Loading...
HomeMy WebLinkAboutWPO201700020 Calculations WPO VSMP 2017-05-24 46 t FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations March 15, 2017 Revised on April 10, 2017 Revised on May 24, 2017 (Updates to the previously reviewed amendment calculations are noted in yellow.) PREPARED BY: COLLINS ENGINEERING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE,VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com It ti w U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 • TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothill Crossing II-VSMP No.2 Designed By:KKW,PE Date: 5/23/2017 Location: Park Ridge Drive&Future Glenbrook at Foothills Checked By:SRC,PE Date: 5/23/2017 Check One: Present X Developed X 1.Runoff curve Number(CN) Soil name and Cover description CN(weighted)= Drainage Area Area Product of CN Calculated hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ Description (Acres) x Area '5'Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area APPROVED DA 1A (Present) Approved Pre-Dev.DA 1 61 16.91 1031.5 61 6.39 APPROVED DA 1A (Proposed) Approved Post-Dev.DA 1 87 16.51 1436.4 87 1.49 FINAL BUILDOUT DA Final Buildout of the Watershed(Includes Glenbrook): 1A Anticipated Impervious Areas 98 10.26 1005.6 79 2.69 (Developed) Remaining Areas classified as Managed Turf 61 11.03 672.8 2.Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 1 2 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,Q-inches 0.57 0.67 1.74 APPROVED DA 1A(Present) Runoff,Q-inches 2.18 2.36 4.14 APPROVED DA lA(Proposed) Runoff,Q-inches 1.55 1.71 3.31 FINAL BUILDOUT DA 1A(Developed) S IIw U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(T,)or Travel Time(Ti) Project: Foothill Crossing II-VSMP No.2 Designed By: FGM,PE Date: 3/15/2017 Location: Park Ridge Drive&Future Glenbrook at Foothi Checked By:SRC,PE Date: 3/15/2017 Check One: Present X Developed X Check One: T, X T, Through subarea n/a APPROVED DA 1A APPROVED DA 1A FINAL BUILDOUT DA 1A Segment ID: (Present) (Proposed) (Developed) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 6 Compute T,=[0.007(n*L)°'8]/P2's s04 0.29 0.22 0.22 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 952 117 210 9 Watercourse slope,s(ft/ft) 0.040 0.026 0.060 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 2.6 4 11 T,=L/3600*V 0.08 I 0.01 0.01 Channel Flow: 12 Cross sectional flow area,a(ft2) 3 E E 13 Wetted perimeter,Pw(ft) o ` o 14 Hydraulic radius,r=a/Pw,(ft) 9 o 99 o 15 Channel Slope,s(ft/ft) E v a, d 16 Manning's Roughness Coeff,n 17 V=[1.49r2/3ss]/n m 1 18 Flow length,L(ft) 19 T,=L/3600*V I 0.00 I 0.00 20 Watershed or subarea T,orT, (Add T,in steps 6,11 and 19) 0.37 J 0.23 I 0.23 I U.S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothill Crossing II-VSMP No.2 Designed By: KKW,PE Date: 5/23/2017 Location: Park Ridge Dr/Glenbrook Checked By: SRC,PE Date: 5/23/2017 Check One: Present X Developed X 1. Data Drainage Area Description Drainage Area Description Drainage Area Description APPROVED DA 1A APPROVED DA 1A FINAL BUILDOUT DA 1A (Present) (Proposed) (Developed) Drainage Area(Am)in miles2= 0.0264 0.0258 0.0160 Runoff curve number CN= 61.0 87.0 78.8 Time of concentration(Tc)= 0.37 0.23 0.23 Rainfall distribution type= II II II Pond and swamp areas spread 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4. Initial Abstraction,la-inches 1.28 1.28 1.28 0.30 0.30 0.30 0.54 0.54 0.54 5.Compute la/P 0.37 0.35 0.23 0.09 0.08 0.05 0.15 0.15 0.10 6.Unit peak discharge,Qu-csm/in 450 480 550 775 775 800 725 725 750 7.Runoff,Qfrom Worksheet 2-inches 0.57 0.67 1.74 2.18 2.36 4.14 1.55 1.71 3.31 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Through The where Qp=Qu Am Q Fp 6.86 8.49 25.44 1.48 1.61 2.39 Amended SWM Facility Watershed Summary for DA 1A: 1-yr,cfs 2-yr,cfs 10-yr,cfs Approved Pre-Development 6.86 8.49 25.44 Approved Post-Development Routings 1.48 1.61 2.39 Amended Post-Development Routings 0.95 0.99 6.46 Final Buildout Post-Dev.Routings 0.91 0.96 6.96 Note: Per the approved 9VAC25-870-66 calculations,this development meets channel protection compliance by having a post-development 1-year peak SCS design storm outflow less than or equal to 1.48 cfs. Post-Development Routing Calculations (The following amended SWM facility 1A routing calculations analyze the approved subarea 1A, as well as the full build out of subarea 1A for the Glenbrook Subdivision.These calculations show water quantity compliance is met for the future Glenbrook Subdivision.) Foothills AMENDED Facility 1A- Approved Watershed BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- Approved Watershed 9 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 624.00 6903.00 0.0 626.00 10454.00 638.3 628.00 14622.00 1562.8 629.00 19510.00 2192.7 630.00 25243.00 3019.1 632.00 29873.00 5058.1 634.00 33734.00 7412.4 636.00 36565.00 10015.4 638.00 39355.00 12826.6 Start_Elevation(ft) 630.00 Vol. (cy) 3019.14 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 5 discharge into riser Page 1 Foothills AMENDED Facility 1A- Approved Watershed Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 1 discharge into riser Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Outlet structure 5 Weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Page 2 Foothills AMENDED Facility 1A- Approved Watershed Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682.513 Page 3 Foothills AMENDED Facility 1A- Approved Watershed OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 0.946 at 15.34 (hrs) water level (ft) 633.199 at 15.74 (hrs) storage (cy) 6435.410 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 40.531 at 11.98 (hrs) discharge (cfs) 0.985 at 15.22 (hrs) water level (ft) 633.456 at 15.86 (hrs) storage (cy) 6742.954 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 6.464 at 12.66 (hrs) water level (ft) 635.049 at 12.66 (hrs) storage (cy) 8752.075 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 89.086 at 12.10 (hrs) water level (ft) 636.666 at 12.10 (hrs) storage (cy) 10927.984 Fri Apr 07 14:59:34 EDT 2017 Page 4 Foothills AMENDED Facility 1A- Final Buildout Watershed-revl BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- Final Buildout Watershed 9 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 624.00 6903.00 0.0 626.00 10454.00 638.3 628.00 14622.00 1562.8 629.00 19510.00 2192.7 630.00 25243.00 3019.1 632.00 29873.00 5058.1 634.00 33734.00 7412.4 636.00 36565.00 10015.4 638.00 39355.00 12826.6 Start_Elevation(ft) 630.00 Vol. (cy) 3019.14 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 Page 1 Foothills AMENDED Facility 1A- Final Buildout Watershed-revl width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 5 discharge into riser Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 1 discharge into riser Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Outlet structure 5 Weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.290 CN 79.000 Type 2 rainfall, P (in) 3.500 Page 2 Foothills AMENDED Facility 1A- Final Buildout Watershed-revl time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 34.810 peak time (hrs) 11.991 volume (cy) 4477.562 Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.290 CN 79.000 Type 2 rainfall, P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 38.297 peak time (hrs) 11.991 volume (cy) 4926.155 Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.290 CN 79.000 Type 2 rainfall, P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 73.903 peak time (hrs) 11.991 volume (cy) 9506.079 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.290 CN 79.000 Type 2 rainfall, P (in) 9.100 Page 3 Foothills AMENDED Facility 1A- Final Buildout Watershed-revl time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 145.366 peak time (hrs) 11.991 volume (cy) 18698.305 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 34.637 at 11.98 (hrs) discharge (cfs) 0.908 at 14.98 (hrs) water level (ft) 632.967 at 15.50 (hrs) storage (cy) 6160.250 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 38.107 at 11.98 (hrs) discharge (cfs) 0.955 at 15.54 (hrs) water level (ft) 633.255 at 15.72 (hrs) storage (cy) 6502.060 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 73.536 at 11.98 (hrs) discharge (cfs) 6.957 at 12.62 (hrs) water level (ft) 635.189 at 12.64 (hrs) storage (cy) 8934.001 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 144.644 at 11.98 (hrs) discharge (cfs) 119.569 at 12.06 (hrs) water level (ft) 636.791 at 12.06 (hrs) storage (cy) 11102.760 Wed May 24 11:06:13 EDT 2017 Page 4 Virginia Runoff Reduction Method Calculations (These calculations show water quality compliance is met for the future Glenbrook Subdivision upland of the amended stormwater management basin 1A.) DA#1A Final Buildout Impervious Area Summary (For Water Quantity&Quality Calculations) * Roadways 201,934 sf *Sidewalks 39,941 sf 5 Lots where Half is Captured 5,000 sf ** 92 Lots where Most or All is Captured 184,000 sf Approved Foothill IV Impervious Area 16,085 sf 446,960 sf * Includes Park Ridge Dr, Fut. Glenbrook Subdvision, Fut. Eastern Connector& Fut Dunnwood Dr. Extension) ** Includes Future Glenbrook Subdivision DA#2B Final Buildout Impervious Area Summary (For Water Quantity&Quality Calculations) Roadways 107,000 sf Sidewalks 32,605 sf 3 Lots where Half is Captured 3,000 sf 37 Lots where Most or All is Captured 74,000 sf Approved Foothill IV Impervious Area 49,658 sf 266,263 sf DA#3C&4C Final Buildout Impervious Area Summary (For Glenbrook at Foothills Water Quality Calculations) Binion Drive (A portion of) 10,132 sf Sidewalks 1,586 sf 8 Lots where Most or All is Captured 16,000 sf 27,718 sf DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 C 2011 BMP Standards and Specifications :C]2013 Draft BMP Standards and Specifications Project Name: Glenbrook at Foothills&Park Ridge Drive CLEAR ALL data input cells 1 Date: 5/4/2017 constant values BMP Design Specifications List:2011 Stds&Specs calculation cells Site Information final results Post-Development Project(Treatment Volume and Loads) Land Cover(acres) A Soils B Soils C Soils D Soils Totals Forest/Open Space(acres)-undisturbed, protected forest/open space or reforested land 2.70 2.70 Managed Turf(acres)-disturbed,graded for yards or other turf to be mowed/managed 23.10 23.10 Impervious Cover(acres) 17 22 17.22 •Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 43.02 Constants Runoff Coefficients(Rv) Annual Rainfall(inches) 43 A Soils B Soils C Soils D Soils Target Rainfall Event(inches) 1.00 Forest/Open Space 0.02 0.03 0.04 0.05 Total Phosphorus(TP)EMC(mg/L) 0.26 Managed Turf 0.15 0.20 0.22 0.25 Total Nitrogen(TN)EMC(mg/L) 1.86 Impervious Cover 0.95 0.95 0.95 0.95 Target TP Load(lb/acre/yr) 0.41 Pj(unitless correction factor) 0.90 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/yr) 30.39 LAND COVER SUMMARY--POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment Volume Forest/Open Space Cover(acres) 2.70 (acre-ft) 1.7550 Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 76,448 %Forest 6% TP Load(lb/yr) 48.03 TN Load(Ib/yr) Managed Turf Cover(acres) 23.10 (Informational Purposes Only) 343.62 Weighted Rv(turf) 0.20 %Managed Turf 54% Impervious Cover(acres) 17.22 Rv(impervious) 0.95 %Impervious 40% Site Area(acres) 43.02 Site Rv 0.49 • 211._WirrIMAI No 2 • • Drainage Area A ea.mm•Lam cam marm A S. 0 Solls CS. 0 U. la. 1.0.r.rity No.0.50.1.1.31 600 600 , ....1.0.18.51 1626 1626 CMS tearimMermambirleMammam da•m/m) 1.6 1.1 21.231 am emagmarermaerma Whom(a DA a frei ..... Morrnwater Best Management Practices(RR=Runoff Reduction) ....A.Oropdown 0.