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HomeMy WebLinkAboutWPO202000017 Calculations 2020-03-23SHIMP ENGINEERING, P.C. Design Focused Engineering March 20, 2020 County of Albemarle Department of Community Development 401 McIntire Road Charlottesville, VA 22902 Regarding: Proffit Road Townhomes South Stormwater Management Plan Dear Reviewer, The purpose of this project is to build 40 single family attached units on the southern side of Proffit Road. The total area of disturbance is 3.30 acres. Runoff from the site in the predevelopment condition is analyzed at two points, labeled POA1 and POA2. However, in the post -development condition runoff to POA2 is collected and piped to an underground detention system comprised of StormTech MC-4500 chambers and an isolation row, which outlets to POA1. Therefore, the runoff from the development is only analyzed at POA1. The proposed storm sewer will outlet into an existing storm sewer further downstream. Runoff from the site will be released at rates that comply with the energy balance equation set forth in 9VAC25-870-66-B(3). The calculations are summarized in the table below. Please note that a small portion of the drainage area to POA1 is from offsite. The flow from offsite was included in the energy balance equation, but no improvement factor was applied to it. Proffit Road Townhomes South Energy Balance Equation 24 Hr 1 year Storm: Qdeveloped!5 I.F. *(Qpre-developed*RVPre-Developed)/RVdeveloped Qdeveloped!5 (Qforested*RVforested)/RVdeveloped Qpre-developed = 0.97 Qpre-offsite 0.08 RVPre-Developed = 0.104 MdXQdeveloped = 0.37 CfS RVDeveloped = 0.282 Qdeveloped = 0.35 Cfs 10 yr pre 6.01 10 yr post 5.77 According to the VRRM spreadsheet included in this packet, the target phosphorus load reduction is 2.83 lb/yr. The StormTech chambers with the isolator row are rated for 40% phosphorous removal, resulting in 1.67 lb/yr phosphorous removal. The remaining phosphorous load 1.16 lb/yr will be effectively reduced by the purchase of nutrient credits. 912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com Contents: Pre -Development Stormwater Management Calculations: Pre -Development SWM Map Pre -Development HydroCAD Analysis Post -Development Stormwater Management Calculations: Post -Development SWM Map Post -Development HydroCAD Analysis Time of Concentration Calculations: Pre -Development Time of Concentration Calculations Nomographs Stormwater Quality Calculations: Pre -Development VRRM Landuse Map Post -Development VRRM Landuse Map VRRM Redevelopment Spreadsheet Independent Reports: Excerpt from NRCS Soils Report NOAA Precipitation Report Pre -Development Stormwater Management Calculations Pre -Development SWM Map Pre -Development HydroCAD Analysis PRE -DEVELOPMENT SWM MAP eni -oNOT INCLUDE-D-IN WATER POLE \ � Q QUALITY CALCULA-TIONS N \ / (REL 6 \ ` co WELL TBR I/ N 0 o POA 1 00 i C 01 ©p I ------ -- ----- I - .ss I 2 / OFFSITE AREA 40 0 0 )8 0 h� — - Scale: 1 "=40' is PreDev On ' e Pre ev POM Subcat Reach on Link Offsite PreDev PreDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/5/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 2 Time span=0.00-36.00 hrs, dt=0.05 hrs, 721 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1 S: PreDev Onsite Runoff Area=2.730 ac 10.26% Impervious Runoff Depth=0.46" Tc=20.0 min CN=64 Runoff=0.97 cfs 0.104 of Subcatchment2S: PreDev Offsite Runoff Area=0.363 ac 0.00% Impervious Runoff Depth=0.35" Tc=20.0 min CN=61 Runoff=0.08 cfs 0.011 of Link 3L: POA1 Inflow=1.06 cfs 0.114 of Primary=1.06 cfs 0.114 of Total Runoff Area = 3.093 ac Runoff Volume = 0.114 of Average Runoff Depth = 0.44" 90.95% Pervious = 2.813 ac 9.05% Impervious = 0.280 ac PreDev PreDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/5/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 3 Summary for Subcatchment 1S: PreDev Onsite Runoff = 0.97 cfs @ 12.17 hrs, Volume= 0.104 af, Depth= 0.46" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 1.060 58 Woods/grass comb., Good, HSG B 1.390 61 >75% Grass cover, Good, HSG B 0.280 98 2.730 64 Weighted Average 2.450 89.74% Pervious Area 0.280 10.