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HomeMy WebLinkAboutWPO201500085 Calculations Stormwater Management Plan 2016-01-27 CHARLOTTESVILLE SELF STOARAGE AT CROZET STORMWATER MANAGEMENT AMENDMENT CALCULATIONS PACKET Date of Calculations January 27, 2016 PREPARED BY: COLLINS 200 GARRETT STREET,SUITE K CHARLOTTESVILLE,VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations Albemarle County,Virginia(VA003) Map Map Unit Name Percent Unit of AOI Symbol 4D Ashe loam, 15 to 25 percent 2.0% slopes 3783 Hayesville clay loam,2 to 7 64.1% percent slopes,severely eroded 91 Urban land 33.9% Totals for Area of Interest 100.0% NOTE: Per NRCS Web Soil Survey Online Database,the soils' properties witin the proposed disturbances are predominantly composed of hydrologic 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: Charlottesville Self Storage at Crozet Designed By:FGM,PE Date: 1/27/2016 Location: 5390 Three Notched Rd,Crozet,VA Checked By:SRC,PE Date: 1/27/2016 Check One: Present X Dev X 1.Runoff curve Number(CN) Draina eArea Soil name and Cover description CN(weighted)= g Area Product of CN Calculated'S' Descri tion hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ p (Appendix A) impervious;unconnected/connected impervious area ratio) (Acres) x Area total area Value DAA Impervious Areas 98 1.51 148.0 (Pre-Develop) B Woods in Good Condition(Appox.1/2of Remaining Area) 55 0.10 5.5 93.3 0.72 Lawns in Good Condition(Appox.1/2of Remaining Area) 61 0.10 6.1 DA A Impervious Areas 98 1.46 143.0 (Developed) B Woods in Good Condition 55 0.00 0.0 92.6 0.80 Lawns in Good Condition(75%+Groundcover) 61 0.25 15.3 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 3.5 3.7 5.6 n/a Runoff,Q-inches 2.77 2.96 4.82 DAA(Pre-Develop) Runoff,Q-inches 2.69 2.88 4.74 DAA(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Tc)or Travel Time(Ti) Project: Charlottesville Self Storage at Crozet Designed By: FGM,PE Date: 1/27/2016 Location: 5390 Three Notched Rd,Crozet,VA Checked By:SRC,PE Date: 1/27/2016 Check One: Present X Developed X Check One: T, X Tt Through subarea n/a DAA DA A Segment ID: (Pre-Develop) (Developed) 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)0.8]/P205 s0.4 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) 11Tt=L/3600*V Channel Flow: 12 Cross sectional flow area,a(ft2) 13 Wetted perimeter,PW(ft) 14 Hydraulic radius,r=a/PH,(ft) 15 Channel Slope,s(ft/ft) 16 Manning's Roughness Coeff,n 17V=[1.49r2/3s03)/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) 0.10 0.10 Note:Most Conservative Tc=0.10 hrs. U.S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Charlottesville Self Storage at Crozet Designed By: FGM,PE Date: 1/27/2016 Location: 5390 Three Notched Rd,Crozet,VA Checked By: SRC,PE Date: 1/27/2016 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description DAA DA A (Pre-Develop) (Developed) Drainage Area(Am)in miles2= 0.0027 0.0027 Runoff curve number CN= 93.3 92.6 Time of concentration(Tc)= 0.10 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 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la-inches 0.14 0.14 0.14 0.16 0.16 0.16 5.Compute la/P 0.04 0.04 0.03 0.05 0.04 0.03 6.Unit peak discharge,Qu-csm/in 1000 1000 1000 1000 1000 1000 7.Runoff,Q from Worksheet 2-inches 2.77 2.96 4.82 2.69 2.88 4.74 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Through where Qp=Qu Am Q Fp 7.39 7.91 12.89 