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HomeMy WebLinkAboutWPO201700052 Calculations WPO VSMP 2018-06-19 DUNLORA OVERLOOK STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations September 22, 2016 Revised January 3, 2018 Revised March 7, 2018 Revised June 19, 2018 PREPARED BY: COLLINS ENGINESPING 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 DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet-Version 3.0 E 2011 BMP Standards and Specifications 02013 Draft BMP Standards and Specifications Project Name:DOVER) 11 data input cellse Date: 9/13/2016(APPROVED)8/22/17-REVISED constant values BMP Design Specifications List:2011 Stds&Specs calculation tells Site Information final results Post-Development Project(Treatment Volume and Loads) Land Cover (acres) A Soils B Soils C Soils D Soils I Totals Forest/Open Space(acres)--undisturbed, protected forest/open space or reforested land 1.09 1.09 f Managed Turf(acres)--disturbed,graded for yards or other turf to be mowed/managed 4.29 i 4.29 Impervious Cover(acres) 3.24 3.24 •Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 8.62 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) 5.52 LAND COVER SUMMARY--POST DEVELOPMENT Land Cover Summary Treatment Volume and Nutrient Loads Treatment Volume Forest/Open Space Cover(acres) 1.09 0.3307 (acre-ft) Weighted Rv(forest) 0.03 Treatment Volume(cubic feet) 14,406 %Forest 13% TP Load(lb/yr) 9.05 I Managed Turf Cover(acres) 4.29 IlnformationalTN Load Puro(Ib/yr) oses Only) 64.75 Weighted Rv(turf) 0.20 %Managed Turf 50% Impervious Cover(acres) 3.24 Rv(impervious) 0.95 %Impervious 38% Site Area(acres) 8.62 Site Rv 0.46 VR _ _omgiaroe_Spre.alweLv3 052016-AMENDMENT2 DA.A Drainage Area A CLEAR BMP AREAS Drainage Mea A Land Cover(acres) A Soils B Soils C Soils D Sails Totals Land Cover to Forest/Open Space(Ares) 0.00 0.00 000 Managed turf(Ares) 1.8S 1.85 0.20 Impervious Lover(ares) 2.14 ( 2.14 0.95 Total Phosphorus Available for Removal in D.A.A(lb/yr) S.40 Total 3.99 Post Development Treatment Volume in D.A A INa) 8.723 Stormwater Best Management Practices(RR=Runoff Reduction) -Select from dropdoW,lists-- Phosphorus Untreated Runoff Managed Turf Impervious Volume FromRemaining Total BMP Phosphorus my oru Phosphorus Remaining Runoff Load from Ph h s Downstream Practice to be Practice Reduction Credit Area Cover Credit Upstream Runoff Treatment Removal o Removed By Phosphorus EmployedCredit(%) (aces) Area(acres) pratlre(ft') Rnduction(N) Oniome(Nal Volume 1NalEKRnR cY1%) PrUapstiea(%) PraLoctacdetIlbl pracice(lb) Load(lb) 1.Vegetated Roof(RR) ,a vegetated Roof Nl(Spec 45) 45 0 0 0 0 000 000 0.00 .b Vegetated Roof 02(Spec 45) 60 0 0 0 0.00 0.00 0.00 .Rooftop Disconnection(RR) 1.a.Simple Disconnection to 4/S Soils 50 0 0 0 0 0.00 0.110 000 0.00 (Spec NI) Ib.Simple Disconnection so fir/Soils 25 0 0 0 0 0 000 0.00 0.00 000 (Spec Nl) 2.c.To Soil Amended Finer Path as per SO specifications lesatalg UD soils)(Spec alai 0 0 0 0 0 000 000 0.00 0.00 h.TO Ory Well or French Drain 02, 50 0 0 0 25 000 000 000 0-00 be.To-lnfilretion 01(Spec 481 O Dry Well or French Ofain 42, 90 0 0 0 25 0.00 000 0.00 0.00 Micro-Infiltration az(Sper N8) 21.to Rain Garden Ol, 40 0 0 0 0 25 000 0.00 000 0.00 Micro-Noretention rel(Spec N9) 28.To Rain Garden fa, 80 0 0 0 50 0.00 000 000 000 Micro-Biorelention 02(Spec.1 2.5.To Rainwater Harvesting(Spec 461 0 0 0 0 0 0 0.00 0.00 0.00 0.00 M.To Stormwater Planter, W 0 0 0 0 25 0.00 000 000 000 Urban Bioretention(Spec a0 Appendix A) S.Permeable Pavement(RR) 3.a Permeable Pavement NI(Spec all 45 0 0 0 0 25 0.00 0.00 0.00 000 3.b.Permeable Pavement.2(Spec PI) 25 0 0 0 25 0.00 000 OM Grass Channel(OR) 4.a.Grits Channel A/B Soils(Spec 43) 20 0 0 0 0 15 000 000 0.00 000 4.6.Grass Channel U0 Soils(Spec 43) 10 0 0 0 0 15 000 000 0.00 0.00 lac.Goss Channelwdth Compost Amended Sails 30 0 0 0 0 15 0.00 000 0.00 0.00 asp r specs(see Spec M) .Dry Swale(RR) Ga.ay Swale 11(Spec 5101 40 0 0 0 0 20 000 000 000 0.00 • 5.b.Dry Swale. 