Loading...
HomeMy WebLinkAboutWPO201700019 Calculations WPO VSMP 2017-07-13Scottsville Elementary School Security Addition ALBEMARLE COUNTY, VIRGINIA MINOR SITE PLAN AMENDMENT DESIGN CALCULATIONS & NARRATIVE FEBRUARY 21, 2017 REVISED APRIL 3, 2017 REVISED JULY 139 2017 .000 0 TIMMONS GROUP YOUR VISION ACHIEVED THROUGH OURS. Prepared by: Craig Kotarski, PE Timmons Group 608 Preston Avenue, Suite 200 Charlottesville, VA 22903 434.327.1688 Q U APPROVED by the Albemarle County Community D vel pment Department Date 1 Zot� File 0 7 !q CRAIG W. J. KO'CARSKI > Lie. No. 0402048507 �o 7/►3 J17 ��� ss� �' Table of Contents Section Title Project Narrative 2 Outlet Protection Sizing Stormwater Quantity Calculations 4 Pre -Developed HydroCAD Calculations Post -Developed HydroCAD Calculations 6 Virginia Runoff Reduction Method ReDevelopment Worksheet Project Narrative: This project includes a building addition to Scottsville Elementary School, an update bus loop, additional parking, sidewalk and associated site work. Limits of disturbance is 0.58 acres. Water Quality Currently there exists 0.41 acres of managed turf and 0.17 acres of impervious cover within the site limits. In the proposed condition, there will be 0.36 acres of managed turf and 0.22 acres of impervious cover. Per the Virginia Runoff Reduction Redevelopment Spreadsheet, this will require that 0.14 lb/yr to be removed. This required reduction is being met through a surplus removal of 0.41 lb/yr that has been achieved on the Woodbrook Elementary School project. See Plan WP0201600075. This surplus removal will be applied to this project, as ownership for both parcels is the same, the Albemarle County School Board, per 9VAC25-870-69 Section A Part 5. Water Quantity Water quantity is addressed through modification of the existing stormwater management facility. The facility will be excavated deeper and slightly wider and the outfall structure will be modified. The modified facility will detain and release stormwater at the appropriate rate for channel and flood protection requirements. Channel Protection (Energy Balance): The Energy Balance Equation has been applied to the 1 year storm for the 3.55 acre drainage area to the existing pond. 0.8 * NPRE—DEVELOPED * RVPRE—DEVELOPED) QDeveloped < I RVpOST—DEVELOPED 3.74 cfs < 0.8 * ((5.03)cfs * (0.381)acft) — 3.83c s Q Developed is 3.74 CFS which is less than the 3.83 CFS satisfying the Energy Balance Equation. Flood Protection (10 year storm): Post -Developed Qlo< Pre -Developed Qio 12.28cfs < 13.07cfs r. N W w 00 w DESIGN OF OUTLET PROTECTION FROM A ROUND PIPE FLOWING FULL MINIMUM TAILWATER CONDITION (TW --- 0.5 DIAMETER) Outlet W = Do + La Pipe2 Min. Diameter, Do La —+Ill �� a T ilwater < 0.500 60� 5q i. i 1 ; s - ro Recommended Min. d5o=6.. ��. 3 5 10 20 50 100 200 500 Q: 144�s Discharges ft3/sec. 4 L w 00 2i) Ex. SW Facility Draina a Area "`7 z 3 EX. SWM Faclity Subcat Reach Aon :Link Routing Diagram for Pre Prepared by Timmons Group, Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 0 2016 HydroCAD Software Solutions LLC Pre Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 2 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 2.320 74 >75% Grass cover, Good, HSG C (2S) 1.230 98 Paved parking, HSG C (2S) 3.550 82 TOTAL AREA Pre Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 3 Pipe Listing (all nodes) Line# Node In -Invert Out -Invert Length Slope n Diam/Width Height Inside -Fill Number (feet) (feet) (feet) (ft/ft) (inches) (inches) (inches) 1 3P 389.91 389.62 53.0 