- 1,1* Ut...0 1.011 .0.050.500500 mivirm tom 0.011 5.5005500To.MP P... mumarms 5.00.505 .....,, m a0 um •••••••• Las.. h.. M.O. Turf.. Corner.. 10.1. R.6.11 AIWA 'MAMA Ala L, ad. .n.0 By mamma WM.. Pa fron,Upomem M..6 LAM 00.00. c,..,, A...,...., y...,...,q.,,,,,,,e, ,ft.) Ye*10.)V.N.00....Y.'Pm..Clal 01•01.OW "*"bi a M) simmer(16)h..05051 sir',mice IMI 50.140 AS 0 0 0 0 CAI IMO OA NE IIEMICIIIIrall Lb 11.22.62611.1.451 40 0 • 0 a AM .0 OM ME 11:111111211= =MIESIE LK 5.0221)=.2.1. .0 0 0 0 • 0 IAA a. OM .0 6/6 AA 0 0 0 • 0 AM .0 OW am a om am kW OW 1.2411 1.14.4.0216.1.11•11.. • 0 0 a o , me me amo 0.0 0 CID LA ILA .0 .112621.122621.CM 2.211.6. . ICON)WA 6 12.11 OMR IL • 0 • , a a me ism ma am so ma am am ma ummmovermiummai mum.in ism mi m o a • • so me om om am as am am mo am )1.tr mamas). o • o • ZS AO .0 OA AO a am me tan am 112660.6...11.4491 hfiere-marman 15...1 M 0 • 0 • M DAM .3 OA OA A COI am cao OM I.O.M... 0 • 0 • • WM OM LA .0 0 am me am am . 2,as........mm a a a a SS OM 0.00 OM GAN al me aa• am am 1.6111...1.1119.4.).A1 . A.0.....1116.47, 45 • a 0 05 ON am ON ON IIIMMI:MEM=1111:1111 IS ea r....21.1.1 11I 2S .... ... ... NM MEMEINEll AL 1.660.....4 GI a 0 • o a ts am am am am 111.111111:111.11:MEMEM 4)....11.1.1.616 LA 0 0 0 0 O ON ON ON ON IENNICIIIICMEMME co am comae mmoomo . a e a e is am ON ON ON " 111:111111:11.1=111:111 S.22......611 5....4113001460 40 0 0 • a m em am 600 OM s.l.0,9.AZO.A101 AO 0 a 0 0 AO OM CM ON 0111 0.077777 f " 0 . • a OS ON 610 ON ON 1111:11111CMCMIEMEZI , 6.12......1.60.6.2126 al . 0 0 0 0 SO 646 ON •A ON EralICE1111:111111:111111:11 I...91 10 0 0 0 • OS .. ON ON ON .1.1111:111111=11.:EZZ T..1.242.11.016 A 0 0 0 0 13 ON ON ON ,.. ERIMIIIIIMMIEZIEM 6.10111.01151 0 0 0 0 0 O ON ON ON ON •=1111:11111111:1111IIMEM 1.5 • 0 0 0 00 600 ON ON 0110 MMIII:11111111=E1111:1111 ,..,,,w„,,,„,,„..,..,,,,,,,, . 0 0 0 • 0 5.0 ON ON ON 11.111.:EM:MEMMII 120•4 011 - • RI 625.2.2.24.26...KA S. . IICEICEMME:11.311 0 0 0 0 0 ON MA ON 601 1.4 411 so • a • a e am am ON ON ivec.•., 11111.EMICICE TOTAL OWERVIO.COVER TREATED., 11.03 AR.CHECK OK. . IOTA MANAGED TOW AREA TREATED.62 ato AREA CXECR.OK. 1-01•1.RUNOFF tiEDUCTION IN D.A.•11.0) 0 'MAL...M..AVML.M.M'''...VA'.D•A A'M''' n' TOTAL 01105.0111.15 REM0.0 W.RUA.REDUCTION PRACTICES IN oro A 01.0 6.2 NI i 13 OGE N RE PAO V E D W IT„R UN 0 fTFPTEADL Uri 07i ZDC fa 71'„'07::AAL,A0,7v:11 ZOO 1 TOTAL WASIWORDS REMAINING AfTER APOLVING RUI/Orr REOURION PItACTICEs PN D.A.A 0b/yr, 1.6 SEE WATER QUA!'TY COMPLIANCE TAB FOR SITE COMPLIANCE.SCUSAPONS SEE waria atmun COMPi.landa rae FOR SaS C4ESEILASIONS r InformoNor onlv) vana, ,z,.r. 10 weI�.�,�i.ice.R I aii.l l�.o xl:l 10..We SA.•t1.e MI a 0 • • • M 000 m• m N 1.111111MIMMEMEME 3.0.1...S......111a •• • • • e w am 0. am ©. IEEM:MOCIIIIIMII va.N......lyan MI • a a a 0 w W u GM m x040 v.1,.•nanmulY.•.11 e a a • 0 SO O. OM •M as 1111211111=11.0. 12 0.000.4 0mn.1.0010 0 o e a •• SO m u OM OA M111 =11114ME va.......w....A MI o • o a 0 n MO Om OM am EM111=1111111CIE4 1T tsil..w.r..1.1.0 141 a 0 a O •• SO OM IVO Om Om ICM.:11111111:11111/1:10.= mi..AA p00.102Rani 1.•115 MI 0 0 0 0 0 n am •m m m MEM:1110.:MEM u rn P.en On.1.1 0 >im 1016 0 0 •..016 as n u 110 001i •n EIMICIIIIIE:111m© un we Pane 0.1.....11.al 0 0 0 0 0 e •m em OW m EM • a a O 0 16 .. a. a. me x0000 IAA....an..T.“.eM.�.n• 0 0 0 0 0 16 OM am 0 OM x0000 1..kNA.,.e,m0A.P.A.M. 0 0 0 0 0 16 ale 000 •M 00000 TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE III,A11 0039 l TOTAL PHOSPHORUS AVAILA0lf FOR REMOVAL IN DA.A Obir, ... TOTAL PHOSPHORUS REMOVED WFTHOUT RUNOFF REDUCTION PRACILICES 4,1 A A OOh.I 20. TOTAL PHOSPHORUS REPROVED WITH RUNOFF REDUCTION P.CACES IN DA.AIAA, GAO TOTAL PHOSPHORUS IOAD REDOCTION ACHIEVED IN OA.A I101n1 20. TOTAL PHOSPHORUS REMAINING AFTER...LANG•APIOAO REDUCTIONS IN P.A.A UO/A) ••. SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WON RUNOFF REDUCTION PRACTI,Es.w A(IOM) A. AAR..REMOVED WITHOUT RUNOFF REDOLTION PRACTICES IN D.A.AleO 77.02 TOTAL NITROGEN REMOVED IN D.A.A(mNl) 7193 • I! •2! III 11 " WW1 II 111 11 11 II 11 1111 Ii..i 7,.T.- 'it MI 1 " ! " i 13 CM Mil Di IN MI IIII DIM 1 i.;; „jh 3E .. 32 " 1 " B ' 11 H1 11 11 II 111111 H . . . . . I2 Iii - E 1 Hi -_'0 11 :1111 11 11 .!-111 II MI i i2 i 2 ., I 2 i i r HI 5 ! 155551551 11 555 5 ! 15 15 15 51 5 !! 1i II: 1 ! 111155111 92 111 5 ! 15 15 5 ! 11 1 r 1 1 II IN • 55 155555555 51 251 11 I ! 59 15 211 a 1 . 1.I 1111 1 . ., 5 . 5 5 1 5 1 Al 1 5 1 1 5 5 5 5 1 5 ! 1 5 2 I 2 2 -f ___ ___. — 1 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . !!!! i i 3 tg ter, iEcRe ill - - . . . . . . . . . - - - - - - - " - - • • • ' - 24 iii i i i A j 1 F;;1 1 i 11• 1 21 . . I I - - - - - _. - — — I i Ill ; I I 2 Li il ji l ''2 -,,•.,,,..F ' ' _ - 11a t'. -- -- -._ t ! i lit 22 95999 9 2 . 2 2t M22 52 22 22 . 2 222 VI i i I- a 1 . A li iF iill ii k 1 ! li idd2! I ! III ti 11 1111iiiiiiIIIIII! Il iill ii !In II iE ilIiii If ; It liWifi''7;'1 1 111 III! I 1 E ,1 1111 E IN ON MI MN 11111 2 I N 1,N !in „gm III ?IIIU iii 131 319 31 13 33 3313 II ! 11 33 13 : 31 ! 311 33 33 33 3333 111 T ig lig :gg.g =gg ;t g 33 1 333,31 * " ---g !!;1; - • • • - - • - !F; Hii; ! ! t g 2-git " . • . . . . . • . , & §li 1 g gi s :14 ! , 2E 11 • 1 , I ! c 11 11i ! gg = , = , • Site Results(Water Quality Compliance) Area Checks I D.A.A D.A.B D.A.C D.A.D D.A.E 1 AREA CHECK FOREST/OPEN SPACE(ac) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER(ac) 10.26 6.11 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED(ac) 10.26 6.11 0.00 0.00 0.00 OK. MANAGED TURF AREA(ac) 11.03 8.19 0.00 0.00 0.00 OK. MANAGED TURF AREA TREATED(ac) 11.03 8.19 0.00 0.00 0.00 OK. AREA CHECK OK. I_ OK. _-_ OK. I OK. I OK.Site Treatment Volume(ft3) 2 Runoff Reduction Volume and TP By Drainage Area IMME=MEMO RUNOFF REDUCTION VOLUME ACHIEVED k' �.. I 0 0 0 _. 0 TP LOAD AVAILABLE FOR REMOVAL(Ib/yr)I 27.26 16.97 0.00 0.00 0.00 44.24 TP LOAD REDUCTION ACHIEVED(Ib/yr)''. 20.42 8.48 0.00 0.00 0.00 28.90 TP LOAD REMAINING(Ib/yr) 6.84 8.50 0.00 0.00 0.00 15.34 1111111111.1111.111111. NITROGEN LOAD REDUCTION ACHIEVED(Ib/yr) 77.92 36.39 0.00 0.00 0.00 114.31 Total Phosphorus El 111 FINAL POST-DEVELOPMENT TP LOAD(Ib/yr)I 48.03 _ TP LOAD REDUCTION REQUIRED(Ib/yr) 30.39 TP LOAD REDUCTION ACHIEVED(lb/yr) 28.90 TP LOAD REMAINING(Ib/yr): 19.13 3 REMAINING TP LOAD REDUCTION REQUIRED(Ib/yr): 1.49 Total Nitrogen(For Information Purposes) POST-DEVELOPMENT LOAD(Ib/yr). 343.62 NITROGEN LOAD REDUCTION ACHIEVED(Ib/yr) 114.31 REMAINING POST-DEVELOPMENT NITROGEN LOAD(Ib/yr) 229.31 I I 1 1 I A j I- 0 v o I o i X I 1 N I x NI NJ A O^ O� N O j j e N N .ni N .4 v I O L 5 I 1 a` o i p 1 E y O O O 1 g tO O O O O 00 c 1+1 I C cc c I N aC > I N I yN O O O L U O O O N 10 W . a j N u 1 C N N p ^ O� N 1 .a N N m E m N ,i j U C d 1 E a a '^ I I c o o O m oo� a m N -G c I CLI Z N - N I 0 10 I L h co > 7. 11 2 ,, c a a a m 1 c 'o m al � c c c r d d d a . 1 O U C 7 c > W ~ •' co. C 1�6 Z •c m • V c W E v C E 3 Q 4 cc c u E ?! o ^ E E z c c E v i 0 C) CO073 H ^ ` o U ~T, H W - o01c ^ cc 0 C J c m 10 m V c u p > m a Fa- •m E nc a v 0 1co c c ' -, E ° 3 3 m m I c p o d " E c c c -o C a m d c 2 F E m e CL V z 1- iz .c .... .c ._ j a U ;; 1.3Z 76 U 0 E E c G y H 1`0 0 E ' Cl.' Z •o " 0 0 0 a1 a a1 w j N ii1 F- F- F- F- t%f F- F- F- C 1r K • '4-.1 O O '-1 10 O N toN If1 o Ol rn H• O N 4 M N N . . N d t iu O O O O W0 O x Q O O O O Q O O 0 0 O O O C 0 O O 9 0 .c 2 C c d o 8 0 Q o 0 0 o Q o o E e0 0 0 0 0 0 0 0 co 0 m c 1 • O O o O Q O O Q 0 O O O 0 0 O O n' O1: O m O1 Q o F21 ,1 Q co• m 0 0 00 o ao m a• O m L N a• C ON1. a o i a o N O N N tV 0 N N E VN ` Q f0R u �u H0CE,p md' elu Qa G 01 9 s Ce C JJ'fpQO\ 13: Za° li '`1 W a m zG :° 2 E ,2 0 I- % - Co• • E j2 o co 61 oA coo 2 "2 § To co 1 _ @ @ ) } [ § I- $ — C ! ) m \ N I- Iii CO I 7 � _ 13-- § E / \ | § ; 7 / S j D 2 # kk ; \ 7 ) § k ■ $ § I § 7 § § ,, ) k ; to . . g) k �) 7 f % « k ; LID M NI N « = o = § 13 E .5.. . . , £ ° 4 4 a o _ _ E . — $ } 2 IA e — k d d | k k ._ E a { ) § & ' ( I « ® ) A 2 1 / } \ \ . } \ \ \ /\ \ 0 3 2 £ I & 1- _ _ _ 1- • ' I I W COI 142 Q 0 0 0 0 0 0 I w O O O O o O O O O O 0 Do N O O O O C O Ie I 6 i0 13 1 to E y Q 0 0 0 0 0 0 W `p cono C O O O O O I .tt c ✓ I G i C 2 1 U a` Ito Q 0 0 0 0 0 o j m o 0 0 0 0 0 o p o O o E 0 0 0 0 0 0 rn c °c I m ce � O m c i IL 2_+ E co m 5 j N I vi m O ri .-i n r4 .-4i_ n ni m m A > c I o 1 Q 1 E m o` I N M mO^ CI O0 N Lo 01 N CI In t +f co 1 to W ^ ..-1l of ^ N ^ T M I' �• 10 c 1 N G 1 _ E ` a .7a :-E' 9 1 .8. u 3 3 8 . 3 x . 3 1 `m mc.3 ¢ c m a c 'm 1 z 'm 1 > °� 3 ; u 3 3 u 3 3 u 1 Ic I2 to I� v m e ota e to iZ a a V E• "' c c 0. O d Z x > > 3 tto c c 00 u ¢ E ii E Id j eo W d to N N -O 1> C 1 10 C m 1C ill , . The following calculations were previously approved with The FooThiII Crossing H VSMP Amendment #1. rov;a e.d i 0 7,-,oL7,1-1-3 0,J..-[DOSE'S 0 rl iy 1:0 "6E-.:SiS7,. CO U Lly • FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations July 28, 2016 PREPARED BY: COLLINS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE,VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com DEQ Virginia Runoff Reduction Method Water Quality Calculations • Virginia Runoff Reduction Method New Development Worksheet-v2.8 -June 2014 To be used w/2011 BMP Standards and Specifications Site Data Project Name:The Villas at Foothills Date:7/28/16 data input cells v *'' x ` 'r calculation cells constant values 1. Post-Development Project& Land Cover Information Constants Annual Rainfall(inches) 43 Target Rainfall Event(inches) 1.00 Phosphorus EMC(mg/L) 0.26 Nitrogen EMC(mg/L) 1.86 Target Phosphorus Target Load(Ib/acre/yr) 0.41 Pj 0.90 Land Cover (acres) A soils B Soils C Soils D Soils Totals Forest/Open Space(acres)-undisturbed, protected forest/open space or reforested land 0.00 0.00 0.00 0.00 0.00/, Managed Turf(acres)--disturbed,graded for yards or other turf to be mowed/managed 0.00 11.83 5.96 0.00 Impervious Cover(acres) 0.00 15.00 5.04 0.00 "'-20.04%.``A A Total 37.883 Rv Coefficients A soils B Soils C Soils D Soils Forest/Open Space 0.02 0.03 0.04 0.05 Managed Turf 0.15 0.20 0.22 0.25 Impervious Cover 0.95 0.95 0.95 0.95 Land Cover Summary Forest/Open Space Cover(acres) 0.00 Weighted Rv(forest) 0,00 Forest "0% Managed Turf Cover(acres) :17-79 Weighted Rv(turf) 021 Managed Turf 47% Impervious Cover(acres) 20.04 Rv(impervious) 0.95 %Impervious 53% Total Site Area(acres) 37.83 Site Rv 0.60 Post-Development Treatment Volume(acre-ft) 1_89 Post-Development Treatment Volume(cubic feet) 84456 Post_Development Load(TP)(Ib/yr) 51.81 Post_Development Load(TN)(Ib/yr) 370.621 Total Load(TP)Reduction Required(lb/yr) 36.30 . 4 1 1 Y (..) w 0 , 0 0 0 0 a w ct < 1 , 8igg8 a a a d. LU , . lc 0000 8: a O 04;3 a La )- EE 0 y 1 I < ' 0 ,- ›- Z 1 0 t .14 0 0 0 a 0 0 a 6.-;0 0 ui CY Lu a .< I-- 1- AC 4,4-10 0 0 0;a 6 ci Ill 0 L1.1 M 111 1 0 Gi LA 0 0 >-- 7CA 0,1 Al CO CA 40 a a v <0.- cs 0 Of in.in at a! o 6 Laito q,:I i 17 mil P I 4 g ..... .., - < a 0, 1 ....., 01 f m CA , 0 0 , ct 0 0 0 0 <0 Y q E a E ,-7-. 0 w w w w 0 ....).,‹ 9...>- -?... Lu ..S. >. ..S.', -.... — L.)W u.W 0 2 0-1 — La 2 0-r cc re 0 ca I- z cr 7 c z COI_ct I- < _i_1 o 0 I- _ _1 00 t., . . w 0 m 111 0 0 L1J LIJ > .9 > > w < -- ill LI' '' 0 a ,5,, ce ii Lt LU- Y 1 0 Si z Ce LUQ u. LL/5 c.) -, - w u.0 --I ti-u)2 Ce 2 u_a z m m z a 11-4 0 z i- Lu 0z D o 1- oz W 0 I- 4i Z 0 M 17- < Z 0 0 re re w re 7 0 0 cc 0 7_0 0 a la _i I 0 0 Lij -J p 2 t Al 1-- Z Z 0 W C4 < Z 0 u) < 2 C2 5 cL,7 z Lu LJJ > (r) •-• 0 La 7 0 I.