SW8030425_COMPLIANCE_20030611

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
--L_
SW _so)3AA,,5
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
�CD30Gl(
YYYYMMDD

WET DETENTION POND ANALYSIS
FILE NAME:
PROJECT #: SW8 030425
PROJECT NAME: Dutch Square Storage
G :IDATAIW P DATAIWQSIP O N D\0 30425. W K 1
REVIEWER: LSMunn
DATE: 11-Jun-03
Receiving Stream: Smith Creek Class: C-SW
Drainage Basin: Cape Fear Index No.
Site Area 2.90 acres
Drainage Area 2fi324 04 : square feet Area in Acres 2.90
IMPERVIOUS AREAS Rational C
building 46290.00 square feet
parking 41976.00 square feet
sidewalk 395.00 square feet
square feet
square feet
square feet
TOTAL t3B6-- 4-- square feet Rational Cc- 0.06
SURFACE AREA CALCULATION
% IMPERVIOUS 70.19%
Des. Depth 6
TSS: 90
SA/DA Ratio 3.91 %
Req. SA 4943 sf
Prov. SA ::,::8205< sf
VOLUME CALCULATION * place a "1" in the box if Rational is used
Req. Volume 717E cf
Vol. Prov. at DP
ORIFICE CALCULATION
FOREBAY
Perm. Pool Volume=
Req. Forebay Volume=
Provided Volume=
Percent= #111lOi
Elevation Area Inc. Vol.
39.00 8205.00
40.00 9628.00 8916.50
IN
Acc. Vol.
8916.50
Avg. Head =
0.47
ft
Q2 Area =
1.81
sq.
inches
Flow Q2, cfs
0.042
cfs
Q5 Area =
0.73
sq.
inches
Flow Q5, cfs
0.017
cfs
Orifice Area
1.77
sq.
inches
No. of Orifices
1',:
Q=
0.040
cfs
Diameter, inches
:, . 1.5(J
weir H x W
:'.:.:.. <. rn
x
:.. rn
Drawdown =
1' >
days
Surface Area @DP =
9628 sq. ft.
Falling Head Drawdown =
3.5 days
COMMENTS
Surface Area , Volume and Orifice are within Design Guidelines.

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STORMWATER SUBMITTAL REQUIREMENTS
DETENTION POND
A. Site Plan
✓ I .
Development/Project Name
2.
Designer=s seal, signature, name and firm.
+/ 3.
Legend
4.
North Arrow
5.
Location Map with direction, distance to named streets, NCSR numbers.
✓ 6.
Scale
7.
Date
171~ 8.
Revision number and date.
9.
Original contours, proposed contours, spot elevations, finished floor elevations.
✓ 10.
Existing drainage, including off -site. Provide a map of any offsite areas.
11.
Property/Project boundary lines, dimensioned.
��- 12.
Mean High Water Line, if project is adjacent surface waters.
Drainage easements, catch basins, pipe sizes, inverts.
Wetlands delineated, or a note on the plans that none exist. Ponds may not be located
in a wetland.
15.
Details of the road, parking, cul-de-sacs, including sidewalks, curb and gutter..
Drainage area to each pond delineated.
el7. `
Dimensions of the permanent pool.
�- 17
Vegetated filter detail if using 85% TSS. This is NOT a connector ditch.
�le 19.
Dimensions of the road, parking cul-de-sacs, sidewalks,,and curb and gutter.
20.
Unit footprint with dimensions and concrete wood deck areas noted.for apartments
or condo development.
21.
Forebay at each inlet. (Prefer one inlet)
22.
Inlets located such that entire pond is used for treatment and no short-circuiting.
23.
Pond/forebay section detail with:
Bottom elevation
Permanent pool elevation PP
Storage pool elevation SP
—�
Slopes: 3:1 above permanent pool
_
Vegetated shelf located below permanent pool, 6:1 slope, with begin and end
elevations around main pond. (Not required inside forebay)
Forebay bottom elevation, 3:1 slopes,
Forebay weir elevation between PP and DP.
24.
Outlet structure detail with trash rack and orifice size specified. Maximum trash rack
y ; 2 P
opening size is 4".
Note on plans that all roof drains must be directed so as to be picked up by the pond.
A 3:1 L: W ratio has been provided for the pond.
^� 27.
Maximum ave. rag, pond depth of 6. (Parts of pond may be deeper -up to 7.5')
28.
Vegetation requirements for pond slopes and wetland species for the 6.1 shelf are listed.
Weeping Love grass is not suitable for use in North Carolina.
t
CFF