0.0055 0.011 24.0 0.0 0.0 Pre Type 11 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment 2S: Ex. SWM Facility Drainage Area Runoff = 13.52 cfs @ 12.14 hrs, Volume= 0.983 af, Depth> 3.32" Runoff by SCS TR -20 method, UH=SCS, Weighted -CN, Time Span= 3.00-20.01 hrs, dt= 0.03 hrs Type II 24 -hr 10 YR Rainfall=5.56" Area (ac) CN Description 1.230 98 Paved parking, HSG C 2.320 74 >75% Grass cover, Good, HSG C 3.550 82 Weighted Average 2.320 65.35% Pervious Area 1.230 34.65% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 19.7 200 0.0300 0.17 Sheet Flow, Grass: Dense n= 0.240 P2= 3.68" 1.8 150 0.0400 1.40 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 21.5 350 Total Subcatchment 2S: Ex. SWM Facility Drainage Area Hydrograph 10 Runoff 14 13 Type II 24 -hr 12 10 YR Rainfall=5.56" Runoff Area=3.550 ac ,o Runoff Volume=0.983 of 8 Runoff DepthA.32" Flow Length=350' 6 Tc=21.5 min 5- A CN=82 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Pre Type // 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD® 10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 5 Hydrograph for Subcatchment 2S: Ex. SWM Facility Drainage Area Time Precip. Excess Runoff (hours) (inches) (inches) (cfs) 3.00 0.19 0.00 0.00 3.30 0.21 0.00 0.00 3.60 0.24 0.00 0.00 3.90 0.26 0.00 0.00 4.20 0.28 0.00 0.00 4.50 0.31 0.00 0.00 4.80 0.33 0.00 0.00 5.10 0.36 0.00 0.00 5.40 0.39 0.00 0.00 5.70 0.42 0.00 0.00 6.00 0.44 0.00 0.00 6.30 0.48 0.00 0.00 6.60 0.51 0.00 0.01 6.90 0.54 0.00 0.02 7.20 0.57 0.01 0.03 7.50 0.61 0.01 0.04 7.80 0.64 0.02 0.06 8.10 0.68 0.02 0.07 8.40 0.72 0.03 0.08 8.70 0.77 0.04 0.11 9.00 0.82 0.06 0.14 9.30 0.87 0.07 0.17 9.60 0.92 0.09 0.19 9.90 0.98 0.11 0.22 10.20 1.05 0.13 0.27 10.50 1.13 0.17 0.34 10.80 1.23 0.21 0.44 11.10 1.35 0.27 0.57 11.40 1.51 0.35 0.80 11.70 1.97 0.63 1.42 12.00 3.69 1.94 8.90 12.30 3.96 2.17 8.93 12.60 4.13 2.32 3.07 12.90 4.26 2.42 1.63 13.20 4.36 2.51 1.19 13.50 4.44 2.59 0.98 13.80 4.52 2.65 0.84 14.10 4.58 2.71 0.73 14.40 4.64 2.76 0.65 14.70 4.69 2.81 0.61 15.00 4.75 2.85 0.57 15.30 4.79 2.90 0.53 15.60 4.84 2.94 0.50 15.90 4.88 2.97 0.46 16.20 4.92 3.01 0.42 16.50 4.96 3.04 0.40 16.80 4.99 3.07 0.39 17.10 5.03 3.10 0.37 17.40 5.06 3.13 0.36 17.70 5.09 3.16 0.35 18.00 5.12 3.19 0.34 18.30 5.15 3.21 0.32 Time Precip. Excess Runoff (hours) (inches) (inches) (cfs) 18.60 5.18 3.24 0.31 18.90 5.21 3.26 0.30 19.20 5.23 3.29 0.28 19.50 5.26 3.31 0.27 19.80 5.28 3.33 0.26 Pre Type // 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 6 Summary for Pond 3P: EX. SWM Faclity Inflow Area = 3.550 ac, 34.65% Impervious, Inflow Depth > 3.32" for 10 YR event Inflow = 13.52 cfs @ 12.14 hrs, Volume= 0.983 of Outflow = 13.07 cfs @ 12.18 hrs, Volume= 0.965 af, Atten= 3%, Lag= 2.4 min Primary = 13.07 cfs @ 12.18 hrs, Volume= 0.965 of Routing by Stor-Ind method, Time Span= 3.00-20.01 hrs, dt= 0.03 hrs / 3 Peak Elev= 393.89' @ 12.18 hrs Surf.Area= 4,385 sf Storage= 3,037 cf Plug -Flow detention time= 14.9 min calculated for 0.965 of (98% of inflow) Center -of -Mass det. time= 7.9 min ( 791.3 - 783.4 ) Volume Invert Avail.Storage Storage Description #1 393.00' 4,931 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq -ft) (cubic -feet) (cubic -feet) 393.00 1,900 0 0 393.50 3,839 1,435 1,435 394.00 4,540 2,095 3,530 394.30 4,800 1,401 4,931 Device Routing Invert Outlet Devices #1 Primary 389.91' 24.0" Round Culvert L= 53.