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Subcatchment 2S: PreDev Offsite Runoff = 0.08 cfs @ 12.19 hrs, Volume= 0.011 af, Depth= 0.35" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 0.000 58 Woods/grass comb., Good, HSG B 0.363 61 >75% Grass cover, Good, HSG B 0.000 98 0.363 61 Weighted Average 0.363 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Link X: POM Inflow Area = 3.093 ac, 9.05% Impervious, Inflow Depth = 0.44" for 1 yr, 24 hr event Inflow = 1.06 cfs @ 12.17 hrs, Volume= 0.114 of Primary = 1.06 cfs @ 12.17 hrs, Volume= 0.114 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs PreDev PreDev Type/1 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/5/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paoe 4 Time span=0.00-36.00 hrs, dt=0.05 hrs, 721 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1 S: PreDev Onsite Runoff Area=2.730 ac 10.26% Impervious Runoff Depth=1.87" Tc=20.0 min CN=64 Runoff=5.40 cfs 0.425 of Subcatchment2S: PreDev Offsite Runoff Area=0.363 ac 0.00% Impervious Runoff Depth=1.63" Tc=20.0 min CN=61 Runoff=0.61 cfs 0.049 of Link 3L: POA1 Inflow=6.01 cfs 0.474 of Primary=6.01 cfs 0.474 of Total Runoff Area = 3.093 ac Runoff Volume = 0.474 of Average Runoff Depth = 1.84" 90.95% Pervious = 2.813 ac 9.05% Impervious = 0.280 ac PreDev PreDev Type/1 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/5/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 5 Summary for Subcatchment 1S: PreDev Onsite Runoff = 5.40 cfs @ 12.14 hrs, Volume= 0.425 af, Depth= 1.87" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 1.060 58 Woods/grass comb., Good, HSG B 1.390 61 >75% Grass cover, Good, HSG B 0.280 98 2.730 64 Weighted Average 2.450 89.74% Pervious Area 0.280 10.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Subcatchment 2S: PreDev Offsite Runoff = 0.61 cfs @ 12.14 hrs, Volume= 0.049 af, Depth= 1.63" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 0.000 58 Woods/grass comb., Good, HSG B 0.363 61 >75% Grass cover, Good, HSG B 0.000 98 0.363 61 Weighted Average 0.363 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Link 3L: POM Inflow Area = 3.093 ac, 9.05% Impervious, Inflow Depth = 1.84" for 10 yr, 24 hr event Inflow = 6.01 cfs @ 12.14 hrs, Volume= 0.474 of Primary = 6.01 cfs @ 12.14 hrs, Volume= 0.474 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-36.00 hrs, dt= 0.05 hrs Post -Development Stormwater Management Calculations Post -Development SWM Map Post -Development HydroCAD Analysis POST -DEVELOPMENT SWM MAP eni -oNOT INCLUDE-9-IN-WATER POLE \ � Q QUALITY CALCULATIONS ` \ _ a u OLE �\ N 58 O \ m GaZ X 2 ` \\ x33°4 \ / N LOT 31 �I \ FFE 527.5 LOT 30 �\ v 34 32 �\ 0 FE527.5 \ ® 1 �T 32 LOT 3 LOT 34 LOT 35 LOT 36 LOT 37 LOT 38 LT 39 LOT 40 X FF \531. FFE 531. FE 533. FFEE\ 534. FFE 534. 32 FFE 535. FFE 534. FFE534. FFE 533. \ 4 \ \ \ / N N LOT 29 \� \ / - _ S° \ FFE 527.0 \ 30 I ) _ ? / / \\ 3 v FFE 527E0 \ \ 3 0 X -�LOT 27 \ o\\ FFE 527.0 \ I O O O POA 1 v ° 2500 O° v \ V ®° T 1 X �\ 2' DI-3� PRIVATE ( A i 2' DI-3B �_7 535.5 \ I o o \\ F E v 4 12' DI-3C W �o \ J 303 \y. MIL \\ � \ - - �T Z AY �R 1 rn N \ \ 35.5 \ W LOT 22 �v v s vv FFE \e rn FFE 526.0 m\ \ X o o a T g 0 of O \ LOT 5 160 \ \ FFO 531.5 - L0�3`3 x D FFE.5 \ 0 FOE560 b O I -- - 10 rn I n LOT 17 x F� 532.0 p/ z FFE 528.0FFE 535• o -- FT 24 FE_ 5265 - --- \ x x LOT 18 x NSPECTI FFO 5 12 0 a \ --- I FFE 528.0 cb � PORT T 25 FEE 527.0 LO( 12 \ / _ I (9 - - - FFE 528.5 / FFE 532.5 / LOT 5 0 I FFE 535. FEE 527 0 26 J LOT 13 // 1 � \ F -LOT / FFE 532.5 LOT 6 534.5 I a a I I LOT o u T _ I -FF-E_5 815_ F O 53534.5 FFE y Lo 533.0FFF_ \, e - - - - - - 28 ® 3250 FF�T 344.0 o I / I 4.69 30 A - / OFFSITE AREA 40 0 0 18 0 910 - - Scale: 1 "=40' 6S 2S 1S 5S Offsite Treated Onsite Tre ted Onsite ntreated Offs' a Untreated A StormTec 4L POA SubCat Reach on Link Drainage Diagram