *H) *86,400)
t = drawdown time
V = treatment volume
Cd = orifice coefficient
A = cross sectional area of orifice
H = driving head (1/3 max. head)

Water Quality Pond Summary Information
Project Briar Chapel - Phase 15 North
Project No. 02735 -0113
Date June 17, 2015
Drainage area to pond
Impervious area in drainage area
754,858 square feet =
338,602 square feet =
17.33 acres
7.77 acres
Bottom of pond elevation
441.00
feet
Normal pool elevation
447.50
feet
Pond volume at normal pool
67,374
cubic feet
Forebay volume at normal pool
13,949
cubic feet
Forbay % of total volume
20.7%
Required volume for design rainfall
28,540
cubic feet
Required surface area for pond
16,940
square feet
Volume provided for storage of design rainfall =
29,861 cubic feet at elevation 449
Surface area provided at normal pool 17,183 square feet
Average Depth 3.92 feet
2015.06.01.Wet Detention Pond #23.xls
Summary Data Page 10 of 18 Printed 6/23/2015 10:44 AM

Pre - Development
Post - Development
0
Z3P
m
SubCat Reach Pon Link Routing Diagram for 2015.06.17.BMP #23.GCA
Prepared by McKim & Creed, Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC

2015.06.17.BMP #23.GCA Type Il 24 -hr 1 -Inch Rainfall = 1.00"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 9
Summary for Pond 3P: BMP #23
Inflow Area = 17.330 ac, 44.84% Impervious, Inflow Depth > 0.13" for 1 -Inch event
Inflow =
3.11 cfs @
12.05 hrs,
Volume=
0.189 of
Outflow =
0.09 cfs @
20.00 hrs,
Volume=
0.051 af, Atten= 97 %, Lag= 477.2 min
Primary =
0.09 cfs @
20.00 hrs,
Volume=
0.051 of
Secondary =
0.00 cfs @
5.00 hrs,
Volume=
0.000 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 447.83' @ 20.00 hrs Surf.Area= 18,920 sf Storage= 6,001 cf
Plug -Flow detention time= 261.0 min calculated for 0.051 of (27% of inflow)
Center -of -Mass det. time= 138.4 min ( 983.7 - 845.3 )
Volume Invert
Avail.Storage Storaqe Description
#1 447.50'
159,133 cf Custom Stage Data (Prismatic)Listed below (Recalc)
Elevation Surf.Area
Inc.Store Cum.Store
(feet)
(sq -ft)
(cubic -feet) (cubic -feet)
447.50
17,183
0 0
448.00
19,795
9,245 9,245
449.00
21,437
20,616 29,861
450.00
23,136
22,287 52,147
451.00
24,892
24,014 76,161
452.00
26,704
25,798 101,959
453.00
28,573
27,639 129,598
454.00
30,498
29,536 159,133
Device Routinq
Invert
Outlet Devices
#1 Primary
444.25'
30.0" Round Culvert
L= 53.8' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 444.25'/444.00' S=0.0046'/' Cc= 0.900
n=0.013 Concrete pipe, bends & connections, Flow Area= 4.91 sf
#2 Device 1
447.50'
2.7" Vert. Orifice /Grate C= 0.600
#3 Device 1
449.00'
36.0" W x 9.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4 Device 1
451.00'
48.0" x 48.0" Horiz. Orifice /Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary
452.00'
40.0' long x 22.0' 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 =0.09 cfs @ 20.00 hrs HW= 447.83' (Free Discharge)
t--1 =Culvert (Passes 0.09 cfs of 32.17 cfs potential flow)
P4=Orif = Orifice/Grate (Orifice Controls 0.09 cfs @ 2.26 fps)
= Orifice /Grate ( Controls 0.00 cfs)
ice /Grate ( Controls 0.00 cfs)
Secondary OutFlow Max =0.00 cfs @ 5.00 hrs HW= 447.50' (Free Discharge)
L5= Broad -Crested Rectangular Weir( Controls 0.00 cfs)