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 389.91'/ 389.62' S=0.0055'/' Cc= 0.900 n=0.011 Concrete pipe, straight & clean, Flow Area= 3.14 sf #2 Device 1 393.26' 24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=13.07 cfs @ 12.18 hrs HW=393.89' (Free Discharge) t-1 --Culvert (Passes 13.07 cfs of 26.11 cfs potential flow) t-2=Orifice/Grate (Weir Controls 13.07 cfs @ 2.59 fps) Pre Type// 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 7 Pond 3P: EX. SWM Faclity Hydrograph ii C O W 1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Pond 3P: EX. SWM Faclity Stage -Discharge U 2 4 6 8 10 12 14 16 18 Discharge (cfs) ■ Inflow ® Primary ® Primary Pre Type l/ 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 8 LU Pond 3P: EX. SWM Faclity Stage -Area -Storage SutlacerHorizontal Wetted Area {sq -ft} 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 Storage (cubic -feet) 0 Surface 0 Storage Pre Type // 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Paae 9 Hydrograph for Pond 3P: EX. SWM Faclity Time Inflow Storage Elevation Primary (hours) (cfs) (cubic -feet) (feet) (cfs) 3.00 0.00 0 393.00 0.00 3.60 0.00 0 393.00 0.00 4.20 0.00 0 393.00 0.00 4.80 0.00 0 393.00 0.00 5.40 0.00 0 393.00 0.00 6.00 0.00 0 393.00 0.00 6.60 0.01 8 393.00 0.00 7.20 0.03 54 393.03 0.00 7.80 0.06 150 393.07 0.00 8.40 0.08 300 393.14 0.00 9.00 0.14 536 393.23 0.00 9.60 0.19 730 393.30 0.17 10.20 0.27 760 393.31 0.25 10.80 0.44 813 393.32 0.40 11.40 0.80 909 393.35 0.73 12.00 8.90 2,115 393.67 6.92 12.60 3.07 1,542 393.53 3.63 13.20 1.19 1,044 393.39 1.26 13.80 0.84 947 393.36 0.87 14.40 0.65 891 393.35 0.67 15.00 0.57 866 393.34 0.58 15.60 0.50 845 393.33 0.51 16.20 0.42 823 393.33 0.43 16.80 0.39 809 393.32 0.39 17.40 0.36 800 393.32 0.37 18.00 0.34 791 393.32 0.34 18.60 0.31 783 393.31 0.31 19.20 0.28 773 393.31 0.29 19.80 0.26 764 393.31 0.26 Pre Type 11 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 10 Elevation Primary (feet) (Cf S) 393.00 0.00 393.01 0.00 393.02 0.00 393.03 0.00 393.04 0.00 393.05 0.00 393.06 0.00 393.07 0.00 393.08 0.00 393.09 0.00 393.10 0.00 393.11 0.00 393.12 0.00 393.13 0.00 393.14 0.00 393.15 0.00 393.16 0.00 393.17 0.00 393.18 0.00 393.19 0.00 393.20 0.00 393.21 0.00 393.22 0.00 393.23 0.00 393.24 0.00 393.25 0.00 393.26 0.00 393.27 0.03 393.28 0.07 393.29 0.14 393.30 0.21 393.31 0.29 393.32 0.38 393.33 0.48 393.34 0.59 393.35 0.71 393.36 0.83 393.37 0.95 393.38 1.09 393.39 1.23 393.40 1.37 393.41 1.52 393.42 1.67 393.43 1.83 393.44 2.00 393.45 2.17 393.46 2.34 393.47 2.52 393.48 2.70 393.49 2.89 393.50 3.08 393.51 3.27 Stage -Discharge for Pond 3P: EX. SWM Faclity Elevation Primary (feet) (Cf S) 393.52 3.47 393.53 3.67 393.54 3.88 393.55 4.09 393.56 4.30 393.57 4.52 393.58 4.74 393.59 4.96 393.60 5.19 393.61 5.42 393.62 5.65 393.63 5.89 393.64 6.13 393.65 6.37 393.66 6.62 393.67 6.87 393.68 7.12 393.69 7.38 393.70 7.64 393.71 7.90 393.72 8.16 393.73 8.43 393.74 8.70 393.75 8.97 393.76 9.25 393.77 9.53 393.78 9.81 393.79 10.09 393.80 10.38 393.81 10.67 393.82 10.96 393.83 11.26 393.84 11.56 393.85 11.86 393.86 12.16 393.87 12.46 393.88 12.77 393.89 13.08 393.90 13.39 393.91 13.71 393.92 14.03 393.93 14.35 393.94 14.67 393.95 14.99 393.96 15.32 393.97 15.65 393.98 15.98 393.99 16.32 394.00 16.57 394.01 16.68 394.02 16.79 394.03 16.90 Elevation Primary (feet) (Cf S) 394.04 17.01 394.05 17.12 394.06 17.23 394.07 17.33 394.08 17.44 394.09 17.55 394.10 17.65 394.11 17.76 394.12 17.86 394.13 17.96 394.14 18.07 394.15 18.17 394.16 18.27 394.17 18.37 394.18 18.47 394.19 18.57 394.20 18.67 394.21 18.77 394.22 18.87 394.23 18.97 394.24 19.07 394.25 19.16 394.26 19.26 394.27 19.36 394.28 