SW3160904_Wet Detention Basin Supplement_20160908

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WET POND #1
Permit No.
-
go be pmvlrlew by DWO)
2pG WATE9O
NCDENR
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STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be filled out,printed and submitted.
The Required Items Checklist(Part I/1)must be printed filled out and submitted along with all of the required information.
I. PROJECT INFORMATION
Project name Cambridge village
Contact person Brian Rosenfeld
Phone number 980-272-3400
Date 9/8/2016
Drainage area number -FA-1
11. DESIGN INFORMATION
Site Characteristics
Drainage area 467,834 ft'
Impervious area,past-development 407,016 ft'
%impervious 87.00%
Design rainfall depth 1.0 in
Storage Volume: Non-SA Waters
Minimum volume required 32,476 ft
Volume provided 32,476 ft'
OK,volume provided is equal to or in excess of volume required.
Storage Volume: SAWaters
1.5'runoH volume ft'
Pre-development 1-yr,24-hr runoff to
Post-development 1-yr,24-hr runoff ft
Minimum volume required ft'
Volume provided it,
Peak Flow Calculations
Is the prelpost control of the 1 yr 24hr storm peak flow required? N (Y or N)
1-yr,24-hr rainfall depth 2.8 in
Rational C,pre-development 0.35(unidess)
Rational C,post-development 0.89(untless)
Rainfall intensity:l-yr,24-hr storm 0.12 in/hr OK
Pre-development 1-yr,24-hr peak flow 6.25 ft/sec:
Post-dmelopment 1-yr,24-hr peak flow 36.29 ft/sec
PreJPost 1-yr,24-hr peak flow control 30.04 ft"/sec
Elevations
Temporary pool elevation 755.88 hnsl
Permanent pool elevation 753.50 first
SHWT elevation(approx.at the perm.pool elevation) N/A first
Top of 10ft vegetated shelf elevation 754.00 first
Bottom of 10ft vegetated shelf elevation 753.00 first
Sediment deanout,top elevation(bottom of pond) 744.00 first
Sediment deanout,bottom elevation 743.00 fmsl
Sediment storage provided 1.00 ft
Is there additional volume stored above the state-mquired temp.pool? WA (Y or N)
Elevation of the top of the additional volume ftnsl
Form SvvQ1-Wet Detention Basin-Rsv."/18112 Parts I.a It.Desgn Summary.Page 1 of 2

Permit No.
(to be pmw,HM by DWQ)
11. DESIGN INFORMATION
Surface Areas
Area,temporary pod 16,228 ft'
Area REQUIRED,permanent pool 10,058 ft
SAIDA ratio 2.15(unitless)
Area PROVIDED,permanent pod,Ap,,,,,. 10,100 fe Of
Area,bottom of I Oft vegetated shelf,Ap ma 5,897 0'
Area,sediment deanout,top elevation(bottom of pond),Amy„a 2,303 fl'
Volumes
Volume,temporary pod 32,47511' OK
Volume,permanent pod,Vp,,,, 28,344 ft
Volume,foebay(sum of forebays if more than one forebay) 3,967 ft'
Forebay%of permanent pool volume 14.0%% Insufficient forebay volume.
SAIDA Table Data
Design TSS removal 85%
Coastal SAIDA Table Used? N (Y or N)
Mountain/Piedmont SAIDA Table Used? Y (Y or N)
SAIDA ratio 2.15(unilless)
Average depth(used in SAIDA table):
Calculation option 1 used?(See Figure 10.2b) N (Y or N)
Volume,permanent pod,Vp„, m 28,344 8'
Area provided,permanent pod,Aps,,,, 10,100 ft2
Average depth calculated ft Need 3 If min.
Average depth used in SAIDA,d,,,(Round to nearest 0.5ft) If
Calculafion option 2 used?(Sea Figure 10.2b) Y (Y or N)
Area provided,permanent pod,A,_,, 10,100ft
Area,bottom of 10ft vegetated shelf,Ap mg 5,897 ft
Area,sediment deanoul,top elevation(bottom of pond),App,-pp„a 2,303 12
'Depth'(distance law bottom of I Oft shelf and top of sediment) 9.00 It
Average depth calculated 6.45 ft OK
Average depth used in SAIDA,d„,(Round to down to nearest 0.510 6.5 ft OK
Drawdown Calculations
Drawdown through orifice? Y (Y or N)
Diameter of orifice(if circular) 2.00 in
Area of odfice(if-non-circular) in2
Coefficient of discharge(Co) 0.60(unitless)
Driving head(H,) 2.14 ft
Drawdown through weir? N (Y Or N)
Weir type (unitless)
Coefficient of discharge(C,) (unitless)
Length of weir(L) ft
Driving head(H) ft
Pre-development 1-yr,24-hr peak flow 6.25 ft'Isec
Post-development 1-yr,24-hr peak flow 36.29 ft'Isec
Storage volume discharge rate(through discharge orifice or weir) 0.15 ft Isec
Storage volume drawdovm time 2A5 days OK,draws down in 2-5 days.
Additional Information
Vegetated side slopes 3:1 OK
Vegetated shelf slope 10:1 OK
Vegetated shelf width 10.0 If OK
Length of flowpath to width ratio 3:1 OK
Length to width ratio 3.2:1 OK
Trash rack for overflow 8 orifice? Y (Y or N) OK
Freeboard provided 1.8 ft OK
Vegetated filter provided? Y (Y or N) OK
Recorded drainage easement provided? N (Y or N) Insufficient. Recorded drainage easement required.
Capures all runoff at ultimate build-out? Y (Y or N) OK
Drain mechanism for maintenance or emergencies is: Pump to drain
Farm SW401-Wet Detention Basin-Rev.& 18112 Parts I.a II.Design Summary,Page 2 of 2