HomeMy WebLinkAboutSW8021126_COMPLIANCE_20030121STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW gm ZZO?
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
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I
DETENTION POND ANALYSIS FILE NAME: G:IDATAIWPDATAIWQSIPOND1021126.WK1
PROJECT #: SW8 021126 REVIEWER: L. Lewis
PROJECT NAME: Dollar General -Hampstead
DATE: 21-Jan-03
Receiving Stream: Harrisons Creek Class: C Sw
Drainage Basin: Cape Fear Index No. CPF23 18-74-49
Site Area 2.69 acres
Drainage Area 11177. square feet Area = 2.69 acres
IMPERVIOUS AREAS
Rational C
Building
12985.00
square feet
Parking
51832.00
square feet
SW
1691.00
square feet
Future
15000,00
square feet
square feet
square feet
TOTAL
8154$ 00'
square feet Rational Cc= 0.06
SURFACE AREA CALCULATION
IMPERVIOUS 69.56%
Des. Depth 5
TSS: 90
VOLUME CALCULATION
Rational ?*
Des. Storm
.,.�.��:.-":inches
Rv=
0.68
Bottom
43 msl
Perm. Pool$
Design Pool
49.5 msl
Design SA
12473 sf
Req. Volume
6601!
cf
Prov. Volume
.....:1 >
cf
ORIFICE CALCULATION
Avg. Head =
Flow Q2, cfs
Flow 05, cfs
No. of Orifices
Diameter, inches
Drawdown =
0.72 ft
0.038 cfs
0.015 cfs
weir HxW
days
SA/DA Ratio 4.97%
Req. SA 5823 sf
Prov. SA681< sf
* place a "1" in the box if Rational is used
Z*P : s 1
Perm. Pool Volume= 32153
Req. Forebay Volume= 6430.6
Provided Volume= 6335.00
Percent=.1 °a
SA @ _
Elevation=
Q2 Area =
Q5 Area =
Orifice Area
Q=
in
COMMENTS
Surface Area , Volume and Orifice are within Design GuidelineE
1.34 sq. in.
0.54 sq. in.
1.23 sq. in.
0.035 cfs
x FTTU
in
TRIPP ENGINEERING, P.C.
41 419 ChCstnut StIVUt
Viilmington, North Carolina 2W]
Phone: (910) 763-7'100 • 1"AX: (910) 763-5631
November 12, 2002 I
NCDENR
Division Water Quality
127 Cardinal Drive
Wilmington, NC 28405-3845
Attn: Ms. Linda Lewis
Re: Dollar General - Hampstead
Pender County, NC
TE 02067
Dear Linda:
NOV 13 Z00Z
Enclosed please find two (2) sets of plans, one (1) signed original and one (1)
copy of the application form with narrative, one (1) wet detention basin supplement, two
(2) sets of calculations and one check for the application fee.
Please review for approval and contact us with any questions or comments.
Thank you.
Sincerely,
Tripp Engineering, P.C.
2)qy,4/ Bapaw
David Brown
DBB:dcb
Enc.
November 12, 2002
Stormwater Narrative
Dollar General - Hampstead
Pender County, NC
TE 02067
Dollar General Hampstead is an existing vacant site of 2.69 acres. A proposed
development of 12,985 sf of commercial building with 51,832 sf of asphalt parking and
1,691 sf of concrete sidewalk will be treated by wet detention. The pond is sized to treat
the State's i" requirement for the proposed development and a future 15,000 sf.
Outflow from the proposed pond will discharge to Harrison Creek, Classification C-SW.
%1W
1111212002
CDC
Total Drainage Area
s . ft.
acres
117,177
2.69
Im envious Area
Land Use
s . ft.
acres
buildings
12,985
0.30
arkin las halt
51,832
1.19
sidewalks
1,691
0.04
Future
15.000
0.34
Total
81,508
1 1.87
Stormwater Calculations:
Time of Concentration
Hydraulic Length (L) = 600 ft.
change in Height (H) = 2 ft,
Tc = (C lH)'S°' 1 128
9.68 min.
Flow for 2 year, 6 hour Storm (02):
QPNE _ (CPRE) x (110) x (Area)
2,86 cfs
QPoST _ (CPoST) x 010) x (Area)
8,46 cfs
,]oil story o Ga acl Tor [ year Jlorm,
CN = (98)(% imp.) + (60)(1-% imp.)
87
P = 3.30 in. for2yr, 6 hr storm
S= 10001CN-10
1.49
Depth (D)= (P-(0.2)(S)121 (P+(0.8)(S)]
2.00 in.
