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HomeMy WebLinkAboutWPO201500057 Calculations 2018-03-29 AVINITY II STORMWATER MANAGEMENT CALCULATIONS PACKET (VSMP Amendment#1) Date of Originally Approved WPO 201600004 Calculations October 26, 2016 Date of WPO Amendment#1 Calculations January 18, 2018 Revised March 29, 2018 PREPARED BY: al COLLINS """" '' " rRING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com Amendment #1 Water Quality Calculations Summary: The proposed amendment modifies the development's impervious areas, includes newly added preservation areas and utilizes an updated Virginia Runoff Reduction Method Spreadsheet (3rd version). The following calculations also remove the previously approved two bioretention basins and two dry swales. The removal of these facilities is offset by the best management practice of purchasing nutrient credits, preserving opening spaces and a manufactured BMP. Soils Mapping (Source: NRCS Web Soil Survey Online Database) 4 `. dry ✓ �! " ' , �� x :11.1111101/4 ,%0 , t% t %Ir fli ..°J.E7' " - . '4 . ' ''' t A r \ 'tt } let : +r14: .:71. ..'. 1. d' 7 "Mho ilik • *. �� ' re .. , „„ 4 • 171, I:, , ..)" ''' by '*. 8 i Nt. iwilli,.. ..- ...,.., * ...,,shik_ , . 0 . lik L SO is Table (Source: NRCS Web Soil Survey Online Database) Albemarle County,Virginia(VA003) Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent of Symbol AOI 71B Rabun clay 35.7% loam, 2 to 7 percent slopes 72C3 Rabun clay, 7 to 49.9% 15 percent slopes, severely eroded 72D3 Rabun clay, 15 13.5% to 25 percent slopes, severely eroded 79B Starr silt loam, 0.9% 2 to 7 percent slopes Totals for Area of 100.0% Interest Note:The NRCS web soil survey has catorgized this parcel's soil types as predominantly consisting of hydrologic group types B. Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) zi-" ' 4 * Map v -- € °` d. u Terrain `'� V cew (2 G� \C' et erg v 4 4 Oof. F.,„, ,ers,t tle d z y�R d 2 8 Z,c1i4 F• � Q-b Star G,e s�L�a U1 _ v� ab Jury ;�,`e 59*. 6, 1c �.aa� 0. ockt,0 I i* oShady' pey'G -': < t'h a o ..° i1,tr.rrn Q �; y Cf eek fi 3 s ,r,. a + 0.4km . �co d.2mi y t' POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90%CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14,Volume 2,Version 3 PDS-based precipitation frequency estimates with 90%confidence intervals(in inches)1 Duration I Average n:anence interval(years) I 1 II 2 11 5 II 10 II 25 II 50 II 100 I[ 200 II we II 1000 I 24414 II (2:3 41) II (3:0-4.12) II (4.2152 7) II (4.96-6.21) 11 (6.06-7 60) II (618121.80) II (7 97-0.1) I (9 04-151 6) II (1011153.8)3.8) II (1194 5 7) Project Name: Avinity II VSMP Amendment#1 ~CLEAR ALL data Input cells Date: 1/18/2018 (Crrl+Shift+R) 1 constant values BMP Design Specifications List: 2011 Stds&Specs calculation cells Site Information ena 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, 0 ' protected forest/open space or reforested land 0.32 32 Managed Turf(acres)--disturbed,graded for yards or other turf to be mowed/managed 5 68 5.68 Impervious Cover(acres) 5 89 5.89 _ •Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 11.89 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 015 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(Ib/acre/yr) 0.41 Pj(unitless correction factor) 0.90 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/yr) 10.50 LAND COVER