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HomeMy WebLinkAboutWPO201300068 Calculations 2013-10-28 SHIMP PROJECT MANAGEMENT CIVIL ENGINEERING LAND PLANNING ENGINEERING December 13, 2013 Albemarle County Community Development Department Regarding: Houndstooth Stormwater Quality and Quantity Plan Enclosed are the calculations and details relating to stormwater quantity and quality. Pollutants are treated with a biofilter which is graded to detain the 25-year storm. Summary Table for project outflows: Pre-Development Post-Development 2-Yr Flow 3.26 cfs 3.16 cfs 10-Yr Flow 15.97 cfs 15.89 cfs Contents: Pre-Development Stormwater Management Calculations: Pre-Development Drainage Map Pre-Development HydroCAD Analysis Post-Development Stormwater Management Calculations: Post-Development Drainage Map Post-Development HydroCAD Analysis Stormwater Quality Calculations: a Albemarle Short Form BMP Calculations Independent Reports: Excerpt from NRCS Soils Report NOAA Precipitation Report arr a a a am. a a Pre-Development Stormwater Management Calculations Pre-Development Drainage Map Pre-Development HydroCAD Analysis o, 0 N / \ \ \ \ \ \ \\ \\\\\ \\ _ � \ \ �/ / / \ \ / f ' \ \ \\ \ \\\ ` \ \ \ \\ \\\ \ 1 < / I I ET E a 7 ' \` 11 \ \\ \ \ \\\� \ \ \ \ 1 1 / _ 1 I I \\ I I I f \ \ 1 \ \ \\\\ \ \ \ V/1 1 r � � J \ I I I / _/ 1 I \\ 1 I1 \\ 1111\\ \I l \ \/ / (/ / / / / ) \1 \ / GI N CD \ \ \ \ \��\1\ \ I\ ( \V/ I 1 \ (' / / //' 77 \ 3 \ \ \ \ 1 II ( I // - -I I / / I \ I I I 2 , ( ) W ° I/ \\ I ,' 1 1 I II \ \"/ 1 / // 7 / 1 / l IA U, — \ ) / / / l / 1 iI / / 1 / ) / o Q Q r\/ / I I ( ` `/ / 1\\\ N/ / / / / i // / // // /� � /7 I I I \ \ \ \ I 1 \ 1 / �/ // / N C a I 1 \ \ \ \ 11/ - - \ I —/ / 7 ' / ] �/ // /l / /) / / i ) I — \ o) 1\ \ Il 7 // K / / � / / / N_/ o° \ 1 / l �� \\ \ / ( J /�/7,/// — -J' / / I � , - -/ . l /��-oo�/ / // 3 CD Q N\ \ i I \ / \ /J / � // /` / 3 \ \ \ \ I N N // — N— _ / / / \ \ \ \ Q N __.-- ---' // \ / 7/ / '- - -640 \ \\ \ � � \ �� �N ---,( \I I // / / 5 CP 1 \ 1 I /I / 7 / 7�-- - - ( ' / I �\�� I / / / / // L- - - �� 0 \ \ 0-,- I)- ■ \ \ \ / I I I \\ // '' j' f j — Ni ' I / / I 1 J / / i I I /J l 1 / / ` / 2/- � \ N 0 / / / �, ' - - — — 3 n / \ I / / / / — r _ — �, , \ I . �/ / //7 \� , - - 1 1 I I A 1 ■ / _.4.r j-, 4,>- /. 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Printed 10/17/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 1 Summary for Subcatchment 1: DA Runoff = 3.26 cfs @ 12.49 hrs, Volume= 0.681 af, Depth> 0.38" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 2yr Rainfall=3.62" Area (ac) CN Description 21.504 55 Woods, Good, HSG B * 0.062 98 Ex. Building and Gravel Drive 21.566 55 Weighted Average 21.504 99.71% Pervious Area 0.062 0.29% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 37.6 Direct Entry, aa. Houndstooth Pre-Development Type 1124-hr 10yr Rainfall=5.46" Prepared by Shimp Engineering, P.C. Printed 10/17/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: DA Runoff = 15.97 cfs @ 12.40 hrs, Volume= 2.155 af, Depth> 1.20" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 10yr Rainfall=5.46" Area (ac) CN Description 21.504 55 Woods, Good, HSG B * 0.062 98 Ex. Building and Gravel Drive .