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HomeMy WebLinkAboutWPO201600063 Calculations WPO VSMP 2016-12-16NORTHTOWN CENTER PHASE IIB STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations OCTOBER 14, 2016 Revised on DECEMBER 16, 2016 Revisions are noted in yellow. Revisions pertain to the inclusion of the 10-year design storm & updated routing calculations) PREPARED BY: COLLINS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com APPROVED by the Albemarle County Community Development Department Date___3131L7 File LOPLO' Cts — SCS TR-55 Calculations Revisions are for the inclusion of the 10-year design storm) Soils Mapping (Source: NRCS Web Soil Survey Online Database) 4'4 ' •.t. .. . 140' i' ft,b. VI k 1,. ' i x yM xArep x: Soils Table (Source: NRCS Web Soil Survey Online Database) Map Unit Legend Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent Symbol of AOI 27B Elioak loam, 2 to 7 5.0% percent slopes 346 Glenelg loam, 2 to 7 0.0% percent slopes 34C Glenelg loam, 7 to 15 46.4% percent slopes 340 Glenelg loam, 15 to 25 48.0% percent slopes 39E Hazel loam, 25 to 45 0.5% percent slopes Totals for Area of Interest 100.0% Note: The proposed development located on TMP 45-110C is generally dominated by type B soils. U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Revisions shown in Yellow) Project: Northtown Phase IIB Designed By: FGM,PE Date: 12/16/2016 Location: Route 29,East of Gander Mountain Checked By:SRC,PE Date: 12/16/2016 Check One: Present X Des X 1.Runoff curve Number(CN) Soil name and Cover description CN(weighted)=Drainage Area Area Product of CN Calculated'S' Description hydrologic group (Cover type,treatment,and hydrologic condition;percent impervious; CN total product/ Appendix A) unconnected/connected impervious area ratio) Acres) x Area Value total area DA A Impervious Areas 98 0.06 5.8 Present) B Woods in Good Condition(Approximately 75%)55 1.99 109.5 57.4 7.42 Lawns in Good Condition(Approximately 25%) 61 0.65 39.7 DAA Impervious Areas 98 2.12 208.0 Developed) B Woods in Good Condition 55 0.32 17.6 89.4 1.19 Lawns in Good Condition(75%+Groundcover) 61 0.26 15.7 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 0.43 0.51 1.47 DA A(Present) Runoff,Q-inches 2.39 2.58 4.39 DA A(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(T c)or Travel Time(rt) Project: Northtown Block 1B Designed By: FGM,PE Date: 10/14/2016 Location: Route 29,East of Gander Mountain Checked By: SRC,PE Date: 10/14/2016 Check One: Present X Developed X Check One: Tc X Tt Through subarea n/a DAA DA A Segment ID: (Present) (Developed) Sheet Flow:(Applicable to Tc only) Woods-Light Woods-Light 1 Surface description(Table 3-1) Underbrush Underbrush 2 Manning's roughness coeff.,n(Table 3-1 0.4 0.4 3 Flow length,L(total L<100)(ft) 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 5 Land slope,s(ft/ft) 0.11 0.11 6 Compute Tt=[0.007(n*L)°'8]/p20.5Z.5 s0.4 0.17 0.17 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved 8 Flow Length,L(ft) 415 100 9 Watercourse slope,s(ft/ft)0.080 0.170 10 Average velocity,V(Figure 3-1)(ft/s)4.6 6.8 11 Tt=L/3600*V 0.03 0.00 Channel Flow: 12 Cross sectional flow area,a(ft 2) E 0 013Wettedperimeter,P.,(ft)tr. vt 14 Hydraulic radius,r=a/PW(ft) v °y 15 Channel Slope,s(ft/ft) a 16 Manning's Roughness Coeff,n oY 17 V=[1.49r213s°'S]/ n b ^ Ln 18 Flow length,L(ft) 19 It=L/3600*V 0.01 20 Watershed or subarea T,or Tt Add Tt in steps 6,11 and 19) 0.20 I 0.18 I U.S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Northtown Phase IIB Designed By: FGM,PE Date: 12/16/2016 Location: Route 29,East of Gander Mountain Checked By:SRC,PE Date: 12/16/2016 Check One: Pres X Developed X Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description DAA DA A Present) Developed) Drainage Area(Am)in miles2= 0.0042 0.0042 Runoff curve number CN= 57.4 89.4 Time of concentration(Tc)= 0.20 0.18 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 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.48 1.48 1.48 0.24 0.24 0.24 5.Compute la/P 0.42 0.40 0.27 0.07 0.06 0.04 6.Unit peak discharge,Qu-csm/in 550 575 750 1000 1000 1000 7.Runoff,Q from Worksheet 2-inches 0.43 0.51 1.47 2.39 2.58 4.39 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Through SWM where Qp=Qu Am Q Fp 1.00 1.24 4.64 