2015.06.17.BMP #23.GCA Type 1124 -hr 1 -Inch Rainfall= 1.00"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 10
Pond 3P: BMP #23
Hydrograph
1 ❑ Inflow
3.11 cfs ❑ outflow
�InflowlArea= 17.330 ac ❑ Primary
❑ Secondary
Peak Elev= 447.83'
3 Storage =6,001 cf
y 2—/
LL
0.09 cfs
� � � %/ lid' J' l�'/' J'/ l�l�// �iiy1' l��il//%-';:; �������������•����������r�������.�

2015.06.17.BMP #23.GCA Type 1124 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 11
Time span= 5.00 -20.00 hrs, dt =0.05 hrs, 301 points
Runoff by SCS TR -20 method, UH =SCS
Reach routing by Stor- Ind +Trans method - Pond routing by Stor -Ind method
Subcatchment1S: Pre - Development RunoffArea= 17.330 ac 0.00% Impervious Runoff Depth >0.61"
Tc =20.0 min CN =70 Runoff =11.52 cfs 0.880 of
Subcatchment2S: Post - Development Runoff Area = 17.330 ac 44.84% Impervious Runoff Depth >1.36"
Tc =10.0 min CN =84 Runoff =38.95 cfs 1.969 of
Pond 3P: BMP #23 Peak Elev= 449.56' Storage= 42,198 cf Inflow =38.95 cfs 1.969 of
Primary =8.41 cfs 1.248 of Secondary =0.00 cfs 0.000 of Outflow =8.41 cfs 1.248 of
Total Runoff Area = 34.660 ac Runoff Volume = 2.850 of Average Runoff Depth = 0.99"
77.58% Pervious = 26.890 ac 22.42% Impervious = 7.770 ac

2015.06.17.BMP #23.GCA Type 1124 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 12
Summary for Subcatchment 1S: Pre - Development
Runoff = 11.52 cfs @ 12.15 hrs, Volume= 0.880 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 (ac) CN Description
17.330 70 Woods, Good, HSG C
17.330 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) Oft) (ft /sec) (cfs)
20.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
, , . r . ,
10 11
11.52 cfs
U _ — Tye Ii -24-�r -
I- -+ ��I�ai- ifalliE2.� " -
Runoff Area =17.330 lac
LRupo� Vo�ump= 0.1880Laf
R� n 6 99 t e
Tc =204 min
&N=710 -
L
I
12 13 14 15 16 17 18 19 20
Time (hours)
■ Runoff
12�
10
9-
8
a 7- /
0 6
-T
LL
4 =�
L _L _11
3-
2-
5
6 7 8 9
, , . r . ,
10 11
11.52 cfs
U _ — Tye Ii -24-�r -
I- -+ ��I�ai- ifalliE2.� " -
Runoff Area =17.330 lac
LRupo� Vo�ump= 0.1880Laf
R� n 6 99 t e
Tc =204 min
&N=710 -
L
I
12 13 14 15 16 17 18 19 20
Time (hours)
■ Runoff

2015.06.17.BMP #23.GCA Type 1124 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 13
Summary for Subcatchment 2S: Post - Development
Runoff = 38.95 cfs @ 12.02 hrs, Volume= 1.969 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 (ac) CN
Description
6.850 74
>75% Grass cover, Good, HSG C
7.770 98
Paved parking, HSG C
2.710 70
Woods, Good, HSG C
17.330 84
Weighted Average
9.560
55.16% Pervious Area
7.770
44.84% Impervious Area
Tc Length
Slope Velocity Capacity Description
(min) (feet)
(ft /ft) (ft /sec) (cfs)
10.0
Direct Entry,
Subcatchment 2S: Post - Development
Hydrograph
42 � � � � 3$.95 cfs � � — — — — �_ -_ � Runoff
40
36 / 71"" li�4C -
34'z-
32 -
/ p y.
30 Rinf1 Ate -'17.330 �C+
28 Ru off Volump-1 989- of
26 4
22 -
�- -F - " -ono# Bepth�1.36��
20 - -c=40 min
LL 18 16 6N =84
14 L
12
8'
6
4
2 4/7/7//
o- -
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)

