BMP 7 Revised calcs

KENNEY DESIGN GROUP, PA
May 21, 2018
Rick Riddle, PE
Environmental Engineer
NCDEQ
DEMLR Stormwater Program
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
1216 PARSONS TRAIL
DENVER, NORTH CAROLINA 28037
PH: 704-634-7186
EMAIL: [e-mail]
LICENSE NO. C-1986
RE: Harkey Creek Subdivision, Union County, Permit No. SW3170702
Revisions to Wet Pond #7
Dear Mr. Riddle:
We have made some revisions to the street and lot configuration of the Harkey
Creek Subdivision. These revisions only affect Wet Pond #7. The revisions will
reduce the drainage area to the pond by 0.75 ac (from 10.65 ac to 9.90 ac) and
reduce the impervious area by 0.10 ac. The pond itself has been slightly altered.
No changes have been made to the outlet device.
Attached are revised plans and calculations for the Wet Pond #7. Please let me
know if you require any addition information. Thank you.
Sincerely,
Jeffrey P. Schmitt, PE

KENNEY DESIGN GROUP, PA
1216 PARSONS TRAIL
DENVER, NORTH CAROLINA 28037
PH: 704-377-6099
EMAIL: [e-mail]
LICENSE NO. C-1986
Harkey Creek Subdivision
Union County, North Carolina
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BMP 7 Calculation Revisions

Wet Pond Calculations
Drainage Area = 9.90 ac
CN = 86
Tc = 0.08 hrs
Impervious Area =
4.92 ac
1 =
50%
Rv =
0.50
WQv =
0.41 ac -ft
WQv =
17870 ft3
Stage at Treatment Vol =
646.8
Permanent Pool Elev. =
646.0
Vpp =
55699 ft3
App =
16677 ft2
Dave =
3.34 ft
Min SADA Ratio =
1.79
SA =
0.38 ac
DA =
9.90 ac
SADA Ratio Provided =
3.87
Main Pool Volume =
55699 ft3
Required Forebay Volume =
8355 ft3 to
Forebay Volume Provided =
10274 ft3
Orifice Sizing
Time to release WQv =
48 hrs
Release Rate =
0.103 cfs
Average Head =
0.4 ft
Orifice Area =
0.034 ft2
Orifice Diameter=
2.50 in
Project: BMP 7 Wet Pond
Date: 15 -Jun -17 Rev 15 -Mar -18
Post Development
Soils = Group C
CN = 98
CN = 74
CN = 70
CN 85
Water Quality Volume
Water Quality Volume
11140 ft3
642.5 to 646
4.92 ac
4.98 ac
0 ac
0 ac
Imperv. Total
Grass, good
Woods, good
Gravel

Project Drainage Areas -, Additional Sheet ',WL ICt
Basin Information
Drainage Area 5
Drainage Area 7
Drainage Area 8
Receiving Stream Name
East Fork
East Fork
East Fork
55, j, i5j
Twelevemile
Twelevemile
Twelevemile
Creek
Creek
Creek
Stream Class
C
C
C
Stream Index Number
11-138-2
11-138-2
11-138-2
Total Drainage Area (sf)
414255n��
96267
On-site Drainage Area (sf)
364265
4&395*
86684
Off-site Drainage Area (sf)
49990
9583
9583
Proposed Impervious Area (sf)
134291
-22155-9- Z► ' 'V'15
29115
% Impervious Area
34
-4-7-- 50'
30
Impervious Surface Area
On-site Building/Lots (sf)
85050
-1422W
i 4Vi5
18900
On-site Streets (sf)
36741
x5-58
55, j, i5j
7835
On-site Parking (sf)
On-site Sidewalks (sf)
12500
2380
Other on-site (sf)
Future (s€)
Off-site (sf)
6000
9583
Existing BUA (sf)
Total (sf)
140291
423.559
'Z I Lf, J '5
38698
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lm
04
64
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Illp
52
Vol
24
20
pp
124
JQ
mi
105
Ila
mv
200
Of 201
Of p
108
cosjall
1-72
7,74,,�-
16
112
241
160
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