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HomeMy WebLinkAboutSDP201700031 Calculations Minor Amendment 2018-07-18 9S DAG ATE A double 36 INCH pipe .Subcat) Reach Pon Link Routing Diagram for Brown Toyota PIPE 2 Prepared by Windows User, Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC ' " -K , _ -v--___, r _ -�mo -- -________ 0 ✓ dp � ---- -----V 7) / � , \ 7 z/7 II: / �t / / //„,0% „'C0 ,\ • m I (V7 /fr_ 7 /moi ''' 49° ' ---\-‘.------ vi ..( > I ,,))`' \ - / ' V \ \ \O D / // Y \__1 V>_. \ , \J r // 2 ..-(,,u4 H .. N-____ ___77:y 4//7 5! v) \ 1 < -ri \ I It/\ / /7 / / \ 77 ,,,,,,, -- ,,,.,,4 /// Y/ /-- Mi89 / 7 / --- \( 7 / 06� . -ailinift 0 8 i --> ( c___ < to 66 7 ---- ,q7')/ / 'I / / I 11\1 : \ / / / 1 7 / / 0 4 \/ /P5>coI 1Z m I / 5 0 0 4/7 m / , m D 7 r o ___, N D 1 I m :Ll 1 ' 0 I '*7 m I Z W I \ / / cDF \ \ ,',;) 1 z I m Brown Toyota PIPE 2 Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 2 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 0.094 61 >75%Grass cover,Good, HSG B (9S) 0.812 98 Paved parking, HSG B (9S) 0.906 94 TOTAL AREA Brown Toyota PIPE 2 Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 3 Soil Listing (all nodes) Area Soil Subcatchment (acres) Group Numbers 0.000 HSG A 0.906 HSG B 9S 0.000 HSG C 0.000 HSG D 0.000 Other 0.906 TOTAL AREA Brown Toyota PIPE 2 Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 4 Ground Covers (all nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.094 0.000 0.000 0.000 0.094 >75%Grass cover,Good 9S 0.000 0.812 0.000 0.000 0.000 0.812 Paved parking 9S 0.000 0.906 0.000 0.000 0.000 0.906 TOTAL AREA Brown Toyota PIPE 2 Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 5 Time span=0.00-20.00 hrs, dt=0.05 hrs, 401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 9S: DA GRATE Runoff Area=39,474 sf 89.65% Impervious Runoff Depth>2.21" Tc=5.0 min CN=94 Runoff=3.57 cfs 0.167 af Pond 10P:double 36 INCH pipe Peak Elev=2.36' Storage=0.021 af Inflow=3.57 cfs 0.167 af Primary=2.40 cfs 0.166 af Secondary=0.00 cfs 0.000 af Outflow=2.40 cfs 0.166 af Total Runoff Area=0.906 ac Runoff Volume=0.167 of Average Runoff Depth =2.21" 10.35%Pervious=0.094 ac 89.65%Impervious=0.812 ac Brown Toyota PIPE 2 Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD® 10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment 9S: DA GRATE [49] Hint: Tc<2dt may require smaller dt Runoff = 3.57 cfs @ 11.95 hrs, Volume= 0 167 af, Depth> 2.21" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1" 24-hour Rainfall=3.00" Area (sf) CN Description 35,389 98 Paved parking, HSG B 4,085 61 >75% Grass cover, Good, HSG B 39,474 94 Weighted Average 4,085 10.35% Pervious Area 35,389 89.65% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, tc Subcatchment 9S: DA GRATE Hydrograph 3.57 cfs _❑ Runoff Type II 24-hr 1" 24-hour Rainfall=3.00" 3 Runoff Area=39,474 sf Runoff Volume=0.167 af Runoff Depth>2.21" 2 Tc=5.0 min T. CN=94 1 0 1 2 3 4 5 6 7 8 9 1011 121314151617181920 Time (hours) Brown Toyota PIPE 2 Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCADO 10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 7 Summary for Pond 10P: double 36 INCH pipe Inflow Area= 0.906 ac, 89.65% Impervious, Inflow Depth > 2.21" for 1" 24-hour event Inflow = 3.57 cfs @ 11.95 hrs, Volume= 0.167 of Outflow = 2.40 cfs @ 12.02 hrs, Volume= 0.166 af, Atten= 33%, Lag=4.2 min