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HomeMy WebLinkAboutWPO201600038 Plan - Stormwater 2016-05-19STORMWATER MANAGEMENT REPORT Landmark Aviation Hangar I)AI ZIJQ AND ASSOCIATES INC REFLECTING TOMORROW 1561 Commerce Road, Suite 401 Verona, VA 24482 540-248-3220 Prepared by: Kent O'Donohue, Jr. Balzer & Associates Project No: 34150050 May 16, 2016 (DKUNT O'DONOHUE, JR. No. 0406001683 Table of Contents: INTRODUCTION.......................................................................................................................... 1 HYDROLOGIC & HYDRAULIC ANALYSIS............................................................................. 1 ExistingConditions................................................................................................................. 1 Pre-Development.................................................................................................................... 1 Table 1: Pre -developed Storm Rates.............................................................................. 1 Post-Development................................................................................................................... 2 Table 2: Post -developed Storm Rates before Detention ................................................ 2 Stormwater Quantity Management......................................................................................... 2 Table 3: Pre- to Post -Developed Storm Rates after Detention ...................................... 3 StormwaterQuality................................................................................................................. 3 AdequateChannel................................................................................................................... 3 Stormwater Conveyance Calculations.................................................................................... 3 OutletProtection..................................................................................................................... 4 Stormwater Maintenance........................................................................................................ 4 Attachments: Pre -development Calculations Page S Post -development Calculations Page 23 Water Quality Calculations Page 54 1 STORMWATER MANAGEMENT REPORT Crozet Business Office INTRODUCTION This project consists of the construction of a 6,350 square foot office building with private utilities and associated parking. The parcel is 1.76 acres with some disturbance on adjacent parcel for construction of a shared access road. The existing site is characterized as vacant with existing impervious areas present. Slopes are gentle to moderate. A total of approximately 1.53 acres will be disturbed during construction. Stormwater compliance for this project is in accordance with current state regulations for a "Re -development" project. (County code 17-302 and State Code 9VAC25-870- 62 thru 9VAC25-870-66). This report documents the storm water design recommended by Balzer & Associates, Inc. After analysis of the site under pre and post -development conditions, a determination of the appropriate stormwater management design was made. HYDROLOGIC & HYDRAULIC ANALYSIS Existing Conditions Currently the site topography consists of a hilltop with stormwater run-off sheet flowing from the hilltop to an existing cultivated swale to the southwest. The northeast portion of the property flows into an existing paved ditch that flows into an existing DI-1 within the R-O-W of Rockfish Gap Turnpike. Existing slopes range from <1 % to 17%. Existing ground cover consists of impervious areas, short grass, brush, and dense trees. Pre -Development Existing topography slopes generally from northeast to southwest in a large natural swale. Ground cover consists of open lawn, woods, and impervious areas. The enclosed Drainage Map (Sheet DA-1) illustrates the drainage area for the site and the path of the pre -developed time of concentration. Based upon a hydrologic analysis of the site (see attached Pre -Development Calculations), the pre -development run-off rates for the identified drainage areas are as follows (DA-A & B were combined as a `Point of Analysis' (POA) since they flow to the same swale): Table 1: Pre -developed Storm Rates Storm Event Flowrate (cfs) DA-A & B DA-C POA Q1 = 0.11 -- Q2 = -- 0.62 Q10 = 1.19 1.06 TOC = 17.3 min. 5.0 min. 2 Stormwater Management Report Crozet Business Office These values were achieved using existing site contours, averaging slopes across the time of concentration lengths, and using appropriate Curve Numbers. The analysis of the pre -development run-off rates for the drainage areas was performed using Hydro-CADO v. 10 computer software. All calculations were performed in general accordance with the TR-55 Method outlined in the Virginia Stormwater Management Handbook. Post -Development For post -development analysis, we have determined the amount of additional impervious area within the drainage areas for the currently proposed site development as well as additional drainage that will be diverted into the bioretention basin (see DA-2, Post Development Drainage Map). Based upon a hydrologic analysis of the site (see attached Post -Development Calculations), the post - development run-off rates are as follows: Table 2: Post -developed Storm Rates