19.45 394.29 19.55 394.30 19.64 Pre Type 11 24 -hr 10 YR Rainfall=5.56" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Paae 11 Stage -Area -Storage for Pond 3P: EX. SWM Facility Elevation Surface Storage (feet) (sq -ft) (cubic -feet) 393.00 1,900 0 393.02 1,978 39 393.04 2,055 79 393.06 2,133 121 393.08 2,210 164 393.10 2,288 209 393.12 2,365 256 393.14 2,443 304 393.16 2,520 354 393.18 2,598 405 393.20 2,676 458 393.22 2,753 512 393.24 2,831 568 393.26 2,908 625 393.28 2,986 684 393.30 3,063 745 393.32 3,141 807 393.34 3,219 870 393.36 3,296 935 393.38 3,374 1,002 393.40 3,451 1,070 393.42 3,529 1,140 393.44 3,606 1,211 393.46 3,684 1,284 393.48 3,761 1,359 393.50 3,839 1,435 393.52 3,867 1,512 393.54 3,895 1,589 393.56 3,923 1,668 393.58 3,951 1,746 393.60 3,979 1,826 393.62 4,007 1,906 393.64 4,035 1,986 393.66 4,063 2,067 393.68 4,091 2,148 393.70 4,119 2,231 393.72 4,147 2,313 393.74 4,175 2,396 393.76 4,204 2,480 393.78 4,232 2,565 393.80 4,260 2,650 393.82 4,288 2,735 393.84 4,316 2,821 393.86 4,344 2,908 393.88 4,372 2,995 393.90 4,400 3,083 393.92 4,428 3,171 393.94 4,456 3,260 393.96 4,484 3,349 393.98 4,512 3,439 394.00 4,540 3,530 394.02 4,557 3,620 Elevation Surface Storage (feet) (sq -ft) (cubic -feet) 394.04 4,575 3,712 394.06 4,592 3,803 394.08 4,609 3,895 394.10 4,627 3,988 394.12 4,644 4,081 394.14 4,661 4,174 394.16 4,679 4,267 394.18 4,696 4,361 394.20 4,713 4,455 394.22 4,731 4,549 394.24 4,748 4,644 394.26 4,765 4,739 394.28 4,783 4,835 394.30 4,800 4,931 (2S) Post SW Facility Draing a Area z 3P Modified SWM Faclity Subcat Reach on Link Routing Diagram for Post Prepared by Timmons Group, Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Post Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 2 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 2.220 74 >75% Grass cover, Good, HSG C (2S) 1.330 98 Paved parking, HSG C (2S) 3.550 83 TOTAL AREA Post Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 3 Pipe Listing (all nodes) Line# Node In -Invert Out -Invert Length Slope n Diam/Width Height Inside -Fill Number (feet) (feet) (feet) (ft/ft) (inches) (inches) (inches) 1 3P 389.91 389.62 53.0 0.0055 0.011 24.0 0.0 0.0 2 3P 390.00 389.95 8.0 0.0063 0.011 12.0 0.0 0.0 Post Type 1124 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD010.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Paae 4 Summary for Subcatchment 2S: Post SWM Facility Draingae Area Runoff = 25.97 cfs @ 12.14 hrs, Volume= 1.953 af, Depth> 6.60" Runoff by SCS TR -20 method, UH=SCS, Weighted -CN, Time Span= 0.00-20.00 hrs, dt= 0.01 hrs Type II 24 -hr 100 YR Rainfall=9.13" Area (ac) CN Description 1.330 98 Paved parking, HSG C 2.220 74 >75% Grass cover, Good, HSG C 3.550 83 Weighted Average 2.220 62.54% Pervious Area 1.330 37.46% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 19.7 200 0.0300 0.17 Sheet Flow, Grass: Dense n= 0.240 P2= 3.68" 1.8 150 0.0400 1.40 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 21.5 350 Total Subcatchment 2S: Post SWM Facility Draingae Area Hydrograph 28 ®Runoff 25.97 cfs 26 Type II 24 -hr 24 22 100 YR Rainfall=9.13" 20 Runoff Area=3.550 ac $ Runoff Volume=1.953 of 16 Runoff Depth>6.60" ° LL t4 Flow Length=350' 12 10 Tc=21.5 min 8 CN=83 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Post Type// 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 5 Hydrograph for Subcatchment 2S: Post SWM Facility Draingae Area Time Precip. Excess Runoff (hours) (inches) (inches) (cfs) 0.00 0.00 0.00 0.00 0.20 0.02 0.00 0.00 0.40 0.04 0.00 0.00 