for PostDev Prepared by {enter your company name here}, Printed 3/16/2020 HydroCADO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC PostDev PostDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 2 Time span=0.00-48.00 hrs, dt=0.05 hrs, 961 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1 S: Onsite Untreated Runoff Area=0.354 ac 0.85% Impervious Runoff Depth=0.35" Tc=5.0 min CN=61 Runoff=0.17 cfs 0.010 of Subcatchment2S: Onsite Treated Runoff Area=2.586 ac 67.67% Impervious Runoff Depth=1.64" Tc=5.0 min CN=86 Runoff=7.57 cfs 0.353 of Subcatchment5S: Offsite Untreated Runoff Area=0.206 ac 0.00% Impervious Runoff Depth=0.35" Tc=5.0 min CN=61 Runoff=0.10 cfs 0.006 of Subcatchment6S: Offsite Treated Runoff Area=0.317 ac 0.00% Impervious Runoff Depth=0.35" Tc=5.0 min CN=61 Runoff=0.15 cfs 0.009 of Pond 5P: StormTech Peak Elev=523.01' Storage=10,658 cf Inflow=7.69 cfs 0.362 of Outflow=0.15 cfs 0.265 of Link 4L: POA Inflow=0.35 cfs 0.282 of Primary=0.35 cfs 0.282 of Total Runoff Area = 3.463 ac Runoff Volume = 0.379 of Average Runoff Depth = 1.31" 49.38% Pervious = 1.710 ac 50.62% Impervious = 1.753 ac PostDev PostDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 3 Summary for Subcatchment 1S: Onsite Untreated Runoff = 0.17 cfs @ 11.99 hrs, Volume= 0.010 af, Depth= 0.35" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 0.351 61 >75% Grass cover, Good, HSG B 0.003 98 0.354 61 Weighted Average 0.351 99.15% Pervious Area 0.003 0.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 2S: Onsite Treated Runoff = 7.57 cfs @ 11.96 hrs, Volume= 0.353 af, Depth= 1.64" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 1.750 98 0.836 61 >75% Grass cover, Good, HSG B 2.586 86 Weighted Average 0.836 32.33% Pervious Area 1.750 67.67% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 5S: Offsite Untreated Runoff = 0.10 cfs @ 11.99 hrs, Volume= 0.006 af, Depth= 0.35" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 0.206 61 >75% Grass cover, Good, HSG B 0.206 100.00% Pervious Area PostDev PostDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 4 Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 6S: Offsite Treated Runoff = 0.15 cfs @ 11.99 hrs, Volume= 0.009 af, Depth= 0.35" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 1 yr, 24 hr Rainfall=2.97" Area (ac) CN Description 0.317 61 >75% Grass cover, Good, HSG B 0.317 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond 5P: StormTech Inflow Area = 2.903 ac, 60.28% Impervious, Inflow Depth = 1.50" for 1 yr, 24 hr event Inflow = 7.69 cfs @ 11.96 hrs, Volume= 0.362 of Outflow = 0.15 cfs @ 16.07 hrs, Volume= 0.265 af, Atten= 98%, Lag= 247.0 min Primary = 0.15 cfs @ 16.07 hrs, Volume= 0.265 of Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Peak Elev= 523.01' @ 16.07 hrs Surf.Area= 3,699 sf Storage= 10,658 cf Plug -Flow detention time= 705.9 min calculated for 0.265 of (73% of inflow) Center -of -Mass det. time= 608.9 min ( 1,433.3 - 824.4 ) Volume Invert Avail.Storage Storage Description #1 520.75' 9,052 cf StormTech MC-4500 x 85 Inside #2 Effective Size= 90.4"W x 60.0"H => 26.46 sf x 4.03'L = 106.5 cf Overall Size= 100.0"W x 60.0"H x 4.331 with 0.31' Overlap #2 518.00' 9,326 cf Custom Stage Data (Prismatic)Listed below (Recalc) 32,366 cf Overall - 9,052 cf Embedded = 23,315 cf x 40.0% Voids 18,378 cf Total Available Storage Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic -feet) (cubic -feet) 518.00 3,699 0 0 526.75 3,699 32,366 32,366 Device Routing Invert Outlet Devices #1 Primary 520.75' 36.0" Round Culvert L= 150.0' Ke= 0.600 Inlet / Outlet Invert= 520.75' / 518.00' S= 0.0183 '/' Cc= 0.900 n= 0.012 #2 Device 1 520.75' 2.0" Vert. Orifice/Grate C= 0.600 PostDev PostDev Type 1124-hr 1 yr, 24 hr Rainfall=2.97" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 5 #3 Device 1 523.02' 10.0" Vert. Orifice/Grate C= 0.600 #4 Primary 526.70' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 0.70 Width (feet) 4.00 4.00 Primary OutFlow Max=0.15 cfs @ 