before Detention Storm Event Flowrate (cfs) DA-A & B DA-C POA Q1 = 1.36 -- Q2 = -- 0.22 Q10 = 3.32 0.48 TOC = 5 & 17.8 min. 5.0 min. Due to the reduction in drainage area and impervious area within DA-C, there is reduced runoff for the 2-yr and 10-yr events and further downstream analysis is not required. DA-A which encompasses the proposed development and DA-B which includes perimeter clearing that will be returned to mostly open space conditions, will be analyzed further to meet Energy Balance and Flood Protection requirements below. Stormwater Quantity Manazement A Level 2 Bioretention basin with 1.0' of surface storage is proposed for stormwater quantity management. This basin will treat runoff from the proposed hangar, as well as capturing some of the runoff from the adjacent hangar that currently flows undetained. As depicted on the Water Quality drainage map, DA-C shrank considerably in size and runoff was reduced in the drainage area due to re-routing of runoff into the DA-A post condition and over detention of pre-existing impervious areas. An analysis of the proposed basin was performed using Hydro-CADO v. 10 computer software. The following table illustrates the reduction in run-off rates when comparing pre -development flowrates and required Energy Balance flowrates to detained post -development flowrates. Stormwater Management Report Crozet Business Office Table 3: Pre- to Post -Developed Storm Rates after Detention Storm Event Flowrate cfs Pre Energy Balance Max Post Q1 = 0.11 0.03 0.03 Q 10 = 1.19 -- 0.72 By providing detention, the post -development stormwater flowrates are flowrates when comparing 1-year pre -developed Energy Balance Runoff to the and pre -developed 10-year to the post -developed 10-year stormwater flowrates. Stormwater Quality below pre -developed 1-year post -developed For water quality analysis, the project site area of 1.76 acres was used to calculate phosphorus loading rates. The existing conditions comprise 0.19 acres (12%) of impervious area. The proposed development will result in total impervious area of 0.59 acres (39%). Based on the proposed development, a total Phosphorous load reduction of 0.94 lbs P/yr is needed. To treat the stormwater quality, the proposed development includes the construction of a level 2 Bioretention Basin. Based on the existing and proposed land use of the area draining to the BMP, the basin obtains a total removal rate of 1.24 lbs P/yr, exceeding the required P removal. We have provided calculations for the water quality measures proposed for the site development (see attached Water Quality Calculations). Adequate Channel Since the Energy Balance method was used and the 10-yr post development discharge rates into the existing conveyance channel are lower than the pre developed condition the existing storm conveyance system is adequate for DA-A & B. DA-C was reduced in size and impervious area resulting in lower discharge rates then preexisting conditions and thus does not require further analysis. Stormwater Conveyance Calculations Stormwater conveyance calculations were not required since the only storm structures proposed are for roof leader collection and a dumpster pad. This runoff does not exceed 1.10 cfs based on preliminary calculations which are more than sufficient for proposed pipe sized. Additionally, there is a permanent diversion proposed along the adjacent parcel. This is to serve as a water collection for the 0.20 cfs flowing to it. When this adjacent parcel is developed this diversion may need to be resized for additional flow by responsibility of that land owner. The flow Stormwater Management Report Crozet Business Office coming to this diversion does not warrant further analysis, but 1' depth and seed cover is adequate based on the grading plan. This diversion acts as a method to keep the adjacent parcel's current and future runoff from entering the proposed bioretention area. Outlet Protection An analysis was not required since there was only one pipe outfall and two curb cuts that all have less discharge then 1.50 cfs which is less than the required 3.0 cfs for outlet protection analysis. Additionally, all three conveyance systems discharge into a proposed rip -rap pretreatment cells which were sized adequately for the bioretention inflow based on the Virginia Stormwater Management Handbook 2nd Edition. Stormwater Maintenance Maintenance of stormwater pipes within the subject property will be the responsibility of the property owner. Maintenance of the Bioretention Basin will be the responsibility of the property owner. PRE DEVELOPMENT CALCULATIONS --------------------------- / — — — — — — — — / -- —— _ — — \ \ 1 \ \! G oyG oy0 \ C \DA-Z P\RE `\ '`\ \ 1-_----- --- \ \7 ACS\ `\ \ \ 0 ACS IMP. \ — --- DA-A 0.70 Raft \\ 0.05 A� 0.53 ACS, ------------ \ 'RE 1CS > IMP \ ` FOREST \ 1 sun Un /mu WM I moo \ 7 I � 171 I I I I I � / I I / I I I I I l I — / I w .balzer.cc seaaaron New River Valley Roanoke Richmond Harrisonburg Balzer and Associates, Inc 1561 Commerce Road Suite 401 Verona, VA 24482 W-248-3220 FAX 540-248-3221 a w a U � w LL a a O w x U � Wz > W ~ O Z z J D N w Q 0 JO a W J m� 0 = Q F— W w O 0 a Ina w U a DRAWN BY DKO DESIGNED BY DKO CHECKED BY ERB DATE 05-16-2016 SCALE REVISIONS: SHEET NO. DA-1 JOB NO. 34150050 lJti-ti IX D 1-VI Al1U IV -VI %-dll,UlALlUllb CA -PRE DA-A PRE POA-PRE B-PRE