Time to Peak Ftow:
TP = ((43.5)(D)(Area)] 1 02,Pov
27.71 min,
Detention Pond Design:
Pond Size:
Elevation
ft.
Surface Area
s , ft.
Normal Pool
48.00
10,608
Flood Pool
49.50
12,473
Top of Bank
50.00
13.123
Bottom of Pool
43.00
2.253
Dollar General
Hampstead
Stormwater Calculations
% impervious = 0.696
= 69.6%
say 70.0%
CPRr: = 0,25
CPosT = (% imp.)(.95)+(1-% imp.)(.25)
0,74
12 = 4,25 inlhr
I,o = 4.92 in/hr
Flow for 10 year, 6 hour Storm (Q,o):
QPRE _ (CPRF) x (125) x (Area)
3,31 cfs
QPosT = (CPosT) x (125) x (Area)
9.79 cfs
Soil Storage Capacity for 10 year Storm:
CN = (98)(% imp.) + (60)(1-% imp.)
= 87:
P = 4.82 in. for 10 yr, 6 hr storm
S = 10001CN - 10
1.49
Depth (D)= [P-(0.2)(S)]2 1 [P+(0.8)(S)]
3.40 in.
Time to Peak Flow:
TP = [(43.5)(D)(Area)1 1 Q,e,POST
40.60 min.
state SurtaCe Area tie ulrement at normalpool:
Pond side slopes = 3 :1
Depth below N.P. = 6 ft.
(Chart for 90% TSS Removal for Wet Detention
Pond without Vegetative Filter
Required SA = (SA1DA) x (Total Drainage Area)
4,570 s . ft.
State Volume Required for Storage of first 1" of runoff:
Provided Story a Volume: Rv = ,05+ ,009(% imp)
Vol. _ ((Normal pool SA + Flood Pool SA) 121 = 0.676038
x (F.P, elev. - N.P. elev.) V= (Design rainfall)(Rv)(Drainage Area)
17,311 cu. ft. 11Lt(VI!!f!!1 — 6,601 cu. ft.
'FFS$/p• 9
RECEIVED 17374
NOV 13 2002 %OREG
DWQ
PROJ # SLvB
�l• �Z•oz
02067pond 1 of 3
02067
11/12/2002 Dollar General 02067
CDC Hampstead
Stormwater Calculations
Pond Volume
Bottom SA = 2,253 sq. ft.
Normal Pool SA= 10,608 sq. ft.
Vol. = ](N.P. SA + Bottom SA)1 21 x (N.P. el. - Bottom al.)
= 32,153 cu. ft.
Foreba :
Required Volume
Vol. = 20% of storage volume
— 6,431 cu. ft,
Outlet Structure Desi n•
Flow for 2-day drawdown.-
for 1st V of stormwater,
Q = Required Vol. 1 172,800 sec. (2-days)
= 0.038 cfs
Required Area of Pipe for 2-day drawdown;
A= Q/ [Cd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft.ls'
h = (F.P. eiev.- N.P. elev.)12
0.75 ft.
A = 0.0092 s5j. ft,
Diameter of Pipe for 2-day drawdown:
DIA. = SQRT[(A x 4) / pi]
= 0.1080 ft.
1.30 in.
'Use: 1,25 in diameter pipe
Outlet Structure Check;
Using a 4' x 4' Basin,
Perimeter L) = 16 ft.
Q = CiA
C = (% imp.)(,95) + (1-% imp.)(.25)
0.74
1 = 4.92 in. for a 25 yr. Storm
A = 2.69 Acres
9.79 cfs
Q= CwxLxHi5
H = [Q ! (Cw x L)]2r3
Cw = 3
= 0.35 ft.
Peak elevation = flood pool elevation + H
49.85 ft.
Provided Volume
Bottom SA = 1,156 sq. ft.
Normal Pool SA = 3,067 sq. ft.
Vol. _ [(N.P. SA + Bottom SA) / 21 x (N.P. at. - Bottc
6,335 cu, ft,
Flow for 5-day drawdown:
for 1st 1" of Stormwater,
Q = Required Vol. / 432,000 see. (5-days)
= 0.015 cfs
Required Area of Pipe for 5-day drawdown
A= 01[CdxSQRT(2xgxh)]
Cd = 0.6
g = 32.2 ft.lsz
h = (F.P: elev. - N.P. elev.) 12
0.75 ft.
A= 0,0037 sq. ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SORT[(A x 4)1 pi]
0.0683 ft.
= 0.82 in.
02067pond 2 of 3