� 21.566 55 Weighted Average 21.504 99.71% Pervious Area 0.062 0.29% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 37.6 Direct Entry, a a a a a a a a a Post-Development Stormwater Management Calculations Post-Development Drainage Map Post-Development HydroCAD Analysis a a a a a im•N•1 • `•■ n.w. ...00l i..•.11 i■. w.... Illmmill i....rI M mli ___ ___ Nom Ili .ma.ri ....a ..••ri ...., CO N LO Q1 O O Uc cn O Vl rt 0 CD < CD n 7 ap 0 o O- -0 3 cn - CD n 0 N -, . W N 3 ZD LP 0 X X 0 In ti_ � O O co co O _. w O n J —. 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Prepared by Shimp Engineering, P.C., Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC a Houndstooth Post-Development Type 1124-hr 2yr Rainfall=3.62" Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: DA-1 Runoff = 4.45 cfs @ 12.41 hrs, Volume= 0.775 af, Depth> 0.45" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 2yr Rainfall=3.62" Area (sf) CN Description 748,231 55 Woods, Good, HSG B 108,900 61 >75% Grass cover, Good, HSG B 9,000 98 New Buildings 19,026 98 New Road 8,717 98 Driveway 893,874 57 Weighted Average 857,131 95.89% Pervious Area 36,743 4.11% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 34.8 Direct Entry, a Summary for Pond 2: Sediment Forebay Inflow Area = 20.521 ac, 4.11% Impervious, Inflow Depth > 0.45" for 2yr event Inflow = 4.45 cfs @ 12.41 hrs, Volume= 0.775 of Outflow = 4.44 cfs @ 12.42 hrs, Volume= 0.764 af, Atten= 0%, Lag= 0.7 min Primary = 4.44 cfs @ 12.42 hrs, Volume= 0.764 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 590.26' @ 12.42 hrs Surf.Area= 1,332 sf Storage= 745 cf Plug-Flow detention time= 10.9 min calculated for 0.764 af(99% of inflow) Center-of-Mass det. time= 3.8 min ( 940.4 - 936.5 ) Volume Invert Avail.Storage Storage Description #1 589.60' 15,280 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.60 955 0 0 a 590.00 1,169 425 425 592.00 2,443 3,612 4,037 594.00 4,184 6,627 10,664 .. 595.00 5,048 4,616 15,280 Device Routing Invert Outlet Devices #1 Primary 590.00' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 2.00 4.00 5.00 Width (feet) 10.00 18.00 57.00 63.00 a Houndstooth Post-Development Type 1124-hr 2yr Rainfall=3.62" �• Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 3 Primary OutFlow Max=4.43 cfs @ 12.42 hrs HW=590.26' (Free Discharge) 1=Custom Weir/Orifice (Weir Controls 4.43 cfs @ 1.64 fps) Summary for Subcatchment 3: DA-2 Runoff = 0.47 cfs @ 11.97 hrs, Volume= 0.021 af, Depth> 0.97" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 2yr Rainfall=3.62" a Area (sf) CN Description 9,376 61 >75% Grass cover, Good, HSG B 2,167 98 New Road 11,543 68 Weighted Average 9,376 81.23% Pervious Area 2,167 18.