° I c 0 0 0 0- LLI u) 0 0 tr. I- 0 2 (f) ea Z 0 a 0 LL I E u) I CO D' 0 0. 0 0 o 0 c Q. z .. C w .4 a. cn -J 0 E Lu - ... cn D 0 co 0 o 0 Al < 4 0 co 0 0 O 2 co I o. z • Virginia Runoff Reduction Method Worksheet Virginia Runoff Reduction Method New Development Worksheet-v2.8-June 2014 Site Data Summary Total Rainfall= 43 inches Site Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 11.83 5.96 0.00 17.79 47.03 Impervious(acres) 0.00 15.00 5.04 0.00 20.04 52.97 37.83 100.00 Site Rv 0.60 Post Development Treatment Volume(ft3) 82456 Post Development TP Load(Ib/yr) 51.81 Post Development TN Load(lb/yr) 370.62 Total TP Load Reduction Required(lb/yr) 36.30 Total Runoff Volume Reduction(ft') 0 Total TP Load Reduction Achieved(Ib/yr) 38 Total TN Load Reduction Achieved(Ib/yr) 143.62 Adjusted Post Development TP Load(Ib/yr) 14.16 Remaining Phosphorous Load Reduction(Lb/yr)Required 0.00 Drainage Area Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 5.99 10.35 1.45 0.00 0.00 17.79 Impervious(acres) 10.52 9.12 0.40 0.00 0.00 20.04 37.83 Drainage Area Compliance Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total TP Load Red.(Ib/yr) 19.21 18.43 0.00 0.00 0.00 37.64 TN Load Red.(Ib/yr) 73.30 70.32 0.00 0.00 0.00 143.62 Summary Print ' Virginia Runoff Reduction Method Worksheet Drainage Area A Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 3.35 2.64 0.00 5.99 r 36.28 Impervious(acres) 0.00 7.30 3.22 0.00 10.52 63.72 16.51 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: 10.52 Turf(Pervious): 5.99 Total Impervious Cover Treated(acres) 10.52 Total Turf Area Treated(acres) 5.99 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 19.21 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 73.30 Drainage Area B Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 7.70 2.65, 0.00 10.35 53.16 Impervious(acres) 0.00 7.36 1.76 0.00 9.12 46.84 19.47 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: 9.12 Turf(Pervious): 10.35 Total Impervious Cover Treated(acres) 9.12 Total Turf Area Treated(acres) 10.35 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 18.43 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 70.32 Drainage Area C Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 0.78 0.67 0.00 1.45 78.38 Impervious(acres) 0.00 0.34 0.06 0.00 0.40 21.62 1.85 BMP Selections Practice Credit Area(acres) Downstream Practice Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Summary Print SCS TR-55 Calculations Soils Mapping (Source: NRC Web<,Soil S d| Su rve,.:. /° »:. ew!«Da tas. basa»e .�.� ..z. w% .. ! %' , *g- , ~ . / J ° d\ •2 yaf �>�f / ° l �/ ,. . • a0k} , 2 « , z -< . . . t> . r ; amps ! © z • U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 • TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothill Crossing II Designed By:KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By:FGM,PE Date: 7/28/2016 Check One: Present X Developed X 1.Runoff curve Number(CN) Soil name and Cover description CN(weighted). Drainage Area Area Product of CN Calculated'5' hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ Description (Acres) x Area Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area B Impervious Areas 98 0.00 0.0 B Woods in Good Condition 55 9.12 501.6 D.A#1 B Lawns in Good Condition(75%+Groundcover) 61 1.93 117.7 61 6.37 (Present) C Impervious Areas 98 0.00 0.0 C Woods in Good Condition 70 4.94 345.8 C Lawns in Good Condition(75%+Groundcover) 74 0.92 68.1 B Impervious Areas 98 0.17 16.7 B Woods in Good Condition 55 5.20 286.0 D.A#2 B Lawns in Good Condition(75%+Groundcover) 61 10.46 638.1 63 5.94 (Present) C Impervious Areas 98 0.00 0.0 C Woods in Good Condition 70 1.14 79.8 C Lawns in Good Condition(75%+Groundcover) 74 3.95 292.3 B Impervious Areas(+Excess Capacity for 5.7 ac Imp.) 98 7.30 715.4 B Woods in Good Condition 55 0.00 0.0 D.A#1A B Lawns in Good Condition(75%+Groundcover) 61 3.35 204.4 87 1.54 (Developed) C Impervious Areas(+Excess Capacity for 2.82 ac Imp.) 98 3.22 315.6 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.64 195.4 B Impervious Areas(+Excess Capacity for 1.36 ac Imp.) 98 7.36 721.3 B Woods in Good Condition 55 0.00 0.0 D.A#26 B Lawns in Good Condition(75%+Groundcover) 61 7.70 469.7 80 2.48 (Developed) C Impervious Areas(+Excess Capacity for 0.39 ac Imp.) 98 1.76 172.5 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.65 196.1 B Impervious Areas 98 0.34 33.3 B Woods in Good Condition 55 0.00 0.0 D.A#2C B Lawns in Good Condition(75%+Groundcover) 61 0.78 47.6 74 3.57 (Developed) C Impervious Areas 98 0.06 5.9 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover; 74 0.67 49.6 2.Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 1 2 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,CI-inches 0.58 0.67 1.75 D.A#1(Present) Runoff,0-inches 0.65 0.75 1.88 D.A#2(Present) Runoff,Q-inches 2.15 2.33 4.10 D.A#1A(Developed) Runoff,Q-inches 1.64 1.80 3.43 D.A#2B(Developed) Runoff,Q-inches 1.22 1.36 2.82 D.A#2C(Developed) • U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Ta)or Travel Time(Ti) Project: Foothill Crossing II Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By:FGM,PE Date: 7/28/2016 Check One: Present X Developed X Check One: T, X Tt Through subarea D.A#1 D.A#2 D.A#1A D.A#2B D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Segment ID: Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 0.04 0.03 6 Compute Tt=[0.007(n*L)°'8]/PZ.S S°'4 0.29 0.22 0.22 0.17 0.19 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 952 755 117 96 237 9 Watercourse slope,s(ft/ft) 0.041 0.066 0.026 0.042 0.059 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 4.2 2.6 3.3 4.5 11 Tt=L/3600*V 0.08 I 0.05 0.01 I 0.01 I 0.01 Channel Flow: a, a` m 12 Cross sectional flow area,a(ft2) N N N E E E 13 Wetted perimeter,P�,(ft) '1',' $ E o L t L 14 Hydraulic radius,r=a/PN,(ft) N/A N/A c o c o c o 15 Channel Slope,s(ft/ft) E v a) o 16 Manning's Roughness Coeff,n li Tu Tu 17 V=[1.49r2/3s°3]/n 18 Flow length,L(ft) it it 1- 19 Tt=L/3600*V 0.00 0.00 0.00 0.00 0.00 20 Watershed or subarea TtorTt (Add Tt in steps 6,11 and 19) 0.37 I 0.27 I 0.23 I 0.18 I 0.20 I • • • U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothill Crossing II Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By: FGM,PE Date: 7/28/2016 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description D.A#1 D.A#2 D.A#1A D.A#28 D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Drainage Area(Am)in miles2= 0.0264 0.0327 0.0258 0.0304 0.0029 Runoff curve number CN= 61 63 87 80 74 Time of concentration(Tc)= 0.37 0.27 0.23 0.18 0.20 Rainfall distribution type= II II II II II Pond and swamp areas spread 0 0 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.273 1.273 1.273 1.187 1.187 1.187 0.308 0.308 0.308 0.497 0.497 0.497 0.713 0.713 0.713 5.Compute la/P 0.36 0.34 0.23 0.34 0.32 0.21 0.09 0.08 0.06 0.14 0.13 0.09 0.20 0.19 0.13 6.Unit peak discharge,Qu-csm/in 450 480 550 560 595 655 - - - - - - 740 755 800 7.Runoff,Qfrom Worksheet 2-inches 0.58 0.67 1.75 0.65 0.75 1.88 2.15 2.33 4.10 1.64 1.80 3.43 1.22 1.36 2.82 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Op-cfs 6.86 8.49 25.44 11.87 14.54 40.29 ROUTED ROUTED 2.61 2.97 6.53 • • Summary of Watersheds Summary of Drainage Areas • 1-Year 2-Year 10-Year Predevelopment Post-Development Predevelopment(cfs)Sost-Develo ment(cfs) Predevelopment(cfs) >ost-Develo ment(cfs)Predevelopment(cfs)5ost-Development(cfs) D.A.#1 16.91 D.A.#1A 16.51 D.A.#1 6.86 D.A.#1A 1.48 D.A.#1 8.49 D.A.#1A 1.61 D.A.#1 25.44 D.A.#1A 2.39 D.A.#2 20.92 D.A.#2B 19.47 D.A.#2 11.87 D.A.#213 0.70 D.A. 14.54 D.A.#213 0.83 D.A.#2 40.29 D.A.#213 45.85 D.A.#2C 1.85 D.A.#2C 2.61 D.A.#2C 2.97 D.A.#2C 6.53 Totals: 37.83 37.83 Totals: 18.73 4.79 Totals: 23.03 5.41 Totals: 65.73 54.77 Post-Development Routing Calculations Villas Level II wet Pond-A-new BasinFlow printout INPUT: Basin: Foothills Crossing II - Wet Pond Level II 'A' Design 12 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 626.00 1409.00 0.0 628.00 3497.00 175.9 629.00 4762.00 328.3 630.00 6141.00 529.7 631.00 9357.00 814.6 632.00 13497.00 1235. 5 632.40 20122.00 1482.9 634.00 24142.00 2792.6 636.00 28144.00 4727.2 638.00 32372.00 6966.7 640.00 36827.00 9527.9 641. 50 40316.00 11670.0 Start_Elevation(ft) 632.00 vol . (cy) 1235.46 6 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 632.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 635.000 multiple 1 discharge into riser outlet structure 2 weir name: Emergency Spillway length (ft) 30.000 side angle 71.500 coefficient 3.300 invert (ft) 640.000 multiple 1 discharge through dam Outlet structure 3 Curve name: Anti-Vortex Device multiple 1 Invert (ft) 638.500 discharge into riser file: thirtysix.txt Page 1 Villas Level II Wet Pond-A-new Outlet structure 4 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 166.000 Slope 0.012 Manning's n 0.013 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 626.000 outlet structure 5 Orifice name: Inverted Pipe area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 631.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Page 2 Villas Level II Wet Pond-A-new Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682.513 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 1.475 at 13.80 (hrs) water level (ft) 635.449 at 13.96 (hrs) storage (cy) 4164.447 Hydrograph 1 Routing Summary of Peaks: 2-Year 24-Hour SCS Method Storm inflow (cfs) 40.531 at 11.98 (hrs) discharge (cfs) 1.606 at 13.92 (hrs) water level (ft) 635.709 at 13.94 (hrs) storage (cy) 4426.913 Hydrograph 2 Routing Summary of Peaks: 10-Year 24-Hour SCS Method Storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 2.386 at 14.40 (hrs) water level (ft) 638.176 at 14.40 (hrs) storage (cy) 7178.537 Hydrograph 3 Routing Summary of Peaks: 100-Year 24-Hour SCS Method Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 51.479 at 12.18 (hrs) water level (ft) 640.195 at 12.18 (hrs) storage (cy) 9795.943 Tue Aug 25 12:31:39 EDT 2015 Page 3 A Villas Level II Wet Pond 2B BasinFlow printout INPUT: Basin: Foothills Crossing II - Wet Pond Level II '2B' Design 11 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 638.00 1154.00 0.0 639.00 1957.00 57.0 640.00 3080.00 149.5 642.00 6230.00 487.5 643.00 8779.00 764.1 644.00 16427.00 1223. 5 644.40 16518.00 1467.6 646.00 19193.00 2524.7 648.00 22740.00 4075.9 650.00 26510.00 5898.2 652.00 30508.00 8008.2 Start_Elevation(ft) 644.00 Vol . (cy) 1223.53 5 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 644.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 648.000 multiple 1 discharge into riser Outlet structure 2 weir name: Emergency Spillway length (ft) 35.000 side angle 78.460 coefficient 3.300 invert (ft) 650.250 multiple 1 discharge through dam Outlet structure 3 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 76.000 Slope 0.008 Manning's n 0.013 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 643.070 Page 1 1 Villas Level II wet Pond 2B Outlet structure 4 Weir name: Riser diameter (in) 60.000 side angle 0.000 coefficient 3.300 invert (ft) 649.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 35. 