SW8010921_COMPLIANCE_20011207 (2)

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT
/&VA I
NO.
SW 20
DOC TYPE
❑CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
;2a2M�0
YYYYMMDD

DETENTION POND ANALYSIS
FILE NAME: S:IWQSIPOND1010921.WK1
PROJECT NAME: Crafter's Pride
REVIEWER:
DATE: 07-Dec-2001
Receiving Stream: Godfrey Creek Class: C SW Chlorides: nla
Drainage Basin: Cape Fear Index No.
Site Area 5.65 acres
Drainage Area "' 246114 OO]square feet Area in Acres 5.65
IMPERVIOUS AREAS
Rational C
Buildings 22500.00 square feet
Parking 31234.00 square feet
Sidewalks 690.00 square feet
Future 110000.00 square feet
square feet
_ square feet
TOTAL 164424`OO square feet Rational Cc= 0.07
SURFACE AREA CALCULATION
% IMPERVIOUS
66.81%
SAIDA Ratio
2.74%
Des. Depth
7
Req. SA
6745 sf
TSS:
90
Prov. SA
:<15.1'72 sf
VOLUME CALCULATION * place a "1" in the box if Rational is used
Zola _:' 1
Perm. Pool Volume= 59956
Req. Forebay Volume= 11991.2
Provided Volume= 11520.00
Percent= 192%
SA @ _
Elevation=
ORIFICE CALCULATION
COMMENTS
Surface Area , Volume and Orifice are within Design Guidelines.ok

•i
�- ' srlsral
CDC
Crafters Pride
Stormwater Calculations
01091
Total Drainage Area
ft.
acres
246.114
5.65
Impervious Area
Land Use
N.ft.
acres
buildings
22,500
0.52
pwkinglasphaft
31,234
0.72
sidewalk
690
0.02
Future
110,000
2,53
Total
164.424
3.77
Stormwater Calculations
Time of Concentration:
Hydraulic Length (L) = 1.300 ft.
change in Height (H) = 4.5 ft.
Tc = (L'!H). 1 128
17.29 min.
Flow for 10 year, 6 hour Storm (Qta)
QPRE _ (CPRE) x (ito) x (Area)
= 8,90 cfs
OPoS _ (CPos-r) x (Ito) x (Area)
= 25.63 cfs
sou store a Gapacjty tor 1U year storm:
CN = (98)(% imp.) + (45)(1-% imp.)
81
P = 4.82 in. forlOyr, 6 hr storm
S = 10001CN - 10
2.35
Depth (D)= (P-(0.2)(S)j2 r [P+(0.8)(S)1
2.83 in.
Time to Peak Flow:
TQ = [(43.5)(D)(Area)] / 02,POST
27.11 min.
Detention Pond Design:
Pond Size:
Elevation
ft.
Surface Area
.ft.
Normal Pool
39.00
15,172
Flood Pool
40.50
17.438
Top of Bank
42.00
19.831
Bottom of Pool
32.00
6.630
Provided Storage Volume:
Vol. _ [(Normal pool SA + Flood Pool SA) 121
x (F.P, elev. - N,P, elev.)
24,458 cu. ft.
% impervious = 0.668
= 66.8%
say 67.0%
CPRE = 0.25
CPosT = (% imp.)(.95)+(1-% imp.)(.25)
0.72
Ito = 6,30 in/hr
125 = 7.13 in/hr
Flow for 25 year, 6 hour Storm (025)
QPRE _ (CPRE) x (125) x (Area)
= 10.07 cis
QPosT = (CPS) x (125) x (Area)
= 29.00 cfs
Soil Storage CaEgedy for 25 year Storm:
CN = (98)(% imp.) + (45)(1-% imp.)
81
P = 5.71 in. for 25 yr, 6 hr storm
S. = 10001CN - 10
2.35
Depth (D)= [P-(0.2)(S)]2! [P+(0.8)(S)]
3.62 in.
Time to Peak Flow:
TP = ((43.5)(D)(Area)] ! oto,Posr
30.68 min.
5tate Surface Area Requirement at normalpool:
Pond side slopes = 3 :1
Depth below N.P. = 7 ft.
SAIDA = 0,0275
(Chart for 90% TSS Removal for Wet Detention
Pond without Vegetative Filter
Required SA = (SAIDA) x (Total Drainage Area)
6,768 s ,ft.
State Volume Required for Storage of first 1" of runoff:
Vol. = [(1/12) x (DA) x (% imp.)] +
[(1112) x (DA) x (1-% imp.) x C]
C = 0.2
15.064 cu.ft.
N
01091POND 1 of 2

9/19101
Crafters Pride
01091
CDC Stormwater Calculations
Pond Volume:
Bottom SA = 6,630 sq. ft.
Normal Pool SA = 15,172 s . ft.
Vol. = [(N.P. SA + Bottom SA) 121 x (N.P, el. - Bottom el.)
59,956 cu.ft.
Forebay:
Required Volume
Vol. = 20% of total permenant storage volume
11,991 cu.ft.
Outlet Structure Design;
Flow for 2-day drawdown:
for 1st 1" of sormwater,
Q = Required Vol./ 172,800 sec. (2-days)
= 0.087 cfs
Required Area of Pipe for 2-day drawdown:
A= 0/[CdxSQRT(2xgxh)]
Cd = 0.6
g = 32.2 ft.ls2
h = (F.P. elev.- N.P. elov.)12
0.75 ft.
A = 0.0209 sq. ft.
Diameter of Pioe for 2-dav drawdown
DIA. = SQRT](A x 4) / pi]
= 0.1631 ft,
1.96 in.
'Use: 1.75 in diameter pip2
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter L = 16 ft.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
= 0.72
1 = 7.13 in. for a 25 yr. Storm
A = 5.65 Acres
= 29.00 cfs
Q= CwxLxH''s
H = [Q 1 (Cw x L)]Tr'
Cw = 3
0.71 ft.
Peak elevation = Flood pool elevation + H
= 41,21 ft.
Provided Volume
Bottom SA =
2,160 sq.fL
Normal Pool SA =
5,520 sq. ft.
Vol, =
[(N.P, SA + Bottom SA) / 21 x (N.P. el. - Bottom el.)
11,520 cu.ft.
depth =
3 ft.
Flow for 5-day drawdown:
for 1st 1' of stormwater,
0 = Required Vol. ! 432,000 sec. (5-days)
0.035 cfs
Required Area of Pipe for 5-day drawdown
A= 01[CdxSQRT(2xgxh)]
Cd = 0.6
g = 32.2 ft.lsz
h = (F.P. elov. - N.P. eiev.)1 2
0.75 ft.
A = 0.0084 s . ft.
Diameter of Pipe for 5-day drawdown:
DIA. = SQRT[(A x 4) / pi]
0.1032 ft.
- 1.24 in.
01091 POND
2of2

September 14, 2001
Stormwater Narrative
Crafter's Pride
Pender County, NC
TE 01091
The total drainage area of this project is 5.65 acres. A proposed building is being
constructed with 22,500 sf. An asphalt access and parking area will total 31,234 sf. A
future impervious area of 110,000 sf totals 164,424 sf of impervious area (690 sf of
sidewalk) which brings the total built upon area to 66, 8% impervious.
Stormwater runoff will be handled by a wet detention pond designed to exceed the state's
requirement of the first one inch of runoff. This pond will drain to the Godfrey Creek
with classification of C-SW. A vegetated filter is not required due to the 90% TSS
removal used in the wet detention design.