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond 4: Biofilter a [81] Warning: Exceeded Pond 2 by 0.78' @ 12.77 hrs Inflow Area = 20.786 ac, 4.30% Impervious, Inflow Depth > 0.45" for 2yr event Inflow = 4.49 cfs @ 12.42 hrs, Volume= 0.786 af Outflow = 3.08 cfs @ 12.72 hrs, Volume= 0.712 af, Atten= 32%, Lag= 18.2 min Primary = 3.08 cfs @ 12.72 hrs, Volume= 0.712 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 590.97' @ 12.72 hrs Surf.Area= 3,775 sf Storage= 5,098 cf Plug-Flow detention time= 71.1 min calculated for 0.711 af(91% of inflow) Center-of-Mass det. time= 27.2 min ( 965.6 - 938.4 ) Volume Invert Avail.Storage Storage Description #1 589.30' 26,885 cf Custom Stage Data (Prismatic)Listed below (Recalc) a Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.30 1,935 0 0 590.00 3,086 1,757 1,757 592.00 4,500 7,586 9,343 594.00 6,329 10,829 20,172 595.00 7,096 6,713 26,885 a yr Houndstooth Post-Development Type 1124-hr 2yr Rainfall=3.62" �. Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 4 Device Routing Invert Outlet Devices #1 Primary 585.50' 24.0" Round Culvert L= 64.7' Ke= 0.500 Inlet/Outlet Invert= 585.50' /585.00' S= 0.0077 '/' Cc= 0.900 n= 0.013 #2 Device 1 590.30' 6.0" Vert. Orifice/Grate X 5.00 C= 0.600 #3 Device 1 591.10' 1.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #4 Device 1 592.80' 4.7' long Sharp-Crested Rectangular Weir 0 End Contraction(s) #5 Primary 593.50' 10.0' long x 127.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 Primary OutFlow Max=3.08 cfs @ 12.72 hrs HW=590.97' (Free Discharge) -'=Culvert (Passes 3.08 cfs of 32.00 cfs potential flow) -2=Orifice/Grate (Orifice Controls 3.08 cfs @ 3.13 fps) -3=Sharp-Crested Rectangular Weir( Controls 0.00 cfs) -4=Sharp-Crested Rectangular Weir( Controls 0.00 cfs) -5=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Subcatchment 5: Bypass Runoff = 0.63 cfs @ 12.04 hrs, Volume= 0.041 af, Depth> 0.62" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 2yr Rainfall=3.62" Area (sf) CN Description 33,982 61 >75% Grass cover, Good, HSG B 33,982 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Summary for Link 6: Point of Analysis Inflow Area = 21.566 ac, 4.14% Impervious, Inflow Depth > 0.42" for 2yr event Inflow = 3.16 cfs @ 12.72 hrs, Volume= 0.752 af Primary = 3.16 cfs @ 12.72 hrs, Volume= 0.752 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs a a Houndstooth Post-Development Type 1124-hr 10yr Rainfall=5.46" Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment 1: DA-1 Runoff = 18.76 cfs @ 12.34 hrs, Volume= 2.291 af, Depth> 1.34" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 10yr Rainfall=5.46" Area (sf) CN Description 748,231 55 Woods, Good, HSG B 108,900 61 >75% Grass cover, Good, HSG B 9,000 98 New Buildings 19,026 98 New Road 8,717 98 Driveway 893,874 57 Weighted Average 857,131 95.89% Pervious Area 36,743 4.11% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 