543 peak time (hrs) 11.970 volume (cy) 4279.362 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 39.021 peak time (hrs) 11.970 volume (cy) 4698.123 Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 74.336 peak time (hrs) 11.970 volume (cy) 8950.069 Page 2 4 Villas Level II Wet Pond 26 Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 144.726 peak time (hrs) 11.970 volume (cy) 17425.020 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 35.543 at 11.96 (hrs) discharge (cfs) 0.702 at 16.28 (hrs) water level (ft) 648.422 at 16.56 (hrs) storage (cy) 4437.189 Hydrograph 1 Routing Summary of Peaks: 2-Year 24-Hour SCS Method Storm inflow (cfs) 39.021 at 11.96 (hrs) discharge (cfs) 0.825 at 15.82 (hrs) water level (ft) 648.738 at 16.00 (hrs) storage (cy) 4715.939 Hydrograph 2 Routing Summary of Peaks: 10-Year 24-Hour SCS Method Storm inflow (cfs) 74.336 at 11.96 (hrs) discharge (cfs) 45.852 at 12.10 (hrs) water level (ft) 649.906 at 12.10 (hrs) storage (cy) 5806.582 C C , I I 1 (,)C i .1 1 0 ( t 4)....,,,, 0 „ (4- `-- i .(S — ,....„, 7/28/16 & FGM, PE : :1 (1a tr. „.... (71 , - ' '-i - ' , ' l 1 )if ri ., .,, „ , ° I b Ai ii 1 t 1 LA ,.......) ., ,;,..t. 0 r , t (.... ,fr -; L i , , , - ,-- , , ii if ,,,,e 1 ,,,, i, 7.--aut ._,.. i,i , ,,,,.„, r.'v V f. ' L,t„ i =,- ,..,_ _.,.,j,,,. ,4vv 1 ) r" e• 4. 7' Ve At I ; 4 6/1 v,44,41' 4 7 I - 747 444, .1.* 4.4( V 7 i il . h.....it , 1 I ,„ i t , c , ,,i.::: t tr ,,,;.ttet.i > i , ,'A.-. c' - - )) .4'' OS"1" DC.V <, k A;61 11)( i i ) r (Or: : -1r,/1:' 71 '11 ' ''1 / ' /:: ' ''', .1:: 1 '.,- !--t7 e '\ ... -.____,—__--------_-----L--,-—°- 1 , ,0 itx ,-7 4......"). 4' ).'")0.4(4 W. IA pos-r 1.44 ' i p, , ; 48 els < 62 . Ur C I .(S.,. / u„.,3 4k RV--, 62r‘cie brrl 1rt --65 , rycf, G J I )( k !3 -IA IA rr -, i i,i; PLAT C;(''V "")‹ ',....2,ee iit,,,‘, ' , . r rt( ,.." / 48 ,ic ..- 0 rt ,...L( 6 SU ( fs4.0 58) /5 ;( C1/)) L48 (10' ..cf / /,.(e. ,, ' t 7 (117 1 it r 1-4 , i , f-, 7 ir L ...) t f ' , J - -.. -(,-,,,7---- , --76-c— ,,...-„) DAt 2e...y.i. C.., 1.:-: ''.., .'',-T ...77'A ,/,-), Pi-C./ r K+ 7 0.70 -f- --- ). (1-01 efIC. I i C,- -)T-' (r', .:----- 3. 31 1 r7 <,I i, , cfS ,.....„-7C-c'r" (gi .. ,„..., L.s, ryi: v 4 ' -- 'f, (a(2 , , , t- i1 -t-... , 7„.43, „,,c. 13, , : , (1.9 (...c )(ctc?„).4- „„,, (,,:...„ ,,..---q•-) 4.- 0 ,ril, K ; -24. I a (:„,'.7,e- tf c,c4x4s1-1- (Li,v4 Y. .1•1 ' ,i t coL. I 3.31 r`•‘,1 4:1S)4 — ., r--# "E,'-'("'17:77,' *-*:'" '°ct-I FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations March 15, 2017 Revised on April 10, 2017 (Updates to the previously reviewed amendment calculations are noted in yellow.) PREPARED BY: LSI 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations (Calculations were revised to reflect a more accurate Basin 1A watershed corresponding to the Glenbrook initial site plan currently under review. Revisions also include the updated basin volumes resulting from the proposed change to 3:1 grades. U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothill Crossing II-VSMP No.2 Designed By:FGM,PE Date: 4/1012017 Location: Park Ridge Drive&Future Glenbrook at Foothills Checked By:SRC,PE Date: 4/10/2017 Check One: Present X Developed X 1.Runoff curve Number(CN) Drainage Area Soil name and Cover description CN(weighted). H Area Product of CN Calculated hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product p / Description (Acres) xArea 'S'Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area APPROVED DA 1A (Present) Approved Pre-Dev.DA 1 61 16.91 1031.5 61.0 6.39 APPROVED DA lA (Proposed) Approved Post-Dev.DA 1 87 16.51 1436.4 87.0 1.49 FINAL BUILDOUT DA Final Buildout of the Watershed(Includes Glenbrook): lA Anticipated Impervious Areas 98 9.90 970.2 78.0 2.83 (Developed) Remaining Areas classified as Managed Turf 61 11.70 713.7 2.Runoff 1-Year Storm 2-Year Storm 10-year Storm Drainage Area Description Frequency-years 1 2 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,Q-inches 0.57 0.67 1.74 APPROVED DA lA(Present) Runoff,Q-inches 2.18 2.36 4.14 APPROVED DA lA (Proposed) Runoff,Q-inches 1.49 '; 1.65 3.22 FINAL BUILDOUT DA lA(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(T,)or Travel Time(T,) Project: Foothill Crossing II-VSMP No.2 Designed By: FGM,PE Date: 3/15/2017 Location: Park Ridge Drive&Future Glenbrook at Foothi Checked By:SRC,PE Date: 3/15/2017 Check One: Present X Developed X Check One: T, X T, Through subarea n/a APPROVED DA 1A APPROVED DA 1A FINAL BUILDOUT DA 1A Segment ID: (Present) (Proposed) (Developed) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 4 Two-year 24-hour rainfall,P,(in.) 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 6 Compute T,_[0.007(n`L)°'e]/P20.5 5" 0.29 0.22 0.22 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 952 117 210 9 Watercourse slope,s(ft/ft) 0.040 0.026 0.060 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 2.6 4 11 Tr,L/3600*V I 0.08 I 0.01 0.01 Channel Flow: 12 Cross sectional flow area,a(ft2) w v E E 13 Wetted perimeter,P�,(ft) o 0 o 14 Hydraulic radius,r=a/Pw,(ft) c o c o 15 Channel Slope,s(ft/ft) E oa, o 16 Manning's Roughness Coeff,n 17 V=[1.49r2/3s0'5]/n �' T. 18 Flow length,L(ft) it it 19 T,=L/3600*V I 0.00 I 0.00 I 20 Watershed or subarea T,or T, (Add T,in steps 6,11 and 19) I 0.37 I 0.23 I 0.23 I I U.S. Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothill Crossing II-VSMP No.2 Designed By: FGM, PE Date: 4/10/2017 Location: Park Ridge Dr/Glenbrook Checked By: SRC, PE Date: 4/10/2017 Check One: Present X Developed X Drainage Area 1. Data Drainage Area Description Drainage Area Description Description APPROVED DA 1A APPROVED DA 1A FINAL BUILDOUT DA 1A (Present) (Proposed) (Developed) Drainage Area(Am)in miles2= 0.0264 0.0258 0.0155 Runoff curve number CN= 61.0 87.0 78.0 Time of concentration(Tc)= 0.37 0.23 0.23 Rainfall distribution type= II II II Pond and swamp areas spread 0 0 0 throughout the watershed= 2. Frequency-years 1 2 10 1 2 10 1 2 10 3. Rainfall, P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4. Initial Abstraction, la-inches 1.28 1.28 1.28 0.30 0.30 0.30 0.57 0.57 0.57 5.Compute la/P 0.37 0.35 0.23 0.09 0.08 0.05 0.16 0.15 0.10 6. Unit peak discharge,Qu-csm/in 450 480 550 775 775 800 725 725 750 7. Runoff,Qfrom Worksheet 2-inches 0.57 0.67 1.74 2.18 2.36 4.14 1.49 1.65 3.22 8. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 1 1 1 9. Peak Discharge,Qp-cfs Routed Through The where Qp=Qu Am Q Fp 6.86 8.49 25.44 1.48 1.61 2.39 Amended SWM Facility Watershed Summary for DA 1A: 1-yr,cfs 2-yr,cfs 10-yr,cfs Approved Pre-Development 6.86 8.49 25.44 Approved Post-Development Routings 1.48 1.61 2.39 Amended Post-Development Routings 0.95 0.99 6.46 Final Buildout Post-Dev. Routings 0.89 0.94 6.75 Note: Per the approved 9VAC25-870-66 calculations,this development meets channel protection compliance by having a post-development 1-year peak SCS design storm outflow less than or equal to 1.48 cfs. Post-Development Routing Calculations (The following amended SWM facility 1A routing calculations analyze the approved subarea 1A, as well as the full build out of subarea 1A for the Glenbrook Subdivision. These calculations show water quantity compliance is met for the future Glenbrook Subdivision.) Foothills AMENDED Facility 1A- Approved Watershed BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- Approved Watershed 9 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 624.00 6903.00 0.0 626.00 10454.00 638.3 628.00 14622.00 1562.8 629.00 19510.00 2192.7 630.00 25243.00 3019.1 632.00 29873.00 5058.1 634.00 33734.00 7412.4 636.00 36565.00 10015.4 638.00 39355.00 12826.6 Start_Elevation(ft) 630.00 Vol. (cy) 3019.14 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 5 discharge into riser Page 1 Foothills AMENDED Facility 1A- Approved Watershed Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 1 discharge into riser Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Outlet structure 5 Weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Page 2 Foothills AMENDED Facility 1A- Approved Watershed Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 16.510 CN 87.000 Type 2 rainfall, P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682.513 Page 3 Foothills AMENDED Facility 1A- Approved Watershed OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 0.946 at 15.34 (hrs) water level (ft) 633.199 at 15.74 (hrs) storage (cy) 6435.410 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 40.531 at 11.98 (hrs) discharge (cfs) 0.985 at 15.22 (hrs) water level (ft) 633.456 at 15.86 (hrs) storage (cy) 6742.954 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 6.464 at 12.66 (hrs) water level (ft) 635.049 at 12.66 (hrs) storage (cy) 8752.075 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 89.086 at 12.10 (hrs) water level (ft) 636.666 at 12.10 (hrs) storage (cy) 10927.984 Fri Apr 07 14:59:34 EDT 2017 Page 4 Foothills AMENDED Facility 1A- Final Buildout Watershed BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- Final Buildout Watershed 9 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 624.00 6903.00 0.0 626.00 10454.00 638.3 628.00 14622.00 1562.8 629.00 19510.00 2192.7 630.00 25243.00 3019.1 632.00 29873.00 5058.1 634.00 33734.00 7412.4 636.00 36565.00 10015.4 638.00 39355.00 12826.6 Start_Elevation(ft) 630.00 Vol. (cy) 3019.14 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 5 discharge into riser Page 1 Foothills AMENDED Facility 1A- Final Buildout Watershed Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 634.000 multiple 1 discharge into riser Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Outlet structure 5 Weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.600 CN 78.000 Type 2 rainfall, P (in) 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 33.769 peak time (hrs) 11.991 volume (cy) 4343.730 Page 2 Foothills AMENDED Facility 1A- Final Buildout Watershed Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.600 CN 78.000 Type 2 rainfall, P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.233 peak time (hrs) 11.991 volume (cy) 4789.311 Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.600 CN 78.000 Type 2 rainfall, P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 72.799 peak time (hrs) 11.991 volume (cy) 9364.014 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 21.600 CN 78.000 Type 2 rainfall, P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 144.694 peak time (hrs) 11.991 volume (cy) 18611.877 Page 3 Foothills AMENDED Facility 1A- Final Buildout Watershed OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 33.602 at 11.98 (hrs) discharge (cfs) 0.894 at 15.08 (hrs) water level (ft) 632.880 at 15.44 (hrs) storage (cy) 6058.891 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 37.049 at 11.98 (hrs) discharge (cfs) 0.941 at 15.36 (hrs) water level (ft) 633.167 at 15.66 (hrs) storage (cy) 6397.372 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 72.437 at 11.98 (hrs) discharge (cfs) 6.754 at 12.64 (hrs) water level (ft) 635.130 at 12.64 (hrs) storage (cy) 8856.868 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 143.976 at 11.98 (hrs) discharge (cfs) 118.265 at 12.06 (hrs) water level (ft) 636.786 at 12.06 (hrs) storage (cy) 11095.806 Fri Apr 07 15:01:50 EDT 2017 Page 4 Virginia Runoff Reduction Method Calculations (These calculations show water quality compliance is met for the future Glenbrook Subdivision upland of the amended stormwater management basin 1A.) DA#1A Final Buildout Impervious Area Summary (For Water Quantity& Quality Calculations) * Roadways 