Primary = 2.40 cfs @ 12.02 hrs, Volume= 0.166 af Secondary= 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 2.36' @ 12.02 hrs Surf.Area= 0.014 ac Storage= 0.021 af Plug-Flow detention time= 6.2 min calculated for 0.166 af (99%of inflow) Center-of-Mass det. time=4.8 min ( 755.7 - 751.0 ) Volume Invert Avail.Storage Storage Description #1A 0.00' 0.014 af 9.50'W x 65.001 x 4.00'H Field A 0.057 af Overall - 0.021 af Embedded = 0.036 af x 40.0% Voids #2A 0.50' 0.021 af CMP_Round 36 x 6 Inside#1 Effective Size= 36.0"W x 36.0"H => 7.06 sf x 20.00'L = 141.1 cf Overall Size= 36.0"W x 36.0"H x 20.00'L 2 Rows of 3 Chambers 7.50' Header x 7.06 sf x 1 =52.9 cf Inside 0.035 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Primary 0.00' 8.0"Vert. Orifice/Grate C= 0.600 #2 Secondary 3.90' 12.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=2.36 cfs @ 12.02 hrs HW=2.31' (Free Discharge) L1=Orifice/Grate (Orifice Controls 2.36 cfs @ 6.77 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=0.00' (Free Discharge) 't2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs) Brown Toyota PIPE 2 Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD©10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 8 Pond 10P: double 36 INCH pipe - Chamber Wizard Field A Chamber Model = CMP_Round 36(Round Corrugated Metal Pipe) Effective Size= 36.0"W x 36.0"H => 7.06 sf x 20.00'L= 141.1 cf Overall Size= 36.0"W x 36.0"H x 20.00'L 36.0" Wide + 18.0" Spacing = 54.0" C-C Row Spacing 3 Chambers/Row x 20.00' Long +3.00' Header x 1 = 63.00' Row Length +12.0" End Stone x 2 = 65.00' Base Length 2 Rows x 36.0" Wide + 18.0" Spacing x 1 + 12.0" Side Stone x 2 = 9.50' Base Width 6.0" Base + 36.0" Chamber Height + 6.0" Cover= 4.00' Field Height 6 Chambers x 141.1 cf + 7.50' Header x 7.06 sf = 899.7 cf Chamber Storage 2,470.0 cf Field - 899.7 cf Chambers = 1,570.3 cf Stone x 40.0% Voids = 628.1 cf Stone Storage Chamber Storage + Stone Storage = 1,527.8 cf= 0.035 of Overall Storage Efficiency= 61.9% Overall System Size = 65.00' x 9.50' x 4.00' 6 Chambers 91.5 cy Field 58.2 cy Stone .ICJ Brown Toyota PIPE 2 Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 9 Pond 10P: double 36 INCH pipe Hydrograph 3.57 cfs I-1 Inflow Inflow Area=0.906 ac Outflow Peak Elev=2.36' , 0 Primary El Secondary Storage=0.021 of 4, r 3 2.40 cfs N V 0 yr' 2 o 1 0.00 cfs 0 0 2 4 6 8 10 12 14 16 18 20 Time (hours) Brown Toyota PIPE 2 Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 10 Time span=0.00-20.00 hrs, dt=0.05 hrs, 401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 9S: DA GRATE Runoff Area=39,474 sf 89.65% Impervious Runoff Depth>4.54" Tc=5.0 min CN=94 Runoff=6.96 cfs 0.343 af Pond 10P: double 36 INCH pipe Peak Elev=4.20' Storage=0.035 af Inflow=6.96 cfs 0.343 af Primary=3.31 cfs 0.314 af Secondary=4.27 cfs 0.028 af Outflow=7.56 cfs 0.342 af Total Runoff Area=0.906 ac Runoff Volume=0.343 af Average Runoff Depth =4.54" 10.35% Pervious=0.094 ac 89.65%Impervious=0.812 ac Brown Toyota PIPE 2 Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment 9S: DA GRATE [49] Hint: Tc<2dt may require smaller dt Runoff = 6.96 cfs @ 11.95 hrs, Volume= 0.343 af, Depth> 4.54" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10-year Rainfall=5.50" Area (sf) CN Description 35,389 98 Paved parking, HSG B 4,085 61 >75% Grass cover, Good, HSG B 39,474 94 Weighted Average 4,085 