2015.06.17.BMP #23.GCA Type// 24 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 14
Summary for Pond 3P: BMP #23
Inflow Area = 17.330 ac, 44.84% Impervious, Inflow Depth > 1.36" for 1 -Yr event
Inflow =
38.95 cfs @
12.02 hrs,
Volume=
1.969 of
Outflow =
8.41 cfs @
12.27 hrs,
Volume=
1.248 af, Atten= 78 %, Lag= 15.2 min
Primary =
8.41 cfs @
12.27 hrs,
Volume=
1.248 of
Secondary =
0.00 cfs @
5.00 hrs,
Volume=
0.000 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 449.56' @ 12.27 hrs Surf.Area= 22,393 sf Storage= 42,198 cf
Plug -Flow detention time= 143.3 min calculated for 1.248 of (63% of inflow)
Center -of -Mass det. time= 69.2 min ( 860.0 - 790.8 )
Volume Invert Avail.Storage Storaqe Description
#1 447.50' 159,133 cf Custom Stage Data (Prismatic)Listed below (Recalc)
Elevation Surf.Area
Inc.Store Cum.Store
(feet)
(sq -ft)
(cubic -feet) (cubic -feet)
447.50
17,183
0 0
448.00
19,795
9,245 9,245
449.00
21,437
20,616 29,861
450.00
23,136
22,287 52,147
451.00
24,892
24,014 76,161
452.00
26,704
25,798 101,959
453.00
28,573
27,639 129,598
454.00
30,498
29,536 159,133
Device Routinq
Invert
Outlet Devices
#1 Primary
444.25'
30.0" Round Culvert
L= 53.8' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 444.25'/444.00' S=0.0046'/' Cc= 0.900
n=0.013 Concrete pipe, bends & connections, Flow Area= 4.91 sf
#2 Device 1
447.50'
2.7" Vert. Orifice /Grate C= 0.600
#3 Device 1
449.00'
36.0" W x 9.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4 Device 1
451.00'
48.0" x 48.0" Horiz. Orifice /Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary
452.00'
40.0' long x 22.0' 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 =8.35 cfs @ 12.27 hrs HW= 449.56' (Free Discharge)
t--1 =Culvert (Passes 8.35 cfs of 47.63 cfs potential flow)
P4=Orif = Orifice/Grate (Orifice Controls 0.27 cfs @ 6.72 fps)
= Orifice /Grate (Orifice Controls 8.08 cfs @ 2.40 fps)
ice /Grate ( Controls 0.00 cfs)
Secondary OutFlow Max =0.00 cfs @ 5.00 hrs HW= 447.50' (Free Discharge)
L5= Broad -Crested Rectangular Weir( Controls 0.00 cfs)

2015.06.17.BMP #23.GCA Type 1124 -hr 1- YrRainfall= 2.96"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 15
Pond 3P: BMP #23
Hydrograph
4—
/
'
38.95 cfs I
❑ inflow
Inflow t4rea= 17.330 ac ❑ El Primary
42
40�
i ,
�—
❑ Secondary
(Peak Elev= 449.56'
38 �
tcrage=
341
/
i
�
- - -
42,198 d
32 �-z
j
-
-
-
-
28V
y 26V
v 24
/
/ /
- -
22;
0 20
U-
18:
14
12
/ /
8.41 cfs
-
10
8'
6-
/
0.0 cfs
0=
5
6
7
8
9
10
11
12 13 14
15
16 17 18 19 20
Time (hours)

2015.06.17.BMP #23.GCA Type 1124 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 16
Time span =5.00 -20.00 hrs, dt =0.05 hrs, 301 points
Runoff by SCS TR -20 method, UH =SCS
Reach routing by Stor- Ind +Trans method - Pond routing by Stor -Ind method
Subcatchment 1 S: Pre - Development Runoff Area = 17.330 ac 0.00% Impervious Runoff Depth >1.96"
Tc =20.0 min CN =70 Runoff =40.81 cfs 2.836 of
Subcatchment2S: Post - Development Runoff Area = 17.330 ac 44.84% Impervious Runoff Depth >3.19"
Tc =10.0 min CN =84 Runoff =88.25 cfs 4.608 of
Pond 3P: BMP #23 Peak Elev= 451.33' Storage= 84,373 cf Inflow =88.25 cfs 4.608 of
Primary=40.34 cfs 3.856 of Secondary=0.00 cfs 0.000 of Outflow =40.34 cfs 3.856 of
Total Runoff Area = 34.660 ac Runoff Volume = 7.445 of Average Runoff Depth = 2.58"
77.58% Pervious = 26.890 ac 22.42% Impervious = 7.770 ac