16.07 hrs HW=523.01' (Free Discharge) Culvert (Passes 0.15 cfs of 27.35 cfs potential flow) 2=Orifice/Grate (Orifice Controls 0.15 cfs @ 7.10 fps) 3=Orifice/Grate ( Controls 0.00 cfs) 4=Custom Weir/Orifice ( Controls 0.00 cfs) Summary for Link 4L: POA Inflow Area = 3.463 ac, 50.62% Impervious, Inflow Depth > 0.98" for 1 yr, 24 hr event Inflow = 0.35 cfs @ 12.00 hrs, Volume= 0.282 of Primary = 0.35 cfs @ 12.00 hrs, Volume= 0.282 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs PostDev PostDev Type/1 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 6 Time span=0.00-48.00 hrs, dt=0.05 hrs, 961 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1 S: Onsite Untreated Runoff Area=0.354 ac 0.85% Impervious Runoff Depth=1.63" Tc=5.0 min CN=61 Runoff=1.02 cfs 0.048 of Subcatchment2S: Onsite Treated Runoff Area=2.586 ac 67.67% Impervious Runoff Depth=3.87" Tc=5.0 min CN=86 Runoff=17.23 cfs 0.834 of Subcatchment5S: Offsite Untreated Runoff Area=0.206 ac 0.00% Impervious Runoff Depth=1.63" Tc=5.0 min CN=61 Runoff=0.59 cfs 0.028 of Subcatchment6S: Offsite Treated Runoff Area=0.317 ac 0.00% Impervious Runoff Depth=1.63" Tc=5.0 min CN=61 Runoff=0.91 cfs 0.043 of Pond 5P: StormTech Peak Elev=526.75' Storage=18,375 cf Inflow=18.13 cfs 0.877 of Outflow=5.17 cfs 0.779 of Link 4L: POA Inflow=5.77 cfs 0.855 of Primary=5.77 cfs 0.855 of Total Runoff Area = 3.463 ac Runoff Volume = 0.953 of Average Runoff Depth = 3.30" 49.38% Pervious = 1.710 ac 50.62% Impervious = 1.753 ac PostDev PostDev Type/1 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 7 Summary for Subcatchment 1S: Onsite Untreated Runoff = 1.02 cfs @ 11.97 hrs, Volume= 0.048 af, Depth= 1.63" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 0.351 61 >75% Grass cover, Good, HSG B 0.003 98 0.354 61 Weighted Average 0.351 99.15% Pervious Area 0.003 0.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 2S: Onsite Treated Runoff = 17.23 cfs @ 11.95 hrs, Volume= 0.834 af, Depth= 3.87" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 1.750 98 0.836 61 >75% Grass cover, Good, HSG B 2.586 86 Weighted Average 0.836 32.33% Pervious Area 1.750 67.67% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 5S: Offsite Untreated Runoff = 0.59 cfs @ 11.97 hrs, Volume= 0.028 af, Depth= 1.63" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 0.206 61 >75% Grass cover, Good, HSG B 0.206 100.00% Pervious Area PostDev PostDev Type // 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/16/2020 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 8 Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment 6S: Offsite Treated Runoff = 0.91 cfs @ 11.97 hrs, Volume= 0.043 af, Depth= 1.63" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10 yr, 24 hr Rainfall=5.43" Area (ac) CN Description 0.317 61 >75% Grass cover, Good, HSG B 0.317 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond 5P: StormTech Inflow Area = 2.903 ac, 60.28% Impervious, Inflow Depth = 3.63" for 10 yr, 24 hr event Inflow = 18.13 cfs @ 11.95 hrs, Volume= 0.877 of Outflow = 5.17 cfs @ 12.10 hrs, Volume= 0.779 af, Atten= 71 %, Lag= 8.6 min Primary = 5.17 cfs @ 12.10 hrs, Volume= 0.779 of Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Peak Elev= 526.75' @ 12.10 hrs Surf.Area= 3,699 sf Storage= 18,375 cf Plug -Flow detention time= 331.6 min calculated for 0.779 of (89% of inflow) Center -of -Mass det. time= 276.0 min ( 1,076.5 - 800.5 ) Volume Invert Avail.Storage Storage Description #1 520.75' 9,052 cf StormTech MC-4500 x 85 Inside #2 Effective Size= 90.4"W x 60.0"H => 26.46 sf x 4.03'L = 106.5 cf Overall Size= 100.0"W x 60.0"H x 4.331 with 0.31' Overlap #2 518.00' 9,326 cf Custom Stage Data (Prismatic)Listed below (Recalc) 32,366 cf Overall - 9,052 cf Embedded = 23,315 cf x 40.0% Voids 18,378 cf Total Available Storage Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic -feet) (cubic -feet) 518.00 3,699 0 0 526.75 3,699 32,366 32,366 Device Routing Invert Outlet Devices #1 Primary 520.75' 36.0" Round Culvert