SW8060229_COMPLETE FILE - HISTORICAL_20060317

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
-7
WYYMMDD

DETENTION POND ANALYSIS FILE NAME: G:IDATA\WPDATA\WQS\POND1060229.WK1
PROJECT#: SW8 060229 REVIEWER: P.Bartlett
PROJECT NAME: Eastern Skateboard
DATE: 17-Mar-06 —
Receiving Stream: Smith Creek Class: C; Sw
Drainage Basin: Cape Fear Index No. 18-74-63
Site Area 1.42 acres
Drainage Area square feet Area = 1.42 acres
IMPERVIOUS AREAS
OS Bldgs
OS Prkg
OS Sidewalks
TOTAL
SURFACE AREA CALCULATION
Rational C
20000.00 square feet 0.95
15056,00 square feet 0.95
1110.00 square feet 0.95
square feet
square feet
square feet
6 :.0
s Q;� quare feet
C9, (Z--
� V�
Rational Cc= 0.64
% IMPERVIOUS
58.47%
SA/DA Ratio
5.15%
Des. Depth
4
Req. SA
3184 sf
TSS:
90
Prov. SA
sf
VOLUME CALCULATION # place a "'I" in the box if Rational is used
Rational ?*
FOREBAY
Des. Storm
inches
Perm. Pool Volume=
13344
Rv=
0.58
Req. Forebay Volume=
2668.8
Bottom
46 msl
Provided Volume=
2552.00
Perm. Pool
msl
Percent=
Design Pool
50,8 msl
Design SA
8316 sf
Req. Volume
SA @ = 1156
5516 6394.00
Prov. Volume
Elevation= 46
50 50,80
(vs 4754 proposed)
ORIFICE CALCULATION
Avg. Head =
0.38 ft
Q2 Area =
0.83
sq. in.
Flow Q2, cfs
0.017 cfs
Q5 Area =
0.33
sq. in.
Flow Q5, cfs
0,007 cfs
Orifice Area
0.44
sq. in.
No. of Orifices
Q=
0.009
cfs
Diameter, inches
:75weir H x W
in
x
1 7 in
Drawdown
days
COMMENTS
Surface Area , Volume and Orifice are within Design Guideline:

