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HomeMy WebLinkAboutWPO201600074 Calculations 2021-06-22 (2)Woodbrook Elementary School COUNTY OF ALBEMARLE, VIRGINIA WPO PLAN SUPPLEMENTAL DESIGN CALCULATIONS & NARRATIVE FOR POST DEVELOPED DRAINAGE AREA B NOVEMBER 21, 2016 REVISED: FEBRUARY 15, 2017 APRIL 6, 2017 MAY 39 2021 JUNE 219 2021 s TIMMONS GROUP YOUR VISION ACHIEVED THROUGH OURS. Prepared by: Clint Shifflett, PE Timmons Group 608 Preston Avenue, Suite 200 Charlottesville, VA 22903 434.962.4337 CLINT W. ;HIFFLETT LLiic. No. 54380 6/21 /2021 Table of Contents Section Title Project Narrative LD 229 — Storm Sewer Design Computations LD 204 — Storm Inlet Design Computations 4 LD 347 — Hydraulic Grade Line Computations Virginia Runoff Reduction Method Worksheet Summary 6 Pre -Developed HyrdoCAD Calculations 7 Post -Developed HydroCAD Calculations (Drainage Area B) Project Narrative: This project includes building additions to Woodbrook Elementary School, additional parking, a new bus and drop off loop, outdoor learning spaces and associated site work. The total limits of clearing and grading are 8.26 acres. This calculations booklet is meant to supplement the approved calculations, dated April 6, 2017. The post development calculations for Drainage Area B have been updated to reflect the revised SWM-B facility design from 170 LF of 72" CMP to 155 LF of 72" CMP. The proposed weir plate has been revised to still meet the 1-year and 10-year post -development flow requirements. Additional capacity beyond the 10-year storm has been reduced. Note, pre and post -developed drainage areas and land cover conditions are unchanged. Water Quality: The disturbed area of 8.26 acres was used for the water quality analysis. In the proposed condition there will be 3.20 acres of managed turf and 5.06 acres of impervious cover. Per the Virginia Runoff Reduction Spreadsheet, this will require that 4.45 lbs. of phosphorus be removed per year. This removal is being achieved with proposed Bayfilter filtration structures, downstream from each storage facility. Water Quantity: The site consists of two major drainage areas. Drainage area A drains to the south and outfalls to the storm sewer system in Idlewood Drive. An underground pipe storage system is being provided to reduce flow back to pre -developed rates for the 2 and 10 year storms. The 1-year storm is being detained and released in accordance with the energy balance equation. Drainage area B drains to the north to the storm sewer system in Brookmere Drive. From there it ultimately outfalls into an existing, offsite pond. An underground pipe storage system is being provided to reduce flow back to pre -developed rates for the 2 and 10 year storms. The 1-year storm is being detained and released in accordance with the energy balance equation. 4S -v 6P Post-Dev. - Area B SWM B Detained 7L v 9S Post-Dev. - Area B Post-Dev. - Area B Combined Un-detained Subcat Reach on Link Woodbrook-REVISED(ShorterPipeSWMB)-ISSPIPE-plotT*ype1124-hr 1YRRainfall=3.01" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD®10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Subcatchment 4S: Post-Dev. - Area B Detained Runoff = 3.91 cfs @ 11.96 hrs, Volume= 0.190 af, Depth> 2.22" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1YR Rainfall=3.01" Area (ac) CN Description 0.190 74 >75% Grass cover, Good, HSG C * 0.840 98 Impervious Area 1.030 94 Weighted Average 0.190 18.45% Pervious Area 0.840 81.55% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft(ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment 4S: Post-Dev. - Area B Detained Hydrogreph ® RunoH 4 Type II 24-hr 1YR Rainfall=3.01" 3.. Runoff Area=1.030 ac Runoff Volume=0.190 of Runoff Depth>2.22" 2- Tc=6.0 min LL CN=94 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotTl-ype 1124-hr 1YR