SUMMARY--POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Forest/Open Space Cover(acres) 0 32 Treatment Volume 0 5618 (acre-ft) Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 24,470 %Forest 3% TP Load(lb/yr) 15.37 Managed Turf Cover(acres) 5.68 TN Load(Ib/yr) 109 99 (Informational Purposes Only) Weighted Rv(turf) 0 20 %Managed Turf 48% Impervious Cover(acres) 5.89 Rv(impervious) 0.95 %Impervious 50% Site Area(acres) 11.89 Site Rv 0.57 VRRItitNw_VS_Anrny II D.A.A Drainage Area A Drainage Area A Land Cover(acres) CLEAR BMP AREAS A Solis B Soils C Soils D Soils Totals Land Cover Rv Forest/Open Space(acres) 0.00 0.00 Managed Turf(acres) 0.23 0.23 0.20 Impervious Cover(acres) 0.45 0.45 0.95 Total Phosphorus Available for Removal in D,A.A(Ib/yr) 1.08 Total 0.68 Post Development Treatment Volume in DA.A(ft') 1,719 Stormwater Best Management Practices(RR=Runoff Reduction) --Select from dropdown lists-- Runoff Managed Turf Impervious Volume front Runoff Remaining Total BMP Phosphorus Phosphorus Untreated Phosphorus Remaining Practice Reduction Credit Area Cover Credit Upstream Reduction Runoff Treatment Removal Load from Phosphorus Removed By Phosphorus Downstream Pre d' to be Credit(%) (acres) Area(acres) Practice(ft') (It') m ( Volu ¢ ft Volume(ft') Efficiency(%) Upstream Wad to Employed Practices(Ib) Practice pb) Practice(lb) Load(lb) I.Vei;nt.and Roof(RR) 1a Vegetated Roof NI(Spec N5) 45 0 0 0 0 000 000 0.00 I.b.Vegetated Roof N2(Spec N5) 60 0 0 0 0 0.00 0 00 000 2.Roof lop D!,coon.•rtio0 lRR) 2.a.Simple(Nsconnection to Wt SoilsSO 0 0 0 0 0 0.00 0.00 0.00 0.00 (Spec 01) 2.b.Simple Disconnection to C/D Soils 25 0 0 0 0 0 0.s%I 0.00 0.00 0.00 (spec al) 2.c.To Sell Amended Finer Path as per " SO V0eNteatbns(NNsong C/D soils)(Spec N4) 0 0 0 0 0 0.00 0.00 0.00 om 2A.To Dry Well or French Drain al, 0 21 SO 0 0 0 0.00 0.00 0.00 0.00 Mkro-InRlraoon RI(Spec at 2.e To Dry Well or French Drain N2, Micro-1400.6,n 42(Spec N81 0 0 0 0 25 0.000.00 0.00 0.00 2.f Op Rain Garden pe 0 0 0 0 25 0.00 0.00 0.00 0.(M] Micro-Bbretentbn RI(Spec N9) 2.g.To Rain Garden N2, 80 0 0 0 0 50 0.00 0.00 0.00 0.00 Mlcro.Bbretentbn N2(Spec a9) 2.h.To Rainwater Harvesting(Spec N6) 0 0 0 0 0 0 0.00 0.00 0.00 0.00 2.1.To Stormwater Planter, 40 0 0 0 0 25 0.00 0,00 0.00 0.00 Urban Bioretentlon(Spec 49,Appendix A) 3.Permeable Pavement(RR) la.Permeable Pavement Nl(Spec N7) 45 0 0 0 0 25 0.00 0.00 0.00 0.00 3.b.Permeable Pavement N2(Spec N7) 75 0 0 0 25 0.00 000 0.00 G,.1,.Cl,aoonl(RIII 4.a.Grass Channel NBSOIh(Spec M3) 20 0 0 0 0 15 0.00 0.00 0.00 0.00 4A.Wass Channel C/D Soils(Spec N3) 10 0 0 0 0 15 0.00 0.00 0.00 0.00 4.c.Wass Channel vnth Compost Amended Sags30 0 0 0 0 15 0.00 0.00 0.00 0.00 as per specs(see Spectre) S Dry Swale(RR1 S.a Dry Swale 11(Spec 0101 40 0 0 0 0 20 0.00 0.00 0.00 0.00 S.b.Dry Swale N2(Spec N10) 60 0 0 0 0 40 0.00 0.00 0.00 0.00 6.Riorelenlion(RR) 6.a Baretention NI or Micro-Bioretentian Ill or Urban Bioretenton(Spec N91 40 0 0 0 0 25 0.00 000 0.00 000 6.b.B'aretention N2 or Micro-Bioretemion N2so 0 0 0 0 50 000 0.00 0.00 0.00 (Spec N9) 7.Infiltration(RR) 7.a Infiltration NI.(Spec NB) SO 0 0 0 0 25 000 0.00 0.00 0.00 7 b.Infiltration N2(Spec e8) 90 0 0 0 0 25 0.00 0.00 0.00 0.00 Si. ,iendnd Del,nt5m Pond(RR) 8.a.ED NI(Spec N15) 0 0 0 0 0 IS 0.00 0.00 000 0.00 8.b.ED 42(Spec 015) 15 0 0 0 0 15 0.00 0.00 0.00 000 _.5h3 3fl,cw to Filo.,/opnn Spar.'