Underground Pipe Nore:Most conservative Qu value is 1,000 csm/in. WATERSHED SUMMARY 1-year Flow, 2-year Flow, 10-year CN Area,ac. cfs cfs Flow,cfs DAA(Pre-Develop) 93.3 1.71 7.39 7.91 12.89 DAA(Developed) 92.6 1.71 5.82 6.24 9.59 Post-Development Routing Calculations Charlottesville Self Storage at Crozet UGD Routing BasinFlow printout INPUT: Basin: Charlottesville Self Storage at Crozet- underground Detention Routing 0 Contour Areas Elevation(ft) Area(sf) Computed Vol . (cy) 1 Storage Pipes Storage pipe 0 name: underground Detention diameter (in) 30.000 length (ft) 98.150 invert (ft) 639.960 angle 0.287 volume (cy) 17.844 Start_Elevation(ft) 639.96 Vol . (cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifice area (sf) 0.349 diameter or depth (in) 8.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 639.960 multiple 1 discharge into riser Outlet structure 1 Culvert name: Barrel multiple 1 discharge out of riser D (in) 30.000 h (in) 0.000 Length (ft) 11.980 Slope 0.010 Manning's n 0.010 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 639.960 outlet structure 2 Orifice name: Emergency Spillway Simulation area (sf) 2.454 diameter or depth (in) 21.213 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 641.210 multiple 1 discharge into riser Page 1 Charlottesville Self Storage at Crozet UGC Routing Outlet structure 3 Weir name: STR. 4- Access diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 644.700 multiple 1 discharge into riser 3 Inflow Hydrographs Hydrograph 0 SCS name: 1- Yr. Storm- SCS Method Area (acres) 1.710 CN 92.600 Type 2 rainfall , P (in) 3.500 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) 5.848 peak time (hrs) 11.917 volume (cy) 619.175 Hydrograph 1 SCS name: 2- Yr. Storm- SCS Method Area (acres) 1.710 CN 92.600 Type 2 rainfall , P (in) 3.700 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) 6.267 peak time (hrs) 11.917 volume (cy) 663.469 Hydrograph 2 SCS name: 10- Yr. Storm- SCS Method Area (acres) 1.710 CN 92.600 Type 2 rainfall , P (in) 5.600 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) 10.292 peak time (hrs) 11.917 volume (cy) 1089.657 Page 2 Charlottesville Self Storage at Crozet UGD Routing OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1- Yr. Storm- SCS Method inflow (cfs) 5.821 at 11.92 (hrs) discharge (cfs) 5.821 at 11.92 (hrs) water level (ft) 641.991 at 11.92 (hrs) storage (cy) 13.593 Hydrograph 1 Routing Summary of Peaks: 2- Yr. Storm- SCS Method inflow (cfs) 6.238 at 11.92 (hrs) discharge (cfs) 6.239 at 11.92 (hrs) water level (ft) 642.042 at 11.92 (hrs) storage (cy) 14.006 Hydrograph 2 Routing Summary of Peaks: 10- Yr. Storm- SCS Method inflow (cfs) 10.244 at 11.92 (hrs) discharge (cfs) 9.594 at 11.92 (hrs) water level (ft) 642. 559 at 11.92 (hrs) storage (cy) 17.260 wed Jan 27 10:41:05 EST 2016 Page 3 Virginia Runoff Reduction Method Calculations Virginia Runoff Reduction Method ReDevelopment Worksheet-v2.8-June 2014 To be used w/2011 BMP Standards and Specifications Site Data Project Name:Charlottesville Self Storage at Crozet - Date:1/27/16 data input cells _ -- calculation cells constant values 1 Post-ReDevelopment Project&Land Cover Information Total Disturbed Acreage Constants Annual Rainfall(inches) ® Target Rainfall Event(inches) 1.00 --- Phosphorus EMC(mg/L) 0.26 Nitrogen EMC(mgiL) 1.86 Target Phosphorus Target Load(lb/acre/yr) 0.41 Pj 0.90 I 1 