0.60 0.06 0.00 0.00 0.80 0.08 0.00 0.00 1.00 0.10 0.00 0.00 1.20 0.12 0.00 0.00 1.40 0.14 0.00 0.00 1.60 0.16 0.00 0.00 1.80 0.18 0.00 0.00 2.00 0.20 0.00 0.00 2.20 0.22 0.00 0.00 2.40 0.25 0.00 0.00 2.60 0.27 0.00 0.00 2.80 0.29 0.00 0.00 3.00 0.31 0.00 0.00 3.20 0.34 0.00 0.00 3.40 0.36 0.00 0.00 3.60 0.39 0.00 0.00 3.80 0.41 0.00 0.00 4.00 0.44 0.00 0.00 4.20 0.46 0.00 0.01 4.40 0.49 0.00 0.02 4.60 0.52 0.01 0.03 4.80 0.55 0.01 0.04 5.00 0.58 0.01 0.05 5.20 0.60 0.02 0.07 5.40 0.64 0.02 0.08 5.60 0.67 0.03 0.09 5.80 0.70 0.04 0.11 6.00 0.73 0.04 0.12 6.20 0.76 0.05 0.14 6.40 0.80 0.06 0.15 6.60 0.83 0.07 0.17 6.80 0.87 0.08 0.19 7.00 0.90 0.10 0.20 7.20 0.94 0.11 0.22 7.40 0.98 0.12 0.24 7.60 1.02 0.14 0.25 7.80 1.06 0.15 0.27 8.00 1.10 0.17 0.29 8.20 1.14 0.19 0.31 8.40 1.18 0.21 0.33 8.60 1.23 0.24 0.37 8.80 1.29 0.26 0.42 9.00 1.34 0.29 0.47 9.20 1.40 0.32 0.52 9.40 1.46 0.36 0.55 9.60 1.52 0.39 0.57 9.80 1.58 0.43 0.61 10.00 1.65 0.47 0.67 10.20 1.73 0.52 0.75 Time Precip. Excess Runoff (hours) (inches) (inches) (cfs) 10.40 1.82 0.57 0.85 10.60 1.91 0.64 0.97 10.80 2.02 0.71 1.11 11.00 2.15 0.80 1.30 11.20 2.29 0.90 1.53 11.40 2.48 1.04 1.89 11.60 2.80 1.29 2.40 11.80 3.93 2.23 5.47 12.00 6.05 4.14 17.80 12.20 6.38 4.44 23.96 12.40 6.62 4.67 10.87 12.60 6.79 4.83 5.63 12.80 6.93 4.96 3.47 13.00 7.05 5.07 2.58 13.20 7.15 5.17 2.12 13.40 7.25 5.26 1.86 13.60 7.34 5.35 1.66 13.80 7.42 5.42 1.49 14.00 7.49 5.49 1.36 14.20 7.55 5.55 1.23 14.40 7.62 5.61 1.15 14.60 7.68 5.67 1.10 14.80 7.74 5.73 1.05 15.00 7.79 5.78 1.01 15.20 7.85 5.83 0.96 15.40 7.90 5.88 0.92 15.60 7.95 5.93 0.88 15.80 7.99 5.97 0.83 16.00 8.03 6.01 0.79 16.20 8.08 6.05 0.75 16.40 8.12 6.09 0.72 16.60 8.16 6.13 0.70 16.80 8.20 6.16 0.68 17.00 8.23 6.20 0.67 17.20 8.27 6.24 0.65 17.40 8.31 6.27 0.64 17.60 8.34 6.30 0.62 17.80 8.38 6.34 0.61 18.00 8.41 6.37 0.59 18.20 8.44 6.40 0.57 18.40 8.47 6.43 0.56 18.60 8.50 6.46 0.54 18.80 8.53 6.49 0.53 19.00 8.56 6.52 0.51 19.20 8.59 6.54 0.50 19.40 8.62 6.57 0.48 19.60 8.64 6.59 0.47 19.80 8.67 6.62 0.45 20.00 8.69 6.64 0.43 Post Type 11 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 6 Summary for Pond 3P: Modified SWM Faclity Inflow Area = 3.550 ac, 37.46% Impervious, Inflow Depth > 6.60" for 100 YR event Inflow = 25.97 cfs @ 12.14 hrs, Volume= 1.953 of Outflow = 23.82 cfs @ 12.20 hrs, Volume= 1.933 af, Atten= 8%, Lag= 4.0 min Primary = 23.82 cfs @ 12.20 hrs, Volume= 1.933 of Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.01 hrs / 3 Peak Elev= 393.39' @ 12.20 hrs Surf.Area= 4,151 sf Storage= 10,170 cf Plug -Flow detention time= 17.1 min calculated for 1.933 of (99% of inflow) Center -of -Mass det. time= 12.7 min ( 778.4 - 765.6 ) Volume Invert Avail.Storage Storage Description #1 390.00' 14,303 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq -ft) (cubic -feet) (cubic -feet) 390.00 2,107 0 0 391.00 2,581 2,344 2,344 392.00 3,094 2,838 5,182 393.00 3,785 3,440 8,621 394.00 4,723 4,254 12,875 394.30 4,800 1,428 14,303 Device Routing Invert Outlet Devices #1 Primary 389.91' 24.0" Round Culvert L= 53.