34.8 Direct Entry, a Summary for Pond 2: Sediment Forebay Inflow Area = 20.521 ac, 4.11% Impervious, Inflow Depth > 1.34" for 10yr event Inflow = 18.76 cfs @ 12.34 hrs, Volume= 2.291 af Outflow = 18.72 cfs @ 12.35 hrs, Volume= 2.279 af, Atten= 0%, Lag= 0.6 min Primary = 18.72 cfs @ 12.35 hrs, Volume= 2.279 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 590.64' @ 12.35 hrs Surf.Area= 1,580 sf Storage= 1,311 cf Plug-Flow detention time= 4.4 min calculated for 2.278 af(99% of inflow) Center-of-Mass det. time= 1.6 min ( 895.7 - 894.1 ) a Volume Invert Avail.Storage Storage Description #1 589.60' 15,280 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.60 955 0 0 a 590.00 1,169 425 425 592.00 2,443 3,612 4,037 594.00 4,184 6,627 10,664 595.00 5,048 4,616 15,280 Device Routing Invert Outlet Devices #1 Primary 590.00' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 2.00 4.00 5.00 Width (feet) 10.00 18.00 57.00 63.00 Houndstooth Post-Development Type 1124-hr 10yr Rainfall=5.46" Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 6 Primary OutFlow Max=18.70 cfs @ 12.35 hrs HW=590.64' (Free Discharge) t-1=Custom Weir/Orifice (Weir Controls 18.70 cfs @ 2.57 fps) Summary for Subcatchment 3: DA-2 Runoff = 1.09 cfs @ 11.96 hrs, Volume= 0.049 af, Depth> 2.21" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 10yr Rainfall=5.46" Area (sf) CN Description 9,376 61 >75% Grass cover, Good, HSG B 2,167 98 New Road 11,543 68 Weighted Average 9,376 81.23% Pervious Area 2,167 18.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond 4: Biofilter a [81] Warning: Exceeded Pond 2 by 2.17' @ 12.56 hrs Inflow Area = 20.786 ac, 4.30% Impervious, Inflow Depth > 1.34" for 10yr event Inflow = 18.85 cfs @ 12.35 hrs, Volume= 2.328 of Outflow = 15.63 cfs @ 12.52 hrs, Volume= 2.248 af, Atten= 17%, Lag= 10.3 min Primary = 15.63 cfs @ 12.52 hrs, Volume= 2.248 af a Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 592.73' @ 12.52 hrs Surf.Area= 5,166 sf Storage= 12,862 cf a Plug-Flow detention time= 31.6 min calculated for 2.248 af(97% of inflow) Center-of-Mass det. time= 13.5 min (908.1 - 894.6) Volume Invert Avail.Storage Storage Description #1 589.30' 26,885 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.30 1,935 0 0 590.00 3,086 1,757 1,757 592.00 4,500 7,586 9,343 594.00 6,329 10,829 20,172 �. 595.00 7,096 6,713 26,885 a Houndstooth Post-Development Type 1124-hr 10yr Rainfall=5.46" Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 7 Device Routing Invert Outlet Devices #1 Primary 585.50' 24.0" Round Culvert L= 64.7' Ke= 0.500 Inlet/Outlet Invert= 585.50' /585.00' S= 0.0077 '/' Cc= 0.900 n= 0.013 #2 Device 1 590.30' 6.0" Vert. Orifice/Grate X 5.00 C= 0.600 #3 Device 1 591.10' 1.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #4 Device 1 592.80' 4.7' long Sharp-Crested Rectangular Weir 0 End Contraction(s) #5 Primary 593.50' 10.0' long x 127.