POINT OF ANALYSIS PRE Subcat Reach on Link 8 2016-05-11 SWM Calcs Prepared by Microsoft HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Printed 5/16/2016 Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.120 0.000 0.000 0.000 0.120 >75% Grass cover, Good A -PRE 0.000 0.050 0.000 0.000 0.000 0.050 Paved parking A -PRE 0.000 1.100 0.000 0.000 0.000 1.100 Woods, Good A -PRE, B-PRE 0.000 1.270 0.000 0.000 0.000 1.270 TOTAL AREA 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentA-PRE: DA-A PRE Runoff Area=0.700 ac 7.14% Impervious Runoff Depth=0.33" Flow Length=160' Slope=0.0875 '/' Tc=16.3 min CN=59 Runoff=0.08 cfs 0.019 of SubcatchmentB-PRE: DA-B PRE Runoff Area=0.570 ac 0.00% Impervious Runoff Depth=0.21" Flow Length=210' Tc=17.8 min CN=55 Runoff=0.03 cfs 0.010 of Link POA-PRE: POINT OF ANALYSIS PRE Inflow=0.11 cfs 0.029 of Primary=0.11 cfs 0.029 of Total Runoff Area = 1.270 ac Runoff Volume = 0.029 of Average Runoff Depth = 0.27" 96.06% Pervious = 1.220 ac 3.94% Impervious = 0.050 ac iN 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment A -PRE: DA-A PRE Runoff = 0.08 cfs @ 12.33 hrs, Volume= 0.019 af, Depth= 0.33" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Area (ac) CN Description 0.050 98 Paved parking, HSG B 0.120 61 >75% Grass cover, Good, HSG B 0.530 55 Woods, Good, HSG B 0.700 59 Weighted Average 0.650 92.86% Pervious Area 0.050 7.14% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.3 160 0.0875 0.16 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" 0.09 0.08 cfs 0.085 0.08 0.075 0.07 0.065 0.06 0.055 U) 0.05 0 0.045 — — LL 0.04 — 0.035 — 0.03 — — 0.025 — — 0.02 — — 0.015 0.01 0.005 Subcatchment A -PRE: DA-A PRE Hydrograph 6rozet E�sine�s 0ic - 1�ain1=3:,06" Runoff Area= 7 ac R�nol Volumel0.01-9 of Runoff Depth=0:33" -f --PIowlLenoth=11160' Slope=�0875 '/' 1 ­4- I Tc-46.3 m in 1 I I 1 I -4-4 - - —CN=59 4 4�� �I �7 1 T T 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff is 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment B-PRE: DA-B PRE Runoff = 0.03 cfs @ 12.60 hrs, Volume= 0.010 af, Depth= 0.21" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Area (ac) CN Description 0.570 55 Woods, Good, HSG B 0.570 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 17.3 150 0.0667 0.14 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" 0.5 60 0.1333 1.83 Shallow Concentrated Flow, Woodland Kv= 5.0 fDs 17.8 210 Total Subcatchment B-PRE: DA-B PRE Hydrograph 0.034 0.032 0.03 cfs — — — — — — — — — — — 0.03 - Crozet B�sin-e�s Office 24-"I1 -Yr 0.028 —177 1 —] 7 7 7 f�ainl=�� 0.026 Runoff Area- 57 c 0.024 R-lunoff volyrnie�0.010 of 0.022 — — — Runoff Depth=0.21" 0.02 Flowl-ength=210' 0.018 Tc A7.8-min c �— CN55 0.016 — —L -L LL 0.014 7 —f 7 7 T T 0.012 0.01 0.008 0.006 0.004 0.002 - 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff Ii" 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Link POA-PRE: POINT OF ANALYSIS PRE Inflow Area = 1.270 ac, 3.94% Impervious, Inflow Depth = 0.27" for 1-yr event Inflow = 0.11 cfs @ 12.47 hrs, Volume= 0.029 of Primary = 0.11 cfs @ 12.47 hrs, Volume= 0.029 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Link POA-PRE: POINT OF ANALYSIS PRE Hydrograph 0.12 0.115 0.11 cfs 0.11 0.1 0.1 - ]1nf1ovv- ear--1�7-0 aE 0.095 - 0.09 0.085 0.08 0.075 N0.07 --1 --1 --4 4 4 4 + 0.065 — — 3 00055 .055 LL 0.05 4 4 4 0.045 - 0.04 0.035 - - - - - - 0.03 0.025 —7 —T —T ::1 1 1 0.02 0.015 0.01 0.005 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow — Primary 13 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 7 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentA-PRE: DA-A PRE Runoff Area=0.700 ac 7.14% Impervious Runoff Depth=1.57" Flow Length=160' Slope=0.0875 '/' Tc=16.3 min CN=59 Runoff=0.75 cfs 0.092 of SubcatchmentB-PRE: DA-B PRE Runoff Area=0.570 ac 0.00% Impervious Runoff Depth=1.27" Flow Length=210' Tc=17.8 min CN=55 Runoff=0.44 cfs 0.060 of Link POA-PRE: POINT OF ANALYSIS PRE Inflow=1.19 cfs 0.152 of Primary=1.19 cfs 0.152 of Total Runoff Area = 1.270 ac Runoff Volume = 0.152 of Average Runoff Depth = 1.44" 96.06% Pervious = 1.220 ac 3.94% Impervious = 0.050 ac 14 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 8 Summary for Subcatchment A -PRE: DA-A PRE Runoff = 0.75 cfs @ 12.20 hrs, Volume= 0.092 af, Depth= 1.57" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.050 98 Paved parking, HSG B 0.120 61 >75% Grass cover, Good, HSG B 0.530 55 Woods, Good, HSG B 0.700 59 Weighted Average 0.650 92.86% Pervious Area 0.050 7.14% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.3 160 0.0875 0.16 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" U) 3 0 LL 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 Subcatchment A -PRE: DA-A PRE Hydrograph �roze�t Bu�iness Office�4-hr 51 10-yr �ainf II=5.56" Runoff Area=0.700 ac R�nol Vol4m0.092 of uno Dep h T57" —�Flov�i Lenbth=160' Slope=0.0875 '/' Tc=16.3-min CN=59 I 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff H61 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 9 Summary for Subcatchment B-PRE: DA-B PRE Runoff = 0.44 cfs @ 12.23 hrs, Volume= 0.060 af, Depth= 1.27" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.570 55 Woods, Good, HSG B 0.570 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 17.3 150 0.0667 0.14 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" 0.5 60 0.1333 1.83 Shallow