SW6130901_Supplement_20130903

Permit
(to be provided by DWQ)
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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/) must be printed, filled out and submitted along with all of the required information.
I. PIROJECT.INFORMATION
Project name Stone Gables Apartments Stormwater BMP
Contact person Samuel J. Powers, PE
Phone number 910.671.9530
Date 29-Aug-13
Drainage area number 1
II:DESIGN JNFORMATION
Site Characteristics
Drainage area
1,883,423'; ft2
Impervious area, post -development
1,610,837' ft2
%impervious `
85.53 %
Design rainfall depth
1.0 in
Storage Volume: Non -SA Waters
Minimum volume required
Volume provided
Storage Volume: SA Waters
1.5" runoff volume
Pre -development 1-yr, 24-hr runoff
Post -development 1-yr, 24-hr runoff
Minimum volume required
Volume provided
Peak Flow Calculations
Is the pre/post control of the lyr 24hr storm peak flow required?
1-yr, 24-hr rainfall depth
Rational C, pre -development
Rational C, post -development
Rainfall intensity: 1-yr, 24-hr storm
Pre -development 1-yr, 24-hr peak flow
Post -development 1-yr, 24-hr peak flow
Pre/Post 1-yr, 24-hr peak flow control
Elevations
Temporary pool elevation
Permanent pool elevation
SHWT elevation (approx. at the perm. pool elevation)
Top of 1 Oft vegetated shelf elevation
Bottom of 10ft vegetated shelf elevation
Sediment cleanout, top elevation (bottom of pond)
Sediment cleanout, bottom elevation
Sediment storage provided
Is there additional volume stored above the state -required temp. pool?
Elevation of the top of the additional volume
128,660,' ft3
222,4031ft3
OK, volume provided is equal to or in excess of volume required.
u�l
N ;(YorN)
3.0 in
0.35(unitless)
0.84,' (unitless)
0.13i in/hr OK
1.92 ft3/sec
4.61 ft3/sec
2.69 ft3/sec
252.00; fmsl
250.00! fmsl
249.50i fmsl
250.50 fmsl
249.50 fmsl
241.00` fmsl
240.00 fmsl
1.00 ft
Y (Y or N)
25ff. fmsl OK
Form SW401-Wet Detention Basin-Rev.9-4/18/12 Parts I. & II. Design Summary, Page 1 of 2