L= 150.0' Ke= 0.600 Inlet / Outlet Invert= 520.75' / 518.00' S= 0.0183 '/' Cc= 0.900 n= 0.012 #2 Device 1 520.75' 2.0" Vert. Orifice/Grate C= 0.600 PostDev PostDev Type/1 24-hr 10 yr, 24 hr Rainfall=5.43" Prepared by {enter your company name here) Printed 3/16/2020 HvdroCAD® 9.10 s/n 07054 © 2011 HvdroCAD Software Solutions LLC Paae 9 #3 Device 1 523.02' 10.0" Vert. Orifice/Grate C= 0.600 #4 Primary 526.70' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 0.70 Width (feet) 4.00 4.00 Primary OutFlow Max=5.14 cfs @ 12.10 hrs HW=526.74' (Free Discharge) Culvert (Passes 5.03 cfs of 67.62 cfs potential flow) 2=Orifice/Grate (Orifice Controls 0.26 cfs @ 11.70 fps) 3=Orifice/Grate (Orifice Controls 4.77 cfs @ 8.75 fps) 4=Custom Weir/Orifice (Weir Controls 0.11 cfs @ 0.67 fps) Summary for Link 4L: POA Inflow Area = 3.463 ac, 50.62% Impervious, Inflow Depth > 2.96" for 10 yr, 24 hr event Inflow = 5.77 cfs @ 12.04 hrs, Volume= 0.855 of Primary = 5.77 cfs @ 12.04 hrs, Volume= 0.855 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Time of Concentrations Calculations Pre -Development Time of Concentration Calculations Nomographs Proffit Road Townhomes South Pre -Development Time of Concentration Calculations POA 1 (Red) 100 ft overland flow -turf 6.2% slope 0.33 C-value 10.8 min. Seelye Chart 238 ft s. c. flow -turf 2.1% slope 1.0 fps velocity 4.0 min. NEH Figure 15-4 187 ft s. c. flow -woods 1.6% slope 0.6 fps velocity 5.2 min. NEH Figure 15-4 20.0 min. 35 I 30 V Paved 9 z 25 o .e 300 Bare o 2 p Cn w 200 Soil Poor Grass z \Surface Q_ 5 w Li w Average i ,4 z 75 0.5 w z L- Grass U 1.0 0 15 w Sp 9 \ 2'0 J cn/ / / H- Dense Grass \ a z 7 0 z \ z a N 6 0 J / 10 Cr o 50 ' 20 Uj CL w = 40 10 zz U 30 9 w z Li z I L g 20 7 10 6 OVERLAND FLOW TIME (Seelye Chart) Source: Data Book for Civil Engineers, E.E. Seelye Plate 5-1 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.09 0.08 0.07 c 0.06 0.05 0.04 0.03 0.02 0.01 0.005 Velocity (ftls) Stormwater Quality Calculations Pre -Development VRRM Landuse Map Post -Development VRRM Landuse Map VRRM Redevelopment Spreadsheet PRE -DEVELOPMENT VRRM LANDUSE MAP MwvNmmsn News, amon Mae sees 0 a am ..�n�.•Na7 mu_■■ •�ees,..64Y.._.._ FMP 32-29D -�� L-IIV ITS OF DISTURBANCE USED AS BOUNDARY FOR WATER QUALITY IMPROVEMENTS 07 o- 7I TMP 32-35 1.92 AC TURF (NO HATCH) 1.06 AC WOODS ASSUMED TO BE CONSERVATIVE 2 60 0.31 AC IMPERVIOUS )I1 0 60 120 ALL HSG B 180 Scale: 1 "=60' POST -DEVELOPMENT VRRM LANDUSE MAP n�.■�n...■■......... oftesm TMP 32-29D LIMITS OF DISTURBANCE USED AS BOUNDARY FOR WATER QUALITY IMPROVEMENTS ALL HSG B :1 Scale: 1 "=60' CLEAR ALL _ _--- - anal reswts Maximum reduction required: 20%--- The sites net increase in impervious cover (acres) is: 1.452 Post -Development TP Load Reduction for Site (Ib/yr): 2.53 - • m Post -Development Land Cover (acres) 11 LAND COVER SUMMARY -- PRE -REDEVELOPMENT -- --=--=--= LAND COVER SUMMARY -- POST DEVELOPMENTWeighted - R,&—t) Treatment Volume and Nutrient Load pmr Redeveloped Are. Post -Development Requirement for Site Area Drainage Area A Drainage Area A Land Cover (acres) Land Cover Land, A Soils B Soils C Soils D Soils Totals Forest/Open Space (acres) 0.00 0.00 Managed Turf (acres) 0.84 0.84 0.20 Impervious Cover (acres) 1.75 1.75 0.95 Total 2.59 Stormwater Best Manaeement Practices (FIR = Runoff Reduction) Total Phosphorus Available for Removal in D.A. A (Ib/yr) 4.17 Post Development Treatment Volume in D.A. A (fta) 6,642 Runoff Managed Impervious Volume from Runoff Remaining Total BMP Phosphorus Phosphorus UntreatedPhosphorus Remaining Practice Reduction Turf Credit Cover Credit Upstream Reduction Runoff Treatment Removal Load m Phosphorus Removed By Phosphoru Credit (%) Area (acres) Area (acres) Practice (ft') (ft') Volume 3 Volume (ft) Efficiency (%) Upstream Upstream Load to Practice (lb) s Load (lb) 14. Treatment a (ft) Practices (lb) Practice (lb) manufactured 14.a. Manufactured Treatment Device- 0 0.84 1.75 0 0 6,642 6,642 40 0.00 4.17 1.67 2.50 