Concentrated Flow, Woodland Kv= 5.0 fDs 17.8 210 Total Subcatchment B-PRE: DA-B PRE Hydrograph 0.48 1 0.46 0.44 cfs - 0.44 ra�et 13ttSIneSS �Ice�4-"1 �-yr 0.42 Ru oII 0.36 0570a0.3s c - 0.32 - � offf Dep h-1 7 w 0.3 028 1 ::�Flovu Lenoth*g10' 0.26 Tc=a 7.8--ruin 3 0.24 CN�55 LL 0.22 - 02 0.18 0.16 - 0.14 1 1 1 1 1 1 I--1-t 0.12 - 0.1 0.08 0.06 - 0.04 I I I I 11 1 1 -4- 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) - Runoff lily 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 10 Summary for Link POA-PRE: POINT OF ANALYSIS PRE Inflow Area = 1.270 ac, 3.94% Impervious, Inflow Depth = 1.44" for 10-yr event Inflow = 1.19 cfs @ 12.22 hrs, Volume= 0.152 of Primary = 1.19 cfs @ 12.22 hrs, Volume= 0.152 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs w w 3 0 LL Link POA-PRE: POINT OF ANALYSIS PRE Hydrograph Inflow Area=1.270 ac 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow —111 — Primary 17 DA-C 2-yr and 10-yr Calculations C-PRE DA-C PRE Subcat Reach on Link 2016-05-11 SWM Calcs Prepared by Microsoft HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Printed 5/16/2016 Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.120 0.000 0.000 0.000 0.120 >75% Grass cover, Good C-PRE 0.000 0.140 0.000 0.000 0.000 0.140 Paved parking C-PRE 0.000 0.260 0.000 0.000 0.000 0.260 TOTAL AREA 19 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Prepared by Microsoft Printed 5/16/2016 HvdroCADO 10.00-12 s/n 07714 © 2014 HvdroCAD Software Solutions LLC Paae 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentC-PRE: DA-C PRE Runoff Area=0.260 ac 53.85% Impervious Runoff Depth=1.87" Tc=5.0 min CN=81 Runoff=0.62 cfs 0.040 of Total Runoff Area = 0.260 ac Runoff Volume = 0.040 of Average Runoff Depth = 1.87" 46.15% Pervious = 0.120 ac 53.85% Impervious = 0.140 ac 20 2016-05-11 SWM Caics Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment C-PRE: DA-C PRE Runoff = 0.62 cfs @ 12.03 hrs, Volume= 0.040 af, Depth= 1.87" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Area (ac) CN Description 0.140 98 Paved parking, HSG B 0.120 61 >75% Grass cover, Good, HSG B 0.260 81 Weighted Average 0.120 46.15% Pervious Area 0.140 53.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment C-PRE: DA-C PRE Hydrograph 0.65 0.62 cfs - - 0.6 — — — - Crotet-!Sushe'ss C ffic�24-14 St 2-yr 0.55 — — �ainfjll.70" 0.5 Runoff Area=0.260 ac R no{Voltame40.040 of f 0.45 -ftnoff Depth='r87" 0.4— ————�— — — —� Tc=5.0min CN=81_ 3 0.35 0 u. 0.3 - 0.25— ———————— _ 0.2 0.05 - 5 10 15 20 25 30 35 40 45 50 55 Time (hours) — Runoff `04I 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HvdroCADO 10.00-12 s/n 07714 © 2014 HvdroCAD Software Solutions LLC Paae 5 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentC-PRE: DA-C PRE Runoff Area=0.260 ac 53.85% Impervious Runoff Depth=3.48" Tc=5.0 min CN=81 Runoff=1.06 cfs 0.075 of Total Runoff Area = 0.260 ac Runoff Volume = 0.075 of Average Runoff Depth = 3.48" 46.15% Pervious = 0.120 ac 53.85% Impervious = 0.140 ac 22 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment C-PRE: DA-C PRE Runoff = 1.06 cfs @ 12.03 hrs, Volume= 0.075 af, Depth= 3.48" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.140 98 Paved parking, HSG B 0.120 61 >75% Grass cover, Good, HSG B 0.260 81 Weighted Average 0.120 46.15% Pervious Area 0.140 53.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 3 0 LL Subcatchment C-PRE: DA-C PRE Hydrograph 1.06 cfs CrozetSu�ine"Ice 24-hr IS"O-yr Rainfall=5.56" Runoff Area=0.260 ac I Runol Volume*0.075 of Runoff Depth=3.48" I Tc=5.0 min CN=81 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 Time (hours) — Runoff 23 POST DEVELOPMENT CALCULATIONS G oyG oy0 C•� 00 M M — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -------------- — — — — DA-C POST �' ---- ---,\ \ \ --- - 0.17 ACS- ,' 0.04-ACS IMP. - - oHu \ 0 \ HU OHU \ \\\ \\ \ \ O \ \ \ \ \ \ \ H \ \\ \\ \ \ \�\ H --ZA-APOST-- \\ --- --- --- 0.77 ACS \ I I \ \\ \ \ 5 ACS \ \ I \ _ I ------------------ F `\ \\ I \ \ \\ \`\ \\\ \\\ \\ \\— \\ \ I I / F \'QA—B\POST �- �----- \\ \\ \ I 0 59Aica--------- \ I I \0.00 `ACS IMP. � — \ \I \ I E \ \ \\\ \\ \ `\ \ 0.31\ ACS \MMACE TAIN ;; __ _ — — �-11 \ � \ \ I I E \ AS OPEN D \ \ I \ \\ `\ \ \ \-- 1 I D \ \ \ I I I G ` \ \ \ \ \ \\ I I / �/ C 7 \ A \ \ / I / / / / I I I A w .balzer.cc seaaaron New River Valley Roanoke Richmond Harrisonburg Balzer and Associates, Inc 1561 Commerce Road Suite 401 Verona, VA 24482 W-248-3220 FAX 540-248-3221 a w Q U LU w L (9 a 0.z aa cr) � z Q > ~� W ~ H `n a Z� z o D �y= w Q 0 2 U no p W� > m N w a O 12� ~ C.)O DRAWN BY DKO DESIGNED BY DKO CHECKED BY ERB DATE 05-16-2016 SCALE 1"=40' REVISIONS: SHEET NO. DA-2 JOB NO. 34150050 1►ob7 Project: Crozet Business Office Project #: 34150050 Date 1 /16/2016 Drainaae Area A: JTotal Disturbed Area: 1 1.36 Jacres 1 Year RVPre-Developed 0.27 Inches RVDeveloped 0.75 Inches Improvement Factor I.F. 0.80 QPre-Developed 0.11 cfs Enercgv Balance Equation: QDeveloped < I.F*(QPre-Developed* RVPre-Developed)/RVDeveloped Maximum QDeveloped to meet Energy Equation: I0.03 cfs Disturbed Area Exceeds 1 Acre Equation from 9VAC25-870-66, Section B. 3. Actual QDeveloped 0.03 cfs Meets Channel Protection Requirements 26 DA-A & B without Detention in Bioretention POINT OF ANALYSIS POST Subcat Reach on Link 27 2016-05-11 SWM Calcs Prepared by Microsoft Printed 