10.35% Pervious Area 35,389 89.65% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tc Subcatchment 9S: DA GRATE Hydrograph 6.96 cfs ❑ Runoff` 7 Type II 24-hr 6 10-year Rainfall=5.50" Runoff Area=39,474 sf N 5 Runoff Volume=0.343 af 4 Runoff Depth>4.54" o Tc=5.0 minEr 3 CN=94 2 1 0 0 1 2 3 4 5 6 7 8 9 1011 121314151617181920 Time (hours) Brown Toyota PIPE 2 Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 12 Summary for Pond 10P: double 36 INCH pipe [93] Warning: Storage range exceeded by 0.20' [88] Warning: Qout>Qin may require smaller dt or Finer Routing Inflow Area= 0.906 ac, 89.65% Impervious, Inflow Depth > 4.54" for 10-year event Inflow = 6.96 cfs @ 11.95 hrs, Volume= 0.343 af Outflow = 7.56 cfs @ 11.96 hrs, Volume= 0.342 af, Atten= 0%, Lag= 0.5 min Primary = 3.31 cfs @ 11.97 hrs, Volume= 0.314 of Secondary= 4.27 cfs @ 11.96 hrs, Volume= 0.028 af Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 4.20'@ 11.97 hrs Surf.Area= 0.014 ac Storage= 0.035 af Plug-Flow detention time= 5.5 min calculated for 0.341 af (100%of inflow) Center-of-Mass det. time= 4.5 min ( 738.5 - 734.1 ) Volume Invert Avail.Storage Storage Description #1A 0.00' 0.014 af 9.50'W x 65.00'L x 4.00'H Field A 0.057 af Overall - 0.021 af Embedded = 0.036 af x 40.0%Voids #2A 0.50' 0.021 af CMP Round 36 x 6 Inside#1 Effective Size= 36.0"W x 36.0"H => 7.06 sf x 20.00'L= 141.1 cf Overall Size= 36.0"W x 36.0"H x 20.00'L 2 Rows of 3 Chambers 7.50' Header x 7.06 sf x 1 = 52.9 cf Inside 0.035 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Primary 0.00' 8.0"Vert. Orifice/Grate C= 0.600 #2 Secondary 3.90' 12.6' long Sharp-Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=3.25 cfs @ 11.97 hrs HW=4.08' (Free Discharge) L1=Orifice/Grate (Orifice Controls 3.25 cfs @ 9.32 fps) Secondary OutFlow Max=3.80 cfs @ 11.96 hrs HW=4.10' (Free Discharge) L2=Sharp-Crested Rectangular Weir (Weir Controls 3.80 cfs @ 1.48 fps) Brown Toyota PIPE 2 Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 sin 08839 ©2015 HydroCAD Software Solutions LLC Pape 13 Pond 10P: double 36 INCH pipe - Chamber Wizard Field A Chamber Model = CMP_Round 36(Round Corrugated Metal Pipe) Effective Size= 36.0"W x 36.0"H => 7.06 sf x 20.00'L= 141.1 cf Overall Size= 36.0"W x 36.0"H x 20.00'L 36.0" Wide + 18.0" Spacing = 54.0" C-C Row Spacing 3 Chambers/Row x 20.00' Long +3.00' Header x 1 = 63.00' Row Length +12.0" End Stone x 2 = 65.00' Base Length 2 Rows x 36.0" Wide + 18.0" Spacing x 1 + 12.0" Side Stone x 2 = 9.50' Base Width 6.0" Base + 36.0" Chamber Height + 6.0" Cover= 4.00' Field Height 6 Chambers x 141.1 cf + 7.50' Header x 7.06 sf = 899.7 cf Chamber Storage 2,470.0 cf Field - 899.7 cf Chambers = 1,570.3 cf Stone x 40.0% Voids = 628.1 cf Stone Storage Chamber Storage + Stone Storage = 1,527.8 cf = 0.035 of Overall Storage Efficiency= 61.9% Overall System Size = 65.00' x 9.50' x 4.00' 6 Chambers 91.5 cy Field 58.2 cy Stone ) CJf Brown Toyota PIPE 2 Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD® 10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 14 Pond 10P: double 36 INCH pipe Hydrograph Fl Inflow 7.56 cfs Outflow Inflow Area=0.906 d- p Primary 8 Peak EIev=4.20' 7 Storage=0.035 of _❑ Secondary 6 .� 5 4.27 cfs 0. Lib 0 4. 2 ••� 1W /Z7 </M 0 ..