Facility Watershed Summary Area,ac. CN 1-yr Flow,cfs 2-yr Flow,cfs 10-yr Flow,cfs DA A(Present) 2.70 57.4 1.00 1.24 4.64 DA A(Developed) 2.70 89.4 0.91 0.93 4.33 Post-Development Routing Calculations The basin was enlarged and the routing calculations were updated accordingly.) Northtown IIB- Early Grading Permit SWM Detention3 BasinFlow printout INPUT: Basin: Northtown Phase IIB- Early Grading Permit SWM Detention 6 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 449.00 225.00 0.0 450.00 651.00 15.5 452.00 1718.00 100.1 454.00 3027.00 273.6 456.00 4504.00 550.7 458.00 6160.00 944.1 Start_Elevation(ft)449.00 Vol. (cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 1.767 diameter or depth (in)18.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 447.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.099 diameter or depth (in) 4.250 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 449.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Riser diameter (in)30.000 side angle 0.000 coefficient 3.300 invert (ft) 456.000 multiple 1 discharge into riser transition at (ft) 0.760 orifice coef. 0.500 orifice area (sf) 4.909 Page 1 Northtown IIB- Early Grading Permit SWM Detention3 Outlet structure 3 Weir name: emergency spillway length (ft)25.000 side angle 0.000 coefficient 3.300 invert (ft) 457.000 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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) 7.209 peak time (hrs)11.970 volume (cy) 867.901 Hydrograph 1 SCS name: 2-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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) 7.770 peak time (hrs)11.970 volume (cy) 935.507 Page 2 Northtown IIB- Early Grading Permit SWM Detention3 Hydrograph 2 SCS name: 10-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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)13.229 peak time (hrs)11.970 volume (cy) 1592.745 Hydrograph 3 SCS name: 100-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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)23.546 peak time (hrs)11.970 volume (cy) 2834.926 Page 3 Northtown IIB- Early Grading Permit SWM Detention3 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr, 24 hr Peak SCS Method Design Storm inflow (cfs) 7.209 at 11.96 (hrs) discharge (cfs) 0.908 at 12.38 (hrs) water level (ft) 454.455 at 12.42 (hrs) storage (cy) 327.245 Hydrograph 1 Routing Summary of Peaks: 2-yr, 24 hr Peak SCS Method Design Storm inflow (cfs) 7.770 at 11.96 (hrs) discharge (cfs) 0.929 at 12.42 (hrs) water level (ft) 454.700 at 12.44 (hrs) storage (cy) 358.294 Hydrograph 2 Routing Summary of Peaks: 10-yr, 24 hr Peak SCS Method Design Storm inflow (cfs)13.229 at 11.96 (hrs) discharge (cfs) 4.330 at 12.16 (hrs) water level (ft) 456.252 at 12.16 (hrs) storage (cy) 593.680 Hydrograph 3 Routing Summary of Peaks: 100-yr, 24 hr Peak SCS Method Design Storm inflow (cfs)23.546 at 11.96 (hrs) discharge (cfs)19.957 at 12.04 (hrs) water level (ft) 456.917 at 12.04 (hrs) storage (cy) 715.980 Thu Dec 15 11:44:56 EST 2016 Page 4 DEQ Virginia Runoff Reduction Method Water Quality Calculations Mitigated via the Best Management Practice of Preserving Open Spaces the Purchasing of Phosphorous Removal Credits) DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 02011 BMP Standards and Specifications 02013 Draft BMP Standards and Specifications Project Name: Northtown Block IB ii.- data input cells Date: 10/14/2016 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 j Totals Forest/Open Space(acres)--undisturbed, protected forest/open space or reforested land 0.60 0.60 Managed Turf(acres)-disturbed,graded for yards or other turf to be mowed/managed 1.03 1.03 Impervious Cover(acres) 2.19 2.19 Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method i 3.82 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) 3.69 LAND COVER SUMMARY--POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment VolumeForest/Open Space Cover(acres)0.60 acre-ft) 0.1920 Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 8,365 Forest 16% TP Load(lb/yr) 5.26 TN Load(lb/yr)Managed Turf Cover(acres) 1.03 37.60 Informational Purposes Onlvl Weighted Rv(turf) 0.20 Managed Turf 27% Impervious Cover(acres) 2.19 Rv(impervious) 0.95 Impervious 57% Site Area(acres) 3.82 Site Rv 0.60 NORTHTOWN CENTER PHASE IIB STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations OCTOBER 14, 2016 PREPARED BY: CE COLLINS ENGINEERING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com APPROVED by the Albemarle County Community Development Department Date 33 /7 o:, .