2015.06.17.BMP #23.GCA Type// 24 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 17
Summary for Subcatchment 1S: Pre - Development
Runoff = 40.81 cfs @ 12.14 hrs, Volume= 2.836 af, Depth> 1.96"
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 (ac) CN Description
17.330 70 Woods, Good, HSG C
17.330 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) Oft) (ft /sec) (cfs)
20.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
�40.81 cfs I
'
_ _ _ _� ■Runoff
-i - - Tyke I i -24 1h--- r -
44= /
1Y I�a+rif�115.1" -
-
42=
—
nQep- h ��'6
_
40= ;
-
6]- LO -
=1 1 - —
38=',,
36�
T
_T : D E -
34=
10 11 12 13
Time (hours)
14 15 16 17 18 19 20
32-
30'
28
26-/
—
24 ='
:E
1
:1
22 =��
0
a 20
18 -_'
14
12_'
1g
Z
Z
6 ='
4-Z
2-
5
6
7
8 9
Hydrograph
�40.81 cfs I
'
_ _ _ _� ■Runoff
-i - - Tyke I i -24 1h--- r -
- - -
1Y I�a+rif�115.1" -
Ranoff Area =1-7.330 lc -
-LRugoff11 Vollump=2.1636t-af -
nQep- h ��'6
_
T _I T�
c=:20AY mm -
-
6]- LO -
=1 1 - —
— — — — — 1—-
T
_T : D E -
10 11 12 13
Time (hours)
14 15 16 17 18 19 20

2015.06.17.BMP #23.GCA Type// 24 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 18
Summary for Subcatchment 2S: Post - Development
Runoff = 88.25 cfs @ 12.01 hrs, Volume= 4.608 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 (ac) CN
Description
6.850 74
>75% Grass cover, Good, HSG C
7.770 98
Paved parking, HSG C
2.710 70
Woods, Good, HSG C
17.330 84
Weighted Average
9.560
55.16% Pervious Area
7.770
44.84% Impervious Area
Tc Length
Slope Velocity Capacity Description
(min) (feet)
(ft /ft) (ft /sec) (cfs)
10.0
Direct Entry,
Subcatchment 2S: Post - Development
Hydrograph
95
90
85--
-
80
75
70
65
60
55
U
50
4
�
2 45
—
—
— —
40--'
-k-
4
35:
_
30 �
-k-
4
25-
20 -�
4
15�
—
10z-/
5 6 7 8
9 10
■Runoff
� 88.25 cfs
T e 124- r
41 0�Yl-kainfal lL-5. f7"
4- Runoff Area #1.330 ac
_Rules, off VQllum� =4.1608. of
4 R�nof �e1p#h 3.'f 17- -
-Tc= 40. -0- min -
4
$4 _.
+- -I- 1II�-
11 12 13 14 15 16 17 18 19 20
Time (hours)

