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Home My WebLink About20170445 Ver 1_SW Wet Detention Basin Supplement_20170414Permit No (to be _vrovided by QWQ) _C, W A TFR�G ARA T� NCDENR fl STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM INET DETENTION BASIN SUPPLEMENT This form must be filled out, printed and submitted The Required Items Checklist (Part 111) must be printed, filled out and submitted along with all of the required information. I. PROJECT INFORMATION Project name Clearwater Creek Subdivision Contact person Adam Freeman Phone number 919.415.2731 Date 12/28/2016 Drainage area number A Ill. DESIGN INFORMATION Site Characteristics Drainage area 1,030,630 ff2 Impervious area, pest -development 306,662 ff % impervious 29.75 % 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 1yr 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 1Oft vegetated shelf elevation Bottom of 1 Oft 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 27,294 ft3 29,456 ft3 OK, volume provided is equal to or in excess of volume required. ft3 ft3 ft3 ft3 rare uy Y (Y or N) 2.9 in 0.20 (unifless) 0.40 (unitless) 0.12 in/hr OK 9.76 f3/sec 31.75 ft3/sec 21.99 f3/sec 288.00 fmsl 286.50 fmsl fmsl 287.00 fmsl 286.00 fmsl 282.00 fmsl 281.00 fmsl 1.00 ft Y (Y or N) 288.0 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 DWQ) 11. DESIGN INFORMATION Surface Areas Volume, temporary pool Area, temporary pool 21,213 ft2 Area REQUIRED, permanent pool 13,707 ft2 SAIDA ratio 1.33 (unitless) Area PROVIDED, permanent pool, Ape ,,,,_p�t 16,999 if OK Area, bottom of 1 Oft vegetated shelf, Ab,,t_shelf 11,943 ft Area, sediment cleanout, top elevation (bottom of pond), Ahot-pond 7,390 ft Volumes Volume, temporary pool 29,456 ft3 OK Volume, permanent pool, Vpe,m pw 59,440 ft3 Volume, forebay (sum of forebays if more than one forebay) 10,860 if Forebay % of permanent pool volume 18.3% % OK 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 1.33 (unitless) Average depth (used in SAIDA table): Calculation option 1 used? (See Figure 10-2b) N (Y or N) Volume, permanent pool, Vp,„_p, 59,440 ft3 Area provided, permanent pool, App,,, 16,999 ft2 Average depth calculated ft Need 3 it min. Average depth used in SAIDA, d.„ (Round to nearest 0.5ft) ft Calculation option 2 used? (See Figure 10-2b) Y (Y or N) Area provided, permanent pool, App,,,,_p,t 16,999 ft2 Area, bottom of 10ft vegetated shelf, kt_shelf 11,943 ft Area, sediment cleanout, top elevation (bottom of pond), Abot pond 7,390 ft2 "Depth" (distance b/w bottom of 10ft shelf and top of sediment) 4.00 ft Average depth calculated 3.00 ft OK Average depth used in SAIDA, da,,, (Round to down to nearest 0.5ft) 3.0 it OK Drawdown Calculations Drawdown through orifice? Y (Y or N) Diameter of orifice (if circular) 2.50 in Area of orifice (if -non -circular) int Coefficient of discharge (DD) 0.60 (unitless) Driving head (Ho) 1.39 It 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 9.76 ft /sec Post -development 1 -yr, 24 -hr peak flow 31.75 If/sec Storage volume discharge rate (through discharge orifice or weir) 0.11 if/see Storage volume drawdown time 2.83 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 ft OK Length of flowpath to width ratio 3 :1 OK Length to width ratio 2.0 :1 OK Trash rack for overflow & orifice? Y (Y or N) OK Freeboard provided 1.5 ft OK Vegetated filter provided? Y (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: None Form SW401-VVet Detention Basin-Rev.9-411&12 Parts I. & 11. Design Summary, Page 2 of 2 Permit No (to be . nroWded by DWQ) A' ...�.