(RR) 9.a.Sheetlbw to Conservation Area,A/8 Soils 75 • 0 0 0 0 0 0.00 00) 0.00 0.00 (Site,oD) 9.0.SlmetBaw to Conservation Area,C/D Soils 50 0 0 0 0 0 0.00 0.00 0.00 0.00 (spec N2) 9.c.Sheedlow to Vegetated Filter Strip,A Soils or Compost Amended8/C/D Soils 50 0 0 0 0 0 0.00 0.00 0.00 0.00 (Spec N2 A w) TOTAL IMPERVIOUS COVER TREATED(ac) 0.00 AREA CHECK OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AREA CHECK.OK. TOTAL RUNOFF REDUCTION IN D.A.A(ft') 0 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN DA.A(Ib/yr) 1.08 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr) 0.00 TOTAL PHOSPHORUS REMAINING AFTER APPLYING RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr) 1.08 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS tat yet mta f2:40 PM VRRM_New_V3_AviMy II D.0.A 10.Wet Swale(no RR) 10.a Wet Swale NI(Spec N11) 0 0 0 0 0 20 0.00 0.00 0.00 0.00 10.b Wet Swale N2(Spec 411) 0 0 0 0 0 40 0.00 0.00 0.00 0.00 11.Filtering Practices(no RR) 11.a.Filtering Practice NI(Spec N12) 0 0 0 0 0 60 0.00 0.00 0.00 0.00 11.b.Filtering Practice N2(Spec N12( 0 0 0 0 0 65 0.00 0.00 0.00 0.00 12.Constructed Wetland(no RR) 12.a.Constructed Wetland Cl(Spec N13) 0 0 0 0 0 50 0.00 0.00 0.00 0.00 12.b Constructed Wetland N2(Spec N13) 0 0 0 0 0 05 0.00 0.00 0.00 0.00 13.Wet Ponds(no RR) 13.a Wet Pond ill(Spec N14) 0 0 0 0 0 50 0.00 0.00 0.00 0.00 13.b Wet Pond Ni(Coastal Plain)(Spec N14) 0 0 0 45 0.00 0.00 0.00 0.00 13.c.Wet Pond N2(Spec#14) 0 0 0 0 0 75 0.00 0.00 0.00 0.00 13.d.Wet Pond N2(Coastal Plain)(Spec 1/14) 0 0 0 0 0 65 0.00 0.00 0.00 0.00 14.Manufactured Treatment Devices(no RR) 144 Manufactured Treatment Device- Hydrotlynamic 0 0 0 0 0 20 0.00 0.00 0.00 0.00 14.b.Manufactured Treatment Device-Filtering 0 0 0 0 0 20 0.00 0.00 0.00 0.00 14.c.Manufactured Treatment Device-Generic 0 0.23 0.45 0 0 1,719 1,719 50 0.00 1.08 0.54 0.54 TOTAL IMPERVIOUS COVER TREATED(ac) 0.45 AREA CHECK OK TOTAL MANAGED TURF AREA TREATED(cc) 0.23 AREA CHECK OK TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE(Ib/yri 10.50 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D A.A(Ib/yr l 1.08 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D A.A(Ib/yr 0.54 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D A.A(Ib/yr 0.00 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A.A(Ib/ye 0.54 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A.A(lb/yr 0.54 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr 0.00 NITROGEN REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr 0.00 TOTAL NITROGEN REMOVED IN D.A.A(Ib/yr) 0.00 3292018 1 of 1244 PM Amendment #1 Water Quantity Calculations Summary: The amended plan continues to include a dry detention cell, which attenuates and decreases outflows for the majority of the development. This SWM facility treats subarea 'A'. The amended plan also includes a plunge pool at the outlet of subarea 'B's storm sewer. The plunge pool dissipates the runoff prior to it exiting the parcel, and provides minor attenuation. This amendment plan and the attached calculations show the proposed modifications result in post-development amendment flows less than or equal to the previously approved post-development 1-, 2- and 10- year flows. The exception is DA 'B's 2-year storm, which remains below the approved pre-development value. Additionally, County engineering previously evaluated and approved the channel