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 erimary OutFlow Max=15.63 cfs @ 12.52 hrs HW=592.73' (Free Discharge) -=Culvert (Passes 15.63 cfs of 37.75 cfs potential flow) -2=Orifice/Grate (Orifice Controls 6.98 cfs @ 7.11 fps) -3=Sharp-Crested Rectangular Weir(Weir Controls 8.66 cfs @ 4.17 fps) -4=Sharp-Crested Rectangular Weir(Controls 0.00 cfs) -5=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Subcatchment 5: Bypass Runoff = 1.93 cfs @ 12.03 hrs, Volume= 0.107 af, Depth> 1.65" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24-hr 10yr Rainfall=5.46" Area (sf) CN Description 33,982 61 >75% Grass cover, Good, HSG B 33,982 100.00% Pervious Area Tc Length Slope Velocity Capacity Description .. (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Summary for Link 6: Point of Analysis Inflow Area = 21.566 ac, 4.14% Impervious, Inflow Depth > 1.31" for 10yr event Inflow = 15.89 cfs @ 12.52 hrs, Volume= 2.355 af Primary = 15.89 cfs @ 12.52 hrs, Volume= 2.355 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Houndstooth Post-Development Type 1124-hr 25yr Rainfall=6.71" .•• Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCADO 9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 8 Summary for Pond 4: Biofilter [81] Warning: Exceeded Pond 2 by 2.62' @ 12.47 hrs Inflow Area = 20.786 ac, 4.30% Impervious, Inflow Depth > 2.10" for 25yr event Inflow = 31.74 cfs @ 12.34 hrs, Volume= 3.643 af Outflow = 29.88 cfs @ 12.42 hrs, Volume= 3.559 af, Atten= 6%, Lag= 5.2 min Primary = 29.88 cfs @ 12.42 hrs, Volume= 3.559 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 593.47' @ 12.42 hrs Surf.Area= 5,842 sf Storage= 16,932 cf Plug-Flow detention time= 23.6 min calculated for 3.559 af(98% of inflow) Center-of-Mass det. time= 11.1 min ( 891.3 - 880.2 ) Volume Invert Avail.Storage Storage Description #1 589.30' 26,885 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.30 1,935 0 0 590.00 3,086 1,757 1,757 592.00 4,500 7,586 9,343 594.00 6,329 10,829 20,172 595.00 7,096 6,713 26,885 Device Routing Invert Outlet Devices #1 Primary 585.50' 24.0" Round Culvert L= 64.7' Ke= 0.500 Inlet/Outlet Invert= 585.50' /585.00' S= 0.0077 'I' Cc= 0.900 n= 0.013 #2 Device 1 590.30' 6.0" Vert. Orifice/Grate X 5.00 C= 0.600 #3 Device 1 591.10' 1.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #4 Device 1 592.80' 4.7' long Sharp-Crested Rectangular Weir 0 End Contraction(s) #5 Primary 593.50' 10.0' long x 127.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 erimary OutFlow Max=29.87 cfs @ 12.42 hrs HW=593.47' (Free Discharge) - =Culvert (Passes 29.87 cfs of 39.93 cfs potential flow) 2=Orifice/Grate (Orifice Controls 8.07 cfs @ 8.22 fps) 3=Sharp-Crested Rectangular Weir(Weir Controls 13.42 cfs @ 5.03 fps) =Sharp-Crested Rectangular Weir(Weir Controls 8.38 cfs @ 2.67 fps) -5=Broad-Crested Rectangular Weir(Controls 0.00 cfs) a a Houndstooth Post-Development Type 1124-hr 100yr Rainfall=8.94" Prepared by Shimp