�Twl WDE14R 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 III) must be printed, filled out and submitted along with all of the required information. I. PROJECT INFORMATION Project name Clearwater Creek Subdivision Contact person Adam Freeman Phone number 919.415.2731 Date 12128/2016 Drainage area number B II. DESIGN INFORMATION Site Characteristics Drainage area 495,713 ft Impervious area, post -development 153,331 fe % impervious 30.93 % Design rainfall depth 1.0 in Storage Volume: Non -SA Waters Minimum volume required 13,565 ft3 Volume provided 13,908 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 Volume provided ft3 Peak Flow Calculations Is the pre/post control of the 1 y 24hr storm peak flow required? Y (Y or N) 1 -yr, 24 -hr rainfall depth 29 in Rational C, pre -development 0.20 (unitless) Rational C, post -development 0.40 (unitless) Rainfall intensity: 1 yr, 24 -hr storm 0.12 in/hr OK Pre -development 1 -yr, 24 -hr peak flow 16.36 ft3/sec Post -development 1 -yr, 24 -hr peak flow 12.16 ft/sec Pre/Post 1 -yr, 24 -hr peak flow control -4.20 f3/sec Elevations Temporary pool elevation 286.50 fmsl Permanent pool elevation 285.00 fmsl SHVVT elevation (approx_ at the perm. pool elevation) fmsl Top of 10ft vegetated shelf elevation 285.50 fmsl Bottom of 10ft vegetated shelf elevation 284.50 fmsl Sediment cleanout, top elevation (bottom of pond) 280.00 fmsl Sediment cleanout, bottom elevation 279.00 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 286.5 fmsl OK Form SW401-Wet Detention Basin-Rov.9-4/18/12 Parts I. & II. Design Summary, Page 1 of 2 Permit No II. DESIGN INFORMATION Surface Areas Area, temporary pool 10,660 fly Area REQUIRED, permanent pool 6,841 fe SAIDA ratio 1.38 (unitless) Area PROVIDED, permanent pool, Ap,,,p,, 9,916 ff OK Area, bottom of IOft vegetated shelf, AW shelf 8,576 ft2 Area, sediment cleanout, top elevation (bottom of pond), Atrot-Pr,d 758 ff Volumes Volume, temporary pool 13,908 ft3 OK Volume, permanent pool, Vp,,,n, p„, 17,133 ft3 Volume, forebay (sum of forebays if more than one forebay) 3,749 ft3 Forebay % of permanent pool volume 21.9% % OK 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 1.38 (unitless) Average depth (used in SAIDA table): Calculation option 1 used? (See Figure 10-2b) N (Y or N) Volume, permanent pool, Vpwm-mol 17,133 ft3 Area provided, permanent pool, Ap,,,,_,,,, 9,916 ff Average depth calculated ft Need 3 ft min. Average depth used in SAIDA, dam, (Round to nearest 0.5ft) ft Calculation option 2 used? (See Figure 10-2b) Y (Y or N) Area provided, permanent pool, Ap,,,,_p,,, 9,916 ftz Area, bottom of 10ft vegetated shelf, Ab t shelf 8,576 ff Area, sediment cleanout, top elevation (bottom of pond), Ahot_pond 758 ftz "Depth” (distance b/w bottom of 1 Oft shelf and top of sediment) 4.50 ft Average depth calculated 3.00 ft OK Average depth used in SAIDA, dv„ (Round to down to nearest 0.5ft) 3.0 ft OK Drawdown Calculations Drawdown through orifice? Y (Y or N) Diameter of orifice (if circular) 2.00 in Area of orifice (rf non -circular) int Coefficient of discharge (Co) 0.60 (unitless) Driving head (Ho) 1.41 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 16.36 ft3/sec Post -development 1 -yr, 24 -hr peak flow 12.16 fl?/sec Storage volume discharge rate (through discharge orifice or weir) 0.08 If/sec Storage volume drawdown time 2.18 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 ft OK Length of flowpath to width ratio 4 :1 OK Length to width ratio 2.8 :1 OK Trash rack for overflow & orifice? Y (Y or N) OK Freeboard provided 2.2 ft OK Vegetated filter provided? Y (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: None (to be provided by DWQ) Form SW401-Wet Detention Basin-Rev.9-4(18112 Parts 1. & 11, Design Summary, Page 2 of 2