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HomeMy WebLinkAboutWPO201600050 Calculations WPO VSMP 2016-07-19 BRIARWOOD PRIMARY RECREATION AREA STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations JULY 19, 2016 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 Communi `1Ewelnpment Department Date la 5//1 FIDE lr)Or) • 7.111._ --- 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 D2011 BMP Standards and Specifications :12013 Draft BMP Standards and Specifications -„ ..„ �Project Name: Briarwood-Primary Recreational Area VSMP Plan , ' data input cells Date: 7/19/2016 G -:«.,..x°1 constant values '. BMP Design Specifications List: 2011 Stds&Specs calculation cells Site Information anal moils 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 10.25 10:25 Managed Turf(acres)-disturbed,graded for d yards or other turf to be mowed/managed 7.83 783 5lmpervious Cover(acres) 1.79 1.79 Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 19.87 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(Ib/acre/yr) 0.41 Pi(tininess correction factor) 0.90 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/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) 10.25 0.2978 (acre-ft) Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) '...12,974 %Forest 52% TP Load(Ib/yr) 8.15 Managed Turf Cover(acres) 7.83 TN Load(Ib/yr) 58:31 (Informs i•n.I Pur••es Only) Weighted Rv(turf) 0.20 %Managed Turf 39% Impervious Cover(acres) '1.79 Rv(impervious) 0.95 %Impervious 9% Site Area(acres) 19.87 Site Rv 0.18 SCS TR-55 Calculations Soils Mapping /Source: NRCSWebSoi| SunxeyDn|ineOatabase\ Soils1.4 ,,,,, ,, , ' ,,,„, 1 t ,, , ,..... , ., , ..,„,, f 1 N, ... . ....:. ir.,.46,,,,,. : ,..,„ .., .,..„.., ..: , „„ „ „ . . , Table (3ource: NR[SVVeb3oi| 3urveyC)n|ineDatabase) AlVirginia .�� Map Unit Map Unit Name Percent Symbol of AOI 14D Chester loam, 15 to 25 15.696 percent slopes 19C Cullen loam, 7to15 54.696 percent slopes 76 Rtvervievw |oann 29.8% Totals for Area of Interest 100.0% Note: Soils' properties witin proposed disturbances are predominantly composed of hydrologic type 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 Primary Recreational Area Designed By: FGM,PE Date: 7/19/2016 Location: St.Ives Access Checked By:SRC,PE Date: 7/19/2016 Check One: Present X Des X 1.Runoff curve Number(CN) Drainage Soil name and Cover description CN(weighted)= rou Area Product of CN Calculated'S' Area hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ Description (Acres) x Area Value p (Appendix A) impervious;unconnected/connected impervious area ratio) total area DA A Impervious Areas 98 0.67 66.0 (Present) B Woods in Good Condition 55 10.54 579.7 57.9 7.26 Lawns in Good Condition(Approx.10%) 61 1.33 80.9 DA A Impervious Areas(Includes Offsite Ex.Imp.Areas) 98 1.79 175.3 (Developed) 8 Woods in Good Condition(conservatively estimated low) 55 3.29 181.0 64.7 5.46 Lawns in Good Condition(75%+Groundcover 61 7.46 455.1 DA A (Forest) B Woods in Good Condition 55 12.54 689.7 55.0 8.18 (Used only for Energy Balance Calculations; 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 0.45 0.53 1.51 DA A(Present) Runoff,Q-inches 0.74 0.84 2.04 DA A(Developed) Runoff,Q-inches 0.35 0.42 1.29 DA A(Forest) 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: Briarwood Primary Recreational Area Designed By: FGM,PE Date: 7/19/2016 Location: St.Ives Access Checked By:SRC,PE Date: 7/19/2016 Check One: Present X Developed X Check One: Tr X Tt Through subarea n/a DAA DAA DA A Segment ID: (Present) (Developed) (Forest) Sheet Flow:(Applicable to Tr only) Woods- 1 Surface description(Table 3-1) Dense Grass Dense Grass Light 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.4 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) 0.1 0.1 0.1 6 Compute T,=[0.007(n*L)°'e]/P205 s°° 0.12 0.12 0.17 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 475 475 475 9 Watercourse slope,s(ft/ft) 0.055 0.059 0.055 10 Average velocity,V(Figure 3-1)(ft/s) 3.8 4.0 3.8 11 Tt=L/3600*V 0.03 I 0.03 I 0.03 I Channel Flow: 12 Cross sectional flow area,a(ft2) 13 Wetted perimeter,P„,(ft) 14 Hydraulic radius,r=a/Pw(ft) 15 Channel Slope,s(ft/ft) 16 Manning's Roughness Coeff,n 17V=[1.49r213s05]/n 18 Flow length,L(ft) 19-ft=L/3600*V I 20 Watershed or subarea Tor T, (Add T,in steps 6,11 and 19) I 0.15 I 0.15 I 0.20 U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Briarwood Primary Recreational Area Designed By: FGM,PE Date: 7/19/2016 Location: St.Ives Access Checked By: SRC,PE Date: 7/19/2016 Check One: Present X DevelopecX Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description DAA DAA DAA (Present) (Developed) (Forest) Drainage Area(Am)in miles2= 0.0196 0.0196 0.0196 Runoff curve number