Permit No.
(to be provided by D4Q) a
11. -DESIGN INFORMATION
Surface Areas
Area, temporary pool 118,650 ft2
Area REQUIRED, permanent pool 50,852 ft'
SAIDA ratio 2.70 (unitless)
Area PROVIDED, permanent pool, Aperm pooh
97,697 ft`
OK
Area, bottom of 1 Oft vegetated shelf, Abet shelf
87,0721 ft`
Area, sediment cleanout, top elevation (bottom of pond), AW wd
58,5741 ft
ml
Volumes
Volume, temporary pool
222,408 ft'
OK
Volume, permanent pool, Vpem PWI
710,525: ft3
Volume, forebay (sum of forebays if more than one forebay)
133,0701 ft3
Forebay % of permanent pool volume
18.7% %
OK
SAIDA Table Data
Design TSS removal
90 %
Coastal SAIDA Table Used?
N (Y or N)
Mountain/Piedmont SAIDA Table Used?
Y (Y or N)
SAIDA ratio
2.70 (unitless)
Average depth (used in SAIDA table):
Calculation option 1 used? (See Figure 10-2b)
N (Y or N)
Volume, permanent pool, Vpen-pool
710,525 ft'
Area provided, permanent pool, Apewpoa
97,697 ft`
Average depth calculated
7.00 ft
OK
Average depth used in SAIDA, da,, (Round to nearest 0.5ft)
7.011 ft
OK
Calculation option 2 used? (See Figure 10-2b)
Y j (Y or N)
Area provided, permanent pool, Apermyool
97,697 ft`
Area, bottom of 10ft vegetated shelf, Abor shelf
87,072 ft2
Area, sediment cleanout, top elevation (bottom of pond). Abot-pond
58,574 ft2
"Depth" (distance b/w bottom of 1Oft shelf and top of sediment)
8.50 ft
Average depth calculated
7.631 ft
OK
Average depth used in SAIDA, da , (Round to down to nearest 0.511)
7.5' ft
OK
Drawdown Calculations
Drawdown through orifice?
Y (Y or N)
Diameter of orifice (if circular)
4.00. in
D C 2 0 2.013
Area of orifice (if -non -circular)
< in2
I
Coefficient of discharge (CD)
0.K (unitless)
Driving head (Ho)
0.67ft
Drawdown through weir?
N (Y or N)
Weir type
(unitless)
Coefficient of discharge (CW)
(unitless)
Length of weir (L)
ft
Driving head (H)
It
Pre -development 1-yr, 24-hr peak flow
1.92, ft3/sec
Post -development 1-yr, 24-hr peak flow
4.611 ft3/sec
Storage volume discharge rate (through discharge orifice or weir)
0.69j;ft3/sec
Storage volume drawdown time
3.751 days
OK, draws down in 2-5 days.
Additional Information
Vegetated side slopes
31:1
OK
Vegetated shelf slope
10 i :1
OK
Vegetated shelf width
10.0' ft
OK
Length of flowpath to width ratio
4', :1
OK
Length to width ratio
3.5:1
OK
Trash rack for overflow & orifice?
Y (Y or N)
OK
Freeboard provided
1.6-ft
OK
Vegetated filter provided?
N (Y or N)
OK
Recorded drainage easement provided?
Y (Y or N)
OK
Capures all runoff at ultimate build -out?
Y (Y or N)
OK
Drain mechanism for maintenance or emergencies is:
Pump Out
Form SW401-Wet Detention Basin-Rev.9-4/18/12 Parts I. & II. Design Summary, Page 2 of 2

Permit
(to be provided by DWQ)
III;`; REQUIRED ITEMS CHECKLIST ,,. , � � �'
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Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been met, attach justification.
Pagel Plan
Initials Sheet No.
SIP C203 1. Plans (1" - 50' or larger) of the entire site showing:
- Design at ultimate build -out,
- Off -site drainage (if applicable),
- Delineated drainage basins (include Rational C coefficient per basin),
- Basin dimensions,
- Pretreatment system,
- High flow bypass system,
- Maintenance access,
- Proposed drainage easement and public right of way (ROW),
- Overflow device, and
- Boundaries of drainage easement.
C'111 2. Partial plan (1" = 30' or larger) and details for the wet detention basin showing:
- Outlet structure with trash rack or similar,
- Maintenance access,
- Permanent pool dimensions,
- Forebay and main pond with hardened emergency spillway,
- Basin cross-section,
- Vegetation specification for planting shelf, and
- Filter strip.
S_ C19 11 3. Section view of the wet detention basin (1" = 20' or larger) showing:
- Side slopes, 3:1 or lower,
- Pretreatment and treatment areas, and
- Inlet and outlet structures.
Sp
C 104
4. If the basin is used for sediment and erosion control during construction, clean out of the basin is specified
. 'UVV%T
on the plans prior to use as a wet detention basin.
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I�QF• D
5. A table of elevations, areas, incremental volumes & accumulated volumes for overall pond and for forebay,
to verify volume provided.
S�Q
C iO4-
6. A construction sequence that shows how the wet detention basin will be protected from sediment until the
Bova
entire drainage area is stabilized.
sN9
WS.R,LS,C
7. The supporting calculations.
S�Q
A
8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
W I A its A 9. A copy of the deed restrictions (if required).
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S�Q "._ 10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County
soil maps are not an acceptable source of soils information.
Form SW401-Wet Detention Basin-Rev.9-4/18/12 Part III. Required Items Checklist, Page 1 of 1