Hydrodynamic TOTAL IMPERVIOUS COVER TREATED (a<) 1.75 AREA CHECK: OK. TOTAL MANAGED TURF AREA TREATED (ac) 0.84 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 2.83 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr)M21 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A (lb/yr) TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. A (lb/yr) TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. A (lb/yr) SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 NITROGEN REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 TOTAL NITROGEN REMOVED IN D.A. A(lb/yr) 0.00 Site Results (Water Quality Compliance) Area Checks D.A. A D.A. B D.A. C D.A. D D.A. E AREA CHECK FOREST/OPEN SPACE (ac) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER (ac) 1.75 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED (ac) 1.75 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA (ac) 0.84 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA TREATED (ac) 0.84 0.00 0.00 0.00 0.00 OK. AREA CHECK OK. OK. OK. OK. OK. Site Treatment Volume (ft3) 7,195 Runoff Reduction Volume and TP By Drainage Area D.A. D D.A. E TOTAL RUNOFF REDUCTION VOLUME ACHIEVED (fe) 0 0 0 0 0 0 TP LOAD AVAILABLE FOR REMOVAL (Ib/yr) 4.17 0.00 0.00 0.00 0.00 4.17 TP LOAD REDUCTION ACHIEVED (Ib/yr) 1.67 0.00 0.00 0.00 0.00 1.67 TP LOAD REMAINING (Ib/yr) 2.51 0.00 0.00 0.00 0.00 2.51 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) 0.00 0.00 0.00 0.00 0.00 0.00 Total Phosphorus FINAL POST -DEVELOPMENT TP LOAD (Ib/yr)jj 4.52 TP LOAD REDUCTION REQUIRED (Ib/yr)jj 2.83 TP LOAD REDUCTION ACHIEVED (Ib/yr) 1.67 TP LOAD REMAINING (Ib/yr): 2.85 REMAINING TP LOAD REDUCTION REQUIRED (Ib/yr): 1.16 Total Nitrogen (For Information Purposes) POST -DEVELOPMENT LOAD (Ib/yr) 32.34 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) REMAINING POST -DEVELOPMENT NITROGEN LOAD (Ib/yr) Virginia Runoff Reduction Method Worksheet DEQ Virginia Runoff Reduction Method Re -Development Compliance Spreadsheet - Version 3.0 BMP Design Specifications List: 2013 Draft Stds & Specs Site Summary Project Title: Proffit South Date: 43887 Total Rainfall (in): 43 Total Disturbed Acreage: 3.30 Site Land Cover Summary Pre-ReDevelopment Land Cover (acres) ®®® ®®® ®®®®®®® ®®®®® Forest/Open (acres) A soils B Soils C Soils D Soils Totals % of Total 0.00 1.06 0.00 0.00 1.06 32 Managed Turf (acres) 0.00 1.92 0.00 0.00 1.92 58 Impervious Cover (acres) 0.00 0.31 0.00 0.00 0.31 9 3.30 100 Post -Re Development Land Cover (acres) ® ® ® ® A soils B Soils C Soils D Soils Totals % of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 0.00 1.53 0.00 0.00 1.53 46 Impervious Cover (acres) 0.00 1.76 0.00 0.00 1.76 54 3.30 100 Site Tv and Land Cover Nutrient Loads Final Post -Development Post- Post-ReDevelo ment ( P Post- Develo Development Adjusted Pre- t ®®® ®®®®®®®®® ®®®®®®®®® ®®®®®®®®® ®®®®®® &New Impervious) ReDevelopment (New Impervious) ReDevelopment Site Rv 0.60 0.33 0.95 0.33 Treatment Volume (ft) 7,195 2,187 5,007 2,187 TP Load (lb/yr) 4.52 1.37 3.15 1.37 Total TP Load Reduction Required (lb/yr) 2.83 0.27 2.55 Final opment Load Pre- ®®®®®®®® ®®®®®®®® ®®®®®®®® ®®®®®®® a opmentl ( Post-ReDe & New Impervious) ReDe elopment TN Load (Ib/yr) 32.34 11.63 Pre- Final Final Post -Development Post-ReDevelopment TP TP Load per acre Load per acre TP Load per acre (Ib/acre/yr) (Ib/acre/yr) (lb/acre/yr) 0.75 1.37 0.75 Summary Print Virginia Runoff Reduction Method Worksheet Site Compliance Summary Maximum %Reduction Required Below 20% Pre-ReDevelopment Load Total Runoff Volume Reduction (ft) 0 Total TP Load Reduction Achieved (Ib/yr) 1.67 Total TN Load Reduction Achieved (lb/yr) 0.00 Remaining Post Development TP Load (lb/yr) 2.85 Remaining TP Load Reduction (lb/yr) Required 1.16 Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area Summary Drainage Area Compliance Surnmar Summary Print Independent Reports Excerpt from NRCS Soils Report NOAA Precipitation Report 3 a" 725010 725040 38° 7 54 N R Custom Soil