and flood protection calculations with the originally approved WPO plan, so this amendment's reduced flows ensure the amendment is still in compliance with County and State minimum requirements. As a result, no further analyses are required for quantity compliance with this amendment. U S Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2 Runoff Curve Number and Runoff Project: Avinity II Designed By FGM,PE Date 1/18/2018 Location South of Avinity I Checked By-SRC,PE Date' 1/18/2018 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 'S'Value (Appendix A) impervious,unconnected/connected impervious area ratio) total area DA A Impervious Areas 98 4.32 423 3 (Amended) B Woods in Good Condition(Offsite) 55 0 76 41.8 80.5 2 42 Lawns in Good Condition(75%+Groundcover) 61 2 87 175.1 Impervious Areas 98 1.44 141 3 DA B (Amended) B Woods in Good Condition 55 0 00 0 0 90 0 1.11 Lawns in Good Condition(75%+Groundcover) 61 0 40 24 3 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 04 3.67 5 55 n/a Runoff,Q-inches 1 31 1 81 3.43 DA A(Amended) Runoff,Q-inches 2.02 2 61 4 41 DAB(Amended) 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(Tt) Project: Avinity II Designed By: FGM,PE Date• 1/18/2018 Location: South of Avinity I Checked By: SRC,PE Date: 1/18/2018 Check One• Present X Developed X Check One: T, X Tt Through subarea n/a DA A DA B Segment ID: (Amended) (Amended) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) 2 Manning's roughness coeff,n(Table 3-1 3 Flow length,L(total L<100)(ft) 4 Two-year 24-hour rainfall,P2(in.) 5 Land slope,s(ft/ft) 6 Compute Tt=[0.007(n*L)°8]/Pz 5 s°4 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) 8 Flow Length,L(ft) 9 Watercourse slope,s(ft/ft) 10 Average velocity,V(Figure 3-1)(ft/s) 11 Tt=L/3600*V Channel Flow: 12 Cross sectional flow area,a(ft2) 13 Wetted perimeter,PW(ft) 14 Hydraulic radius,r=a/PW(ft) 15 Channel Slope,s(ft/ft) 16 Manning's Roughness Coeff,n 17 V=[1.49r213s°5]/n 18 Flow length,L(ft) 19 Tt=L/3600*V 20 Watershed or subarea T,or Tt (Add Tt in steps 6, 11 and 19) 0.21 0.10 (Approved Tc) U.S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Amity II Designed By. FGM,PE Date: 1/18/2018 Location: South of Avinity I Checked By: SRC,PE Date: 1/18/2018 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description DA A DA B (Amended) (Amended) Drainage Area(Am)in miles2= 0.0124 0.0029 Runoff curve number CN= 80.5 90.0 Time of concentration(Tc)= 0.21 0.10 Rainfall distribution type= II II Pond and swamp areas spread 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 3 Rainfall,P(24 hour)-inches 3.04 3.67 5.55 3.04 3.67 5.55 4.Initial Abstraction,la-inches 0.48 0.48 0.48 0.22 0.22 0.22 5.Compute la/P 0.16 0.13 0.09 0.07 0.06 0.04 6.Unit peak discharge,Qu-csm/in 1000 1000 1000 1000 1000 1000 7.Runoff,Qfrom Worksheet 2-inches 1.31 1.81 3 43 2.02 2 61 4.41 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs See Routing where Qp=Qu Am Q Fp Calculations See Routing Calculations Avinity II Detention Basin A BasinFlow printout INPUT: Basin: Avinity II Detention Basin A 6 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 489.00 3425.00 0.0 490.00 4009.00 137.5 492.00 5260.00 479.8 494.00 6630.00 919.2 496.00 8130.00 1464.9 497.75 9340.00 2030.6 Start_Elevation(ft) 489.00 Vol.(cy) 0.00 5 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 0.785 diameter or depth (in) 12.