Engineering, P.C. Printed 12/11/2013 HydroCAD®9.10 s/n 07054 ©2010 HydroCAD Software Solutions LLC Page 9 Summary for Pond 4: Biofilter [81] Warning: Exceeded Pond 2 by 2.91' @ 12.42 hrs Inflow Area = 20.786 ac, 4.30% Impervious, Inflow Depth > 3.66" for 100yr event Inflow = 58.02 cfs @ 12.33 hrs, Volume= 6.336 af Outflow = 56.63 cfs @ 12.37 hrs, Volume= 6.245 af, Atten= 2%, Lag= 2.7 min Primary = 56.63 cfs @ 12.37 hrs, Volume= 6.245 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 594.17' @ 12.37 hrs Surf.Area= 6,460 sf Storage= 21,266 cf Plug-Flow detention time= 17.2 min calculated for 6.242 af(99% of inflow) Center-of-Mass det. time= 9.1 min ( 873.1 - 864.0 ) Volume Invert Avail.Storage Storage Description #1 589.30' 26,885 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area I nc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 589.30 1,935 0 0 590.00 3,086 1,757 1,757 592.00 4,500 7,586 9,343 594.00 6,329 10,829 20,172 595.00 7,096 6,713 26,885 Device Routing Invert Outlet Devices #1 Primary 585.50' 24.0" Round Culvert L= 64.7' Ke= 0.500 Inlet/Outlet Invert= 585.50' /585.00' S= 0.0077 '/' Cc= 0.900 n= 0.013 �,. #2 Device 1 590.30' 6.0" Vert. Orifice/Grate X 5.00 C= 0.600 #3 Device 1 591.10' 1.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #4 Device 1 592.80' 4.7' long Sharp-Crested Rectangular Weir 0 End Contraction(s) #5 Primary 593.50' 10.0' long x 127.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 Primary OutFlow Max=56.61 cfs @ 12.37 hrs HW=594.17' (Free Discharge) -=Culvert (Inlet Controls 41.89 cfs @ 13.34 fps) -2=Orifice/Grate (Passes < 8.99 cfs potential flow) -3=Sharp-Crested Rectangular Weir(Passes < 17.35 cfs potential flow) -4=Sharp-Crested Rectangular Weir(Passes < 24.66 cfs potential flow) -5=Broad-Crested Rectangular Weir(Weir Controls 14.71 cfs @ 2.19 fps) a a Stormwater Quality Calculations Albemarle Short Form BMP Calculations a a a a a a a a a a Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method ... Plan: Houndstooth Water Resources Area: Drinking Water Watershed Preparer: Lauren Gilroy Date: 06-Jun-13 Project Drainage Area Designation Site Area .. L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 I percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 8.74 C pollutant concentration, mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv. area= A(1)43560(0.5/12)/27 RR required removal , L(post)-f x L(pre) .. %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item . pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 21193 0 0 0 0 0 0 "' 0 0 0 0 0 0 0 21193 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 160 10 5 8000 00 0 0 0 0 0 0 0 0 0 0 8000 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 0 0 Gravel areas Area Area x0.70= 0 x0.70= 0 Structures Area no. subtotal Area no. subtotal „ 0 0 0 3000 3 9000 0 0 0 0 0 0 0 0 0 0 0 9000 Actively-grazed pasture& Area Area ... yards and cultivated turf x 0.08= 0 0 x 0.08= 0 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas .• 0 Impervious Cover 0% 10% l(pre) ((post) Rv(post) V 0.14 58.9 New Development(For Development Areas,existing impervious cover<=20%' C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type .. 0.70 1.00 20% 0.23 12.34 7.53 -4.81 -64% Development Area 0.35 1.00 0% 0.05 1.34 3.76 2.42 64% Drinking Water Watersheds 0.40 1.00 1% 0.06 1.81 4.30 2.49 58% Other Rural Land s.. *min.values Redevelopment(For Development Areas,existing impervious cover>20%; C f I(pre)* Rv(pre) L(pre) L(post) RR % RR Area Type ... 0.70 0.90 20% 0.23 12.34 7.53 -3.58 -48% Development Area 0.35 0.85 0% 0.05 1.34 3.76 2.62 70% Drinking Water Watersheds 0.40 0.85 1% 0.06 1.81 4.30 2.76 64% Other Rural Land 0. Independent Reports Excerpt from NRCS Soils Report NOAA Precipitation Report a a a a a a a a a z z MIS 009TZZ4 OOSTZZV 006TZZb 00£TZZb OOZTZZb 00T TUT, M.1T ZE o8L M„LT Z£o8L N N. N MIMI 8 N n n MN i N k. N MO A N G n R O j Q- O ° N t- ° MI U O = 0 n a O U_ o O . co >' 8 2 N. N z U) azi NM lg cd x N pp ig u // C > 4° 2 .m 8 S* i J " r co 8 a sA \ s. ^ 5 w ft S 0 N QQ{� V O N,,_ 1 2 -0 0 r. z Q M SS Z£o8L . M SS Z£AL N OOSTZZ4 OOVIZZb GOETZZV OOZZTZZV GOT TZZb OOOTZZ4 w z z s Custom Soil Resource Report a Table—Hydrologic Soil Group a Hydrologic Soil Group—Summary by Map Unit—Albemarle County,Virginia(VA003) Map unit symbol Map unit name Rating Acres in AOI Percent of AO1 36B Hayesville loam,2 to 7 B 35.8 58.5% percent slopes 36C Hayesville loam,7 to 15 B 22.9 37.3% r percent slopes 56B Meadowville loam,2 to 7 B 2.6 4.2% percent slopes Totals for Area of Interest 61.3 100.0% Rating Options—Hydrologic Soil Group Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher a a a a a a a a 19 a NOAA Atlas 14,Volume 2,Version 3 II"I'' 'N Location name:Charlottesville,Virginia, US" ", r� Coordinates:38.1156, -78.5450 °` " i Elevation:615 f�:.k 0 ++r °$.*ty a' *source:Google Maps "...,„o' POINT PRECIPITATION FREQUENCY ESTIMATES wr 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 a PF tabular ... PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 IAverage recurrence interval (years) Duration 1 2 5 10 25 I 50 100 200 500 1000 - 5-min 0.346 0.414 0.487 0.547 0.618 0.672 0.724 0.773 0.833 0.882 (0.313-0.384) (0.374-0.459) (0.439-0.538) (0.493-0.605) (0.553-0.681) (0.599-0.741) (0.641-0.797) (0.679-0.852) (0.724-0.922) (0.759-0.980) 10-min 0.553 1 0.662 0.780 0.875 0.984 1.07 1.15 1.23 1.32 1.39 (0.499-0.613) (0.598-0.733) (0.703-0.862) (0.788-0.967) (0.881-1.09)I (0.954-1.18) (1.02-1.27) (1.08-1.35) (1.15-1.46) (1.20-1.54) Mil 15 min 0.691 0.832 0.987 1.11 1.25 � 1.36 1.45 1.55 1.66 1.74 (0.624-0.766) (0.752-0.922) (0.889-1.09) (0.996-1.22) (1.12-1.38) (1.21-1.49) (1.29-1.60) (1.36-1.71) ! (1.44-1.84) (1.50-1.94) 30-min 0.947 1.15 1.40 1.60 1.85 , 2.04 2.23 2.41 i 2.64 2.82 (0.856-1.05) (1.04-1.27) (1.26-1.55) (1.44-1.77) (1.65-2.04) (1.82-2.25) (1.97-2.45) (2.11-2.65) (2.29-2.92) (2.43-3.14) M. 