Rainfall=3.01" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD@ 10 00-19 s/n 06538 ©2016 HydroCAD Software Solutions LLC Summary for Subcatchment 9S: Post-Dev. - Area B Un-detained Runoff = 1.42 cfs @ 12.06 hrs, Volume= 0.079 af, Depth> 0.97" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1YR Rainfall=3.01" Area (ac) CN Description 0.130 80 >75% Grass cover, Good, HSG D 0.350 98 Impervious Area 0.490 61 >75% Grass cover, Good HSG B 0.970 77 Weighted Average 0.620 63.92% Pervious Area 0.350 36.08% Impervious Area Tc Length Slope min) (feet) (f ift) 12.8 170 0.0250 Description 0.22 Sheet Flow, Grass: Short n= 0.150 P2= 3.65" Subcatchment 9S: Post-Dev. - Area B Un-detained ® Runolf Type II 24-hr 1YR Rainfall=3.01" Runoff Area=0.970 ac 1 Runoff Volume=0.079 of Runoff Depth>0.97" Flow Length=170' Slope=0.0250 T Tc=12.8 min CN=77 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hour) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotTrype 11 24-hr 1YR Rainfall=3.01 " Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD® 10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Pond 6P: SWM B Inflow Area = 1.030 ac, 81.55% Impervious, Inflow Depth > 2.22" for 1YR event Inflow = 3.91 cfs @ 11.96 hrs, Volume= 0.190 of Outflow = 0.77 cfs @ 12.15 hrs, Volume= 0.190 af, Atten= 80%, Lag= 11.4 min Primary = 0.77 cfs @ 12.15 hrs, Volume= 0.190 of Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 484.18' @ 12.15 hrs Surf.Area= 0.021 ac Storage= 0.065 of Plug -Flow detention time=26.7 min calculated for 0.190 of (100% of inflow) Center -of -Mass det. time= 26.6 min ( 778.3 - 751.7 ) Volume Invert Avail.Storage Storage Description #1 479.94' 0.101 of 72.0" Round Pipe Storage L= 155.0' S= 0.0070 T Device Routing Invert Outlet Devices #1 Primary 479.94' 15.0" Round Culvert L= 40.0' RCP, groove end projecting, Ke= 0.200 Inlet / Outlet Invert= 479.94' / 475.94' S= 0.1000 T Cc= 0.900 n= 0.013, Flow Area= 1.23 sf #2 Device 1 479.94' 3.8" Vert. Orifice/Grate C= 0.600 #3 Device 1 484.45' 24.0" W x 5.2" H Vert. Orifice/Grate C= 0.600 #4 Device 1 485.77' 3.0' long Sharp -Crested Rectangular Weir 2 End Contraction(s) ZmPrimary OutFlow Max=0.77 cfs @ 12.15 hrs HW=484.18' (Free Discharge) lvert (Passes 0.77 cfs of 14.03 cfs potential flow) 2=Orifice/Grate (Orifice Controls 0.77 cfs @ 9.72 fps) 3=Orifice/Grate ( Controls 0.00 cfs) =Sharp -Crested Rectangular Weir( Controls 0.00 cfs) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotTType 1124-hr 1YR Rainfall=3.01" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD® 10.00-19 s/n 06538 © 2016 HvdroCAD Software Solutions LLC Pond 6P: SWM B Hydrograph ■ Inflav ■ Primary 4 Inflow Area=1.030 ac Peak Elev=484.18' 3_ Storage=0.065 of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotTlype 1124-hr 1YR Rainfall=3.01" Prepared by TIMMONS GROUP Printed 5/7/2021 HvdroCAD®10.00-19 s/n 06538 © 2016 HvdroCAD Software Snll_ltions LLC Summary for Link 7L: Post-Dev. - Area B Combined Inflow Area = 2.000 ac, 59.50% Impervious, Inflow Depth > 1.61" for 1YR event Inflow = 2.17 cfs @ 12.06 hrs, Volume= 0.269 of Primary = 2.17 cfs @ 12.06 hrs, Volume= 0.269 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Link 7L: Post-Dev. - Area B Combined Hydrograph ■ Inflow IS Primary Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotTrype 1124-hr 2YR Rainfall=3.65" Prepared by TIMMONS GROUP Printed 5/712021 HydroCAD®10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Subcatchment 4S: Post-Dev. - Area B Detained Runoff = 4.87 cfs @ 11.96 hrs, Volume= 0.241 af, Depth> 2.81" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 2YR Rainfall=3.65" Area (ac) CN Description * 0.190 74 >75% Grass cover, Good, HSG C * 0.840 98 Impervious Area 1.030 94 Weighted Average 0.190 18.45% Pervious Area 0.840 81.55% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (fUft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment 4S: Post-Dev. - Area B Detained ® Runofr Type II 24-hr 2YR Rainfall=3.65" 4- Runoff Area=1.030 ac Runoff Volume=0.241 of Runoff Depth>2.81" LL Tc=6.0 min 2- CN=94 0 0 1 2 3 5 6 7 8 9 10 11 12 13 14 15 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotlType 1124-hr 2YR Rainfall=3.65' Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD® 10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Subcatchment 9S: Post-Dev. - Area B Un-detained Runoff = 2.06 cfs @ 12.05 hrs, Volume= 0.114 af, Depth> 1.41" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 2YR Rainfall=3.65" Area (ac) CN Description 0.130 80 >75% Grass cover, Good, HSG D * 0.350 98 Impervious Area 0.490 61 >75% Grass cover, Good, HSG B 0.970 77 Weighted Average 0.620 63.92% Pervious Area 0.350 36.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 12.8 170 0.0250 0.22 Sheet Flow, Grass: Short n= 0.150 P2= 3.65" Subcatchment 9S: Post-Dev. - Area B Un-detained Hydrograph B RunoH 2- Type II 24-hr 2YR Rainfall=3.65" Runoff Area=0.970 ac Runoff Volume=0.114 of I Runoff Depth>1.41" Flow Length=170' Slope=0.0250 '/' Tc=12.8 min CN=77 2 3 4 5 6 7 a 9 10 11 12 13 14 15 16 17 16 19 20 Time (hours) Wood brook -REVISE D(ShonerNipeswmt3)-lob rlrt-plot Iype Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD@ 10 00-19 s/n 06538 ©2016 HydroCAD Software Solutions LLC Summary for Pond 6P: SWM B Inflow Area = 1.030 ac, 81.55% Impervious, Inflow Depth > 2.81" for 2YR event Inflow = 4.87 cfs @ 11.96 hrs, Volume= 0.241 of Outflow = 2.14 cfs @ 12.08 hrs, Volume= 0.241 af, Atten= 56%, Lag= 7.1 min Primary = 2.14 cfs @ 12.08 hrs, Volume= 0.241 of Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 484.80' @ 12.08 hrs Surf.Area= 0.019 ac Storage= 0.077 of Plug -Flow detention time=27.3 min calculated for 0.241 of (100% of inflow Center -of -Mass det. time= 27.2 min ( 773.2 - 746.0 ) Volume Invert Avail.Storage Storage Description #1 479.94' 0.101 of 72.0" Round Pipe Storage L= 155.0' S= 0.00707 Device Routing Invert Outlet Devices #1 Primary 479.94' 15.0" Round Culvert L= 40.0' RCP, groove end projecting, Ke= 0.200 Inlet / Outlet Invert= 479.94' / 475.94' S= 0.1000 7' Cc= 0.900 n= 0.013, Flow Area= 1.23 sf #2 Device 1 479.94' 3.8" Vert. Orifice/Grate C= 0.600 #3 Device 1 484.45' 24.0" W x 5.2" H Vert. Orifice/Grate C= 0.600 #4 Device 1 485.77' 3.0' long Sharp -Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=2.05 cfs @ 12.08 hrs HW=484.78' (Free Discharge) tE ulvert (Passes 2.05 cfs of 15.17 cfs potential flow) Orifice/Grate (Orifice Controls 0.82 cfs @ 10.42 fps) =Orifice/Grate (Orifice Controls 1.22 cfs @ 1.85 fps) =Sharp -Crested Rectangular Weir( Controls 0.00 cfs) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotT ype 1124-hr 2YR Rainfall=3.65" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD®10 00-19 s/n 06538 ©2016 HydroCAD Software Solutions LLC Pond 6P: SWIM B Hydrograph ■ Inflow IN Primary Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-I55 PIPE-plotTrype 11 24-hr 2YR Rainfall=3.65" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD®10 00-19 s/n 06538 ©2016 HydroCAD Software Solutions LLC Summary for Link 7L: Post-Dev. - Area B Combined Inflow Area = 2.000 ac, 59.50% Impervious, Inflow Depth > 2.13" for 2YR event Inflow = 4.19 cfs @ 12.07 hrs, Volume= 0.355 of Primary = 4.19 cfs @ 12.07 hrs, Volume= 0.355 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Link 7L: Post-Dev. - Area B Combined ■ Inflow B Primary Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-I55 PIPE-plotType // 24-hr 10YR Rainfall=5.51" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD®10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Subcatchment 4S: Post-Dev. - Area B Detained Runoff = 7.62 cfs @ 11.96 hrs, Volume= 0.390 af, Depth> 4.55" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10YR