5/17/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.000 0.000 0.000 0.000 0.000 TOTAL AREA 28 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/17/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Link POA-POST: POINT OF ANALYSIS POST Inflow=1.36 cfs 0.099 of Primary=1.36 cfs 0.099 of 29 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/17/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Link POA-POST: POINT OF ANALYSIS POST Inflow Area = 1.360 ac, 0.00% Impervious, Inflow Depth = 0.87" for 1-yr event Inflow = 1.36 cfs @ 12.03 hrs, Volume= 0.099 of Primary = 1.36 cfs @ 12.03 hrs, Volume= 0.099 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs a U 3 0 LL 1 0 Link POA-POST: POINT OF ANALYSIS POST Hydrograph Inflow Area=1.360 ac 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow —111 — Primary Kit] 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/17/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 5 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Link POA-POST: POINT OF ANALYSIS POST Inflow=3.32 cfs 0.290 of Primary=3.32 cfs 0.290 of 191 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/17/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Link POA-POST: POINT OF ANALYSIS POST Inflow Area = 1.360 ac, 0.00% Impervious, Inflow Depth = 2.56" for 10-yr event Inflow = 3.32 cfs @ 12.03 hrs, Volume= 0.290 of Primary = 3.32 cfs @ 12.03 hrs, Volume= 0.290 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Link POA-POST: POINT OF ANALYSIS POST Hydrograph w 3 0 LL 3 I Inflow Area=1.360 ac Ni 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow —111 — Primary 32 DA-A & B Post 1-yr Energy Balance Compliance /BMP Bio-Retention POA-POST A-POST1 DA-A POST 1-yr INT OF ANALYSIS POST B-POST1 DA-B POST 1-yr SubCat Reach on Link Routing Diagram for 2016-05-11 SWM Calcs Prepared by Microsoft, Printed 5/16/2016 Hydro CAD®® 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC 33 2016-05-11 SWM Calcs Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchi (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.000 0.000 0.000 1.360 1.360 Adjusted CN from VRRM Spreadsheet 0.000 0.000 0.000 0.000 1.360 1.360 TOTAL AREA 34 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentA-POST1: DA-A POST 1-yr Runoff Area=0.770 ac 0.00% Impervious Runoff Depth=1.17" Tc=5.0 min CN=78 Runoff=1.15 cfs 0.075 of SubcatchmentB-POST1: DA-B POST 1-yr Runoff Area=0.590 ac 0.00% Impervious Runoff Depth=0.21" Flow Length=210' Tc=17.8 min CN=55 Runoff=0.03 cfs 0.010 of Pond BMP: Bio-Retention Peak Elev=705.01' Storage=3,270 cf Inflow=1.15 cfs 0.075 of Outflow=0.01 cfs 0.001 of Link POA-POST: POINT OF ANALYSIS POST Inflow=0.03 cfs 0.011 of Primary=0.03 cfs 0.011 of Total Runoff Area = 1.360 ac Runoff Volume = 0.086 of Average Runoff Depth = 0.75" 100.00% Pervious = 1.360 ac 0.00% Impervious = 0.000 ac 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment A-POST1: DA-A POST 1-yr Runoff = 1.15 cfs @ 12.03 hrs, Volume= 0.075 af, Depth= 1.17" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Area (ac) CN Description 0.770 78 Adjusted CN from VRRM Spreadsheet 0.770 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, w 3 0 U. Subcatchment A-POST1: DA-A POST 1-yr Hydrograph Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Runoff Area=0.770 ac Runoff Volume=0.075 of Runoff Depth=1.17" Tc=5.0 min CN=78 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment B-POST1: DA-B POST 1-yr Runoff = 0.03 cfs @ 12.60 hrs, Volume= 0.010 af, Depth= 0.21" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Area (ac) CN Description 0.590 55 Adjusted CN from VRRM Spreadsheet 0.590 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 17.3 150 0.0667 0.14 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" 0.5 60 0.1333 1.83 Shallow Concentrated Flow, Woodland Kv= 5.0 fDs 17.8 210 Total Subcatchment B-POST1: DA-B POST 1-yr Hydrograph 0.036 0.034 cfs - 0.03 0.032 0.03 �Croz'et l3i sine s Office'24-hi� S1 1- r y 0.028 �ainf411=3�6" 0.026 Runoff Area- .59 ac Rpnofff Vol�ii mej0.01�af 0.024 Runoff Depth=0.21" 0.022 �— jlo [Il Ith-- 10' 0.0z Tc=17.8 min 3 0.018 —1 1 -T � -rCN�55 �° 0.016 0.014 I I I I -1 A t+ 0.012 0.01--�--� -� - -1 4 4 4 4 4 0.008 — — — — — 1 1 0.006 -1 0.004 7 T 0.002 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff RYA 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Pond BMP: Bio-Retention Inflow Area = 0.770 ac, 0.00% Impervious, Inflow Depth = 1.17" for 1-yr event Inflow = 1.15 cfs @ 12.03 hrs, Volume= 0.075 of Outflow = 0.01 cfs @ 24.10 hrs, Volume= 0.001 af, Atten= 100%, Lag= 724.0 min Primary = 0.01 cfs @ 24.10 hrs, Volume= 0.001 of Routing by Stor-Ind method, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs / 2 Peak Elev= 705.01' @ 24.10 hrs Surf.Area= 2,309 sf Storage= 3,270 cf Plug -Flow detention time= 900.2 min calculated for 0.001 of (1% of inflow) Center -of -Mass det. time= 646.0 min ( 1,517.4 - 871.4 ) Volume Invert Avail.Storage Storage Description #1 699.17' 5,983 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (%) (cubic -feet) (cubic -feet) (sq-ft) 699.17 925 145.0 0.0 0 0 925 700.17 925 145.0 40.0 370 370 1,070 701.00 925 145.0 40.0 307 677 1,190 702.50 1,200 200.0 25.0 397 1,074 2,722 704.00 1,200 200.0 25.0 450 1,524 3,022 705.00 2,300 235.0 100.0 1,720 3,245 4,253 706.00 3,200 283.0 100.0 2,738 5,983 6,249 Device Routing Invert Outlet Devices #1 Primary 705.00' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 0.50 0.50 1.00 Width (feet) 0.67 0.67 6.00 9.00 Primary OutFlow Max=0.00 cfs @ 24.10 hrs HW=705.01' (Free Discharge) L1=Custom Weir/Orifice (Weir Controls 0.00 cfs @ 0.34 fps) 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 7 Pond BMP: Bio-Retention Hydrograph 3 0 LL l l l Inflow lArea=0.770 ac Leak 6Iev=�05.0i Storage=3I,270 cf 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow — Primary 39 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 1-yr Rainfall=3.06" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 8 Summary for Link POA-POST: POINT OF ANALYSIS POST Inflow Area = 1.360 ac, 0.00% Impervious, Inflow Depth = 0.10" for 1-yr event Inflow = 0.03 cfs @ 12.60 hrs, Volume= 0.011 of Primary = 0.03 cfs @ 12.60 hrs, Volume= 0.011 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs 0.03E 0.034 0.032 0.03 0.02E 0.02E 0.024 0.022 w 0.02 3 0.01 a LL 0.01 E 0.014 0.012 0.01 0.00a 0.00E 0.004 0.002 0.03 cfs Link POA-POST: POINT OF ANALYSIS POST Hydrograph � Inflow Area=1.366ac A A- I� : A -1 T T T A-4 4 4 4 T T 11I-1-AJJITTT -1 1 7 TTTT7TT] 5 10 15 20 25 30 35 40 45 5( Time (hours) 75 80 85 90 — Inflow — Primary 40 DA-A & B Post 10-yr Calculations E10 /1B/M P DA-A POST 10-yr Bio-Retentii POA-POST OF ANALYSIS POST �B-POST1 0 DA-B POST 10-yr Subcat Reach on Link 41 2016-05-11 SWM Calcs Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchi (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.000 0.000 0.000 1.360 1.360 Adjusted CN from VRRM Spreadsheet 0.000 0.000 0.000 0.000 1.360 1.360 TOTAL AREA 42 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentA-POST10: DA-A POST 10-yr Runoff Area=0.770 ac 0.00% Impervious Runoff Depth=3.49" Tc=5.0 min CN=81 Runoff=3.14 cfs 0.224 of Subcatchment B-POST10: DA-B POST 10-yr Runoff Area=0.590 ac 0.00% Impervious Runoff Depth=1.34" Flow Length=210' Tc=17.8 min CN=56 Runoff=0.50 cfs 0.066 of Pond BMP: Bio-Retention Peak Elev=705.48' Storage=4,438 cf Inflow=3.14 cfs 0.224 of Outflow=0.72 cfs 0.149 of Link POA-POST: POINT OF ANALYSIS POST Inflow=1.11 cfs 0.215 of Primary=1.11 cfs 0.215 of Total Runoff Area = 1.360 ac Runoff Volume = 0.290 of Average Runoff Depth = 2.56" 100.00% Pervious = 1.360 ac 0.00% Impervious = 0.000 ac 43 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment A-POST10: DA-A POST 10-yr Runoff = 3.14 cfs @ 12.03 hrs, Volume= 0.224 af, Depth= 3.49" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.770 81 Adjusted CN from VRRM Spreadsheet 0.770 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, U 3 0 LL Subcatchment A-POST10: DA-A POST 10-yr Hydrograph Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Runoff Area=0.770 ac Runoff Volume=0.224 of Runoff Depth=3.49" Tc=5.0 min CN=81 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff 44 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment B-POST10: DA-B POST 10-yr Runoff = 0.50 cfs @ 12.23 hrs, Volume= 0.066 af, Depth= 1.34" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.590 56 Adjusted CN from VRRM Spreadsheet 0.590 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 17.3 150 0.0667 0.14 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.60" 0.5 60 0.1333 1.83 Shallow Concentrated Flow, Woodland Kv= 5.0 fDs 17.8 210 Total 0.55 0.3 3 i° 0.25 0.2 0.15 0.1 0.05 0 0.50 cfs Subcatchment B-POST10: DA-B POST 10-yr Hydrograph i I I ��I I �I �I Crozet Bu�iness Office4-hr 51 10-yr �a1n11=53I6'" Runoff Area j.59tl ac Rlunoj Volume�0.066 of -Runoff Depth=1.34" Flow Length=210' Tc=17.8-min 1 CN=56 1 -1 -1 A - 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Runoff 45 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Pond BMP: Bio-Retention Inflow Area = 0.770 ac, 0.00% Impervious, Inflow Depth = 3.49" for 10-yr event Inflow = 3.14 cfs @ 12.03 hrs, Volume= 0.224 of Outflow = 0.72 cfs @ 12.52 hrs, Volume= 0.149 af, Atten= 77%, Lag= 29.5 min Primary = 0.72 cfs @ 12.52 hrs, Volume= 0.149 of Routing by Stor-Ind method, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs / 2 Peak Elev= 705.48' @ 12.52 hrs Surf.Area= 2,711 sf Storage= 4,438 cf Plug -Flow detention time= 239.0 min calculated for 0.149 of (67% of inflow) Center -of -Mass det. time= 120.9 min ( 949.5 - 828.6 ) Volume Invert Avail.Storage Storage Description #1 699.17' 5,983 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (%) (cubic -feet) (cubic -feet) (sq-ft) 699.17 925 145.0 0.0 0 0 925 700.17 925 145.0 40.0 370 370 1,070 701.00 925 145.0 40.0 307 677 1,190 702.50 1,200 200.0 25.0 397 1,074 2,722 704.00 1,200 200.0 25.0 450 1,524 3,022 705.00 2,300 235.0 100.0 1,720 3,245 4,253 706.00 3,200 283.0 100.0 2,738 5,983 6,249 Device Routing Invert Outlet Devices #1 Primary 705.00' Custom Weir/Orifice, Cv= 2.62 (C= 3.28) Head (feet) 0.00 0.50 0.50 1.00 Width (feet) 0.67 0.67 6.00 9.00 Primary OutFlow Max=0.72 cfs @ 12.52 hrs HW=705.48' (Free Discharge) L1=Custom Weir/Orifice (Weir Controls 0.72 cfs @ 2.26 fps) 46 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 7 3 0 LL 3.14 cfs 1 0.72 cfs Pond BMP: Bio-Retention Hydrograph I rtnfrowl Area 0.776 ac I I Beak 6evl=iO A�' Storage=4I,438 cf Time (hours) — Inflow — Primary 47 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 8 Summary for Link POA-POST: POINT OF ANALYSIS POST Inflow Area = 1.360 ac, 0.00% Impervious, Inflow Depth = 1.90" for 10-yr