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 389.91'/389.62' S=0.0055'/' Cc= 0.900 n=0.011 Concrete pipe, straight & clean, Flow Area= 3.14 sf #2 Device 1 392.47' 24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Device 1 390.00' 12.0" Round Culvert L= 8.0' RCP, square edge headwall, Ke= 0.500 Inlet /Outlet Invert= 390.00'/ 389.95' S=0.0063'/' Cc= 0.900 n=0.011 Concrete pipe, straight & clean, Flow Area= 0.79 sf Primary OutFlow Max=23.82 cfs @ 12.20 hrs HW=393.39' (Free Discharge) L1=Culvert (Inlet Controls 23.82 cfs @ 7.58 fps) L2=Orifice/Grate (Passes < 18.47 cfs potential flow) 3=Culvert (Passes < 6.43 cfs potential flow) Post Type // 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 7 Pond 3P: Modified SWM Faclity Hydrograph N V 3 O LL 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Pond 3P: Modified SWM Facility Stage -Discharge 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Discharge (cfs) IN Inflow Primary ® Primary Post Type // 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 © 2016 HydroCAD Software Solutions LLC Page 8 C 0 m w Pond 3P: Modified SWM Faclity Stage -Area -Storage SurfaceHorizorltal'Wetted Area fsq-fu 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Storage (cubic -feet) 11 Surface 0 Storage Post Type// 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Paae 9 Hydrograph for Pond 3P: Modified SWM Faclity Time Inflow Storage Elevation Primary (hours) (cfs) (cubic -feet) (feet) (cfs) 0.00 0.00 0 390.00 0.00 0.50 0.00 0 390.00 0.00 1.00 0.00 0 390.00 0.00 1.50 0.00 0 390.00 0.00 2.00 0.00 0 390.00 0.00 2.50 0.00 0 390.00 0.00 3.00 0.00 0 390.00 0.00 3.50 0.00 0 390.00 0.00 4.00 0.00 0 390.00 0.00 4.50 0.02 17 390.01 0.00 5.00 0.05 80 390.04 0.01 5.50 0.09 181 390.09 0.02 6.00 0.12 293 390.14 0.06 6.50 0.16 396 390.18 0.11 7.00 0.20 483 390.22 0.16 7.50 0.24 558 390.26 0.20 8.00 0.29 624 390.29 0.25 8.50 0.35 695 390.32 0.30 9.00 0.47 807 390.37 0.40 9.50 0.56 933 390.42 0.51 10.00 0.67 1,028 390.46 0.60 10.50 0.91 1,203 390.54 0.78 11.00 1.30 1,486 390.66 1.10 11.50 2.12 1,982 390.86 1.72 12.00 17.80 7,488 392.69 8.34 12.50 7.63 7,604 392.72 9.01 13.00 2.58 4,937 391.92 4.51 13.50 1.76 2,582 391.09 2.45 14.00 1.36 1,872 390.81 1.58 14.50 1.12 1,586 390.70 1.22 15.00 1.01 1,452 390.64 1.06 15.50 0.90 1,355 390.60 0.95 16.00 0.79 1,260 390.56 0.84 16.50 0.71 1,170 390.52 0.75 17.00 0.67 1,117 390.50 0.69 17.50 0.63 1,077 390.48 0.65 18.00 0.59 1,039 390.47 0.61 18.50 0.55 1,000 390.45 0.57 19.00 0.51 961 390.43 0.53 19.50 0.47 920 390.42 0.50 20.00 0.43 878 390.40 0.46 Post Type 11 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD610.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 10 Elevation Primary (feet) (Cf S) 390.00 0.00 390.05 0.01 390.10 0.03 390.15 0.07 390.20 0.13 390.25 0.19 390.30 0.27 390.35 0.36 390.40 0.46 390.45 0.57 390.50 0.69 390.55 0.81 390.60 0.94 390.65 1.08 390.70 1.23 390.75 1.38 390.80 1.53 390.85 1.69 390.90 1.85 390.95 2.01 391.00 2.17 391.05 2.33 391.10 2.48 391.15 2.62 391.20 2.76 391.25 2.88 391.30 2.98 391.35 3.08 391.40 3.26 391.45 3.44 391.50 3.61 391.55 3.77 391.60 3.92 391.65 4.06 391.70 4.14 391.75 4.23 391.80 4.31 391.85 4.39 391.90 4.47 391.95 4.55 392.00 4.63 392.05 4.71 392.10 4.78 392.15 4.86 392.20 4.93 392.25 5.00 392.30 5.07 392.35 5.14 392.40 5.21 392.45 5.28 392.50 5.48 392.55 6.01 Stage -Discharge for Pond 3P: Modified SWM Facility Elevation Primary (feet) (Cf S) 392.60 6.71 392.65 7.54 392.70 8.49 392.75 9.55 392.80 10.69 392.85 11.93 392.90 13.23 392.95 14.62 393.00 16.07 393.05 17.59 393.10 19.18 393.15 20.83 393.20 22.53 393.25 22.92 393.30 23.26 393.35 23.61 393.40 23.87 393.45 24.11 393.50 24.34 393.55 24.58 393.60 24.81 393.65 25.04 393.70 25.27 393.75 25.49 393.80 25.72 393.85 25.94 393.90 26.16 393.95 26.37 394.00 26.59 394.05 26.80 394.10 27.02 394.15 27.23 394.20 27.44 394.25 27.65 394.30 27.85 Post Type // 24 -hr 100 YR Rainfall=9.13" Prepared by Timmons Group Printed 7/11/2017 HydroCAD®10.00-19 s/n 