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HomeMy WebLinkAboutWPO201600054 Calculations 2016-10-10 BRIARWOOD PHASE VI STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations AUGUST 12, 2016 APPROVED by the Albemarle County Community Develop nt epartment Date o File 0/ 00 PREPARED BY: COLLINS °' NGINEERING 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 (Mitigated via the Best Management Practice of Preserving Open Spaces) DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 own BMP Standards and Specifications 02013 Draft IMP Standards and Specifications Project Name: Brlarwood Phase VI VSMP Plan -_— CLEAR ALL data input cells Date: 8/12/2016 constant values BMP Design Specifications List. 2011 Stds&Specs nkulatbn 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 8 77 8 77 Managed Turf(acres)--disturbed,graded for yards or other turf to be mowed/managed 6.62 6.62 Impervious Cover(acres) 1.53 1 53 *Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 16 92 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(lb/yr) 0.00 ** TP LOAD REDUCTION NOT REQUIRED LAND COVER SUMMARY--POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment Volume Forest/Open Space Cover(acres) 8 77 0 2534 (acre-ft) Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 11,037 %Forest 52% TP Load(lb/yr) 6 93 Managed Turf Cover(acres) 6.62 TN Load(Ib/yr) 49 61 (informational Purposes only) Weighted Rv(turf) 0 20 %Managed Turf 39% Impervious Cover(acres) 1 53 Rv(impervious) 095 %Impervious 9% Site Area(acres) 16.92 Site Rv 0.18 SCS TR-55 Calculations U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2 Runoff Curve Number and Runoff Project Briarwood Phase VI VSMP Plan Designed By FGM,PE Date: 8/12/2016 Location Sunset Drive Extension Checked By SRC,PE Date. 8/12/2016 Check One Present X Developed X 1 Runoff curve Number(CN) Cover description Drainage Soil name and CN(weighted)= (Cover type,treatment,and hydrologic condition, Area Product of Calculated Area hydrologic group CN total product/ Description (Appendix A) percent impervious,unconnected/connected (Acres) CN x Area total area 'S'Value impervious area ratio) DA A&B Impervious Areas 98 0.31 30 7 B Woods in Good Condition 55 2 76 151 6 59 9 6.69 (Present) Lawns in Good Condition 61 145 88.5 DA A Impervious Areas 98 1.34 131 3 B Woods in Good Condition 55 016 8.8 81 3 2 31 (Developed) Lawns in Good Condition(75%+Groundcover) 61 0 90 54 9 DA B Impervious Areas 98 0.35 34 6 B Woods in Good Condition 55 1 15 63 3 63.9 5 65 (Developed) Lawns in Good Condition(75%+Groundcover) 61 0.62 37 6 DA A&B B Woods in Good Condition 55 4.52 248 6 55 0 8.18 (Forest) (Used only for Energy Balance Calculations) 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 0.53 0 62 DA A&B(Present) Runoff,Q-inches 173 1.89 DA A(Developed) Runoff,Q-inches 0 70 0.80 DAB(Developed) Runoff,Q-inches 0.35 0 42 DA A&B(Forest) U S Department of Agriculture Natural Resources Conservation Service FL-ENG-21A 06/04 TR 55 Worksheet 3 Time of Concentration(T)or Travel Time(T,) Project Briarwood Phase VI VSMP Plan Designed By. FGM,PE Date: 8/12/2016 Location. Sunset Drive Extension Checked By:SRC,PE Date• 8/12/2016 Check One: Present X Developed X Check One: T, X T, Through subarea n/a DAA&B DAA DAB DAA&B Segment ID (Present) (Developed) (Developed) (Forest) Sheet Flow (Applicable to Tc only) Woods-Light 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass Underbrush 2 Manning's roughness coeff,n(Table 3-1 0 24 0 24 0 24 0.4 3 Flow length,L(total L<100)(ft) 100 100 100 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.1 0.1 0.12 0 1 6 Compute T,=[0.007(n•L)°8]/P2°5 s°'4 0.12 0.12 0.11 0.17 