� 0 2 4 6 8 10 12 14 16 18 20 Time (hours) Brown Toyota PIPE PRE Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 1 Summary for Subcatchment 9S: DA GRATE PRE [49] Hint: Tc<2dt may require smaller dt Runoff = 3.57 cfs @ 11.95 hrs, Volume= 0.167 af, Depth> 2.21" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1" 24-hour Rainfall=3.00" Area (sf) CN Description 35,389 98 Paved parking, HSG B 4,085 61 >75% Grass cover, Good, HSG B 39,474 94 Weighted Average 4,085 10.35% Pervious Area 35,389 89.65% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tc Subcatchment 9S: DA GRATE PRE Hydrograph 3.57 cfs _❑ Runoff Type II 24-hr 1" 24-hour Rainfall_3.00" 3 Runoff Area=39,474 sf Runoff Volume-0.167 of Runoff Depth>2.21" 2 Tc=5.0 min c:3 CN=94 1 0 0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota PIPE PRE Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD® 10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 9S: DA GRATE PRE [49] Hint: Tc<2dt may require smaller dt Runoff = 6.96 cfs @ 11.95 hrs, Volume= 0.343 af, Depth> 4.54" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10-year Rainfall=5.50" Area (sf) CN Description 35,389 98 Paved parking, HSG B 4,085 61 >75% Grass cover, Good, HSG B 39,474 94 Weighted Average 4,085 10.35% Pervious Area 35,389 89.65% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tc Subcatchment 9S: DA GRATE PRE Hydrograph 6.96 cfs _❑ Runoff` 7 Type II 24-hr 6 10-year Rainfall-5.50" Runoff Area=39,474 sf 5 Runoff Volume=0.343 af 1 4 Runoff Depth>4.54" Tc=5.0 min 3 CN=94 2 1 Cr 0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota GRAVEL PRE Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 1 Summary for Subcatchment 1S: GRAVEL PRE [49] Hint: Tc<2dt may require smaller dt Runoff = 0.15 cfs @ 11.99 hrs, Volume= 0.008 af, Depth> 0.31" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1" 24-hour Rainfall=3.00" Area (sf) CN Description 0 85 Gravel roads, HSG B 13,336 61 >75%Grass cover, Good, HSG B 0 98 Paved parking, HSG B 13,336 61 Weighted Average 13,336 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tcA Subcatchment 1S: GRAVEL PRE Hydrograph 0.16: 0.15 cfs _❑ Runoff` Type II 24-hr 0.14 1" 24-hour Rainfall_3.00" 0.12= Runoff Area=13,336 sf Runoff Volume=0.008 of 0.1 / Runoff Depth>0.31" 3 0.08 Tc=5.0 min ° - CN=61 0.06 0.04 • 0.02 . 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota GRAVEL PRE Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Pale 2 Summary for Subcatchment 1S: GRAVEL PRE [49] Hint: Tc<2dt may require smaller dt Runoff = 0.91 cfs @ 11.97 hrs, Volume= 0.039 af, Depth> 1.51" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10-year Rainfall=5.50" Area (sf) CN Description 0 85 Gravel roads, HSG B 13,336 61 >75%Grass cover, Good, HSG B 0 98 Paved parking, HSG B 13,336 61 Weighted Average 13,336 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tcA Subcatchment 1S: GRAVEL PRE Hydrograph 1 0.91 cfs ❑ Runoff Type II 24-hr 10-year Rainfall=5.50" Runoff Area=13,336 sf Runoff Volume=0.039 of Runoff Depth>1.51" o Tc=5.0 min CN=61 PA 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota GRAVEL POST Type 1124-hr 1"24-hour Rainfall=3.00" Prepared by Windows User Printed 5/11/2017 HydroCAD®10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 1 Summary for Subcatchment 1S: GRAVEL POST [49] Hint: Tc<2dt may require smaller dt Runoff = 1.14 cfs @ 11.95 hrs, Volume= 0.052 af, Depth> 2.02" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 1" 24-hour