In
C.
STORMWATER SUBMITTAL REQUIREMENTS
DETENTION POND (cont)
Calculations
1. 85% or 90% TSS Chart noted.
2. Pond depth.
3. SA/DA ratio calculation.
4. Required surface area at permanent pool.
5. Provided surface area at permanent pool (Based on pond dimensions)
6. Provided surface area at temporary design pool.
7. Required volume calculation.
8. Provided volume calculation.
9. Orifice size based on required 1" volume, using average head to design pool elevation.
10. Designer—s seal.
11. Built -upon area to each pond.
12. Forebay designed to hold 20% of the permanent pool volume. (Range of 18-22 OK.)
13. Non -erosive flow for 10 yr. storm in the vegetated filter, if using 85% TSS.
Supporting Documentation
l . Completed permit application and supplement.
a. is the person who signed the landowner or a leasee? Must be landowner.
b. All sections and blanks completely filled in.
C. Check signature per .1003 (e). Make sure title is provided.
d. If agent signs, signatory authorization from owner.
e. Wet detention supplement sheet provided.
f. Mailing address & phone of applicant- no CIO.
g. Verify water body classification.
h. Justifications for,not meeting a design requirement.
i. If a modification, include Designer=s Certification.
j. Hand initial design requirements.
2. Proposed deed restrictions
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3/11 /2003
CDC
Dutch Square Storage
Stormwater Pond Calculations
02084
Total Drainage Area
s q. ft.
I acres
126,455
1 2.90
Impervious Area
Land Use
s q, ft,
acres
building
46,290
1.06
asphalt
41,976
0.96
ravel
0
0.00
concrete
395
0.01
Iota I
1 88,661
1 2.04
Stormwater Calculations:
Time of Concentration:
Hydraulic Length (L) = 600 ft.
hange in Height (H) = 2 ft.
Tc = (L° IH)''..' / 128
9.68 min.
Flow for 10 year, 6 hour Storm (Q10):
QPRE - (CPRE) x (110) x (Area)
4.57 cfs
QPosr = (CPosr) x (110) x (Area)
13.72 cis
Detention Pond Design:
Pond Size:
Elevation
ft.
Surface Area
(sq. ft.
Normal Pool
39.00
8,205
Flood Pool
40.00
9,628
Top of Bank
42.50
13,282
Bottom of Pool
33.00
333
Total Provided Storage Volume:
Vol. _ [(Normal pool SA + Flood Pool SA) / 2]
x (F.P. elev, - N.P. elev.)
8,917 cu. ft.
% impervious = 0.701
= 70.1%
say 71.0%
CPRE = 0.25
CPo,T= (%imp,)(.95)+(1%imp.)(.25)
0.75
110 = 6.30 inlhr
150 = 7.79 in/hr
Flow for 50�year, 6 hour Storm (Q50)
QPRE (CPRE) x (119).x (Area)
5.65 cfs
QPosT = (CPosT) x (110) x (Area)
16.96 cfs
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Pond side slopes = 3 :1
Depth below N.P. = 6 ft.
SA/DA = 0.0397
(Chart for 90% TSS Removal for Wet Detention
Pond without Vegetative Filter
Required SA = (SA/DA) x (Total Drainage Area)
= 5,020 s . ft.
State Volume Requirement for Storaae of first 1" runoff:
Vol. = [(1/12) x (DA) x (% imp.)] +
[(1/12) x (DA) x (1-% imp.) x C]
C = 0.2
8,018 cu. ft.
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02084POND 1 of 2

3/11 /2003
CDC
Pond Volume:
Dutch Square Storage
Stormwater Pond Calculations
Bottom SA = 333 sq. ft.
Normal Pool SA = 8,205 sq. ft.
Vol [(N.P. SA+ Bottom SA)1 2] x (N.P. el. - Bottom ei.)
- 25,614 cu. ft.
Forebaw
Required Volume
Vol. = 20% of storage volume
= 5,123 cu. ft.
Provided Volume
Bottom SA= 1,063 sq. ft.
Normal Pool SA = 2,575 sq. ft.
Vol. _ [(N.P. SA + Bottom SA) 2] x (N.P. el. - Bottom el.)
- 5,457 cu. ft.
depth = 3 ft.
Outlet Structure Design:
Flow for 2-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. / 172,800 sec. (2-days)
— 0.046 cfs
Neouired Area oT i we Tor 2-aav drawdown:
A= Q/ [Cd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft./sz
h= (F.P. elev.-N.P. elev.)12
= 0.5 ft.
A = 0,0136 sq. ft.
Diameter of Pioe for 2-dav drawdown:
DIA. SQRT[(A x 4) / pi]
I` 0.1317 ft.
1.58 in.
Use 1.5" orifice
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter L = 16 ft.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
0,75
1 = 6.30 in. for a 10 yr. Storm
A = 2.90 Acres
13.72 cfs
Flow for 5-day drawdown:
far 1st 1" of stormwater,
Q = Required Vol. 1432,000 sec. (5-days)
0.019 cfs
uirea Area oT r�11Je Tor b-dav drawdown:
A= Q/[CdxSQRT(2xgxh)]
Cd = 0.6
g = 32.2 ft./S2
h = (F. P. elev. - N.P. elev.) / 2
0.5 ft.
A = 0.0055 sq, ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SQRT[(A x 4) / pi]
0.0833 ft.
— 1.00 in.
Q= CwxLXH'
H [Q 1 (Cw x L)]2r3
Cw = 3
0.43 ft.
Peak elevation = flood pool elevation + H
40A3 ft.
02084
02084POND 2 of 2

April 16, 2003
Stormwater Narrative
Dutch Square Storage
New Hanover County, NC
TE 02084
Dutch Square Storage is an existing 2.90 acre site proposed for a high density RV storage
facility. Runoff will be treated by wet detention. The pond will treat both the State 1"
requirement and the County 25-year pre -post requirement. The pond is designed for
70.1% impervious coverage. 46,290 sf of building, 41,976 sf of parking and 395 sf of
concrete sidewalk are proposed. Outflow from the pond will be to Smith Creek,
classification C-SW.