216,050 sf * Sidewalks 48,175 sf 19 Lots where Half is Captured 19,000 sf ** 74 Lots where Most or All is Captured 148,000 sf 431,225 sf * Includes Park Ridge Dr, Fut. Glenbrook Subdvision, Fut. Eastern Connector& Fut Dunnwood Dr. Extension) ** Includes Future Glenbrook Subdivision and a credit for 9 future lots south of Glenbrook/Garland Lane. Glenbrook at FoothillIs- Uncaptured Impervious Areas (For Glenbrook at Foothills Water Quality Calculations) Binion Drive (A portion of) 14,275 sf Fernhill Drive (A portion of) 9,200 sf 9 Lots where Half is Not Captured 9,000 sf 32,475 sf ,„,_-,- DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 [:2011 BMP Standards and Specifications in 2013 Draft BMP Standards and Specifications Project Name: Glenbrook at Foothills&Park Ridge Drive from Foothill Crossing II i data input cells Date: 4/10/2017 ��'-* M constant values BMP Design Specifications List:2011.Stds&Specs calculation cells Site Information Post-Development Project(Treatment Volume and Loads) (Land Cover (acres) A Soils B Soils C Soils D Soils Totals Forest/Open Space(acres)-undisturbed, 4protected forest/open spate or reforested land 0-� ?Managed Turf(acres)-disturbed,graded for -yards or other turf to be mowed/managed 12.21 '..2- Impervious Cover(acres) 10:65 '-0.65 22.86 ?Constants Runoff Coefficients(Rv) Annual Rainfall(inches) 43 I A Soils B Soils C Soils D Soils Target Rainfall Event(inches) 1.00 Forest/Open Space 0.02 0.03 0.04 0.05 Total Phosphorus(TP)EMC(mg/LI 0.26 Managed Turf 0.15 0.20 0.22 0.25 Total Nitrogen(TN)(MC(mg/L) 1.86 Impervious Cover 0.95 0.95 0.95 0.95 Target TP Load(lb/acre/yr) 0.41 Pj(unitless correction factor) 0.90 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/yr) 1917' LAPD COVER SUMMARY-POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment Volume Forest/Open Space Cover(acres) 0.00 1.0466 (acre-ft) Weighted Rv(forest) 0.00 Treatment Volume(cubic feet) 45,591 %Forest 0% TP Load(lb/yr) 28.64 TN Load(Ib/yr) Managed Turf Cover(acres) 12.21 (Informational Purposes Only) 204'92 Weighted Rv(turf) 0.20 %Managed Turf 53% Impervious Cover(acres) 10.65 Rv(impervious) 0.95 %Impervious 47% Site Area(acres) 22.86 Site Rv 0.55 Drainage Area A A.. trU. 0 GO 12 iL, 1120 2oul exxxxx. Veljet62-0 21W teal • Isx0.22.2 , . x . . °°- rsox c 224 x.t [spec 2.x s.cxxxxc Fen.. Aocxeo2 .o Exe woo io2 xxx x L. ,x • ....*"V.'•"4OJI. • aremRe • „„. • xe 2[22252.42s1 , 22 main. comex.ncx Art. xxx al ' - • rIMM:====nin eo‘ eec SEE WATER QUALITY COMPLIANCE JAB FOP SITE COMPLIANCE CA1CULATIONS Site Results (Water Quality Compliance) Area Checks D.A.A D.A.B D.A.C D.A.D 1 D.A.E I AREA CHECK FOREST/OPEN SPACE(ac) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER(ac) 9.90 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED(ac) 9.90 0.00 0.00 7 0.00 0.00 I OK. MANAGED TURF AREA(ac) 11.70 0.00 0.00 0.00 0.00 MANAGED TURF AREA TREATED(ac) 11.70 0.00 0.00 0.00 0.00 AREA CHECK I OK. --- OK. L__ O K. -..I __.. OK. L.,----OK----- Site Treatment Volume(ft3) 1 I. Runoff Reduction Volume and TP By Drainage Area i D.A.A 6 D.A.B I, D.A.C D.A.D I� D.A.E TOTAL RUNOFF REDUCTION VOLUME ACHIEVED(ft') 0 0 0 0 0 0 TP LOAD AVAILABLE FOR REMOVAL(Ib/yr) 26.79 0.00 0.00 0.00 i 0.00 26.79 TP LOAD REDUCTION ACHIEVED(Ib/yr) 20.07 0.00 1 0.00 0.00 0.00 20.07 TP LOAD REMAINING (Ib/yr) 6.72 li 0.00 I 0.00 0.00 0.00 II 6.72 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr)r 76.57 II 0.00 II 0.00 II 0.00 0.00 II 76.57 Total Phosphorus FINAL POST-DEVELOPMENT TP LOAD(Ib/yr) 28.64 TP LOAD REDUCTION REQUIRED(Ib/yr) 19.27 TP LOAD REDUCTION ACHIEVED(Ib/yr)IMMEMEll TP LOAD REMAINING(Ib/yr):IMENIMIN REMAINING TP LOAD REDUCTION REQUIRED(Ib/yr): 0.00 *' **TARGET TP REDUCTION EXCEEDED BY 0.8 LB/YEAR** Total Nitrogen(For Information Purposes) POST-DEVELOPMENT LOAD(Ib/yr)r 204.92 NITROGEN LOAD REDUCTION ACHIEVED(Ib/yr) 76.57 REMAINING POST-DEVELOPMENT NITROGEN LOAD(Ib/yr) 128.35 i 1 I 1 1 i 1 70 1 o m o rn ^a o I `o 1 I Tim 1 .cm Co CO 0 N el)00 3 F ri o `N N ~ N g * 1 cc I _ N W c g > -d \ Z m o).o0cc o coc 1 0 0 0 0 0 } Co °c Mm 1 o C O cc o w 1 0 E W c' cuto> v I 5 ^ W I d o O O Z z v o 0 o O I 01 r -0 V 1 A a a CI W I s a a 1 o c r _ -, In O N D W 1 1o. N O C7 E m c " C 1 O 1- u * 1 c u + a u E a a Co ‘a. n O 0b Ln ,-I N I 0 0 0 Co en eft `o a ^! o Q v00i o W H Q o o o o a o Co°".' O t^O 1 3 1 01 N Z — Co I -0 y 'B o CO Y J — — ^ • o > >_ ma I7c 0 u uCi 5. i > > o w m ~ c I Z Q L C Co E ._ 0. E u u OJ O cc O7;3I I I E d g E y c c C c 1 Q Q G _O O o , 1 O O 0 h ^ ` i0 U u H E C u & K C 4 > C ` j c d C 7 N W Q 00 I m A w Q : w O J > \ C 10 oC C mE V 7 U 'Q > \ A a 13 -o o o.. to n) 1 a a c vo m ... .0 JE o o m m c c c 1 • v) m > > E m F A 0. OV ¢ ? .�r c m U a au am o yWiQ E E D in n 2 r in oczsI- - H z I _ t- O 71 0 r4 1 O O k.0N H N N. N N L 0000 W .6 Q O O O O Q O O 3 d O O O C C O O 0 0 L N o U a �o p p E cc Q O O O O Q o O 6 O O O O 6 O O EN C lc o E ro Q O O O O Q O O O O O O O O QOOOOQOOOOOOO¢ oo ¢ nQoon � �o opO 1N0ON I:: f0 CE C 3 H d u C I A co ` O a a 'o u `o > y co a Q C 7 'Jo. Q N ; L ` o/ K C C r m .5 ¢ C ` A 'O •@ N O g d C o. 0 @ J ❑ i f-� ❑ F Z E j" O « 9 .. c p a O la W I- on as C C .o > O1 E \ 'o c a 6 z a r v 7: a C C > o C t, C d 0 z 2° a r v 01 ^ aO a h m o 0 0 o r a ,o o n p, ,o .p « n 3 I- o p, N a - o 2 N -p i a L C 2 2 = G c 4 E o E a c s 2.1 .� m Z E o 0 o v : v o E 0 0 0 0 0 J a••' '2 o o . CC m O a m^ > E '^ 0 0 0 0 m ° v a E m u o 0 o F p a• o a m 0 =o y 0 0 0 0 o rn > u` V m 0 alA r 0 0 0 0 ,a, < E, ^ o N o m " u ti •m ti < O O O C d ,,,ey 01 ti o n E U < < O 0 a C_ E u m v v a > L. y ^ y a E ). N t, u u a N m V < < E ^ V R C C 3 " -p y d O O H ` C > a o o c a Q E a u E 4 , co E m > r a, a a z E = t o c3 0 a▪ a a r u " .a. o o ° aJm aE s z = u mV 'mv a c a' a m m m m i. ,_ - LL a 2 O 0 0 0 E m r r r =-I- `. } } The following calculations were previously approved with the Foothill Crossing II VSMP Amendment #1 (These calculations are provided for informational purposes only to assist County Engineering.) FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations July 28, 2016 PREPARED BY: COLLINS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com DEQ Virginia Runoff Reduction Method Water Quality Calculations Virginia Runoff Reduction Method New Development Worksheet -v2.8 -June 2014 To be used w/2011 BMP Standards and Specifications Site Data Project Name:The Villas at Foothills Date: 7/28/16 data input cells _ , calculation cells _ constant values 1. Post-Development Project& Land Cover Information Constants Annual Rainfall(inches) 43 Target Rainfall Event(inches) 1.00 Phosphorus EMC(mg/L) 0.26 Nitrogen EMC(mg/L) 1.86 Target Phosphorus Target Load(Ib/acre/yr) 0.41 Pj 0.90 - Land Cover (acres) A soils B Soils C Soils D Soils Totals Forest/Open Space(acres)--undisturbed, protected forest/open space or reforested land 0.00 0.00 0.00 0.00 0.00 Managed Turf(acres)-disturbed,graded for yards or other turf to be mowed/managed 0.00 11.83 5.96 0.00 17.79 Impervious Cover(acres) 0.00 15.00 5.04 0.00 20.04 Total 37.83 Rv Coefficients A soils B Soils C Soils D Soils Forest/Open Space 0.02 0.03 0.04 0.05 Managed Turf 0.15 0.20 0.22 0.25 Impervious Cover 0.95 0.95 0.95 0.95 Land Cover Summary Forest/Open Space Cover(acres) 0.00 Weighted Rv(forest) 0.00 F Forest 0% - Managed Turf Cover(acres) 17.79_ Weighted Rv(turf) 0.21 - %Managed Turf 47% Impervious Cover(acres) 20.04 Rv(impervious) 0.95 °io Impervious 53% --- ---- ._ _ Total Site Area(acres) 37.83 Site Rv 0.60 Post-Development Treatment Volume(acre-ft) 1.89 Post-Development I reatment Volume(cubic feet) 82,456 Post_Development Load(TP)(Ib/yr) 51.81 . " - I 370.621 Total Load(TP)Reduction Required(Ib/yr) 36.30 Y C.) W 2 U Y Y 1 Y Q 0 0 0 0 W C 0 oro,ox 0000' 0 0 0 0: W 0 0I o o0: it 0000. W ›- CI❑ m 4 0 1 t9 O > m z 0 F 0 0 0 0 0 o 0 0 0 > 0 0 o ' o w O C F Q 0 ICU O 4 w x I- sn N [n C.) 0 of mooW w W to W 4 s., 0 U X C M O Y ' _ NN CI,03 tO a` O a OD z tDri toLi-to 01tn Q O > I- XI- 1.1.1. w W vY .0 O `. .a O ¢¢ ¢x z 0 w w' Z CI O W Ly W 0 IE C OJ W 2 0 J Q,0 W 0— =w ~ C O = W F.- 0 O W W > 0 0 > o > 0 > 0 12 O a ¢ Z C4 X s 0 m z w W 0 J - z 0 0 P. > �a. I1-w O z O I- 0 ¢ W F ¢ a 0 Z > K z O 0 S U ¢ O a. FO KU n O F, CO K d J U O z ¢ O Q 00 2 00 Ct d 0 y0 z z F.w 0 F, ¢ 0 F 0 w C ¢ z JO O ¢ a < O a y O O 0 rn a n = z w CO 0 11.1 > C 0 w= a C 0 O O O n 0 O W z '' 0 W O r a € z O co x O a 0 O 0 0 0 x n z c w .� n 0 Z ca 0 an Q F - 0 _ 0 K O O CC ¢ C C ¢ 0) y N 0 w Co 1 Z Virginia Runoff Reduction Method Worksheet Virginia Runoff Reduction Method New Development Worksheet-v2.8-June 2014 Site Data Summary Total Rainfall= 43 inches Site Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 11.83 5.96 0.00 17.79 47.03 Impervious(acres) 0.00 15.00 5.04 0.00 20.04 52.97 37.83 100.00 Site Rv 0.60 Post Development Treatment Volume(ft3) 82456 Post Development TP Load(Ib/yr) 51.81 Post Development TN Load(lb/yr) 370.62 Total TP Load Reduction Required(lb/yr) 36.30 Total Runoff Volume Reduction(ft') 0 Total TP Load Reduction Achieved(lb/yr) 38 Total TN Load Reduction Achieved(Ib/yr) 143.62 Adjusted Post Development TP Load(Ib/yr) 14.16 Remaining Phosphorous Load Reduction(Lb/yr)Required 0,03 Drainage Area Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 5.99 10.35 1.45 0.00 0.00 17.79 Impervious(acres) 10.52 9.12 0.40 0.00 0.00 20.04 37.83 Drainage Area Compliance Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total TP Load Red.(Ib/yr) 19.21 18.43 0.00 0.00 0.00 37.64 TN Load Red.(Ib/yr) 73.30 70.32 0.00 0.00 0.00 143.62 Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area A Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 3.35 2.64 0.00 5.99 36.28 Impervious(acres) 0.00 7.30 3.22 0.00 10.52 63.72 16.51 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: _ 10.52 Turf(Pervious): 5.99 Total Impervious Cover Treated(acres) 10.52 Total Turf Area Treated(acres) 5.99 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 19.21 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 73.30 Drainage Area B Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 7.70 2.65 0.00 10.35 53.16 Impervious(acres) 0.00 7.36 1.76 0.00 9.12 46.84 19.47 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: 9.12 Turf(Pervious): 10.35 Total Impervious Cover Treated(acres) 9.12 Total Turf Area Treated(acres) 10.35 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 18.43 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 70.32 Drainage Area C Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 0.78 0.67 0.00 1.45 78.38 Impervious(acres) 0.00 0.34 0.06 0.00 0,40 21.62 1.85 BMP Selections Practice Credit Area(acres) Downstream Practice Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Summary Print SCS TR-55 Calculations SODS• Mapping (Source: NRCS Web Soil Survey Online Database) / rw . a i ` ° .'