2015.06.17.BMP #23.GCA Type// 24 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 19
Summary for Pond 3P: BMP #23
Inflow Area = 17.330 ac, 44.84% Impervious, Inflow Depth > 3.19" for 10 -Yr event
Inflow =
88.25 cfs @
12.01 hrs,
Volume=
4.608 of
Outflow =
40.34 cfs @
12.15 hrs,
Volume=
3.856 af, Atten= 54 %, Lag= 8.5 min
Primary =
40.34 cfs @
12.15 hrs,
Volume=
3.856 of
Secondary =
0.00 cfs @
5.00 hrs,
Volume=
0.000 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 451.33' @ 12.15 hrs Surf.Area= 25,483 sf Storage= 84,373 cf
Plug -Flow detention time= 91.2 min calculated for 3.856 of (84% of inflow)
Center -of -Mass det. time= 43.2 min ( 815.3 - 772.1 )
Volume Invert
Avail.Storage Storaqe Description
#1 447.50'
159,133 cf Custom Stage Data (Prismatic)Listed below (Recalc)
Elevation Surf.Area
Inc.Store Cum.Store
(feet)
(sq -ft)
(cubic -feet) (cubic -feet)
447.50
17,183
0 0
448.00
19,795
9,245 9,245
449.00
21,437
20,616 29,861
450.00
23,136
22,287 52,147
451.00
24,892
24,014 76,161
452.00
26,704
25,798 101,959
453.00
28,573
27,639 129,598
454.00
30,498
29,536 159,133
Device Routinq
Invert
Outlet Devices
#1 Primary
444.25'
30.0" Round Culvert
L= 53.8' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 444.25'/444.00' S=0.0046'/' Cc= 0.900
n=0.013 Concrete pipe, bends & connections, Flow Area= 4.91 sf
#2 Device 1
447.50'
2.7" Vert. Orifice /Grate C= 0.600
#3 Device 1
449.00'
36.0" W x 9.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4 Device 1
451.00'
48.0" x 48.0" Horiz. Orifice /Grate C= 0.600
Limited to weir flow at low heads
#5 Secondary
452.00'
40.0' long x 22.0' 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 =40.07 cfs @ 12.15 hrs HW= 451.32' (Free Discharge)
t--1 =Culvert (Passes 40.07 cfs of 57.03 cfs potential flow)
P4=Orif = Orifice/Grate (Orifice Controls 0.37 cfs @ 9.27 fps)
= Orifice /Grate (Orifice Controls 30.18 cfs @ 6.71 fps)
ice /Grate (Weir Controls 9.52 cfs @ 1.85 fps)
Secondary OutFlow Max =0.00 cfs @ 5.00 hrs HW= 447.50' (Free Discharge)
L5= Broad -Crested Rectangular Weir( Controls 0.00 cfs)

2015.06.17.BMP #23.GCA Type 1124 -hr 10 -Yr Rainfall = 5.17"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 20
Time (hours)
❑ Inflow
❑ outflow
❑ Primary
❑ Secondary
Pond 3P: BMP #23
Hydrograph
88.25 cfs �
—
i
Inflow Area= 17.330 ac
95JI/
90/
�_
C
C
E
E
E E
Peak Elev= 451.33'
85/
80/
-�Stgrage =84, 73 cf
70
60 -
55 .
—
50�lz
/ i
_
40.34 cfs
_
LL 40/
35=Z
30�
/
— —
25
20
15j�
%
0.00 cfs
Time (hours)
❑ Inflow
❑ outflow
❑ Primary
❑ Secondary

2015.06.17.BMP #23.GCA Type 1124 -hr 100 -Yr Rainfall= 7.62 "
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 21
Time span= 5.00 -20.00 hrs, dt =0.05 hrs, 301 points
Runoff by SCS TR -20 method, UH =SCS
Reach routing by Stor- Ind +Trans method - Pond routing by Stor -Ind method
Subcatchment1S: Pre - Development RunoffArea= 17.330 ac 0.00% Impervious Runoff Depth >3.81"
Tc =20.0 min CN =70 Runoff =79.29 cfs 5.497 of
Subcatchment2S: Post - Development Runoff Area = 17.330 ac 44.84% Impervious Runoff Depth >5.37"
Tc =10.0 min CN =84 Runoff = 143.98 cfs 7.750 of
Pond 3P: BMP #23 Peak Elev= 452.48' Storage= 114,982 cf Inflow= 143.98 cfs 7.750 of
Primary =62.44 cfs 6.602 of Secondary =35.87 cfs 0.369 of Outflow =98.31 cfs 6.970 of
Total Runoff Area = 34.660 ac Runoff Volume = 13.247 of Average Runoff Depth = 4.59"
77.58% Pervious = 26.890 ac 22.42% Impervious = 7.770 ac