I !g
r
s wg C)G0

,
317/2006
CDC
Eastern Skateboard
Pond Calculations
05193
Total Drainage Area
s . ft.
acres
61,855
1.42
tm ervious Area
Land Use
s . ft.
acres
buildings
20,000
0.46
arkin !as halt
15,056
0.35
sidewalks
1,110
0.03
Total
36.166
0.83
Stormwater Calculations:
Time of Concentration
Hydraulic Length (L) = 300 ft.
change in Height (H) = 2 ft.
Tc = (L' /H) 4"' 1 128
4.34 min.
Flow for 2 year, 6 hour Storm (QA
()PRE _ (CPRF) x 010) x (Area)
- 2,09 cfs
QPosT = (CPosT) x (110) x (Area)
5.51 cfs
ooR ocora a e,apaciry ror c year aLorm:
CN = (98)(°% imp.) + (60)(1-°% imp.)
83
P = 3.30 in. for2yr, 6 hr storm
S = 1000ICN - 10
2.05
Depth(D)= [P-(0.2)(S)12/(P+(0.8)(S)1
= 1,69 in.
Time to Peak Flow:
TP = [(43.5)(D)(Area)] I Q2,PosT
= 18.96 min.
Detention Pond Design:
Pond Size:
Elevation
ft.)
Surface Area
(s . ft.)
Normal Pool
50.00
5,516
Flood Pool
50.30
6.394
Top of Bank
53.25
9,350
Bottom of Pool
46.00
1,156
Inc. Vol
(cuff.)
Accumulated Vol.
(cu. ft.)
Normal Pool
13,344
13,344 ✓
Flood Pool
4.764
18,108
Top of Bank
19,286
37,394
Bottom of Pool
0.00
0
impervious = 0.585
= 58.5°%
say 59.0
CPRE = 0.25
CPosT = (°% imp.)(.95)+(1-0% imp.)(.25)
= 0.66
12 = 5.88 in/hr
110 = 7.23 inlhr
Flow for 10 year, 6 hour Storm (Q,o):
QPRE _ (CPRE.) X (125) x (Area)
2.57 cfs
QPosT = (CPosT) x (125) x (Area)
6.78 cfs
om oteia a iapaciry ror fu ear z [wrm:
CN = (98)(°% imp.) + (60)(1-0% imp.)
= 83
P = 4.82 in. for 10 yr, 6 hr storm
S = 10001CN - 10
2.05
Depth (D)= [P-(0.2)(S)121(P+(0.8)(S)]
= 3.01 in.
Time to Peak Flow:
TP = [(43.5)(0)(Area)] / 010,Posr
27.45 min.
- . -j
State Surface Area Requirement at normalpool:
Pond side slopes = 3 :1
Depth below N.P. = 4 ft.
SAIDA = 0.0520
(Chart for 90°% TSS Removal for Wet Detention
Pond without Vegetative Fifter
Required SA = (SAIDA) x (Total Drainage Area)
3.216 s . ft.
State Volume Required for Storage of first 1" of runoff:
Rv = .05+ .009(°% imp)
= 0.576221
V= (Design rainfall)(Rv)(Drainage Area)
= 2,970 cu. ft.
�Q4R�04r. ovide
�IV
O f•0iESSI6% 9 =
4�
SEAL.
-a 27374
y A }aOf EG
r
Storage Volume: _
_ [(Normal pool SA + Flood Pool SA)1
x (F.P. elev. - N.P. elev.)
4.764 cu. ft.
MAR 0 9 Z006
05193pond
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JAY,,

317/2006 Eastern Skateboard
CDC Pond Calculadons
Pond Volume:
Bottom SA = 1.156 sq. ft.
Normal Pool SA = 5,516 s . ft.
Vol. _ [(N.P. SA + Bottom SA)12] x (N.P. el. - Bottom el.)
— 13,344 cu. ft.
Foreb
Required Volume
Vol. = 20% of storage volume
= 2,669 cu. ft.
Outlet Structure Design:
Flow for 2-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. 1172,800 sec. (2-days)
0.017 cfs
Required Area of Pipe for 2-day drawdown:
A= Q/ [Cd x SQRT(2 )(g x h)]
Cd = 0.6
9 = 32.2 ftJs2
h = (F.P. elev: N.P. elev.)-12
= 0.4 ft.
A = 0.0056 s . ft.
Diameter of Pipe for 2-day drawdown
DIA. = SQPT((A x 4) 1 pi]
0 L1848 ft.
1.02 in.
-Use:.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)
= 0.66
1 = 7.23 in. for a 25 yr. Storm
A = 1.42 Acres
6.78 cfs
Q= CwxLxH
H = [Q / (Cw x L)]y'
Cw = 3
= 0.27 ft.
Peak elevation = flood pool elevation + H
51.07 ft.
Provided Volume
Bottom SA = 301 sq. ft.
Normal Pool SA = 1,400 s , ft,
Vol. _ [(N.P. SA + Bottom SA) 12] x (N.P, el. - Bottom el.)
2,552 cu. ft. V
Flow for 5-day drawdown:
for 1 st 1" of stcrmwater,
Q = Required Vo1.1432,000 sec. (5-days)
0.007 cfs
Required Area of Pipe for 5-day drawdown:
A= Q 1 [Cd x SQRT(2 x g x h)]
Cd = 0.6
9 = 32.2 ftJs'
h = (F.P. elev. - N.P. elev.)12
0.4 ft.
A = 0.0023 s . ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SQRT](A x 4) 1 pi]
-- 0.0536 ft.
= 0.64 in.
05193
05193pond 2 of 2