Rainfall=3.00" Area (sf) CN Description 0 85 Gravel roads, HSG B 2,136 61 >75%Grass cover, Good, HSG B 11,200 98 Paved parking, HSG B 13,336 92 Weighted Average 2,136 16.02% Pervious Area 11,200 83.98% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tcA Subcatchment 1S: GRAVEL POST Hydrograph 1 .14 cfs D Runoff II Type II 24-hr 1 1" 24-hour Rainfall_3.00" Runoff Area-13,336 sf Runoff Volume-0.052 of Runoff Depth>2.02" Tc=5.0 min ° ji CN-92 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota GRAVEL POST Type 1124-hr 10-year Rainfall=5.50" Prepared by Windows User Printed 5/11/2017 HydroCADO 10.00-16 s/n 08839 ©2015 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1S: GRAVEL POST [49] Hint: Tc<2dt may require smaller dt Runoff = 2.29 cfs @ 11.95 hrs, Volume= 0.109 af, Depth> 4.29" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr 10-year Rainfall=5.50" Area (sf) CN Description 0 85 Gravel roads, HSG B 2,136 61 >75% Grass cover, Good, HSG B 11,200 98 Paved parking, HSG B 13,336 92 Weighted Average 2,136 16.02% Pervious Area 11,200 83.98% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,tcA Subcatchment 1S: GRAVEL POST Hydrograph 2.29 cfs D Runoff Type II 24-hr 2 10-year Rainfall-5.50" RunoA =13,336 sf Runoff ff Volume rea -0.109 of Runoff Depth>4N.-2992" 0 Tc=5.0 min 0 rc 1 C 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) Brown Toyota Site Plan Amendment Stormwater Summary May 16, 2017 Brown Toyota is on a 8.54 acre parcel with Commercial Mixed Use zoning. The parcel was originally developed in the 1960's and has received additional improvements over the years. Recently, within the past 5 years, some grading was done to expand a gravel parking area at the rear of the developed portion of the property. The grading increased the gravel area by approximately 11,200 sq. ft. In addition, the grading impacted an area of preserved slopes, as well as created new steep slopes, ultimately decreasing the on-site steep slopes area approximately 1,420 sq. ft. Runoff from the gravel area sheet-flows across the steep slopes area and there are no signs of erosion along the slopes. To address the stormwater requirements created by the additional gravel area, the plan proposes to install the required detention in an adjacent drainage area, where stormwater runoff is being captured in significant quantity. This approach will allow the sheet flow condition to remain, rather than using new curb, and detention in the gravel area, which would require installing new storm piping across the steep slopes. Per the calculations below, the required allowable runoff for the gravel area is calculated, and that amount is detained in the adjacent drainage system. Gravel Parking Drainage Area Pre-development Runoff Q(1)Pre-Development = 0.15 cfs (1)Pre-Development = 0.31 Post-Development Runoff Q(1)Post-Development before SWM = 1.14 cfs RV(1)Post-Development before SWM = 2.02 Q(1)Allowable = I.F. x (Q(1)Pre-Development X RV(1)Pre-Development)/ RV(1)Post-Development before SWM = 0.9 x (0.15 x 0.31)/2.02 = 0.02 cfs Thus, Q(1) must be reduced by Q(1)post- Q(1)Allowable = 1.14-0.02 = 1.12 cfs Grate Drainage Area Q(1)Grate = 3.57 cfs Q(1)Reduction = 1.12 cfs Therefore, Q(1)Allowable = Q(1)Grate - Q(1)Reduction = 3.57 cfs - 1.12 cfs = 2.45 cfs. Per attached calculations: Q(1)Post-Development w/SWM = 2.40 cfs (Less than 2.45, OK)