SW8050721_COMPLIANCE_20050726

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
❑CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYMMDD

DETENTION POND ANALYSIS FILE NAME: G:\DATA\WPDATA\WQS\POND1050721.WK1
PROJECT#: SW8 050721 REVIEWER: P.Bartlett
PROJECT NAME: Mount Olive Baptist Church
DATE:
26-Jul-05
Receiving Stream:
Beaverdam Swamp
Class:
C; Sw
Drainage Basin:
Lumber River
Index No.
15-25-1-12-3
Site Area
22.72 acres
Drainage Area
. 221j7,2 square feet
Area =
5.09 acres
IMPERVIOUS AREAS
Rational C
blds
21590.00
square feet
0.95
prkg
70825.00
square feet
0.95
sidewalks
1110.00
square feet
0.95
square feet
square feet
71
square feet
TOTAL
square feet
Rational Cc= 0.52
SURFACE AREA CALCULATION
% IMPERVIOUS
42.18%
SA/DA Ratio
2.23%
Des. Depth
6
Req. SA
4946 sf
TSS:
90
Prov. SA
2$34 sf
VOLUME CALCULATION
place a "l " in the box if Rational is used
Rational ?*
1
FOREBAY
Des. Storm
06. inches
Perm. Pool Volume=
87957
Rv=
0.43
Req. Forebay Volume=
17591.4
Bottom
34.5 msl
Provided Volume=
17690.00
Perm. Pool
4.0,5ti msl
Percent=
Design Pool
41.5 msl
Design SA
23496 sf
Req. Volume
cf
SA @
8485
20834 23496.00
Prov. Volume
cf
Elevation=
34.5
40.5 41.50
ORIFICE CALCULATION
Avg. Head =
0.47
ft
Q2 Area =
2.41
sq. in.
Flow Q2, cfs
0.055
cfs
Q5 Area =
0.96
sq. in.
Flow Q5, cfs
0.022
cfs
Orifice Area
1.77
sq. in.
No. of Orifices
0.040
cfs;
Diameter, inches
weir H x W
in
X
in
Drawdown =7
days
COMMENTS
Surface Area , Volume and Orifice are within Design Guideline

7/12/2005
JWH
Mount Olive Baptist Church
Pond Calculations
05106
Total Draina a Area
s . ft, acres
221,700 5.09
Im ervious Area
Land Use
s . ft.
acres
buildings
21,590
0.50
arkin Ias halt
70,825
1.63
sidewalks
1,110
0,03
Total
93,525
2.15
Stormwater Calculations:
Time of Concentration:
Hydraulic Length (L) = 1,000 ft.
change in Height (H) = 6 ft,
Tc = (L,1H) "' 1 128
11.43 min.
Flow for 2 year, 6 hour Storm (Q2):
QpRE = (CpRE) x (110) x (Area)
- 5.41 cfs
QPosr = (CposT) x (lio) x (Area)
= 11.90 cfs
Sou atora a UaeaCR Tor L Xear atorm:
CN = (98)(% imp.) + (60)(1-% imp.)
= 77
P = 3.30 in. for2yr, 6 hr storm
S = 10001CN - 10
- 2.99
Depth A= [P-(0.2)(S)]21 (P+(0.8)(S)]
1.28 in.
Time to Peak Ftow:
Tp = ((43.5)(D)(Area)j / Q2,P05T
23.89 min.
Detention Pond Design:
Pond Size:
Elevation
(ft.)
Surface Area
(sq. ft.)
Normal Pool
40.50
20,834
Flood Pool
41.50
23.496
Tc of Bank
43,00
26.788
Bottom of Pool
34.50
8,485
Provided Storage Volume:
Vol, _ [(Normal pool SA + Fiocd Pool SA) 121
FP 1 NP I
05030ponci
% impervious = 0,422
= 42.2%
say 43.0%
CPRE = 0,25
CposT = (°,6 imp.)(.95)+(1-% imp.)(,25)
= 0.55
12 = 4.25 in/hr
Iia = 4.92 in/hr
Flow for 10 year, 6 hour Storm (010):
OPRE _ (CPRL) x (125) x (Area)
6.26 cfs
QPosT = (CPCST) x (125) x (Area)
= 13.77 cfs
Sou atom e L a act for to ear Storm:
CN = (98)(% imp.) + (60)(1-% imp.)
77
P = 4.82 in. for 10 yr, 6 hr storm
S= 10001CN-10
2.99
Depth (D)= ]P-(02)(S)]21 [P+(0.8)(S)1
= 2.47 in.
Time to Peak Flow:
Tp = [(43,5)(0)(Area)] 1 oro,posT
39.76 min.
5tate Surface Area Requirement at normalpool:
Pond side slopes = 3 :1
Depth below N.P. = 6 ft.
SA/DA = 0.0228
(Chart for 90% TSS Removal for Wet Detention
Pond without Vegetative Riter)
Required SA = (SAlDA) x (Total Drainage Area)
- 5.055 s . ft.
State Volume Required for Storage of first 1" of runoff:
RV = .05+ .009(% imp)
x ( , e ev. - . e ev.} = 0,429668
= 22,165 cu. ft. \\\\\������ V= (Design rai nfail) (Rv) (Drainage Area)
%% t,AR 0� '�� = 7,938 cu. ft.
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o rhop
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y:
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7l1212005
Mount Olive Baptist Church
05106
JWH Pond Calculations
Pond Volume:
Bottom SA = 8,485 sq. ft.
Normal Pool SA = 20,834 sq, ft.
Vol. _ '[(N.P. SA + Bottom SA) 12] x (N.P, el. - Bottom el.)
87,957 cu. ft.
Forebay:
Required Volume
Vol. = 20% of storage volume
17,591 cu, ft.
Outlet Structure Design:
Now for 2-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. 1 172,800 sec. (2-days)
0.046 cfs
Reg uired Area of Pipe for 2-day drawdown:
A= Q I [Cd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft.ls�
h = (F.P. elev.- N.P. elev.) 12
0.5 ft.
A = 0.0135 sq. ft.
Diameter of PiDe for 2-dav drawdown
DIA. = SQRT[(A x 4)1 pi]
= 0,1311 ft.
= 1.57 in.
'Use: 1.5 in diameter pipe
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter L = 16 ft.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
= 0.55
1 = 4.92 in. for a 25 yr. Storm
A = 5.09 Acres
13.77 cfs
Q= CWxLXH'
H = (Q / (Cw x I-)]"
Cw = 3
0.44 ft.
Peak elevation = flood pool elevation + H
41.94 ft.
Provided Volume
Bottom SA = 4.586 sq, ft,
Normal Pool SA = 7,207 sq, ft.
Vol. _ ((N.P. SA+ Bottom SA)12] x (N.P. el. - Bottom el.)
17.690 cu. ft.
Flow for 5-day drawdown:
for 1st i' of stormwater,
Q = Required Vol. 1432,000 sec, (5-days)
= 0.018 cfs
Required Area of Pipe for 5-day drawdown'
A= Q I [Cd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft.fs'
h = (F.P. elev, - N.P. elev.)12
= 0.5 ft.
A = 0.0054 sq, ft.
Diameter of Pipe for 5-day drawdown:
01A. = SQRT((A x 4) 1 pi]
- 0.0829 ft.
= 0.99 in.
05030pond
2of2