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 488.440 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Fow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 489.000 multiple 1 discharge into riser Outlet structure 2 Orifice name: Low-Fow Orifice area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 493.500 multiple 3 discharge into riser Page 1 Avinity II Detention Basin A Outlet structure 3 Weir name: Riser diameter (in) 24.000 side angle 0.000 coefficient 3.300 invert (ft) 495.330 multiple 1 discharge into riser transition at (ft) 0.608 orifice coef. 0.500 orifice area (sf) 3.142 Outlet structure 4 Weir name: Emergency Spillway length (ft) 55.000 side angle 0.000 coefficient 3.300 invert (ft) 496.330 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr SCS 24-hr Design Storm Area (acres) 7.950 CN 80.500 Type 2 rainfall, P (in) 3.040 time of conc. (hrs) 0.2100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 11.181 peak time (hrs) 11.982 volume (cy) 1400.926 Page 2 Avinity II Detention Basin A Hydrograph 1 SCS name: 2-yr SCS 24-hr Design Storm Area (acres) 7.950 CN 80.500 Type 2 rainfall, P (in) 3.670 time of conc. (hrs) 0.2100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 15.421 peak time (hrs) 11.982 volume (cy) 1932.256 Hydrograph 2 SCS name: 10-yr SCS 24-hr Design Storm Area (acres) 7.950 CN 80.500 Type 2 rainfall, P (in) 5.550 time of conc. (hrs) 0.2100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 29.204 peak time (hrs) 11.982 volume (cy) 3659.258 Hydrograph 3 SCS name: 100-yr SCS 24-hr Design Storm Area (acres) 7.950 CN 80.500 Type 2 rainfall, P (in) 9.130 time of conc. (hrs) 0.2100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 57.554 peak time (hrs) 11.982 volume (cy) 7211.424 Page 3 Avinity II Detention Basin A OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS 24-hr Design Storm inflow (cfs) 11.173 at 11.98 (hrs) discharge (cfs) 1.042 at 12.54 (hrs) water level (ft) 492.840 at 12.60 (hrs) storage (cy) 651.910 Hydrograph 1 Routing Summary of Peaks: 2-yr SCS 24-hr Design Storm inflow (cfs) 15.410 at 11.98 (hrs) discharge (cfs) 2.093 at 12.42 (hrs) water level (ft) 493.893 at 12.44 (hrs) storage (cy) 892.990 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS 24-hr Design Storm inflow (cfs) 29.183 at 11.98 (hrs) discharge (cfs) 8.498 at 12.20 (hrs) water level (ft) 496.217 at 12.20 (hrs) storage (cy) 1530.914 Hydrograph 3 Routing Summary of Peaks: 100-yr SCS 24-hr Design Storm inflow (cfs) 57.512 at 11.98 (hrs) discharge (cfs) 55.866 at 11.98 (hrs) water level (ft) 496.737 at 11.98 (hrs) storage (cy) 1693.487 Thu Jan 11 16:05:10 EST 2018 Page 4 Avinity II - Basin B - Plunge Pool New Routing with 3/29/18 Revision BasinFlow printout INPUT: Basin: Avinity II Detention Basin B 5 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 491.00 279.00 0.0 492.00 463.00 13.6 494.00 933.00 64.3 496.00 1511.00 154.0 498.00 2189.00 290.2 Start_Elevation(ft) 491.00 Vol.(cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 491.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.127 diameter or depth (in) 4.830 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 491.