06538 @2016 HydroCAD Software Solutions LLC Page 11 Stage -Area -Storage for Pond 3P: Modified SWM Facility Elevation Surface Storage (feet) (sq -ft) (cubic -feet) 390.00 2,107 0 390.05 2,131 106 390.10 2,154 213 390.15 2,178 321 390.20 2,202 431 390.25 2,226 542 390.30 2,249 653 390.35 2,273 766 390.40 2,297 881 390.45 2,320 996 390.50 2,344 1,113 390.55 2,368 1,231 390.60 2,391 1,350 390.65 2,415 1,470 390.70 2,439 1,591 390.75 2,463 1,714 390.80 2,486 1,837 390.85 2,510 1,962 390.90 2,534 2,088 390.95 2,557 2,216 391.00 2,581 2,344 391.05 2,607 2,474 391.10 2,632 2,605 391.15 2,658 2,737 391.20 2,684 2,870 391.25 2,709 3,005 391.30 2,735 3,141 391.35 2,761 3,279 391.40 2,786 3,417 391.45 2,812 3,557 391.50 2,838 3,699 391.55 2,863 3,841 391.60 2,889 3,985 391.65 2,914 4,130 391.70 2,940 4,276 391.75 2,966 4,424 391.80 2,991 4,573 391.85 3,017 4,723 391.90 3,043 4,875 391.95 3,068 5,027 392.00 3,094 5,182 392.05 3,129 5,337 392.10 3,163 5,494 392.15 3,198 5,653 392.20 3,232 5,814 392.25 3,267 5,977 392.30 3,301 6,141 392.35 3,336 6,307 392.40 3,370 6,474 392.45 3,405 6,644 392.50 3,440 6,815 392.55 3,474 6,988 Elevation Surface Storage (feet) (sq -ft) (cubic -feet) 392.60 3,509 7,162 392.65 3,543 7,339 392.70 3,578 7,517 392.75 3,612 7,696 392.80 3,647 7,878 392.85 3,681 8,061 392.90 3,716 8,246 392.95 3,750 8,433 393.00 3,785 8,621 393.05 3,832 8,811 393.10 3,879 9,004 393.15 3,926 9,199 393.20 3,973 9,397 393.25 4,020 9,597 393.30 4,066 9,799 393.35 4,113 10,003 393.40 4,160 10,210 393.45 4,207 10,419 393.50 4,254 10,631 393.55 4,301 10,845 393.60 4,348 11,061 393.65 4,395 11,279 393.70 4,442 11,500 393.75 4,489 11,724 393.80 4,535 11,949 393.85 4,582 12,177 393.90 4,629 12,407 393.95 4,676 12,640 394.00 4,723 12,875 394.05 4,736 13,111 394.10 4,749 13,349 394.15 4,761 13,586 394.20 4,774 13,825 394.25 4,787 14,064 394.30 4,800 14,303 DEQ Virginia Runoff Reduction Method Re-De.elopment CIMPhal- sp—aishce Versi-3.0 Scottsville EI! e ta ALL uEAnJIF -- _��_ Site Information I t 'Post -Development Project (Treatment Volume and Loads) Enter,Total Di st'rbed, Area (acres) s s Maximum reduction required: 10% The site's net increase in impervious cover (.crest is: 0.05 Post -Development TP Load Reduction Jor Site (Ib/yrf: !­R,�ueloprnent Land . -__—_ _1111"111d.11111111, 't—rIll LAND COVER SUMMARY -• PRE -REDEVELOPMENT ----- LAND COVER SUMMARY— POST DEVELOPMENT MUM ®® IBE® ■ ■ ,-■ Post -Development Requirement for Site Area DEQ Virginia Runoff Reduction Method Re -Development Compliance Spreadsheet - Version 3.0 132011 BMP Standards and Specifications 0 2013 Draft BMP Standards and Specifications Project Name: Scottsville Elementary Addtion CLEAR ALL data input cells Date: 7/11/2017 constant values Linear Development Project? No calculation cells Site Information Post -Development Project (Treatment Volume and Loads) Enter Total Disturbed Area (acres) -> 0.75 Check: BMP Design Specifications List: 2013 Draft Stds & 5 ecs Linear project? No low r r Land cover areas entered correctly? V Total disturbed area entered? ✓ Pre- ReDevelopment Land Cover (acres) A Soils B Soils C Soils D Soils Totals Forest/Open Space (acres)-- undisturbed, protected forest/open space or reforested land 0.00 Managed Turf (acres) -- disturbed, graded for yards or other turf to be mowed/managed 0.41 0.41 Impervious Cover (acres) 0.17 0.17 0.58 Post -Development Land Cover (acres) A Soils B Soils C Soils D Soils Totals Forest/Open Space (acres)-- undisturbed, rotected forest/open space or reforested land 0.00 