event Inflow = 1.11 cfs @ 12.32 hrs, Volume= 0.215 of Primary = 1.11 cfs @ 12.32 hrs, Volume= 0.215 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs w 3 0 LL Link POA-POST: POINT OF ANALYSIS POST Hydrograph Inflow Area=1.360 ac 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Time (hours) — Inflow —111 — Primary 48 DA-C Post 2-yr & 10-yr Residual Calculations DA-C POST Subcat Reach on Link 49 2016-05-11 SWM Calcs Prepared by Microsoft HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Printed 5/16/2016 Page 2 Ground Covers (selected nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 0.130 0.000 0.000 0.000 0.130 >75% Grass cover, Good C-POST 0.000 0.040 0.000 0.000 0.000 0.040 Paved parking C-POST 0.000 0.170 0.000 0.000 0.000 0.170 TOTAL AREA 6111 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Prepared by Microsoft Printed 5/16/2016 HvdroCADO 10.00-12 s/n 07714 © 2014 HvdroCAD Software Solutions LLC Paae 3 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentC-POST: DA-C POST Runoff Area=0.170 ac 23.53% Impervious Runoff Depth=1.12" Tc=5.0 min CN=70 Runoff=0.22 cfs 0.016 of Total Runoff Area = 0.170 ac Runoff Volume = 0.016 of Average Runoff Depth = 1.12" 76.47% Pervious = 0.130 ac 23.53% Impervious = 0.040 ac 61 2016-05-11 SWM Caics Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment C-POST: DA-C POST Runoff = 0.22 cfs @ 12.03 hrs, Volume= 0.016 af, Depth= 1.12" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 2-yr Rainfall=3.70" Area (ac) CN Description 0.040 98 Paved parking, HSG B 0.130 61 >75% Grass cover, Good, HSG B 0.170 70 Weighted Average 0.130 76.47% Pervious Area 0.040 23.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment C-POST: DA-C POST Hydrograph 0.25 0.24 0.23 0.22 cfs 0.22 I ICrotet4I sine'ss�i e 24--� S�- 0.21 0.2 - ali 0.19 Runo rea- .1 0.18 0.16 - - - - - -Runoff Depth=4-.1 0.15 w 0.14 - Ci1� =0.13 - 0 0.12 LL 0.11 0.1 0.09 - 0.08 0.07 1 I I 11 1 1 4 4--1-4 0.06 - - - 0.05 0.04 0.03 0.01 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 Time (hours) - Runoff 52 2016-05-11 SWM Calcs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HvdroCADO 10.00-12 s/n 07714 © 2014 HvdroCAD Software Solutions LLC Paae 5 Time span=0.10-90.00 hrs, dt=0.01 hrs, 8991 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentC-POST: DA-C POST Runoff Area=0.170 ac 23.53% Impervious Runoff Depth=2.43" Tc=5.0 min CN=70 Runoff=0.48 cfs 0.034 of Total Runoff Area = 0.170 ac Runoff Volume = 0.034 of Average Runoff Depth = 2.43" 76.47% Pervious = 0.130 ac 23.53% Impervious = 0.040 ac 53 2016-05-11 SWM Caics Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Prepared by Microsoft Printed 5/16/2016 HydroCADO 10.00-12 s/n 07714 © 2014 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment C-POST: DA-C POST Runoff = 0.48 cfs @ 12.03 hrs, Volume= 0.034 af, Depth= 2.43" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.10-90.00 hrs, dt= 0.01 hrs Crozet Business Office 24-hr S1 10-yr Rainfall=5.56" Area (ac) CN Description 0.040 98 Paved parking, HSG B 0.130 61 >75% Grass cover, Good, HSG B 0.170 70 Weighted Average 0.130 76.47% Pervious Area 0.040 23.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment C-POST: DA-C POST Hydrograph 0.5 — — 0.48 cfs 0.48 — — 0.46 0.44 0.42- 0.4 0.38 0.36 0.34 — 0.32 w 0.3 — 0.28 3 0.28 �—°° 0.24 0.22 — 0.2 0.18 0.16 0.14 0.12 0.1— 1IIIII 0.08 0.06 0.04 �roze�t �u�inec 4-h 1 -�-yr Rtmof -Are .1 ac R�uno�f Vol imej0.03� of — — -Runoff Depth=3.43" — Tc5.9-min CN=70 10 15 20 25 30 35 40 45 50 Time (hours) — Runoff 54 WATER QUALITY CALCULATIONS Virginia Runoff Reduction Method Worksheet 611 DEQ Virginia Runoff Reduction Method Re -Development Compliance Spreadsheet - Version 3.0 BMP Design Specifications List: 2011 Stds & Specs Site Summary Total Rainfall (in): 43 Total Disturbed Acreage: 1.53 Site Land Cover Summary Pre-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals % of Total Forest/Open (acres) 0.00 1.09 0.00 0.00 1.09 71 Managed Turf (acres) 0.00 0.25 0.00 0.00 0.25 16 Impervious Cover (acres) 0.00 0.19 0.00 0.00 0.19 12 1.53 100 Post-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals % of Total Forest/Open (acres) 0.00 0.37 0.00 0.00 0.37 24 Managed Turf (acres) 0.00 0.57 0.00 0.00 0.57 37 Impervious Cover (acres) 0.00 0.59 0.00 0.00 0.59 39 * Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 1.53 100 Site Tv and Land Cover Nutrient Loads Final Post -Development Post Post- Adjusted Pre- M= (Post-ReDevelopment ReDevelopment Development ReDevelopment Impervious) & New Im p ) (New Impervious) Site Rv 0.45 0.27 0.95 0.22 Treatment Volume (ft) 2,489 1,109 1,379 912 TP Load (lb/yr) 1.56 0.70 0.87 0.57 Baseline TP Load (lb/yr): 0.4633* *Reduction below new development load limitation not required Total TP Load Reduction Required (lb/yr) 0.94 0.23 0.70 Final Post -Development Load (Post-ReDevelopment & New Impervious) Pre- ReDevelopment TN Load (Ib/yr) 11.19 4.29 Pre- ReDevelopment Final Post -Development Post-ReDevelopment TP TP Load per acre TP Load per acre Load per acre (lb/acre/yr) (lb/acre/yr) (lb/acre/yr) 0.51 1.02 0.62 Summary Print Virginia Runoff Reduction Method Worksheet Site Compliance Summary Maximum % Reduction Required Below 20% * Note: % Reduction will reduce post -development TP load to less than or equal to baseline load of 0.46 lb/yr (0.41 Ib/ac/yr) Pre-ReDevelopment Load [Required reduction for Post-ReDev. = Post-ReDev TP load -baseline load of 0.46331b/yr], baseline load = site area x 0.41 Ib/ac/yr Total Runoff Volume Reduction (ft) 1,765 Total TP Load Reduction Achieved (Ib/yr) 1.24 Total TN Load Reduction Achieved (lb/yr) 9.03 Remaining Post Development TP Load (lb/yr) 0.33 Remaining TP Load Reduction (lb/yr) Required 0.00 *Reduction below new development load limitation not required ** TARGET TP REDUCTION EXCEEDED BY 0.3 LB/YEAR ** Summary Print Virginia Runoff Reduction Method Worksheet 6YA Drainage Area Summary D.A. A D.A. B D.A. C D.A. D D.A. E Total Forest/Open (acres) 0.00 0.37 0.00 0.00 0.00 0.37 Managed Turf (acres) 0.22 0.22 0.13 0.00 0.00 0.57 Impervious Cover (acres) 0.55 0.00 0.04 0.00 0.00 0.59 Total Area (acres) 0.77 0.59 0.17 0.00 0.00 1.53 Drainage Area Compliance Summary D.A. A D.A. B D.A. C D.A. D D.A. E Total TP Load Reduced (lb/yr) 1.16 0.08 0.00 0.00 0.00 1.24 TN Load Reduced (lb/yr) 8.49 0.54 0.00 0.00 0.00 9.03 Summary Print Virginia Runoff Reduction Method Worksheet 61.3 Drainage Area A Summary Land Cover Summary Forest/Open (acres) A Soils 0.00 B Soils 0.00 C Soils 0.00 D Soils 0.00 Total 0.00 % of Total 0 Managed Turf (acres) 0.00 0.22 0.00 0.00 0.22 29 Impervious Cover (acres) 0.00 0.55 0.00 0.00 0.55 71 0.77 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit s Volume (ft) Upstream to Practice (Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) Area (acres) Practices (lb,) 6.b. Bioretention #2 or Micro-Bioretention #2 (Spec #9) 0.22 0.55 2,056.40 0.00 1.29 1.16 0.13 Total Impervious Cover Treated (acres) 0.55 Total Turf Area Treated (acres) 0.22 Total TP Load Reduction Achieved in D.A. (lb/yr) 1.16 Total TN Load Reduction Achieved in D.A. (Ib/yr) 8.49 Summary Print Virginia Runoff Reduction Method Worksheet 01 Drainage Area B Summary Land Cover Summ Forest/Open (acres) A Soils 0.00 B Soils 0.37 C Soils 0.00 D Soils 0.00 Total 0.37 % of Total 63 Managed Turf (acres) 0.00 0.22 0.00 0.00 0.22 37 Impervious Cover (acres) 0.00 0.00 0.00 0.00 0.00 0 0.59 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit a Volume (ft) Upstream to Practice (Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) Area (acres) Practices (Ibs) 9.a. Sheetflow to Conservation Area, A/B Soils (Spec #2) 0.22 159.72 0.00 0.10 0.08 0.03 Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.22 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.08 Total TN Load Reduction Achieved in D.A. (lb/yr) 0.54 Summary Print Virginia Runoff Reduction Method Worksheet 60 Drainage Area C Summary Land Cover Summ Forest/Open (acres) A Soils 0.00 B Soils 0.00 C Soils 0.00 D Soils 0.00 Total 0.00 % of Total 0 Managed Turf (acres) 0.00 0.13 0.00 0.00 0.13 76 Impervious Cover (acres) 0.00 0.04 0.00 0.00 0.04 24 0.17 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit I a Volume (ft) Upstream to Practice (Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) Area (acres) Practices (Ibs) Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.00 Total TN Load Reduction Achieved in D.A. (lb/yr) 0.00 Summary Print Virginia Runoff Reduction Method Worksheet 61 Runoff Volume and CN Calculations 1-year storm I 2-year storm ) 10-yearstorm (Target Rainfall Event (in) 1 3.06 1 3.70 1 5.56 1 Drainage Areas RV & CN Drainage Area A Drainage Area B Drainage Area C Drainage Area D Drainage Area E CN 87 57 70 0 0 RR (ft3) 1,645 120 0 0 0 1-year return period RV wo RR (ws-in) 1.79 0.26 0.75 0.00 0.00 RVwRR(ws-in) 1.20 0.21 0.75 0.00 0.00 CN adjusted 78 55 70 0 0 2-year return period RV wo RR (ws-in) 2.36 0.49 1.13 0.00 0.00 RVwRR(ws-in) 1.77 0.44 1.13 0.00 0.00 CN adjusted 80 56 70 0 0 10-year return period RV wo RR (ws-in) 4.10 1.42 2.46 0.00 0.00 RV w RR (ws-in) 3.51 1.36 2.46 0.00 0.00 CN adjusted 81 56 70 0 0 Summary Print 62 mm SPECIFICATION #9 - BIORETENTION BASIN A WORKSHEET —Q ASSQQ. 9S -C PROJECT NAME: Crozet Business Office PROJECT #: 34150050 �o o�R�w Design Level DATE: 5/11/2016 �.,..a Level #2 BY: DKO BMP Sizing Data Transcribed Runoff Reduction Worksheet Inflow Area (A) Treatment Volume (Tv) Level #2 Impervious 1,645 (cf) Impervious 0.55 (ac) Level #2 Turf (cf) Turf 0.22 (ac) Treatment Level Treatment Volume Total Coefficient (Tv) TvBMP 1.25 * 1,645 (cf) = 2,056 (cf) Equivalent Storage Depth Surface Storage Bioretention Soil Media & Mulch Choker Stone Additional Gravel Required Gravel Below Underdrain Total Depth Required Surface Area Treatment Volume Equivalent Storage Depth Pond Desien Elevations (ft Top of Bioretention Berm Top of Storage, High Flow Weir, Top of Riser P.T. Cell Low Flow Weir Top of Media Bottom of Media / Geotextile Fabric Bottom of Choker Stone Underdrain Invert Bottom of Gravel Flow Path Length of shortest flow path w/ >20% contributing DA Overall length Ratio Pre -Treatment Measures Measure 1 Measure 2 Pre -Treatment Cell Design Design Cell Surface Area Design Cell Depth Provided Storage Required Storage (TvBMP*0.15) Void Ratios Storage Equiv. 1.00 (ft) 1 1.00 (ft) 3.00 (ft) 0.25 0.75 (ft) 0.33 (ft) 0.4 0.13 (ft) 0.00 (ft) 0.4 0.00 (ft) 1.00 (ft) 0.4 0.40 (ft) 5.33 (ft) 2.28 (ft) nsr L./-6 = 901 (sf) 706.00 705.00 704.25 704.00 701.00 700.67 700.17 699.17 65 (ft) 80 (ft) 0.81 No Baffle Required Pre -Treatment Cell 220 (sf) 1.50 (ft) 330 (cf) 308 (cf) Suggested Plant Material 4 (ea.) I Trees, 1" Caliper Minimum (and) 1 per 250 (sf)