Resource Report Soil Map 725070 725100 725130 725160 'l f a. w it p may not be valid at M'i scale: ; 38° 7' 46" N 725010 725D40 725070 725100 725130 3 Map Scale: 1:1,270 W printed on A portrait (8.5" x 11") sheet Meters N 0 15 30 60 90 Feet 0 50 100 200 300 Map projection: Web Mercator Comer coordinates: WCS84 Edge tics: UTM Zone 17N WGS84 6 725160 3 a" 725190 91 38° 7S4" N 38° 746" N 725190 3 MAP LEGEND Area of Interest (AOI) 0 Area of Interest (AOI) Soils 0 Soil Map Unit Polygons im 0 Soil Map Unit Lines ■ Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit .4 Gravelly Spot 0 Landfill Lava Flow Marsh or swamp + Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip oa Sodic Spot Custom Soil Resource Report MAP INFORMATION A Spoil Area The soil surveys that comprise your AOI were mapped at 1:15,800. Stony Spot Very Stony Spot Warning: Soil Map may not be valid at this scale. Wet Spot Enlargement of maps beyond the scale of mapping can cause Other misunderstanding of the detail of mapping and accuracy of soil .- Special Line Features line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed Water Features scale. - Streams and Canals Transportation Please rely on the bar scale on each map sheet for map �}} Rails measurements. Interstate Highways Source of Map: Natural Resources Conservation Service US Routes Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Major Roads Local Roads Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts Background distance and area. A projection that preserves area, such as the Aerial Photography Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Albemarle County, Virginia Survey Area Data: Version 13, Sep 17, 2019 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: May 20, 2019—Aug 1, 2019 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 7 Custom Soil Resource Report Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 27B Elioak loam, 2 to 7 percent slopes Totals for Area of Interest 4.0 4.0 100.0% 100.0% Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit. A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils. Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a given area, the contrasting minor components are identified in the map unit descriptions along with some characteristics of each. A few areas of minor components may not have been observed, and consequently they are not mentioned in the descriptions, especially where the pattern was so complex that it was impractical to make enough observations to identify all the soils and miscellaneous areas on the landscape. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The objective of mapping is not to delineate pure taxonomic classes but rather to separate the landscape into landforms or landform segments that have similar use and management requirements. The delineation of such segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, however, onsite investigation is needed to define and locate the soils and miscellaneous areas. 0 Custom Soil Resource Report Albemarle County, Virginia 2713—Elioak loam, 2 to 7 percent slopes Map Unit Setting National map unit symbol: kb8y Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: All areas are prime farmland Map Unit Composition Elioak and similar soils: 80 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Elioak Setting Landform: Hillslopes Landform position (two-dimensional): Summit Landform position (three-dimensional): Interfluve Down -slope shape: Convex Across -slope shape: Convex Parent material: Residuum weathered from mica schist Typical profile H1 - 0 to 8 inches: loam H2 - 8 to 39 inches: silty clay H3 - 39 to 79 inches: silt loam Properties and qualities Slope: 2 to 7 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.20 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Moderate (about 6.6 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 2e Hydrologic Soil Group: B Hydric soil rating: No 10 11/1/2019 Precipitation Frequency Data Server q) NOAA Atlas 