SW8010918_COMPLIANCE_20011204

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
El CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
ire
DOC DATE
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DETENTION POND ANALYSIS FILE NAME- S:\WQS\POND\ 010918.WK1
PROJECT#: SW8 010918 REVIEWER- nml
PROJECT NAME:
Shallotte Microtel
DATE: 04-Dec-2001
Receiving Stream:
ut Shallotte River
Class.
C Sw HQW Chlorides: n/a
Drainage Basin:
Index No.
Site Area
1.90 acres
Drainage Area
square feet
Area in Acres
1.90
IMPERVIOUS AREAS
Rational C
Buildings
8156.00
square feet
Parking
33019.00
square feet
Sidewalks
1882.00
square feet
square feet
square feet
square feet
TOTAL L
square feet
Rational Cc= 0.10
SURFACE AREA CALCULATION
% IMPERVIOUS
52.02%
SA/DA Ratio
2.00%
Des. Depth
7
Req. SA
1656 sf
TSS:
90
Prov, SA
VOLUME CALCULATION * place a "'I" in the box if Rational is used I
Rational ?*
Des. Storm
inches
Rv=
0.52
Bottom
21 msI
Perm. Pool
]msI
Design Pool
30 msl
Design SA
6807 sf
Req. Volume
•cf
Prov. Volume
856': cf
ORIFICE CALCULATION
FOREBAY
Perm. Pool Volume=
Req. Forebay Volume=
Provided Volume=
Percent=
SA @
Elevation--
13984
2796.8
2817.00
..i�20.-.1�%�`
Avg. Head =
0.98 ft Q2 Area =
0.62 in 2
Flow Q2, cfs
0 ' '021 cfs Q5 Area =
0.25 in 2
Flow Q5, cfs
0.008 cfs Orifice Area
0.44 in'
No. of Orifices
0.015 cfs
Diameter, inches
or weir H x W in
x
Drawdown =
2-8':days
COMMENTS
Surface Area , Volume and Orifice are within Design Guidelines,ok

- �J119101 Shallotte Microtel
CDC Stormwater Calculations
01094
Total Drainage Area
s , ft. acres
82,764 1.90
Impervious Area
Land Use
sq.ft.
acres
buildings
8.156
0.19
parkingiasphalt
1,882
0,04
sidewalk
33,019
0.76
Total
43,057
0.99
Stormwater Calculations:
Time of Concentration
Hydraulic Length (L) - 1.300 ft.
change in Height (H) = 4.5 ft.
Tc = (Ls I H)-�'" 1 128
17.29 min.
Flow for 10 year, 6 hour Storm (Qio):
QPRE _ (CPRE) X (110) x (Area)
2,99 cfs
QPoS _ (CPon) x 010) x (Area)
7.42 cfs
Soil Storage Capacity for 10 year Storm:
CN = (98)(% imp.) + (45)(1-% imp.)
73
P - 4.82 in_ forl0yr, 6 hr storm
S = 10001CN - 10
3,70
Depth (D)= [P-(0.2)(S)]21 jP+(0.8)(3)]
- 2.14 in,
Time to Peak Flaw:
Tp = [(43.5)(D)(Area)] I O2,Posr
23.84 min.
Detention Pond Design:
Pond Size:
Elevation
ft.
Surface Area
(sq. ft.
Normal Pool
28.00
5,049
Flood Pool
30.00
6,807
Top of Bank
31.00
7,770
Bottom of Pool
21.00
36
% impervious = 0.520
= 52.0%
saX 52.0%
CPRE = 0.25
CposT = (% imp.)(.95)+(1-% imp.)(.25)
0.62
l�o = 6.30 inlhf
12s = 7.13 in/hr
Flow for 25 year, 6 hour Storm (Q25):
QPRE _ (CPRE) x (I25) x (Area)
3.39 cfs
Qpos _ (Cps) x (125) x (Area)
8.40 cfs
Soil Storage Cmacq for. 25 xear, Storm:
CN = (98)(% imp.) + (45)(1-% imp.)
73
P = 5.71 in. for 25 yr, 6 hr storm
S = 1000/CN - 10
3.70
Depth (D)= [P-(0.2)(S)121 [P+(0.8)(S)j
2.85 in.
Time to Peak Flow:
Tp = [(43.5)(D)(Area)1 I QjgPosT
28,04 min.
,ytate 7urwe Area Keguirement
at normal pooi:
Pond side slopes =
3 :1
Depth below N.P. =
7 ft.
SAMA =
0.0200
(Chart for 90% TSS Removal
for Wet Detention
Provided Storage Volume: Required SA = (SAIDA) x (Total Drainage Area)
Vol. _ [(Normal pool SA + Flood Pool SA) ! 2] = 1. 55 sq. ft.
x (F.P. elev. - N.P. elev.)
11.856 cu. ft. State Volume R uired for Storage of first 1' of runoff:
Vol. = j(1112) x (DA) x (% imp.)] +
J/7i [(1/12) x (DA) x (1-% imp.) x C]
`�`��.��.�� CARplii, C = 0.2
2Q5 SI 9 4,250 cu. ft.
17374 Q
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01094POND 1 of 2

9119/01 Shallotte Microtel
CDC Stormwater Calculations
Pond Volume:
Bottom SA = 36 sq. It,
Normal Pool SA = 5,049 sq, ft.
Vol. _ [(N.P. SA + Bottom SA) 1 2] x (N.P. el. - Bottom el.)
13,984 cu.ft.
Forebay:
Required Volume
Vol. 20% of total permenant storage volume
2,797 cu. ft.
Outlet Structure Design:
Flow for 2-day drawdown:
for ist 1' of stormwater,
Q = Required Vol. 1 172,800 sec. (2-days)
= 0.025 cfs
Required Area of Pipe for 2-day drawdown:
A= Q 1(Cd x SQRT(2 x g x h))
Cd = 0.6
g = 32.2 fl.ls2
In = (F.P. elev.- N.P. elev.) 12
A = 0,0051 SCI.ft,
Diameter of Pipe for 2-dav drawdown
DIA. = SQRT[(A x 4) 1 pi]
— 0.0806 fl.
0.97 in.
'Use: 0,75 in diameter pipe
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter L = 16 ft.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
a 0.62
1 = 7.13 in. for a 25 yr. Storm
A = 1.90 Acres
= 8.40 cfs
Q= Cwx Lx H1.5
H= [01(CwxQfm
Cw = 3
Peak elevation = flood pool elevation + H
= 30.31 ft,
Provided Volume
Bottom SA = 560 sq. ft.
Normal Pool SA = 1,318 sq. ft.
Vol. _ [(N.P. SA + Bottom SA) / 21 x (N.P. el. - Bottom el.)
2,817 cu.ft.
depth = 3 ft.
Flow for 5-day drawdown:
for 1st 1' of stormwater,
Q = Required Vol. 1432.000 sec. (5-days)
= 0.010 cis
Required Area of Pipe for 5-day drawdown:
A= Q I ICd x SQRT(2 x g x h)]
Cd = 0.6
g = 32.2 ft.1s2
h = (F.P. elev. - N.P. elev.)12
1 ft.
A= 0,0020 . ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SQRT[(A x 4)1 pij
0,0510 ft,
0.61 in.
r rr•M
01094PON D
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