Shallow Concentrated Flow 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 370 180 325 370 9 Watercourse slope,s(ft/ft) 0 186 0 150 0 240 0.186 10 Average velocity,V(Figure 3-1)(ft/s) 6.8 6.2 7.9 6.8 11 T,=L/3600*V 002 001 001 002 Channel Flow. 12 Cross sectional flow area,a(ft2) E 3 = o 13 Wetted perimeter,P,(ft) a o 14 Hydraulic radius,r=a/P(ft) C 0 15 Channel Slope,s(ft/ft) 5 E 16 Manning's Roughness Coeff,n o v 17V=[1.49r2/3s05]/n o 0 18 Flow length,L(ft) N 19 Tt=L/3600`V 0 01 20 Watershed or subarea T,or Tt (Add T,in steps 6,11 and 19) 0.14 0.14 0.12 0.19 U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Bnarwood Phase VI VSMP Plan Designed By: FGM,PE Date: 8/12/2016 Location: Sunset Drive Extension Checked By: SRC,PE Date• 8/12/2016 Check One: Present X Develop X Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description DAA&B DAA DAB DAA&B (Present) (Developed) (Developed) (Forest) Drainage Area(Am)in miles2= 0.0071 0.0038 0 0033 0.0071 Runoff curve number CN= 59.9 81.3 63.9 55.0 Time of concentration(Tc)= 0.14 0.14 0.12 0.19 Rainfall distribution type= II II II II Pond and swamp areas spread 0 0 0 0 throughout the watershed= 2.Frequency-years 1 2 1 2 1 2 1 2 3.Rainfall,P(24 hour)-inches 3.5 3.7 3 5 3.7 3.5 3.7 3.5 3.7 4.Initial Abstraction,la-inches 1.34 1.34 0 46 0.46 1.13 1.13 1.64 1.64 5.Compute la/P 0.38 0.36 0.13 0.12 0.32 0.31 0.47 0.44 6.Unit peak discharge,Qu-csm/in 725 750 900 900 850 875 450 525 7.Runoff,Qfrom Worksheet 2-inches 0.53 0.62 1.73 1.89 0.70 0.80 0.35 0.42 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Thru where Qp=Qu Am Q Fp 2.70 3.26 SWM Facility 1.97 2.33 1.10 1.54 WATERSHED SUMMARY Pre-Development Post-Development CN Area, 1-year 2-year CN Area, 1-year 2-year ac. Flow,cfs Flow,cfs ac. Flow,cfs Flow,cfs DAA&B 59.9 4.52 2.70 3.26 81.3 2.40 0.11 0.11 63.9 2.12 0.20 0.88 Total= 4.52 0.31 0.99 Post-Development Routing & Energy Balance Calculations Briarwood SWM Facility A- Phase VI BasinFlow printout INPUT: Basin: Briarwood SWM Facility A- Phase VI 5 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 418.00 740.00 0.0 420.00 1568.00 83.6 422.00 2590.00 236.0 424.00 3747.00 469.4 426.00 5025.00 793.1 Start_Elevation(ft) 418.00 vol . (cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 416.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low-Flow orifice area (sf) 0.012 diameter or depth (in) 1.500 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 418.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Riser Standpipe diameter (in) 30.000 side angle 0.000 coefficient 3.300 invert (ft) 423.500 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 75.960 coefficient 3.300 invert (ft) 424.500 multiple 1 discharge through dam Page 1 Briarwood SWM Facility A- Phase VI 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr SCS Peak 24-hr Design Storm Area (acres) 2.400 CN 81.300 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.1400 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 4.934 peak time (hrs) 11.935 volume (cy) 557.865 Hydrograph 1 SCS name: 2-yr SCS Peak 24-hr Design storm Area (acres) 2.400 CN 81.300 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1400 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 5.402 peak time (hrs) 11.935 volume (cy) 610.807 Hydrograph 2 SCS name: 10-yr SCS Peak 24-hr Design Storm Area (acres) 2.400 CN 81.300 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1400 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 10.123 peak time (hrs) 11.935 volume (cy) 1144.675 Hydrograph 3 SCS name: 100-yr SCS Peak 24-hr Design Storm Area (acres) 2.400 CN 81.300 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1400 