Brightwater Science and Technology Campus Phase 2A - Wet Basin Supplemental Form

Permit No.______________________
(to be provided by DWQ)
I. PROJECT INFORMATION
Project name
Contact person
Phone number
Date
Drainage area number
II. DESIGN INFORMATION
Site Characteristics
Drainage area 1,668,348 ft2
Impervious area, post-development 943,074 ft2
% impervious 56.53 %
Design rainfall depth 1.0 in
Storage Volume: Non-SA Waters
Minimum volume required 77,682 ft3
OK, volume provided is equal to or in excess of volume required.
Storage Volume: SA Waters
1.5" runoff volume ft3
Pre-development 1-yr, 24-hr runoff ft3
Post-development 1-yr, 24-hr runoff ft3
Minimum volume required ft3
Peak Flow Calculations
Is the pre/post control of the 1yr 24hr storm peak flow required?Y (Y or N)
1-yr, 24-hr rainfall depth 3.0 in
Rational C, pre-development 62.00 (unitless)
Rational C, post-development 77.00 (unitless)
Rainfall intensity: 1-yr, 24-hr storm 3.02 in/hr OK
Pre-development 1-yr, 24-hr peak flow 8.01 ft3/sec
Post-development 1-yr, 24-hr peak flow 7.00 ft3/sec
Pre/Post 1-yr, 24-hr peak flow control -1.01 ft3/sec
Elevations
Temporary pool elevation 297.50 fmsl
Permanent pool elevation 169.50 fmsl
SHWT elevation (approx. at the perm. pool elevation)fmsl
Top of 10ft vegetated shelf elevation 170.00 fmsl
Bottom of 10ft vegetated shelf elevation 169.00 fmsl
Sediment cleanout, top elevation (bottom of pond)166.00 fmsl
Sediment cleanout, bottom elevation 165.00 fmsl
Sediment storage provided 1.00 ft
Is there additional volume stored above the state-required temp. pool?Y (Y or N)
Elevation of the top of the additional volume 297.5 fmsl OK
919.535.5139
8/14/2018
This form must be filled out, printed and submitted.
WET DETENTION BASIN SUPPLEMENT
Volume provided
ft3
ft3
Brightwater Drive, Phase 2A
Volume provided 112,123
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
Ken Jesneck, PE
401 CERTIFICATION APPLICATION FORM
The Required Items Checklist (Part III) must be printed, filled out and submitted along with all of the required information.
5
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 DWQ)
II. DESIGN INFORMATION
Surface Areas
Area, temporary pool 876 ft2
Area REQUIRED, permanent pool 30,577 ft2
SA/DA ratio 1.83 (unitless)
Area PROVIDED, permanent pool, Aperm_pool 31,098 ft2 OK
Area, bottom of 10ft vegetated shelf, Abot_shelf 28,990 ft2
Area, sediment cleanout, top elevation (bottom of pond), Abot_pond 23,646 ft2
Volumes
Volume, temporary pool 112,123 ft3 OK
Volume, permanent pool, Vperm_pool 105,116 ft3
Volume, forebay (sum of forebays if more than one forebay)18,979 ft3
Forebay % of permanent pool volume 18.1%%OK
SA/DA Table Data
Design TSS removal 85 %
Coastal SA/DA Table Used?N (Y or N)
Mountain/Piedmont SA/DA Table Used?Y (Y or N)
SA/DA ratio 1.83 (unitless)
Average depth (used in SA/DA table):
Calculation option 1 used? (See Figure 10-2b)N (Y or N)
Volume, permanent pool, Vperm_pool 105,116 ft3
Area provided, permanent pool, Aperm_pool 31,098 ft2
Average depth calculated 3.38 ft OK
Average depth used in SA/DA, dav, (Round to nearest 0.5ft)3.5 ft OK
Calculation option 2 used? (See Figure 10-2b)Y (Y or N)
Area provided, permanent pool, Aperm_pool 31,098 ft2
Area, bottom of 10ft vegetated shelf, Abot_shelf 28,990 ft2
Area, sediment cleanout, top elevation (bottom of pond), Abot_pond 23,646 ft2
"Depth" (distance b/w bottom of 10ft shelf and top of sediment)3.00 ft
Average depth calculated 3.66 ft OK
Average depth used in SA/DA, dav, (Round to down to nearest 0.5ft)3.5 ft OK
Drawdown Calculations
Drawdown through orifice?Y (Y or N)
Diameter of orifice (if circular)3.50 in
Area of orifice (if-non-circular)in2
Coefficient of discharge (CD)0.60 (unitless)
Driving head (Ho)0.63 ft
Drawdown through weir?N (Y or N)
Weir type (unitless)
Coefficient of discharge (Cw)(unitless)
Length of weir (L)ft
Driving head (H)ft
Pre-development 1-yr, 24-hr peak flow ?ft3/sec
Post-development 1-yr, 24-hr peak flow ?ft3/sec
Storage volume discharge rate (through discharge orifice or weir)0.26 ft3/sec
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 ft OK
Length of flowpath to width ratio ?:1 OK
Length to width ratio ?:1 OK
Trash rack for overflow & orifice?Y (Y or N)OK
Freeboard provided ?ft OK
Vegetated filter provided?N (Y or N)Insufficient. Vegetated filter required.
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:4" drain
Storage volume drawdown time 3.46 days
Form SW401-Wet Detention Basin-Rev.9-4/18/12 Parts I. & II. Design Summary, Page 2 of 2