Pre-ReDevelopment Land Cover(acres) -"- A soils B Soils C Soils D Sulk Totals ForesVOpen 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 0.20 0.00 0.00 0.20 _ Impervious Cover(acres) 0.00 _ 1.51 0.00 0.00 1.51 Total 1.71 Post-ReDevelopment Land Cover(acres) J 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 0.25 0.00 0.00 _ 0.25 _ Impervious Cover(acres) 0.00 1.46 0.00 0.00 1.46 Total 1.71 Area Check Oka Oka Oka Oka 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 Listed Adjusted' Land Cover Summary Land Cover Summary Pre-ReDevelopment Post-ReDevelopment Post-ReDevelopment New Impervious Forest/Open Space 1 ForesVOpen Space Cover(acres) 0.00 0.00 Cover(acres) 0.00 Composite Composite Rv(forest) _ 0.00 0.00 _ Rv(forest) 0.00 %Forest 0% 0% _ %Forest 0% Managed Turf Managed Turf Cover(acres) 0.20 0.20 Cover(acres) 0.25 Composite Rv(turf) 0.20 0.20 Com site Rv(turf) 0.20 %Managed Turf 12% 12% '%Managed Turf 15% ReDev.Impervious Impervious Cover(acres) 1.51 1.51 Cover(acres) 1.46 New Impervious Cover(acres), 0.00 Rv(impervious) 0.95 0.95 Rv(impervious) 0.95 Rv(impervious) 0.95 %Impervious 88% 88% %Impervious 85% %Impervious Check Area Total ReDev.Site Total Site Area(acres) 1.71 1.71 Area(acres) 1.71 Total New Dev.Site Area(acres) 0.00 Site Rv 0.86 0.86 ReDev.Site Rv 0.84 New Dev.Site Rv 0.95 Post- ReDevelopment Treatment Volume Post-Development Treatment Pre-Development Treatment Volume(acre-ft) 0.1229 0.1229 (acre-ft) 0.1198 Volume(acre-ft) 0.0000 Post- ReDevelopment Pre-Development Treatment Volume(cubic Treatment Volume Post-Development Treatment feet) 5,352 5,352 (cubic feet) 5,216 Volume(cubic feet) 0 ost- ReDevelopment Pre-Development Load(TP)(lb/yr) 3.36 3.36 Load(TP)(Ib/yr) 3.28 Post-Development Load(TP)(lb/yr) 0.00 'Adjusted Land Cover Summary reflects the pre redevelopment I Maximum%Reduction Required Below land cover minus the pervious land cover(forest/open space or Pre-ReDevelopment Load 20% managed turf)acreage proposed for new impervious cover.The I - adjusted total acreage is consistent with the Post Redevelopment TP Load Reduction Required for TP Load Reduction Required for acreage(minus the acreage of new impervious cover).The load Redeveloped Area(Ib/yr) 0.59 New Impervious Area(lb/yr) 0.00 reduction requriement for the new impervious cover to meet the new I , development load limit is computed in Column I. Total Load Reduction Required (lb/yr) 0.59 Pre-Development Load(I N)(Ib/yr) i 24.061 Post-Development Load(TN)(lb/yr) . Site Results . . . D.A.A D.A.B : D.A.C D.A.D . DA.E AREA CHECK IMPERVIOUS COVER 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED 0.00 0.00 0.00 0.00 0.00 OK. TURF AREA 000 0.00 0.00 0.00 0.00 OK. TURF AREA TREATED 0.00 000 0.00 0.00 0.00 OK. AREA CHECK cm Ok OK. OK. OK. . . . . : . . . Phosphorous -----4 • j. TOTAL PHOSPHOROUS LOAD REDUCTION REQUIRED(LB(YEAR)] 0.901 . . . . RUNOFF REDUCTION(cf) 0 PHOSPHOROUS LOAD REDUCTION ACHIEVED(LB/YR) BOO ADJUSTED POST-DEVELOPMENT PHOSPHOROUS LOAD(TP)(lb/yr)! 3.281 ' REMAINING PHOSPHOROUS LOAD REDUCTION(LB/YR)NEEDED 0.59: ' , Nitrogen(for Information purposes) : . RUNOFF REDUCTION(ct) 0- . NITROGEN LOAD REDUCTION ACHIEVED(LB/YR) 0.00. ' . ' , . ' . ADJUSTED POST-DEVELOPMENT NITROGEN LOAD(TP)(1b/yr)) 23.45f ' . • Stormwater Quality & Quantity Compliance Summary I ( 1v C 4-1AALCR1 ESVI LL W M - W A A. 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