14, Volume 2, Version 3, Location name: Charlottesville, Virginia, 9 USA*J Latitude: 38.1309°, Longitude: -78.420 Elevation: 538.71 ft** � source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PF tabular I PF graphical I Maps & aerials PF tabular 11 PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 11 luration Average recurrence interval (years) 000 1 2 5 10 25 5-min (0.3115-0386) (0.3776-0461) (0.441---0541) (0.495-0609) (0.556-0685) ���� 10-min 0.557 0.666 0.784 0.881 0.990 1.08 ) ( 1.16 ) ( 1.23 ) ( 1.33 ) (0.503-0.617) (0.602-0.738) (0.707-0.866) (0.792-0.974) (0.886-1.09) (0.960-1.19 1.03-1.27 1.09-1.36 1.15-1.47 1.40 (1.21-1.55) 0.697 0.837 0.991 1.11 1.25 1.36 1.46 1.56 1.67 1.76 1 5-min (0.629-0.772) (0.756-0.928) (0.894-1.10) (1.00-1.23) (1.12-1.38) (1.22-1.50) (1.30-1.61) (1.37-1.72) (1.45-1.85) (1.51-1.95) 0.955 1.16 1.41 1.61 1.86 2.06 2.24 2.42 2.66 2.85 30-min (0.862-1.06) (1.05-1.28) (1.27-1.56) (1.45-1.79) (1.66-2.05) 1.45 1.81 2.10 2.48 (1.83-2.26) (1.99-2.47) (2.13-2.67) (2.31-2.94) (2.45-3.16) 1.19 2.78 3.09 3.40 3.82 4.15 60-min (1.08-1.32) (1.31-1.61) (1.63-2.00) (1.89-2.32) (2.22-2.73) (2.48-3.07) (2.74-3.40) (2.99-3.75) (3.32-4.22) (3.58-4.61) 1.43 1.74 2.18 2.56 3.06 3.47 3.90 4.35 4.99 5.52 2-hr (1.27-1.62) (1.54-1.97) (1.93-2.46) (2.27-2.88) (2.69-3.43) 1.90 2.38 2.79 3.33 (3.04-3.90) (3.39-4.38) (3.75-4.89) (4.25-5.61) (4.66-6.23) 1.57 3.79 4.27 4.77 5.47 6.07 3-hr (1.38-1.79) (1.67-2.17) (2.09-2.71) (2.45-3.18) (2.91-3.79) 2.41 2.99 3.52 4.23 (3.29-4.30) (3.68-4.84) (4.07-5.41) (4.61-6.22) (5.06-6.91) 1.99 4.86 5.52 6.23 7.26 8.17 6-hr (1.77-2.26) (2.13-2.74) (2.64-3.39) (3.09-3.99) (3.69-4.80) (4.21-5.49) (4.73-6.24) (5.29-7.05) (6.07-8.22) (6.73-9.26 ) 6.26 11.1 12-hr (2.21 2985) (2. 6-03.44) (3.31 4529) (3. 045406) (4. 0 6014) 3.60 4.60 5.43 6.67 (5. 0-7..11) (6. 3 8017) (6.91 9333) (8.04761.1) (9.02-12.7) 2.97 7.73 8.90 10.2 12.1 13.8 24-hr (2.67-3.35) (3.23-4.05) (4.11-5.17) (4.84-6.10) (5.91-7.47) 4.25 5.40 6.34 7.71 (6.80-8.64) (7.76-9.93) (8.79-11.3) (10.3-13.5) (11.5-15.3) 3.50 8.86 10.1 11.5 13.4 15.1 2-day (3.16-3.91) (3.83-4.74) (4.85-6.02) (5.68-7.07) (6.86-8.57) 4.52 5.74 6.74 8.20 (7.83-9.84) (8.86-11.2) (9.97-12.7) (11.5-15.0) (12.8-16.9) 3.73 9.41 10.7 12.2 14.2 16.0 3-day (3.39-4.14) (4.10-5.01) (5.20-6.36) (6.09-7.46) (7.36-9.06) (8.40-10.4) (9.50-11.9) (10.7-13.4) (12.4-15.8) (13.7-17.8) 3.96 4.79 6.08 7.15 8.68 9.97 11.4 12.9 15.0 16.9 4-day (3.62-4.37) (4.38-5.29) (5.55-6.71) (6.50 7.86) (7.86-9.54) 5.54 6.92 8.06 9.69 (8.97-11.0) (10.1-12.5) (11.4-14.1) (13.2-16.6) (14.6-18.7) 4.60 11.0 12.5 14.1 16.3 18.2 7-day (4.21-5.05) (5.07-6.07) (6.33-7.59) (7.35-8.83) (8.79-10.6) (9.97-12.1) (11.2-13.7) (12.5-15.4) (14.3-17.9) (15.8-20.0) 7.73 10-day (4. 05?68) (5.767 6?81) (7.11 8 40) (8. 9 9369) (9.69-111.5) 8.19 9.89 11.2 13.0 (10.9-13.0) 14.5 (12 13 4.6) (13.4- 6.3) 17.4 (15 2-18.7) (16.6 0.7) 6.86 15.9 19.4 21.0 20-day (6.41-7.38) (7.65-8.80) (9.22-10.6) (10.4-12.0) (12.1-14.0) 9.98 11.8 13.2 15.0 (13.4-15.5) 16.4 (14.7-17.1) 17.7 (15.9-18.7) (17.7-20.9) (19.0-22.7) 8.42 19.0 20.8 22.1 30-day (7.91-8.99) (9.38-10.7) (11.1-12.6) (12.4-14.1) (14.0-16.0) (15.3-17.5) 19.6 (16.5-18.9) (17.6-20.3) (19.1-22.3) (20.2-23.7) 10.5 12.4 14.5 16.1 18.1 21.0 22.4 24.2 25.5 45-day (9.91-11.2) (11.7-13.2) (13.7-15.4) (15.1-17.0) (17.0-19.2) (18.4-20.8) (19.6-22.3) (20.9-23.8) (22.4-25.8) (23.5-27.2) 12.4 14.5 16.8 18.4 20.6 22.1 23.6 28.1 25.0 26.8 60-day (11.7-13.1) (13.7-15.4) (15.8-17.7) (17.4-19.5) (19.4-21.7) (20.8-23.4) (22.2-25.0) (23.5-26.5) (25.0-28.4) (26.1-29.9) Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top �� 50 100 200 500 1000 0.677 0.729 0.778 0.839 0.889 (0.603 0.745) (0.645 0.802) (0.684 0.858) (0.730 0.928) (0.766-0.986) https://hdsc. nws. noaa.gov/hdsc/pfds/pfds_printpage.html?lat=38.1309&Ion=-78.4283&data=depth&units=engl ish&series=pds 1 /4 https://hdsc. nws. noaa.gov/hdsc/pfds/pfds_printpage.html?lat=38.1309&Ion=-78.4283&data=depth&units=engl ish&series=pds 1 /4