Rainfall=5.51" Area (ac) CN Description * 0.190 74 >75% Grass cover, Good, HSG C * 0.840 98 Impervious Area 1.030 94 Weighted Average 0.190 18.45% Pervious Area 0.840 81.55% Impervious Area Tc Length Slope Description 6.0 Direct Entry, Subcatchment 4S: Post-Dev. - Area B Detained Hydrograph O Runoff Type II 24-hr 10YR Rainfall=5.51rr Runoff Area=1.030 ac Runoff Volume=0.390 of _ 5 Runoff Depth>4.55rr 4_ Tc=6.0 min LL 3 CN=94 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 26 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-I55 PIPE-plotType 1124-hr 10YR Rainfall=5.51" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCADO 10 00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Summary for Subcatchment 9S: Post-Dev. - Area B Un-detained Runoff = 4.09 cfs @ 12.05 hrs, Volume= 0.228 af, Depth> 2.82" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10YR Rainfall=5.51" Area (ac) CN Description 0.130 80 >75% Grass cover, Good, HSG D * 0.350 98 Impervious Area 0.490 61 >75% Grass cover, Good, HSG B 0,970 77 Weighted Average 0.620 63.92% Pervious Area 0.350 36.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (f /sec) (cfs) 12.8 170 0.0250 0.22 Sheet Flow, Grass: Short n= 0.150 P2= 3.65" Subcatchment 9S: Post-Dev. - Area B Un-detained ® Runafl 4- Type II 24-hr 10YR Rainfall=5.51" Runoff Area=0.970 ac 3 Runoff Volume=0.228 of Runoff Depth>2.82" 21 Flow Length=170' Slope=0.0250 '/' Tc=12.8 min CN=77 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-I55 PIPE-plotType 11 24-hr 10YR Rainfall=5.51 " Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD® 10 00-19 s/n 06538 @ 2016 HydroCAD Software Solutions LLC Summary for Pond 6P: SWM B Inflow Area = 1.030 ac, 81.55% Impervious, Inflow Depth > 4.55" for 10YR event Inflow = 7.62 cfs @ 11.96 hrs, Volume= 0.390 of Outflow = 6.01 cfs @ 12.02 hrs, Volume= 0.390 af, Atten= 21%, Lag= 3.6 min Primary = 6.01 cfs @ 12.02 hrs, Volume= 0.390 of Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 485.95' @ 12.02 hrs Surf.Area= 0.011 ac Storage= 0.096 of Plug -Flow detention time= 23.1 min calculated for 0.389 of (100% of inflow) Center -of -Mass det. time= 23.0 min ( 757.8 - 734.8 ) Volume Invert Avail Storage Storage Description #1 479.94' 0.101 of 72.0" Round Pipe Storage L= 155.0' S= 0.0070 T Device Routing Invert Outlet Devices #1 Primary 479.94' 15.0" Round Culvert L= 40.0' RCP, groove end projecting, Ke= 0.200 Inlet / Outlet Invert= 479.94' / 475.94' S= 0.1000 T Cc= 0.900 n= 0.013, Flow Area= 1.23 sf #2 Device 1 479.94' 3.8" Vert. Orifice/Grate C= 0.600 #3 Device 1 484.45' 24.0" W x 5.2" H Vert. Orifice/Grate C= 0.600 #4 Device 1 485.77' 3.0' long Sharp -Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=5.75 cfs @ 12.02 hrs HW=485.86' (Free Discharge) t -Culvert (Passes 5.75 cfs of 17.00 cfs potential flow) 2=Orifice/Grate (Orifice Controls 0.91 cfs @ 11.56 fps) 3=Orifice/Grate (Orifice Controls 4.56 cfs @ 5.26 fps) =Sharp -Crested Rectangular Weir(Weir Controls 0.28 cfs @ 1.00 fps) Woodbrook-REVISED(ShorterPipeSWMB)-155 PIPE-plotType 11 24-hr 10YR Rainfall=5.51" Prepared byTIMMONS GROUP Printed 5/7/2021 HvdroCAD® 10.00-19 s/n 06538 02016 HydmCAD Software Solutions LLC Pond 6P: SWM B Hydrograph ■ Inflow ■ Pdmary 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Woodbrook-REVISED(ShorterPipeSWMB)-I55 PIPE-plotType /l 24-hr 10YR Rainfall=5.51" Prepared by TIMMONS GROUP Printed 5/7/2021 HydroCAD®10 00-19 s/n 06538 C 2016 HydroCAD Software Solutions LLC Summary for Link 7L: Post-Dev. - Area B Combined Inflow Area = 2.000 ac, 59.50% Impervious, Inflow Depth > 3.71" for 10YR event Inflow = 9.95 cfs @ 12.03 hrs, Volume= 0.618 of Primary = 9.95 cfs @ 12.03 hrs, Volume= 0.618 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Link 7L: Post-Dev. - Area B Combined Hydrograph ■ InFlow ® Pnmary Time (hours)