- -- SCS TR-55 Calculations SODS Mapping (Source: MRCS Web Soil Survey Online Database) 14,4:::,%' 1;'$," 4r4.7.- elign, :44 4-.4,,„ i. s.,,,,, JAW' iiti,/,, , a, -,'..,,., ,,--- /7 .,;°- e.•:.:ti„::: - 4 •y af W-". s ' i a ha' y xnt •2 s; 5 Soils Table (Source: NRCS Web Soil Survey Online Database) Map unit Legend Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent Symbol of AOln 276 Eloak loam, 2 to 7 5.0% percent slopes 346 Glenelg loam, 2 to 7 0.0% percent slopes 34C Glenelg loam, 7 to 15 46.4% percent slopes 34D Glenelg loam, 15 to 25 48,0% percent slopes 39E Hazel loam, 25 to 45 0.5% percent slopes Totals far Area of Interest 100.0% Note: The proposed development located on IMP 45-110C is generally dominated by type B soils. U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Northtown Block 1B Designed By: FGM,PE Date: 10/14/201E Location: Route 29,East of Gander Mountain Checked By: SRC,PE Date: 10/14/201f Check One: Present X DeN X 1.Runoff curve Number(CN) a Soil name and Cover descriptionDrainage CN(weighted)= Cover type,treatment,and hydrologic Area Product of CalculatedAreahydrologicgroupCNtotalproduct/ Description condition;percent impervious;unconnected/ Acres) CN x Area S'Value p Appendix A) total areaconnectedimperviousarearatio) DA A Impervious Areas 98 0.06 5.8 Present) B Woods in Good Condition(Approximately 75%)55 1.99 109.5 57.4 7.42 Lawns in Good Condition(Approximately 25%)61 0.65 39.7 DA A Impervious Areas 98 2.12 208.0 Developed) B Woods in Good Condition 55 0.32 17.6 89.4 1.19 Lawns in Good Condition(75%+Groundcover) 61 0.26 15.7 2.Runoff 1-Year Storm 2-Year Storm Drainage Area Description Frequency-years 1 2 n/a Rainfall,P(24 hour)-inches 3.5 3.7 n/a Runoff,Q-inches 0.43 0.51 DA A(Present) Runoff,Q-inches 2.39 2.58 DA A(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(T c)or Travel Time(Tx) Project: Northtown Block 1B Designed By: FGM,PE Date: 10/14/2016 Location: Route 29,East of Gander Mountain Checked By: SRC,PE Date: 10/14/2016 Check One: Present X Developed X Check One: Tc X Tt Through subarea n/a DAA DAA Segment ID: (Present) (Developed) Sheet Flow:(Applicable to T,only) Woods-Light Woods-Light 1 Surface description(Table 3-1) Underbrush Underbrush 2 Manning's roughness coeff.,n(Table 3-1 0.4 0.4 3 Flow length,L(total L<100)(ft) 100 100 4 Two-year 24-hour rainfall,P 2(in.) 3.7 3.7 5 Land slope,s(ft/ft) 0.11 0.11 6 Compute Tt=[0.007(n*L)08)/P205 s"0.17 0.17 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved 8 Flow Length,L(ft) 415 100 9 Watercourse slope,s(ft/ft)0.080 0.170 10 Average velocity,V(Figure 3-1)(ft/s)4.6 6.8 11 Tt=L/3600*V 0.03 0.00 Channel Flow: 12 Cross sectional flow area,a(ft 2) o ° --13 Wetted perimeter,PW(ft)LL vt w 14 Hydraulic radius,r=a/PW(ft) u, o 15 Channel Slope,s(ft/ft) a — fO m 16 Manning's Roughness Coeff,n o ` 17 V=[1.49r2/3s°s j/n o a ",Lr) 18 Flow length,L(ft) 19 Tt=L/3600*V 0.01 20 Watershed or subarea T,or Tt Add TL in steps 6,11 and 19) 0.20 0.18 U.S. Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4: Graphical Peak Discharge Method Project: Northtown Block 1B Designed By: FGM, PE Date: 10/14/2016 Location: Route 29, East of Gander Mountain Checked By: SRC, PE Date: 10/14/2016 Check One: Pres X Developed X Drainage Area Drainage Area Drainage Area Drainage Area 1. Data Description Description Description Description DAA DA A Present) (Developed) Drainage Area (Am) in miles2= 0.0042 0.0042 Runoff curve number CN= 57.4 89.4 Time of concentration (Tc)= 0.20 0.18 Rainfall distribution type= II II Pond and swamp areas spread 0 0 throughout the watershed= 2. Frequency-years 1 2 1 2 3. Rainfall, P(24 hour)- inches 3.5 3.7 3.5 3.7 4. Initial Abstraction, la- inches 1.48 1.48 0.24 0.24 5. Compute la/P 0.42 0.40 0.07 0.06 6. Unit peak discharge,Qu-csm/in 550 575 1000 1000 7. Runoff,Q from Worksheet 2-inches 0.43 0.51 2.39 2.58 8. Pond and Swamp adjustment factor, F 1 1 1 1 9. Peak Discharge,Qp-cfs Through SWM where Qp=Qu Am Q Fp 1.00 1.24 Facility Watershed Summary Area,ac. CN 1-yr Flow,cfs 2-yr Flow,cfs DAA (Present)2.70 57.4 1.00 1.24 DA A(Developed) 2.70 89.4 0.95 1.17 Post-Development Routing Calculations Northtown Blk 1B- Early Grading Permit SWM Detention BasinFlow printout INPUT: Basin: Northtown Blk 1B- Early Grading Permit SWM Detention 5 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 452.00 535.00 0.0 454.00 1567.00 74. 