2015.06.17.BMP #23.GCA Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 22
Summary for Subcatchment 1S: Pre - Development
Runoff = 79.29 cfs @ 12.13 hrs, Volume= 5.497 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 (ac) CN Description
17.330 70 Woods, Good, HSG C
17.330 100.00% Pervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft /ft) (ft /sec) (cfs)
20.0 Direct Entry,
Subcatchment 1S: Pre - Development
Hydrograph
85-
80
_ L
Type II 24 -hr
75-
7-
7
-7 1
70=
— 1
Runoff Depth >3.81" -
65_
-_ 1—
�
CN =70 -
60-
55-
I-
1
N 50-
3 45-
-
-° 40-
LL
35-
30-
25-
20 _
/-
15
0
5
6
7
8 9
79.29 cfs
-
1
Type II 24 -hr
100 -Yr Rainfall-7.62'
t
Runoff Area = 17.330 ac
— 1 Runoff. Volume= 5.497 of
— 1
Runoff Depth >3.81" -
Tc =20.0 min -
-_ 1—
�
CN =70 -
10 11
Time (hours)
17 18
❑ Runoff

2015.06.17.BMP #23.GCA Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 23
Summary for Subcatchment 2S: Post - Development
Runoff = 143.98 cfs @ 12.01 hrs, Volume= 7.750 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 (ac) CN
Description
6.850 74
>75% Grass cover, Good, HSG C
7.770 98
Paved parking, HSG C
2.710 70
Woods, Good, HSG C
17.330 84
Weighted Average
9.560
55.16% Pervious Area
7.770
44.84% Impervious Area
Tc Length
Slope Velocity Capacity Description
(min) (feet)
(ft /ft) (ft /sec) (cfs)
10.0
Direct Entry,
Subcatchment 2S: Post - Development
Time (hours)
Hydrograph
/
-,
160-
—
—
❑Runoff
50-:/
143.98 cfs
140: /
Type 11 24-hr
130 =/I
L
1
-1
100 -Yr Rainfall= 7.62"
120 =i1—
Runoff Area = 17.330 ac
110
100 =/
-4
I Runoff Vc- lume =7.7 -50 a_f
90
U
Runoff Depth >5.37"
3 80= /I
LL 70_/
Tc =10.0 min
60
rt
—
— — - CN =8 -4
50= /
—
+
_4 —
— — — 4 --1 —
40- /
30 =/
_
/
10_
o���f/
-
- - / /I
P .
5
6
7
8 9
10 11 12 13 14 15 16 17 18 19 20
Time (hours)

2015.06.17.BMP #23.GCA Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 24
Summary for Pond 3P: BMP #23
[82] Warning: Early inflow requires earlier time span
Inflow Area = 17.330 ac, 44.84% Impervious, Inflow Depth > 5.37" for 100 -Yr event
Inflow =
143.98 cfs @
12.01 hrs,
Volume=
7.750 of
Outflow =
98.31 cfs @
12.11 hrs,
Volume=
6.970 af, Atten= 32 %, Lag= 5.8 min
Primary =
62.44 cfs @
12.11 hrs,
Volume=
6.602 of
Secondary =
35.87 cfs @
12.11 hrs,
Volume=
0.369 of
Routing by Stor -Ind method, Time Span= 5.00 -20.00 hrs, dt= 0.05 hrs
Peak Elev= 452.48' @ 12.11 hrs Surf.Area= 27,600 sf Storage= 114,982 cf
Plug -Flow detention time= 72.6 min calculated for 6.970 of (90% of inflow)
Center -of -Mass det. time= 38.2 min ( 798.3 - 760.1 )
Volume
Invert Avail.Storage Storaqe Description
#1
447.50'
159,133 cf Custom
Stage Data (Prismatic)Listed below (Recalc)
Elevation
Surf.Area
Inc.Store
Cum.Store
(feet)
(sq -ft)
(cubic -feet)
(cubic -feet)
447.50
17,183
0
0
448.00
19,795
9,245
9,245
449.00
21,437
20,616
29,861
450.00
23,136
22,287
52,147
451.00
24,892
24,014
76,161
452.00
26,704
25,798
101,959
453.00
28,573
27,639
129,598
454.00
30,498
29,536
159,133
Device Routinq Invert Outlet Devices
#1
Primary
444.25'
30.0" Round Culvert
L= 53.8' RCP, square edge headwall, Ke= 0.500
Inlet/ Outlet Invert= 444.25'/ 444.00' S=0.0046'/' Cc= 0.900
n=0.013 Concrete pipe, bends & connections, Flow Area= 4.91 sf
#2
Device 1
447.50'
2.7" Vert. Orifice /Grate C= 0.600
#3
Device 1
449.00'
36.0" W x 9.0" H Vert. Orifice /Grate X 2.00 C= 0.600
#4
Device 1
451.00'
48.0" x 48.0" Horiz. Orifice /Grate C= 0.600
Limited to weir flow at low heads
#5
Secondary
452.00'
40.0' long x 22.0' 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 =62.37 cfs @ 12.11 hrs HW= 452.46' (Free Discharge)
L' = Culvert (Inlet Controls 62.37 cfs @ 12.71 fps)
=2= Orifice /Grate (Passes < 0.42 cfs potential flow)
-3= Orifice /Grate (Passes < 38.05 cfs potential flow)
-4= Orifice /Grate (Passes < 92.62 cfs potential flow)
Secondary OutFlow Max =34.18 cfs @ 12.11 hrs HW= 452.46' (Free Discharge)
5= B road-C rested Rectangular Weir (Weir Controls 34.18 cfs @ 1.84 fps)