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Riser diameter (in) 10.000 side angle 0.000 coefficient 3.300 invert (ft) 495.920 multiple 1 discharge into riser Page 1 Avinity II Detention Basin B-2nd Submittal-enlarged pond-final transition at (ft) 0.253 orifice coef. 0.500 orifice area (sf) 0.545 Outlet structure 3 Weir name: Emergency Spillway length (ft) 50.000 side angle 0.000 coefficient 3.300 invert (ft) 497.920 multiple 1 discharge through dam 3 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr SCS 24-hr Design Storm Area (acres) 1.840 CN 90.000 Type 2 rainfall, P (in) 3.040 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 4.718 peak time (hrs) 11.917 volume (cy) 499.516 Hydrograph 1 SCS name: 2-yr SCS 24-hr Design Storm Area (acres) 1.840 CN 90.000 Type 2 rainfall, P (in) 3.670 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 6.088 peak time (hrs) 11.917 volume (cy) 644.523 Hydrograph 2 Page 2 Avinity II Detention Basin B-2nd Submittal-enlarged pond-final SCS name: 10-yr SCS 24-hr Design Storm Area (acres) 1.840 CN 90.000 Type 2 rainfall, P (in) 5.550 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 10.293 peak time (hrs) 11.917 volume (cy) 1089.689 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS 24-hr Design Storm inflow (cfs) 4.696 at 11.92 (hrs) discharge (cfs) 1.098 at 12.12 (hrs) water level (ft) 495.827 at 12.12 (hrs) storage (cy) 144.458 Hydrograph 1 Routing Summary of Peaks: 2-yr SCS 24-hr Design Storm inflow (cfs) 6.059 at 11.92 (hrs) discharge (cfs) 2.692 at 12.06 (hrs) water level (ft) 496.408 at 12.06 (hrs) storage (cy) 177.741 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS 24-hr Design Storm inflow (cfs) 10.244 at 11.92 (hrs) discharge (cfs) 4.416 at 12.04 (hrs) water level (ft) 497.919 at 12.04 (hrs) storage (cy) 283.704 Thu Mar 29 10:53:07 EDT 2018 Page 3 TMP 91 16C / PHYSICAL SURVEY �s N/F MOSS ACQUISITIONS LLC / IMP 9f f60 TAX MAP 91, PARCELS 16A & 16E D B 4319-247 D B 558-379(plat) /' N/F SCOTTSVILLE ROAD_______________ LOCATED ON STATE ROUTE 20 %©' IF HOLDINGS LLC ALBEMARLE COUNTY,VIRGINIA S49'12'03`E 434.73' D 13.3257-702 (TOTAL) D B 558-379(plat) 'li` Pr THIS IS TO CERTIFY THAT ON AUGUST f9,2013 .�'i� IF _-__- --- I SURVEYED B THE PRALERTYINES SHOWN HERWALLS OF AND ThE 91 36' THE BOAOARY LINES AND MALLS OF iME IMP 9 VONBUILDINGS ARE AS SHOO N/F AVON w PROPERTIES LLCNO TITLE REPORT PROVIDED , D B 401B-497(plat) o rn UTILITIES EASEMENTS OTHER o THAN THOSE SHOWN MAY EXIST V,.. m NON" INONUMENTT FOUND PFF.IRON FOUND IS PIPE FOUND =IRON SET m z %SECT PROPERTY APPEARS TO LIE IN FLOOD IONE•X•(UNSHIDED/AREAS DETERMINED TO BE OUTSIDE THE 0 29 ANNUAL CHANCE FLOODPLAIN AS SHOWN ON FLODO INSURANCE RATE MAP ------�'F 51003C0 426D,EFFECTIVE DATE FEBRUARY 4,2005 TMP 90-35H N/F MOSS 0 B 2108-54 w u m v T • O1 TMP 91-16E z N/F SCOTTS 1LLLE ROAD 2Z., 4 98 Ac. - HOLDINGS LLC TMP 90-35D N/F HUGHES Q D.B 3257-702 N/F HYDRA NC NPANY I SAND D B 599-239(plat) m D B.862-200 `^ D B 781-472(plat) --- ePF / O m ~S /[ , m y {I In MtRE FENCE(t VP 1 '' 0,y \� r— ,—• -t + IF \" r: TI:�,� T IMP 90 35B ! 99 -'7 h ,L .0 .IN SOUTHSIDE �� ,02 ,_A38�. / 1 fi �RC DB83932 tv (( .---'—D 8.755-353(Olat) CU —� fRlT S564449W ¢LIA,J.I,r;E�rsi m MI20 (LY_„l —�`�' ovEPk 'DD g 12LBETM+-T1 Lc=f42.71' 2 LC No.1507•a = �` A=f42.67' z p l J�*-�-` R=858.53' I. 9�!{./tod /'' ►�� 1 57 59 E urlL levP 'S n�ti • ��`�°,,, 561'57'53'E ' / _- 73.46' IF .70 / S51'45'23'W o0�y" irDx*^ ® /+ 42.06' /) DETAIL "A" (tyP) — ON / _ TMP 91-16A S50'43'27'M ' I. 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