�u, ,.,u °, ,Z ,. _ n, .w .k-? - ms's. U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothill Crossing II Designed By:KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By: FGM,PE Date: 7/28/2016 Check One: Present X Developed X 1.Runoff curve Number(CN) Drainage Area Soil name and Cover description CN(weighted). g Area Product of CN Calculated'S' Description hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ (Acres) x Area Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area B Impervious Areas 98 0.00 0.0 B Woods in Good Condition 55 9.12 501.6 D.A#1 B Lawns in Good Condition(75%+Groundcover) 61 1.93 117.7 61 6.37 (Present) C Impervious Areas 98 0.00 0.0 C Woods in Good Condition 70 4.94 345.8 C Lawns in Good Condition(75%+Groundcover) 74 0.92 68.1 B Impervious Areas 98 0.17 16.7 B Woods in Good Condition 55 5.20 286.0 D.A#2 B Lawns in Good Condition(75%+Groundcover) 61 10.46 638.1 63 5.94 (Present) C Impervious Areas 98 0.00 0.0 C Woods in Good Condition 70 1.14 79.8 C Lawns in Good Condition(75%+Groundcover) 74 3.95 292.3 B Impervious Areas(+Excess Capacity for 5.7 ac Imp.) 98 7.30 715.4 B Woods in Good Condition 55 0.00 0.0 D.A#1A B Lawns in Good Condition(75%+Groundcover) 61 3.35 204.4 87 1.54 (Developed) C Impervious Areas(+Excess Capacity for 2.82 ac Imp.) 98 3.22 315.6 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.64 195.4 B Impervious Areas(+Excess Capacity for 1.36 ac Imp.) 98 7.36 721.3 B Woods in Good Condition 55 0.00 0.0 D.A#213 B Lawns in Good Condition(75%+Groundcover) 61 7.70 469.7 80 2.48 (Developed) C Impervious Areas(+Excess Capacity for 0.39 ac Imp.) 98 1.76 172.5 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.65 196.1 B Impervious Areas 98 0.34 33.3 B Woods in Good Condition 55 0.00 0.0 D.A#2C B Lawns in Good Condition(75%+Groundcover) 61 0.78 47.6 74 3.57 (Developed) C Impervious Areas 98 0.06 5.9 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover 74 0.67 49.6 2.Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 1 2 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,Q-inches 0.58 0.67 1.75 D.A#1(Present) Runoff,Q-inches 0.65 0.75 1.88 D.A#2(Present) Runoff,Q-inches 2.15 2.33 4.10 D.A#1A(Developed) Runoff,Q-inches 1.64 1.80 3.43 D.A#2B(Developed) Runoff,Q-inches 1.22 1.36 2.82 D.A#2C(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Ta)or Travel Time(Tt) Project: Foothill Crossing II Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By: FGM,PE Date: 7/28/2016 Check One: Present X Developed X Check One: T, X Tt Through subarea D.A#1 D.A#2 D.A#1A D.A#2B D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Segment ID: Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 100 100 4 Two-year 24-hour rainfall,Pz(in.) 3.7 3.7 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 0.04 0.03 6 Compute Tt=[0.007(n*L)°'a]/P2°'s s0 4 0.29 0.22 0.22 0.17 0.19 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 952 755 117 96 237 9 Watercourse slope,s(ft/ft) 0.041 0.066 0.026 0.042 0.059 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 4.2 2.6 3.3 4.5 11 Tt=L/3600*V 0.08 I 0.05 I 0.01 0.01 0.01 Channel Flow: a`, v a` 12 Cross sectional flow area,a(ft') 3 3 N E E E 13 Wetted perimeter,Pw(ft) o '^ `o o ej 14 Hydraulic radius,r=a/Pw(ft) N/A N/A o c o c o 15 Channel Slope,s(ft/ft) £ ocu o £ o 16 Manning's Roughness Coeff,n - - - 17 V=[1.49rz13s°'s]/n >> > to to to 18 Flow length,L(ft) it it it 19 Tt=L/3600*V 0.00 0.00 0.00 0.00 0.00 20 Watershed or subarea'icor Tt (Add Tt in steps 6,11 and 19) 0.37 0.27 0.23 0.18 I 0.20 U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothill Crossing II Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By: FGM,PE Date: 7/28/2016 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description D.A#1 D.A#2 D.A#1A D.A#2B D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Drainage Area(Am)in miles2= 0.0264 0.0327 0.0258 0.0304 0.0029 Runoff curve number CN= 61 63 87 80 74 Time of concentration(Tc). 0.37 0.27 0.23 0.18 0.20 Rainfall distribution type= II II II II II Pond and swamp areas spread 0 0 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.273 1.273 1.273 1.187 1.187 1.187 0.308 0.308 0.308 0.497 0.497 0.497 0.713 0.713 0.713 5.Compute la/P 0.36 0.34 0.23 0.34 0.32 0.21 0.09 0.08 0.06 0.14 0.13 0.09 0.20 0.19 0.13 6.Unit peak discharge,Qu-csm/ir 450 480 550 560 595 655 - - - - - - 740 755 800 7.Runoff,Qfrom Worksheet 2-inches 0.58 0.67 1.75 0.65 0.75 1.88 2.15 2.33 4.10 1.64 1.80 3.43 1.22 1.36 2.82 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs 6.86 8.49 25.44 11.87 14.54 40.29 ROUTED ROUTED 2.61 2.97 6.53 Summary of Watersheds Summary of Drainage Areas 1-Year 2-Year 10-Year Predevelopment Post-Development Predevelopment(cfs) 5ost-Development(cfs) Predevelopment(cfs) lost-Development(cfs)Predevelopment(cfs)5ost-Development(cfs) D.A.#1 16.91 D.A.#1A 16.51 D.A.#1 6.86 D.A.#1A 1,48 D.A.#1 8.49 D.A.#1A 1.61 D.A.#1 25.44 D.A.#1A 2.39 D.A.#2 20.92 D.A.#213 19.47 D.A.#25 0.70 D.A.#2B 0.83 D.A.#2 D.A.#2B 45.85 D.A.#20 1.85 D.A.#2 11.87 D.A.#2C 2.61 D.A.#2 14.54 D.A.#20 2.97 40.29 D.A.#2C 6.53 Totals: 37.83 37.83 Totals: 18.73 4.79 Totals: 23.03 5.41 Totals: 65.73 54.77 Post-Development Routing Calculations Villas Level II Wet Pond-A-new BasinFlow printout INPUT: Basin: Foothills Crossing II - Wet Pond Level II 'A' Design 12 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 626.00 1409.00 0.0 628.00 3497.00 175.9 629.00 4762.00 328. 3 630.00 6141.00 529.7 631.00 9357.00 814.6 632 .00 13497.00 1235. 5 632 .40 20122 .00 1482.9 634.00 24142.00 2792.6 636.00 28144.00 4727.2 638.00 32372.00 6966.7 640.00 36827.00 9527.9 641. 50 40316.00 11670.0 Start_Elevation(ft) 632 .00 Vol . (cy) 1235.46 6 outlet Structures Outlet structure 0 orifice name: Low-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 632.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 635 .000 multiple 1 discharge into riser Outlet structure 2 weir name: Emergency Spillway length (ft) 30.000 side angle 71. 500 coefficient 3. 300 invert (ft) 640.000 multiple 1 discharge through dam outlet structure 3 Curve name: Anti-Vortex Device multiple 1 Invert (ft) 638. 500 discharge into riser file: thirtysix.txt Page 1 Villas Level II Wet Pond-A-new Outlet structure 4 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 166.000 Slope 0.012 Manning's n 0.013 Inlet coeff. Ke 0. 500 Equation constant set 3 Invert (ft) 626.000 Outlet structure 5 Orifice name: Inverted Pipe area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 631.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Page 2 Villas Level II Wet Pond-A-new Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 9. 100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682. 513 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 1.475 at 13.80 (hrs) water level (ft) 635.449 at 13.96 (hrs) storage (cy) 4164.447 Hydrograph 1 Routing summary of Peaks: 2-Year 24-Hour SCS Method Storm inflow (cfs) 40. 531 at 11.98 (hrs) discharge (cfs) 1.606 at 13.92 (hrs) water level (ft) 635.709 at 13.94 (hrs) storage (cy) 4426.913 Hydrograph 2 Routing summary of Peaks: 10-Year 24-Hour SCS Method storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 2. 386 at 14.40 (hrs) water level (ft) 638.176 at 14.40 (hrs) storage (cy) 7178. 537 Hydrograph 3 Routing Summary of Peaks: 100-Year 24-Hour SCS Method Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 51.479 at 12.18 (hrs) water level (ft) 640.195 at 12 .18 (hrs) storage (cy) 9795.943 Tue Aug 25 12 :31:39 EDT 2015 Page 3 villas Level II Wet Pond 2B BasinFlow printout INPUT: Basin: Foothills Crossing II - Wet Pond Level II '2B' Design 11 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 638.00 1154.00 0.0 639.00 1957.00 57.0 640.00 3080.00 149. 5 642 .00 6230.00 487. 5 643.00 8779.00 764.1 644.00 16427.00 1223. 5 644.40 16518.00 1467.6 646.00 19193.00 2524.7 648.00 22740.00 4075.9 650.00 26510.00 5898.2 652 .00 30508.00 8008.2 Start_Elevation(ft) 644.00 Vol . (cy) 1223. 53 5 outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 644.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 648.000 multiple 1 discharge into riser Outlet structure 2 Wei r name: Emergency Spillway length (ft) 35.000 side angle 78.460 coefficient 3. 300 invert (ft) 650.250 multiple 1 discharge through dam Outlet structure 3 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 76.000 Slope 0.008 Manning's n 0.013 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 643.070 Page 1 Villas Level II Wet Pond 2B Outlet structure 4 Wei r name: Riser diameter (in) 60.000 side angle 0.000 coefficient 3.300 invert (ft) 649.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 35. 543 peak time (hrs) 11.970 volume (cy) 4279. 362 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 39.021 peak time (hrs) 11.970 volume (cy) 4698.123 Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 74. 336 peak time (hrs) 11.970 volume (cy) 8950.069 Page 2 Villas Level II Wet Pond 2B Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 9. 100 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 144.726 peak time (hrs) 11.970 volume (cy) 17425.020 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 35. 543 at 11.96 (hrs) discharge (cfs) 0.702 at 16.28 (hrs) water level (ft) 648.422 at 16. 56 (hrs) storage (cy) 4437.189 Hydrograph 1 Routing Summary of Peaks : 2-Year 24-Hour SCS Method Storm inflow (cfs) 39.021 at 11.96 (hrs) discharge (cfs) 0.825 at 15.82 (hrs) water level (ft) 648. 738 at 16.00 (hrs) storage (cy) 4715.939 Hydrograph 2 Routing summary of Peaks: 10-Year 24-Hour SCS Method Storm inflow (cfs) 74. 336 at 11.96 (hrs) discharge (cfs) 45.852 at 12 .10 (hrs) water level (ft) 649.906 at 12 .10 (hrs) storage (cy) 5806. 582 1,,,, /v.' c").1P*, , .,,.;-22.'.'''' ; N .e' "w.a.Y,? .,i '•d. "ate-.+; 'x;V m°'"., ,4$ ..h" y` c �vl r •� „. -.-l',4,..,,,,k,,Q,".--....-4,<L,,Vt,4-*:',,,:,-,---'----',.".,A''''S'"7:""''''''''''''''teX--4,, „:''''.7,D,,l'O' , , v x t ' I x '7,,' LT) r:- r v '' !:.-ii, 1.1:::.,', t;,:.,,, . m tis , 741 ft ( ,- ,,,, - w r1,c% . *a ," $A'e°ava.'l+a.,,,,,,,,,t.,L"w d-",, ,,, .,,..............-.......,....,amp...... ,""atm. ,- .3.d.«.. ice' ,3 :--': ' FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations March 15, 2017 PREPARED BY: COLLI NS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations (Additions to the approved calculations are to show the full build out of subarea 1A.The full build out takes into consideration the recently approved rezoning for this property.) U.S.Department of Agriculture Natural Resources Conservation Service FL-ENG-21A 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothills-VSMP No.2 Designed By: FGM,PE Date: 3/15/2017 Location: Park Ridge Drive Checked By: SRC,PE Date: 3/15/2017 Check One: Present X Developed X 1.Runoff curve Number CN Drainage Area Soil name and Cover description CN(weighted)= hydrologic group (Cover type,treatment, hydrologic condition;percent CN Area Product of Calculated Description total product/ 'SValue N z ' (Appendix A) impervious;unconnected/connected impervious area ratio) (Acres) CArea total area APPROVED DA 1A (Present) Approved Pre-Dev.DA 1 61 16.91 1031.5 61.0 6.39 APPROVED DA 1A (Proposed) Approved Post-Dev.DA 1 87 16.51 1436.4 87.0 1.49 ha tip ou o e Watershed(Worst Case Scen DAlA 2.Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 12 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,O-inches 0.57 0.67 1.74 APPROVED DA 1A(Present) Runoff,Q-inches 2.18 2.36 4.14 APPROVED DA 1A Pro.osed U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Ta)or Travel Time(Ti) Project: Foothills-VSMP No.2 Designed By: FGM,PE Date: 3/15/2017 Location: Park Ridge Drive Checked By:SRC,PE Date: 3/15/2017 Check One: Present X Developed X Check One: T, X T, Through subarea n/a APPROVED DA 1A APPROVED DA 1A FINAL BIJILDOUT DA 1,' Segment ID: (Present) (Proposed) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 6 Compute T,=[0.007(n*L)°8]/pZos So.a 0.29 0.22 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpav ; 8 Flow Length,L(ft) 952 117 210 , 9 Watercourse slope,s(ft/ft) 0.040 0.026 0.060 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 2.6 4 11 T,=L/3600*V 0.08 0.01 0.01 Channel Flow: `, 12 Cross sectional flow area,a(ft2) v 3 t E E 13 Wetted perimeter,Pw,(ft) o ', $ Lew -c 14 Hydraulic radius,r=a/Pw(ft) •S o ? .S o 15 Channel Slope,s(ft/ft) v 0 S- a o E v E v 16 Manning's Roughness Coeff,n a r- 17 V=[1.49r2/3so5]/n 18 Flow length,L(ft) ' F 19T,=L/3600*V 0.00 20 Watershed or subarea T,or T, (Add T,in steps 6,11 and 19) 0.37 0.23 - U.S. Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothills-VSMP No.2 Designed By: FGM,PE Date: 3/15/2017 Location: Park Ridge Drive Checked By: SRC,PE Date: 3/15/2017 Check One: Present X Developed X 1. Data Drainage Area Description Drainage Area Description Drainage Area Description APPROVED DA 1A APPROVED DA 1A FINAL BUILDOUT DA 1A (Present) (Proposed) (Developed) Drainage Area(Am)in miles2= 0.0264 0.0258 0.0255 Runoff curve number CN= 61.0 87.0 91.0 Time of concentration(Tc)= 0.37 0.23 0.23 Rainfall distribution type= II II II Pond and swamp areas spread 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 '' 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.28 1.28 1.28 0.30 0.30 0.30 0.20 0.20 0.20 5.Compute la/P 0.37 0.35 0.23 0.09 0.08 0.05 ' 0.06 0.05 0.04 6.Unit peak discharge,Qu-csm/in 450 480 550 775 775 800 800 800 800 7.Runoff,Qfrom Worksheet 2-inches 0.57 0.67 1.74 2.18 2.36 4.14 " 2.54 2.73 4.56 8. Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs , Routed Through The where Qp=Qu Am Q Fp 6.86 8.49 25.44 1.48 1.61 2.39 Watershed Summary for DA 1A: 1-yr,cfs 2-yr,cfs 10-yr,cfs Approved Pre-Development 6.86 8.49 25.44 Approved Post-Development Routings 1.48 1.61 2.39 Final Buildout Post-Dev.Routings Note:Per the approved 9VAC25-87 - ca cu ations,this development meets channel protection compliance by having a post-development 1-year peak SCS design storm outflow less than or equal to 1.48 cfs. Post-Development Routing Calculations (The following amended SWM facility 1A routing calculations a droved subarea 1A, as well as the full build out of subarea 1A. These routing calculations were also updated to reflect the enlarged facility shown with this amendment.) , Foothills AMENDED Facility 1A- Approved Watershed BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- APPROVED WATERSHED 10 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 624.00 11245.00 0.0 626.00 13979.00 932.4 628.00 16968.00 2076.8 629.00 21326.00 2784.4 630.00 26890.00 3675.3 630.40 30164.00 4097.7 632.00 32495.00 5953.8 634.00 35499.00 8471.3 636.00 37499.00 11174.6 638.00 39355.00 14020.8 Start_Elevation(ft) 630.00 Vol . (cy) 3675.30 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 634.000 multiple 5 discharge into riser Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0. 545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 634.000 multiple 1 discharge into riser Page 1 Foothills AMENDED Facility 1A- Approved Watershed Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0. 500 orifice area (sf) 12. 566 Outlet structure 5 weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 16. 510 CN 87.000 pe rainfall , PT(in) 2 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 16. 510 CN 87.000 pe rainfall , PT(in) 2 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Page 2 Foothills AMENDED Facility 1A- Approved Watershed Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682.513 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 0.905 at 15.24 (hrs) water level (ft) 632.949 at 15.84 (hrs) storage (cy) 7121.030 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 40. 531 at 11.98 (hrs) discharge (cfs) 0.945 at 15.50 (hrs) water level (ft) 633.195 at 15.96 (hrs) storage (cy) 7431.235 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 5.493 at 12.82 (hrs) water level (ft) 634.810 at 12.82 (hrs) storage (cy) 9548. 534 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 76.184 at 12.12 (hrs) water level (ft) 636.605 at 12.12 (hrs) storage (cy) 12020.372 wed Mar 15 09:49:30 EDT 2017 Page 3 Foothills AMENDED Facility 1A- Final Buildout Watershed BasinFlow printout INPUT: Basin: Foothills AMENDED Facility 1A- FINAL BUILD OUT WATERSHED 10 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 624.00 11245.00 0.0 626.00 13979.00 932.4 628.00 16968.00 2076.8 629.00 21326.00 2784.4 630.00 26890.00 3675.3 630.40 30164.00 4097.7 632.00 32495.00 5953.8 634.00 35499.00 8471.3 636.00 37499.00 11174.6 638.00 39355.00 14020.8 Start_Elevation(ft) 630.00 Vol . (cy) 3675.30 6 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 625.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 630.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 634.000 multiple 5 discharge into riser Outlet structure 3 Orifice name: Mid-Flow Orifice area 0. 545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 634.000 multiple 1 discharge into riser Page 1 Foothills AMENDED Facility 1A- Final Buildout Watershed Outlet structure 4 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 635.330 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0. 500 orifice area (sf) 12. 566 Outlet structure 5 Weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 636.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr. 24-hr. Peak SCS Design Storm Area (acres) 20.160 CN 91.000 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 53.488 peak time (hrs) 11.991 volume (cy) 6880.121 Hydrograph 1 SCS name: 2-yr. 24-hr. Peak SCS Design Storm Area (acres) 20.160 CN 91.000 pe rainfall , PT(in) 2 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 57.484 peak time (hrs) 11.991 volume (cy) 7394.138 Page 2 Foothills AMENDED Facility 1A- Final Buildout Watershed Hydrograph 2 SCS name: 10-yr. 24-hr. Peak SCS Design Storm Area (acres) 20.160 CN 91.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 96.114 peak time (hrs) 11.991 volume (cy) 12363.111 Hydrograph 3 SCS name: 100-yr. 24-hr. Peak SCS Design Storm Area (acres) 20.160 CN 91.000 pe rainfall , PT(in) 2 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 168.646 peak time (hrs) 11.991 volume (cy) 21692.765 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 53.223 at 11.98 (hrs) discharge (cfs) 1.299 at 15.06 (hrs) water level (ft) 634.096 at 15.10 (hrs) storage (cy) 8597.053 Hydrograph 1 Routing Summary of Peaks: 2-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 57.199 at 11.98 (hrs) discharge (cfs) 2.187 at 13.86 (hrs) water level (ft) 634.233 at 13.86 (hrs) storage (cy) 8777.941 Hydrograph 2 Routing Summary of Peaks: 10-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 95.637 at 11.98 (hrs) discharge (cfs) 21.812 at 12.30 (hrs) water level (ft) 635.793 at 12.30 (hrs) storage (cy) 10887.822 Hydrograph 3 Routing Summary of Peaks: 100-yr. 24-hr. Peak SCS Design Storm inflow (cfs) 167.809 at 11.98 (hrs) discharge (cfs) 150.486 at 12.04 (hrs) water level (ft) 636.902 at 12.04 (hrs) storage (cy) 12441.425 Wed Mar 15 09:48:27 EDT 2017 Page 3 The following calculations were previously approved with the Foothill Crossing II VSMP Amendment #1 (These calculations are provided for informational purposes only to assist County Engineering.) FOOTHILL CROSSING II STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations July 28, 2016 PREPARED BY: COLLINS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com DEQ Virginia Runoff Reduction Method Water Quality Calculations Virginia Runoff Reduction Method New Development Worksheet-v2.8 -June 2014 To be used w/2011 BMP Standards and Specifications Site Data Project Name: The Villas at Foothills Date: 7/28/16 data input cells calculation cells constant values 1. Post-Development Project& Land Cover Information Constants Annual Rainfall(inches) Target Rainfall Event(inches) 71.00 Phosphorus EMC(mg/L) Nitrogen EMC(mg/L)11111111111.Target Phosphorus Target Load(Ib/acre/yr)Pj Land Cover (acres) A soils B Soils C Soils D Soils Totals Forest/Open Space(acres)--undisturbed, protected forest/open space or reforested land 0.00 Managed Turf(acres)–disturbed,graded for yards or other turf to be mowed/managed 17 79 Impervious Cover(acres) 20.04 Total 37.83 Rv Coefficients A soils B Soils C Soils D Soils Forest/Open Space 0.02 0.03• 0.04 Ow 0.05 Managed Turf 0.15 0.20 - 0.22 0.25 ` Impervious Cover 0.95 0.95 0.95 0.95 Land Cover Summary —Forest/Open Space Cover(acres) 0.00 Weighted Rv(forest) 0.00 %Forest 0% Managed Turf Cover(acres) 17 79 Weighted Rv(turf) 0.21 %Managed Turf 47% Impervious Cover(acres) 20.04 Rv(impervious) 0.95 %Impervious 53% Total Site Area(acres) 37.83 Site Rv 0.60 Post-Development Treatment Volume(acre-ft) 1.89 Post-Development Treatment Volume(cubic feet) 82,456 Post_Development Load(TP)(Ib/yr) 51.81 Post_Development Load(TN)(Ib/yr) Total Load(TP)Reduction Required(Ib/yr) 36.30 I Y V w S < 0000 ul d. Q l 8888 0 0 0 0 1 w D 0 0000 re 000 0 - - 0 J Q Y Q 0 .. >- m m Q 00.4, - 0 v v o 0 0 I 00.-0 0 w U IX Q p w : O K w I HILI. CO w X U 0 0 w 7 0 h 4N',U Qom,0S N 0 0 .I ''.et0) Q 0 N �_) 00uio P - - el 40 Q N l'�') 09 r J 01 1- N Y H 0 I 0 2 O, U w w w w 0 .2.a �} ). w Y u j, >HKFw p a w w z `� a ? -IvI- z J0?I- -I o H 0 Hr wa I- 2 IX li O m Z O 0. 0.„ - 7 mW LLa 7 2 w LLQ 2 pp - w 2 D.4 re z = O _ : 2 p 0 IX i_0 rto • a CG0 , n. <I-0 w N K a. .:7,1 a z 0 0 X a 0 tl~O ct z H w p H a- •H p w 0 N d D J 0 ._ J O Q: O 2 W rn re J O a 00 111 p O 0 a a HO I- a O O 0 ll a € z a O a O 0 O p a a z c ~ p w N JF Q 0 L OF G K m a ate+ Z r y n. =1 Virginia Runoff Reduction Method Worksheet Virginia Runoff Reduction Method New Development Worksheet-v2.8-June 2014 Site Data Summary Total Rainfall= 43 inches Site Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 11.83 5.96 0.00 17.79 47.03 Impervious(acres) 0.00 15.00 5.04 0.00 20.04 52.97 37.83 100.00 Site Rv 0.60 Post Development Treatment Volume(ft3) 82456 Post Development TP Load(Ib/yr) 51.81 Post Development TN Load(Ib/yr) 370.62 Total TP Load Reduction Required(Ib/yr) 36.30 Total Runoff Volume Reduction(ft3) 0 Total TP Load Reduction Achieved(Ib/yr) 38 Total TN Load Reduction Achieved(Ib/yr) 143.62 Adjusted Post Development TP Load(Ib/yr) 14.16 Remaining Phosphorous Load Reduction(Lb/yr)Required 0.00 Drainage Area Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 5.99 10.35 1.45 0.00 0.00 17.79 Impervious(acres) 10.52 9.12 0.40 0.00 0.00 20.04 37.83 Drainage Area Compliance Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total TP Load Red.(Ib/yr) 19.21 18.43 0.00 0.00 0.00 37.64 TN Load Red.(Ib/yr) 73.30 70.32 0.00 0.00 0.00 143.62 Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area A Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 3.35 2.64 0.00 5.99 36.28 Impervious(acres) 0.00 7.30 3.22 0.00 10.52 63.72 16.51 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: 10.52 Turf(Pervious): 5.99 Total Impervious Cover Treated(acres) 10.52 Total Turf Area Treated(acres) 5.99 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 19.21 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 73.30 Drainage Area B Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 7.70 2.65 0.00 10.35 53.16 Impervious(acres) 0.00 7.36 1.76 0.00 9.12 46.84 19.47 BMP Selections Practice Credit Area(acres) Downstream Practice 13.c.Wet Pond#2(Spec#14) Impervious: 9.12 Turf(Pervious): 10.35 Total Impervious Cover Treated(acres) 9.12 Total Turf Area Treated(acres) 10.35 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 18.43 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 70.32 Drainage Area C Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Turf(acres) 0.00 0.78 0.67 0.00 1.45 78.38 Impervious(acres) 0.00 0.34 0.06 0.00 0.40 21.62 1.85 BMP Selections Practice Credit Area(acres) Downstream Practice Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A.A(Ib/yr) 0.00 Summary Print SCS TR-55 Calculations Soils Mapping (Source: NRCS Web Soil Survey Online Database) „ - , • •.