5 456.00 2852.00 235.8 458.00 4324.00 499.7 459.00 4744.00 667.6 Start_Elevation(ft)452.00 vol . (cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 1.767 diameter or depth (in)18.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 450.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow Orifice area (sf) 0.110 diameter or depth (in) 4.500 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 452.000 multiple 1 discharge into riser outlet structure 2 Weir name: Riser diameter (in)30.000 side angle 0.000 coefficient 3. 300 invert (ft) 456.900 multiple 1 discharge into riser transition at (ft) 0.760 orifice coef. 0. 500 orifice area (sf) 4.909 Outlet structure 3 weir name: emergency spillway length (ft)25.000 side angle 0.000 coefficient 3.300 invert (ft) 457.900 multiple 1 discharge through dam Page 1 Northtown Blk 1B- Early Grading Permit SWM Detention 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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) 7.209 peak time (hrs)11.970 volume (cy) 867.901 Hydrograph 1 SCS name: 2-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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) 7.770 peak time (hrs)11.970 volume (cy) 935. 507 Hydrograph 2 SCS name: 10-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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)13.229 peak time (hrs)11.970 volume (cy) 1592.745 Hydrograph 3 SCS name: 100-yr, 24 hr Peak SCS Method Design Storm Area (acres) 2.700 CN 89.400 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)23. 546 peak time (hrs)11.970 volume (cy) 2834.926 Page 2 Northtown Blk 1B- Early Grading Permit SWM Detention OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr, 24 hr Peak SCS Method Design Storm inflow (cfs) 7.209 at 11.96 (hrs) discharge (cfs) 0.949 at 12 .32 (hrs) water level (ft) 456.781 at 12 .40 (hrs) storage (cy) 325.991 Hydrograph 1 Routing Summary of Peaks: 2-yr, 24 hr Peak SCS Method Design Storm inflow (cfs) 7.770 at 11.96 (hrs) discharge (cfs) 1.167 at 12.26 (hrs) water level (ft) 456.939 at 12.26 (hrs) storage (cy) 346.201 Hydrograph 2 Routing Summary of Peaks: 10-yr, 24 hr Peak SCS Method Design Storm inflow (cfs)13.229 at 11.96 (hrs) discharge (cfs)11.268 at 12.04 (hrs) water level (ft) 457.439 at 12.04 (hrs) storage (cy) 414.502 Hydrograph 3 Routing Summary of Peaks: 100-yr, 24 hr Peak SCS Method Design Storm inflow (cfs)23. 546 at 11.96 (hrs) discharge (cfs)21.141 at 12.02 (hrs) water level (ft) 457.986 at 12.02 (hrs) storage (cy) 497.449 Fri Oct 14 10:29:10 EDT 2016 Page 3 DEQ Virginia Runoff Reduction Method Water Quality Calculations Mitigated via the Best Management Practice of Preserving Open Spaces the Purchasing of Phosphorous Removal Credits) DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 J 2011 BMP Standards and Specifications 02013 Draft BMP Standards and Specifications Project Name: Northtown Block IB y, data input cells Date: 10/14/2016 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 0.60 0:60 Managed Turf(acres)-disturbed,graded for yards or other turf to be mowed/managed 1.03 03 Impervious Cover(acres) 2.19 2.19 Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 3.82 Constants Runoff Coefficients(Rv) h•:Annual Rainfall(inches) 43 A Soils B Soils C Soils D Soils 7arget 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(Ib/acre/yr) 0.41 Pj(unitless correction factor)0.90 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/yr) 3.69 LAND COVER SUMMARY POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment Volume p 1920Forest/Open Space Cover(acres)0:60 acre-ft) Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 8,360 Forest 16% TP Load(lb/yr) 5.26 TN load(ib/yr) Managed Turf Cover(acres) 1.03'. 37.60JlnfprmationalPprgsOnlvl Weighted Rv(turf) 0.20 Managed Turf 27% Impervious Cover(acres) 2.19 Rv(impervious) 0:95 Impervious 57% Site Area(acres) 3.82 Site Rv 0.60 .