60-min 1.18 1.44 1.80 2.09 2.46 i 2.77 3.07 3.38 1 3.79 4.12 (1.07-1.31) (1.30-1.60) (1.62-1.99) (1.88-2.31) (2.20-2.71) (2.46-3.05) (2.71-3.38) (2.96-3.72) (3.29-4.19) (3.54-4.58) 2-hr 1.42 1.72 2.16 2.54 3.03 3.43 3.86 4.30 4.92 5.44 a (1.25-1.61) (1.52-1.95) (1.91-2.45) (2.24-2.87) (2.65-3.41) (3.00-3.87) (3.34-4.34) (3.70-4.84) (4.18-5.55) (4.57-6.15) 3-hr 1.55 1.88 2.36 2.77 3.30 3.75 4.22 4.71 5.40 5.98 (1.37-1.77) (1.66-2.15) (2.07-2.70) (2.42-3.15) (2.88-3.75) (3.25-4.26) (3.63-4.79) (4.02-5.35) (4.55-6.14) (4.99-6.82) ,,,, 6-hr 1.98 2.40 2.98 3.51 4.22 4.84 5.49 6.20 , 7.22 8.11 (1.76-2.24) (2.13-2.71) (2.64-3.37) (3.09-3.96) (3.69-4.75) (4.20-5.44) (4.72-6.18) (5.27-6.98) (6.04-8.14) (6.69-9.17) 12-hr 2.50 3.02 3.76 4.45 5.41 1 6.27 7.20 8.23 9.76 11.1 (2.21-2.85) I (2.67-3.44) (3.32-4.29) (3.91-5.06) (4.71-6.14) (5.40-7.10) (6.13-8.16) (6.91-9.32) (8.03-11.1) (9.00-12.7) a 24-hr 2.99 1 3.62 4.62 5.46 6.71 7.77 8.94 10.2 12.2 13.8 (2.69-3.35) (3.26-4.05) (4.15-5.17) (4.89-6.09) (5.96-7.46) (6.86-8.62) (7.83-9.90) (8.86-11.3) (10.4-13.4) (11.6-15.2) 2-day 3.52 4.27 5.42 6.38 7.75 8.90 10.1 11.5 13.5 15.1 (3.17-3.93) I (3.85-4.77) (4.88-6.05) (5.72-7.10) (6.90-8.61) I (7.87-9.87) (8.90-11.3) (10.0-12.8) (11.6-15.0) (12.8-16.9) a.. 3-day 3.75 4.54 5.77 6.78 8.23 9.45 10.8 12.2 14.3 16.0 (3.41-4.16) (4.13-5.04) (5.23-6.39) (6.13-7.50) (7.40-9.09) I (8.44-10.4) (9.54-11.9) (10.7-13.5) (12.4-15.8) (13.8-17.7) 4-day 3.98 4.82 6.12 7.18 8.72 I 10.0 11.4 12.9 15.1 16.9 (3.64-4.39) (4.41-5.31) (5.58-6.74) (6.54-7.89) (7.91-9.58) (9.02-11.0) (10.2-12.5) (11.4-14.2) i (13.2-16.6) (14.7-18.6) aria 7-da 4.63 5.57 6.96 8.10 9.73 11.1 12.5 14.1 16.3 18.1 y (4.24-5.06) (5.11-6.09) (6.37-7.61) (7.39-8.85) (8.84-10.6) I (10.0-12.1) (11.2-13.7) (12.5-15.4) (14.3-17.9) (15.8-19.9) 10 day 5.25 6.30 7.77 8.97 10.6 1 12.0 13.4 15.0 ; 17.1 18.9 •r (4.83-5.69) (5.81-6.83) (7.15-8.43) (8.23-9.71) (9.73-11.5) I (10.9-13.0) (12.2-14.6) (13.4-16.2) (15.2-18.6) (16.6-20.6) 6.90 8.23 9.94 11.3 13.1 14.5 16.0 17.5 I 19.5 21.0 20-day (6.46-7.41) (7.70-8.83) (9.28-10.7) (10.5-12.1) (12.2-14.0) (13.4-15.6) (14.7-17.2) (16.0-18.8) � (17.7-21.0) (19.0-22.8) 8.47 10.0 11.9 13.3 15.1 16.4 17.8 19.1 20.8 22.1 .+. 30-day (7.97-9.04) (9.45-10.7) (11.2-12.6) (12.4-14.1) (14.1-16.1) (15.4-17.5) (16.6-19.0) (17.7-20.4) I (19.2-22.3) (20.4-23.8) 45-day 10.6 12.5 14.6 16.2 18.2 19.7 21.1 22.5 24.3 25.6 OA (9.98-11.2) (11.8-13.3) (13.8-15.5) (15.2-17.1) (17.1-19.3) (18.4-20.8) (19.7-22.4) (20.9-23.9) (22.5-25.9) (23.6-27.3) 60 day 12.4 1.4.6,- 16.8 18.5 20.6 22.2 23.7 25.1 26.9 28.2 (11.8-13.1) (13.8-15.4) (15.9-17.8) (17.5-19.5) (19.5-21.8) (20.9-23.4) (22.3-25.0) (23.6-26.5) (25.1-28.5) (26.2-29.9) 1 1 Precipitation frequency(PF)estimates in this table are based on frequency analysis of partial duration series(PDS). .m. 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 a PF graphical