2015.06.17.BMP #23.GCA Type 1124 -hr 100 -Yr Rainfall= 7.62"
Prepared by McKim & Creed Printed 6/23/2015
HydroCADO 10.00 s/n 04927 © 2011 HydroCAD Software Solutions LLC Page 25
Pond 3P: BMP #23
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)
Hydrograph
F
F
F
F F F F
zz
xz--�
143.98 cfs
I
Inflow Area= 17.330 ac
❑ Inflow
❑ outflow
❑ Primary
160=
150
/
-
❑ Secondary
Peak Elev= 452.48'
140
—
130-
/
Sto�agp= 114,982 cf
120-
/
98.31 cfs
110
100-/
go-
/
80
/
{
62.44 cfs
— —
.2 70�/
/
—
—
60�
—
—
50
35.87 cfs
40
/
30�
20=
/
,
10
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (hours)

PROJECT NAME: Briar Chapel - Phase 15 North
PROJECT LOCATION: Chatham County, NC
Pond Name=
BMP #23
Riser Outer Width =
5 ft
Riser Outer Length =
5 ft
Riser Inner Width =
4 ft
Riser Inner Length =
4 ft
Riser Height =
7.25 ft
Concrete Base Length = 7 ft
Concrete Base Width = 7 ft
Concrete Base Depth = 15 in
DATE: 06/17/2015
PROJECT NO:
02735 -0113
Riser Resisting Force =
Base Resisting Force =
Total Resisting Force =
Riser Buoyant Force =
Base Buoyant Force =
Total Buoyant Force =
Factor of Safety
DESIGNED BY: GCA
CHECKED BY: GML
9,788 lb
9,188 lb
18,975 lb
11,310 lb
3,822 lb
15,132 lb
1.25 Design Acceptable

rKwtU i NAIVit: tsnar cnapei - rnase .i oiv
PROJECT LOCATION: Chatham County, NC
Storm Outlet Structure
Structure= HW -BMP #23
Size=
30
in
Q10 =
40.34
cfs
Qfull =
45.16
cfs
Vfull =
6.39
fps
From Fig. 8.06.b.1:
From Fig. 8.06.b.2:
3
Length
Zone
D50
DMAX
Riprap Class
Apron Thickness
Apron Length
Apron Width = 3 x Dia
DATE: 06/12/2015 DESIGNED BY:
BSS
PROJECT NO: CHECKED BY
02735 -0113 GCA
Q10 /Qfull = 0.89
V /Vfull = 1.29
V = 9.03 fps
= 3
= 10 in
15 in
1
= 24 in
20.0 ft
= 8.0 ft