CN= 57.9 64.7 55.0 Time of concentration(Tc)= 0.15 0.15 0.20 Rainfall distribution type= II II II Pond and swamp areas spread 0 0 0 throughout the watershed= 2.Frequency-years i 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.5 3.7 5.6 i 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 1.45 1.45 1.45 1.09 1.09 1.09 1.64 1.64 1.64 5.Compute la/P 0.41 0.39 0.26 0.31 0.29 0.19 0.47 0.44 0.29 6.Unit peak discharge,Qu-csm/in 650 675 825 800 825 850 450 500 725 7.Runoff,Q from Worksheet 2-inches 0.45 0.53 1.51 0.74 0.84 2.04 0.35 0.42 1.29 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Through where Qp=Qu Am Q Fp 5.74 7.03 24.39 The SWM Facility 3.05 4.07 18.38 WATERSHED SUMMARY Pre-Development Post-Development 1-year Flow, 2-year Flow, 10-year 1-year Flow, 2-year Flow, 10-year Flow, CN Area,ac. cfs cfs Flow,cfs CN Area,ac. cfs cfs cfs DA'A' 57.9 12.54 5.74 7.03 24.39 64.7 12.54 0.23 1.04 18.43 Post-Development Routing & Energy Balance Calculations Briarwood Primary Recreational SWM Facility BasinFlow printout INPUT: Basin: Briarwood Primary Recreational SWM Facility 3 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 378.00 13875.00 0.0 380.00 17117.00 1145.8 382.00 20586.00 2540.2 Start_Elevation(ft) 378.00 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) 376.420 multiple 1 discharge out of riser Outlet structure 1 orifice name: Low-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0. 500 invert (ft) 378.000 multiple 1 discharge into riser Outlet structure 2 Weir name: Riser Top diameter (in) 30.000 side angle 0.000 coefficient 3. 300 invert (ft) 379. 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) 60.000 side angle 0.000 coefficient 3. 300 invert (ft) 380. 500 multiple 1 discharge through dam Page 1 Briarwood Primary Recreational SWM Facility 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr peak 24-hr SCS Method Design Storm Area (acres) 12 . 540 CN 64.700 Type 2 rainfall , P (in) 3. 500 time of conc. (hrs) 0.1500 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 10.772 peak time (hrs) 11.930 volume (cy) 1242.867 Hydrograph 1 SCS name: 2-yr peak 24-hr SCS Method Design Storm Area (acres) 12. 540 CN 64.700 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.1500 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 12 . 322 peak time (hrs) 11.930 volume (cy) 1421.656 Hydrograph 2 SCS name: 10-yr peak 24-hr SCS Method Design Storm Area (acres) 12. 540 CN 64.700 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1500 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 29.789 peak time (hrs) 11.930 volume (cy) 3436.871 Hydrograph 3 SCS name: 100-yr peak 24-hr SCS Method Design Storm Area (acres) 12. 540 CN 64.700 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1500 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 69. 556 peak time (hrs) 11.930 volume (cy) 8024.960 Page 2 Briarwood Primary Recreational SWM Facility OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr peak 24-hr SCS Method Design Storm inflow (cfs) 10.762 at 11.94 (hrs) discharge (cfs) 0.233 at 13. 52 (hrs) water level (ft) 379. 502 at 13.62 (hrs) storage (cy) 837.797 Hydrograph 1 Routing Summary of Peaks: 2-yr peak 24-hr SCS Method Design Storm inflow (cfs) 12 . 311 at 11.94 (hrs) discharge (cfs) 1.036 at 12 . 56 (hrs) water level (ft) 379. 598 at 12 . 54 (hrs) storage (cy) 896.043 Hydrograph 2 Routing Summary of Peaks: 10-yr peak 24-hr SCS Method Design Storm inflow (cfs) 29. 761 at 11.94 (hrs) discharge (cfs) 18.432 at 12.06 (hrs) water level (ft) 380.628 at 12 .06 (hrs) storage (cy) 1556. 389 Hydrograph 3 Routing Summary of Peaks: 100-yr peak 24-hr SCS Method Design Storm inflow (cfs) 69.491 at 11.94 (hrs) discharge (cfs) 67. 350 at 11.98 (hrs) water level (ft) 380.939 at 11.98 (hrs) storage (cy) 1768.626 Tue Jul 19 13:40:48 EDT 2016 Page 3 it VAC ;5-F10 -64 ‘i FoM,4E 15p-v 1(k90D '?(Z -�.�tlkP`y SCC-T4ON b: C.KAN (- Q o� R-1.P 5w14' Qt-AN ttwATE(( StiAIL& 'RC-c.t? e 3rd A .5\IDAMwATe '�(�51+� �n�cErscaRi�a s�R Co>JvElpi•IC>< s'Is; . t shAu- Mee-T -11-t , CR' 1-E-P-itcl SwSosyss v 1;a 3 or- 7 -t5 SUOSEC'iqN,.,'t 'F SECT-.IDN .3,a- No CONO27 DN St-°1-1- QOEV, b€ EA-TER Tk QUE-Oev. !a°& S\\au. aoe,. �3t t�UNb�IZ \ �� 'R a�z( a To 5S [-ESs TKR+N► 'Tf-_t- cA tau t.�t TE-0 E �'Q vF+�-4.oN (Q ,e�sr x.��R 1/Rv oE"E��o Mrtxz.rku,� 3 aev = 1��-lownS3t E � 5 y� NFdtesr� Qt�ISt SCS -viz.-.SS v�KtcsriT 1 a c En3TLEa0 69s,ck{S�i- Qep1c ScHAR.6E � 9 10 V�,Eti�t�o ik\I (\eVR i �� S ,`0, j 5 .5C-5 TA'55 WaT3ON o�- C3 05)Cp.3 ) , 5tiovv>v ow S-5 7-R-5S wOf11251-tE r a sf 0.'1 LI 5t� , 4, e,)T-4-T,.€0`liZuNOFt ' 1,L .;:k3/s MRS. &p`u, A.0 o w R-DLE- — Q QRs- - 5,'-vi Y5 x - (:).1.3 't-VS (1-SSS 11Wa 'T(cE N ''` Qct,, Plt:awABCt •TcNJ Scu"A2i05-)