Managed Turf (acres) - disturbed, graded for yards or other turf to be mowed/managed 0.36 0.36 Impervious Cover (acres) 0.22 0 22 Area Check OK. OK. OK. OK. 0.58 Constants Runoff Coefficients Rv Annual Rainfall (inches) 43 A Soils B Soils C Soils D Soils Target Rainfall Event (inches) 1.00 coyest/Open Space 0.02 0.03 0.04 0.05 Total Phosphorus (TP) EMC (mg/L) 0.26 Managed Turf 0.15 0.20 0.22 0.25 Total Nitrogen (TN) EMC (mg/L) 1.86 Impervious Cover 0.95 0.95 0.95 0.95 Target TP Load (Ib/acre/yr) 0.41 Pj oritless correction factor) 0.90 1 • 1 • 'LAND COVER SUMMARY POST DEVELOPMENT Land Cover Summary -Pre Land Cover Summary -Post (Final) Land Cover Summary -Post Land Cover Summary -Post Pre-ReDevelopment Listed Adjusted' Post ReDev. & New Impervious Post-ReDevelopment Post -Development New Impervious Forest/Open Space Cover (acres) 0.00 0.00 Forest/Open Space 0.00 Forest/Open Space 0.00 Cover acres) Cover (acres) Weighted Rv(forest) 0.00 0.00 Weighted Rv(forest) 0.00 Weighted Rv(forest) 0.00 %Forest 0% 0% %Forest 0% %Forest 0% Managed Turf Cover (acres) 0.41 Managed Turf Cover 0.36 0.36 Managed Turf Cover 0.36 (acres) (acres) Weighted Rv(turf) 0.22 0.22 Weighted Rv (turf) 0.22 Weighted Rv (turf) 0.22 %Managed Turf 71% 68% %Managed Turf 62% %Managed Turf 68% Impervious Cover (acres) 0.17 0.17 Impervious Cover O L2 ReDev. Impervious 0.17 New Impervious Cover O.OS (acres) Cover (acres) (acres) Rv(impervious) 0.95 0.95 Rvhmpervious) 0.95 Rv(impervious) 0.95 Rv(,mperwous) 0.95 %Impervious 29% 32% %Impervious 38% %Impervious 32% Total Site Area (acres) 0.58 0.53 Final Site Area (acres) 0.58 Total ReDev. Site Area (acres) 0.53 Site Rv 0.43 0.45 Final Post Dev Site Rv 0.50 ReDev Site Rv 0.45 Treatment Volume and Nutrient Load Treatment Volume and Nutrient Load Final Post- Pre-ReDevelo ment Treatment Volume p Development Post -Re Development Post -Development 0.0210 (acre -ft) 0.0201 Treatment Volume 0.0240 Treatment Volume 0.0201 Treatment Volume 0.0040 (acre -ft) (acre -ft) (acre -ft) Final Post- Pre-ReDevelo ment Treatment Volume p Development Post-ReDevelopment Post -Development 914 (cubic fee[) 874 Treatment Volume 1,046 Treatment Volume 874 Treatment Volume (cubic 172 (cubic feet) (cubic feet) feet) Pre-ReDevelopment TP Load Final Post- Post-ReDevelopment (Ib/yr) 0.57 0.55 Development TP Load 0.66 Load (TP) 0.55 Post -Development TP 0.11 (Ib/yr) (Ib/yr)' Load (Ib/yr) Pre- ReDevelopment TP Load per acre Final Post -Development TP post. N,.i,,. 0.99 ()b/acre/yr) 1.04 Load per acre 1.13 eg h- pacre 7.04 (Ib/acre/yr) xx (Ib/acre/yr) Baseline TP Load (Ib/yr) Max. Reduction Required (0.41 lbs/ace/yr applied to pre -redevelopment area excluding pervia.. 0.11 (Below Pre- 10% land proposed for new impervious cover) ReDevelopment Load) ' Adjusted Land Cover Summary: TP Load Reduction Pre ReDevelopment land cover minus pervious land cover (forest/open space o: Required for TP Load Reduction. managed turf) acreage proposed for new impervious cover. Redeveloped Area 0.05 Required for New 0.09 (Ib/yr) Impervious Area (Ib/y- Adjusted total acreage is consistent with Post-ReDevelopment acreage (minus acreage of new impervious cover). Column I shows load reduction requriement far new impervious cover (based on new development load limit, 0.41 Ibs/ocre/year). Post -Development Requirement for TP Load Reduction Required (Ib/yr) 0.14 Nitrogen Loads (Informational Purposes Only) I final Post -Development TN Load Pre-ReDevelopment TN Load (lb/yr) 4.11 (Post-ReDevelopment & New 4.70 Impervious) (Ib/yr)