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 19.453 peak time (hrs) 11.935 volume (cy) 2199.601 Page 2 Briarwood SWM Facility A- Phase VI OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS Peak 24-hr Design Storm inflow (cfs) 4.913 at 11.94 (hrs) discharge (cfs) 0.112 at 14.04 (hrs) water level (ft) 423.232 at 15.52 (hrs) storage (cy) 369.592 Hydrograph 1 Routing Summary of Peaks: 2-yr SCS Peak 24-hr Design Storm inflow (cfs) 5.379 at 11.94 (hrs) discharge (cfs) 0.114 at 13.00 (hrs) water level (ft) 423.465 at 13.78 (hrs) storage (cy) 398.501 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS Peak 24-hr Design Storm inflow (cfs) 10.080 at 11.94 (hrs) discharge (cfs) 8.783 at 12.00 (hrs) water level (ft) 423.982 at 12.00 (hrs) storage (cy) 466.853 Hydrograph 3 Routing Summary of Peaks: 100-yr SCS Peak 24-hr Design Storm inflow (cfs) 19.369 at 11.94 (hrs) discharge (cfs) 16.942 at 12.00 (hrs) water level (ft) 424.610 at 12.00 (hrs) storage (cy) 558.131 Fri Aug 12 10:38:58 EDT 2016 Page 3 Briarwood SWM Facility B- Phase VI BasinFlow printout INPUT: Basin: Briarwood SWM Facility B- Phase VI 4 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 404.00 76.00 0.0 406.00 531.00 19.9 408.00 1116.00 79.6 410.00 1804.00 186.8 Start_Elevation(ft) 404.00 vol . (cy) 0.00 4 Outlet Structures Outlet structure 0 orifice name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 403.500 multiple 1 discharge out of riser Outlet structure 1 orifice name: Low-Flow orifice area (sf) 0.022 diameter or depth (in) 2.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 404.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Riser Standpipe diameter (in) 30.000 side angle 0.000 coefficient 3.300 invert (ft) 407.900 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 75.960 coefficient 3.300 invert (ft) 408.900 multiple 1 discharge through dam Page 1 Briarwood SWM Facility B- Phase VI 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr SCS Peak 24-hr Design Storm Area (acres) 2.120 CN 63.900 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 1.822 peak time (hrs) 11.922 volume (cy) 199.483 Hydrograph 1 SCS name: 2-yr SCS Peak 24-hr Design Storm Area (acres) 2.120 CN 63.900 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 2.091 peak time (hrs) 11.922 volume (cy) 228.845 Hydrograph 2 SCS name: 10-yr SCS Peak 24-hr Design Storm Area (acres) 2.120 CN 63.900 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 5.137 peak time (hrs) 11.922 volume (cy) 562.312 Hydrograph 3 SCS name: 100-yr SCS Peak 24-hr Design Storm Area (acres) 2.120 CN 63.900 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 12.134 peak time (hrs) 11.922 volume (cy) 1328.214 Page 2 Briarwood SWM Facility B- Phase VI OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS Peak 24-hr Design storm inflow (cfs) 1.819 at 11.92 (hrs) discharge (cfs) 0.202 at 12.16 (hrs) water level (ft) 407.911 at 12.16 (hrs) storage (cy) 76.004 Hydrograph 1 Routing Summary of Peaks: 2-yr 5C5 Peak 24-hr Design storm inflow (cfs) 2.087 at 11.92 (hrs) discharge (cfs) 0.878 at 12.06 (hrs) water level (ft) 407.991 at 12.06 (hrs) storage (cy) 79.229 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS Peak 24-hr Design Storm inflow (cfs) 5.128 at 11.92 (hrs) discharge (cfs) 4.986 at 11.94 (hrs) water level (ft) 408.225 at 11.94 (hrs) storage (cy) 89.220 Hydrograph 3 Routing Summary of Peaks: 100-yr SCS Peak 24-hr Design Storm inflow (cfs) 12.113 at 11.92 (hrs) discharge (cfs) 10.624 at 11.98 (hrs) water level (ft) 408.784 at 11.98 (hrs) storage (cy) 115.572 Fri Aug 12 10:36:02 EDT 2016 Page 3 &Ui Arno vh_NEE�. 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