„44- • 111,14 % 4 _ I I 1111 411 ( # 41441, 4414 414 + lit + 4 ***401,110. #11t. 44". 11 • Pk t k . .N.446 anir $ Of) ..4000 • . . . ' U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Foothill Crossing II Designed By:KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By:FGM,PE Date: 7/28/2016 Check One: Present X Developed X 1.Runoff curve Number(CN) Soil name and Cover description Drainage Area p Area Product of CN CN(weighted)= Calculated'S' hydrologic group (Cover type,treatment,and hydrologic condition;percent CN Description (Acres) x Area total product/ Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area B Impervious Areas 98 0.00 0.0 B Woods in Good Condition 55 9.12 501.6 D.A#1 B Lawns in Good Condition(75%+Groundcover) 61 1.93 117.7 (Present) C Impervious Areas 98 0.00 0.0 61 6.37 C Woods in Good Condition 70 4.94 345.8 C Lawns in Good Condition(75%+Groundcover) 74 0.92 68.1 B Impervious Areas 98 0.17 16.7 B Woods in Good Condition 55 5.20 286.0 D.A#2 B Lawns in Good Condition(75%+Groundcover) 61 10.46 638.1 (Present) C Impervious Areas 98 0.00 0.0 63 5.94 C Woods in Good Condition 70 1.14 79.8 C Lawns in Good Condition(75%+Groundcover) 74 3.95 292.3 B Impervious Areas(+Excess Capacity for 5.7 ac Imp.) 98 7.30 715.4 B Woods in Good Condition 55 0.00 0.0 D.A#1A B Lawns in Good Condition(75%+Groundcover) 61 3.35 204.4 (Developed) C Impervious Areas(+Excess Capacity for 2.82 ac Imp.) 98 3.22 315.6 87 1.54 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.64 195.4 B Impervious Areas(+Excess Capacity for 1.36 ac Imp.) 98 7.36 721.3 B Woods in Good Condition 55 0.00 0.0 D.A#2B B Lawns in Good Condition(75%+Groundcover) 61 7.70 469.7 (Develo d 80 2.48 pe ) C Impervious Areas(+Excess Capacity for 0.39 ac Imp.) 98 1.76 172.5 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover) 74 2.65 196.1 B Impervious Areas 98 0.34 33.3 B Woods in Good Condition 55 0.00 0.0 D.A#2C B Lawns in Good Condition(75%+Groundcover) 61 0.78 47.6 (Developed) C Impervious Areas 98 0.06 5.9 74 3.57 C Woods in Good Condition 70 0.00 0.0 C Lawns in Good Condition(75%+Groundcover; 74 0.67 49.6 2.Runoff 1-year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 1 2 10 n/a Rainfall,P(24 hour)-inches 3.5 3.7 5.6 n/a Runoff,0-inches 0.58 0.67 1.75 D.A#1(Present) Runoff,0-inches 0.65 0.75 1.88 D.A#2(Present) Runoff,Q-inches 2.15 2.33 4.10 D.A#1A(Developed) Runoff,Q-inches 1.64 1.80 3.43 D.A#2B(Developed) Runoff,0-inches 1.22 1.36 2.82 D.A#2C(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Ty)or Travel Time(Ti) Project: Foothill Crossing Il Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By:FGM,PE Date: 7/28/2016 Check One: Present X Developed X Check One: T, X T, Through subarea D.A#1 D.A#2 D.A#1A D.A#2B D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Segment ID: Sheet Flow:(Applicable to Tt only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.01 0.02 0.02 0.04 0.03 6 Compute T,=[0.007(n*L)°'S]/P2o.s s°'4 0.29 0.22 0.22 0.17 0.19 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 952 755 117 96 237 9 Watercourse slope,s(ft/ft) 0.041 0.066 0.026 0.042 0.059 10 Average velocity,V(Figure 3-1)(ft/s) 3.2 4.2 2.6 3.3 4.5 11 Tt=L/3600*V 0.08 I 0.05 I 0.01 0.01 I 0.01 Channel Flow: a`, a`, a`, 12 Cross sectional flow area,a(ft2) v N w E E E 13 Wetted perimeter,Pw(ft) o o `oej 14 Hydraulic radius,r=a/Pw(ft) N/A N/A c c c ~ Q c o 15 Channel Slope,s(ft/ft) E ov E o v E o v 16 Manning's Roughness Coeff,n - - - 17 V=[1.49r2/3s0'5 j/n > > > m m m 18 Flow length,L(ft) H F 4 19-It=L/3600*V 0.00 0.00 0.00 0.00 0.00 20 Watershed or subarea TtorT, (Add T,in steps 6,11 and 19) I 0.37 I 0.27 I 0.23 I 0.18 I 0.20 U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Foothill Crossing II Designed By: KKW,PE Date: 7/28/2016 Location: Crozet,VA Checked By: FGM,PE Date: 7/28/2016 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description D.A#1 D.A#2 D.A#1A D.A#2B D.A#2C (Present) (Present) (Developed) (Developed) (Developed) Drainage Area(Am)in miles'= 0.0264 0.0327 0.0258 0.0304 0.0029 Runoff curve number CN= 61 63 87 80 74 Time of concentration(Tc)= 0.37 0.27 0.23 0.18 0.20 Rainfall distribution type= II II II II II Pond and swamp areas spread 0 0 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.273 1.273 1.273 1.187 1.187 1.187 0.308 0.308 0.308 0.497 0.497 0.497 0.713 0.713 0.713 5.Compute la/P 0.36 0.34 0.23 0.34 0.32 0.21 0.09 0.08 0.06 0.14 0.13 0.09 0.20 0.19 0.13 6.Unit peak discharge,Qu-csm/in 450 480 550 560 595 655 - - - - - - 740 755 800 7.Runoff,Q from Worksheet 2-inches 0.58 0.67 1.75 0.65 0.75 1.88 2.15 2.33 4.10 1.64 1.80 3.43 1.22 1.36 2.82 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs 6.86 8.49 25.44 11.87 14.54 40.29 ROUTED ROUTED 2.61 2.97 6.53 Summary of Watersheds Summary of Drainage Areas 1-Year 2-Year 10-Year Predevelopment Post-Development Predevelopment(cfs) sost-Development(cfs) Predevelopment(cfs) sost-Develo ment(cfs)Predevelo ment(cfs)'ost-Development(cfs) D.A.#1 16.91 D.A.#1A 16.51 DA.#1 ll 6.86 D.A.#1A 1.48 D.A.#1 8.49 D.A.#1A 1.61 D.A.#1 25.44 D.A.#1A 2.39 D.A.#2 20.92 D.A.#2B 19A7 D.A.#28 0.70 D.A.#28 0.83 D.A.#2 D.A.#28 45.85 D.A.#2C 1.85 D.A.M2 11.87 D.A.#2C 2.61 D.A.#2 14.54 D.A.#2C 2.97 40.29 D.A.#2C 6.53 Totals: 37.83 37.83 Totals: 18.73 4.79 _Totals: 23.03 5.41 Totals: 65.73 54.77 Post-Development Routing Calculations Villas Level II Wet Pond-A-new BasinFlow printout INPUT: Basin: Foothills Crossing II - Wet Pond Level II 'A' Design 12 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 626.00 1409.00 0.0 628.00 3497.00 175.9 629.00 4762.00 328.3 630.00 6141.00 529.7 631.00 9357.00 814.6 632.00 13497.00 1235.5 632.40 20122.00 1482.9 634.00 24142.00 2792.6 636.00 28144.00 4727.2 638.00 32372.00 6966.7 640.00 36827.00 9527.9 641. 50 40316.00 11670.0 Start_Elevation(ft) 632.00 vol . (cy) 1235.46 6 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 632.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 635.000 multiple 1 discharge into riser Outlet structure 2 weir name: Emergency Spillway length (ft) 30.000 side angle 71. 500 coefficient 3.300 invert (ft) 640.000 multiple 1 discharge through dam Outlet structure 3 Curve name: Anti-Vortex Device multiple 1 Invert (ft) 638. 500 discharge into riser file: thirtysix.txt Page 1 Villas Level II Wet Pond-A-new Outlet structure 4 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 166.000 Slope 0.012 Manning's n 0.013 Inlet coeff. Ke 0. 500 Equation constant set 3 Invert (ft) 626.000 Outlet structure 5 Orifice name: Inverted Pipe area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 631.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 37.621 peak time (hrs) 11.991 volume (cy) 4839.119 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 40.733 peak time (hrs) 11.991 volume (cy) 5239.494 Page 2 Villas Level II Wet Pond-A-new Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 71.287 peak time (hrs) 11.991 volume (cy) 9169.618 Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 16. 510 CN 87.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.2300 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 129.695 peak time (hrs) 11.991 volume (cy) 16682. 513 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 37.434 at 11.98 (hrs) discharge (cfs) 1.475 at 13.80 (hrs) water level (ft) 635.449 at 13.96 (hrs) storage (cy) 4164.447 Hydrograph 1 Routing Summary of Peaks: 2-Year 24-Hour SCS Method Storm inflow (cfs) 40. 531 at 11.98 (hrs) discharge (cfs) 1.606 at 13.92 (hrs) water level (ft) 635.709 at 13.94 (hrs) storage (cy) 4426.913 Hydrograph 2 Routing Summary of Peaks: 10-Year 24-Hour SCS Method Storm inflow (cfs) 70.933 at 11.98 (hrs) discharge (cfs) 2.386 at 14.40 (hrs) water level (ft) 638.176 at 14.40 (hrs) storage (cy) 7178. 537 Hydrograph 3 Routing Summary of Peaks: 100-Year 24-Hour SCS Method Storm inflow (cfs) 129.051 at 11.98 (hrs) discharge (cfs) 51.479 at 12.18 (hrs) water level (ft) 640.195 at 12.18 (hrs) storage (cy) 9795.943 Tue Aug 25 12:31:39 EDT 2015 Page 3 Villas Level II Wet Pond 2B BasinFlow printout INPUT: Basin: Foothills Crossing II - wet Pond Level II '2B' Design 11 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 638.00 1154.00 0.0 639.00 1957.00 57.0 640.00 3080.00 149. 5 642.00 6230.00 487.5 643.00 8779.00 764.1 644.00 16427.00 1223. 5 644.40 16518.00 1467.6 646.00 19193.00 2524.7 648.00 22740.00 4075.9 650.00 26510.00 5898.2 652.00 30508.00 8008.2 Start_Elevation(ft) 644.00 vol . (cy) 1223. 53 5 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 644.000 multiple 1 discharge into riser Outlet structure 1 orifice name: Mid-Flow Orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 648.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Emergency Spillway length (ft) 35.000 side angle 78.460 coefficient 3.300 invert (ft) 650.250 multiple 1 discharge through dam Outlet structure 3 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 76.000 Slope 0.008 Manning's n 0.013 Inlet coeff. Ke 0. 500 Equation constant set 3 Invert (ft) 643.070 Page 1 Villas Level II wet Pond 2B Outlet structure 4 Weir name: Riser diameter (in) 60.000 side angle 0.000 coefficient 3.300 invert (ft) 649.000 multiple 1 discharge into riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 35.543 peak time (hrs) 11.970 volume (cy) 4279.362 Hydrograph 1 SCS name: 2-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 39.021 peak time (hrs) 11.970 volume (cy) 4698.123 Hydrograph 2 SCS name: 10-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 74.336 peak time (hrs) 11.970 volume (cy) 8950.069 Page 2 Villas Level II Wet Pond 2B Hydrograph 3 SCS name: 100-Year 24-Hour SCS Method Storm Area (acres) 19.470 CN 80.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1800 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 144.726 peak time (hrs) 11.970 volume (cy) 17425.020 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24-Hour SCS Method Storm inflow (cfs) 35.543 at 11.96 (hrs) discharge (cfs) 0.702 at 16.28 (hrs) water level (ft) 648.422 at 16.56 (hrs) storage (cy) 4437.189 Hydrograph 1 Routing Summary of Peaks: 2-Year 24-Hour SCS Method Storm inflow (cfs) 39.021 at 11.96 (hrs) discharge (cfs) 0.825 at 15.82 (hrs) water level (ft) 648.738 at 16.00 (hrs) storage (cy) 4715.939 Hydrograph 2 Routing Summary of Peaks: 10-Year 24-Hour SCS Method Storm inflow (cfs) 74.336 at 11.96 (hrs) discharge (cfs) 45.852 at 12.10 (hrs) water level (ft) 649.906 at 12.10 (hrs) storage (cy) 5806.582 Hydrograph 3 Routing Summary of Peaks: 100-Year 24-Hour SCS Method Storm inflow (cfs) 144.725 at 11.96 (hrs) discharge (cfs) 131.980 at 12.02 (hrs) water level (ft) 650.929 at 12.02 (hrs) storage (cy) 6841.343 wed Jul 27 16:39: 52 EDT 2016 Page 3 7/28/16 & FGM, PE q 1116 ,.-)i:::,__ ; --i CI- (r tt (11 tt ; ; Ee ri t s-'_ `' tv. rA r-,6):;`T I l , 14 V ( '''r ' --i . 65 7.x14 Ifso - ` i 48 S6 c isZ0,5.0 O r),A k ()00"--- 48 L. 0.70 . - , .. - „_ t. , 31 --1 <i), ;�� r dC". # ` mo47 if' i. ¢��- 3.31 ci , --) L � -oa(s