510) 60 0 0 0 0 40 000 0.00 090 0.00 6.Bioretention(RR) 6.a.Bieenhon 11 or Micro- tent nNla 44 0 0 0 0 25 0.00 0.00 0.00 000 urban alpretennon(Spec x91 io St.8loretenno n 02 or Micro-Noretention 42 (Spec N9) 80 185 2.14 0 6,928 1,745 8,223 50 0.00 5.47 493 0.55 7.Infiltration(RR) ].a.Infiltration 4l(Spec 48) SO 0 0 0 0 05 000 000 000 000 7.b.Infiltrationxz(spec Ne) 90 0 0 0 0 zs 0.110 0.00 000 00o 8.Extended Detention Pond(RR) 0.a.ED N1(Spec P151 0 0 0 0 0 15 0.0 000 000 000 8.14E002(Spec 0151 IS 0 0 0 0 15 000 090 000 OOo '.Sheetflow to Filter/Open Spare(RR) 9.a.Sheetfluw to Conservation Area.Alt Soils 0 75 0 0 0 0.000 O. 0.00 000 0.00 (Spec p2l 9.6.Sheetilow to Conservation Area,UD Sails50 0 0 0 0 0 000 0.00 000 0.00 (Spec PO 9.c.SheetMw to Vegetated Filter Strip,A Soils or Compost Amended 8/C/D Soils 50 0 0 0 0 0 0.00 000 0.00 0.00 (Spec N2 8 4N) TOTAL IMPERVIOUS COVER TREATED(ad 2.14 AREA CHECK:OK. TOTAL MANAGED TURF AREA TREATED)ac) 1.85 AREA CHECK:OK. TOTAL RUNOFF REDUCTION IN D.A.A(ft) 6,978 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A.A(Ib/yr) 5.48 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN OA A(1b/yr) 4.93 TOTAL PHOSPHORUS REMAINING AFTER APPLYING RUNOFF REDUCTION PRACTICES IN D.A.A(lb/yr) 0.55 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS 10126/19/2018 11 2a AM 0,0.00 VRRM_New_Compliance_SpreadsheeL03_052016-AMENDMENT2 DA, 10.Wet Swale(no RR) 10.0 Wet Swale al(5,P11) 0 0 0 0 0 20 0.00 0.00 0.00 0.00 urn Wet Swale aa)saac an0 0 0 0 0 40 0.00 0.00 0.00 000 II Filtering Practices Inn RR) 110.Filtering Practice al(Spec R12) 0 0 0 0 0 60 0.00 0.00 0.00 0.00 11.6.Filtering P1.0100#2(Spec 1112) 0 0 0 0 0 65 0.00 0.00 0.00 0.00 I. .nn.tr acted Wetland Inn kr1 12.a.CorreOwted Wetland#1(Spec 013) 0 0 0 0 0 50 0.00 0.00 0.00 0.00 Constructed Wetland a2)Spec ala) 0 IIA Constructed 0 0 0 TS 0.00 0.00 000 0.00 13.Wrl fonds Ina RR) 13.a.Wet Pond M.(Spec VW a 0 0 0 O 50 0.00 0.00 0.00 OM 13.6.Wet Pond al(Coastal Plain)ISpec X141 0 0 0 0 0 45 0.00 0.00 0.00 0.00 03.0.Wet Pond.(Spec a14) 0 0 0 0 0 25 0.00 0.00 0.00 0.00 13.d.Wet Pond 02(Coastal Plain)(Spec 434) 0 0 0 0 65 0.00 0.00 0.00 0.00 14.0 Manufactured Treatment Pewee- 0 20 OW 000 0.00 0.00 RyarpayrMmm o o a 100 MarnfacMred Treatment Device-Filtering 0 0 0 0 0 20 0.00 000 0.00 000 14.c.Manufactured Treatment Device-Generic 0 0 0 0 0 20 0.00 0.00 0.00 0.00 TOTAL IMPERVIOUS COVER TREATED(a4)MEIN AREA CHECK:OR. TOTAL MANAGED TURF AREA TREATED(an MEM AREA CHECK:OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE(Ib/yri 5.52 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A.A(Ib/yr 5.48 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A.A(lb/yr 4.93 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A.A(Ib/yr 4.93 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A.A(lb/yr 0.55 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr 36.03 NITROGEN REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A.A(Ib/yr 0.00 TOTAL NITROGEN REMOVED IN O.A.A(Ib/yr 36.03 2of2 Site Results(Water Quality Compliance) Area Checks D.A.A D.A.B D.A.C D.A.D D.A.E AREA CHECK FOREST/OPEN SPACE(ac) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER(ac) 2.14 0.68 0.00 0.00 0.00 I OK. I IMPERVIOUS COVER TREATED(ac) 2.14 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA(ac) 1.85 0.37 0.00 0.00 0.00 OK. MANAGED TURF AREATREATED(ac) 1.85 0.00 0.00 0.00 0.00 I OK. AREA CHECK I OK. II OK. II OK. II OK. II OK. Site Treatment Volume(ft3) o Runoff Reduction Volume and TP By Drainage Area I D.A.A II D.A.B II D.A.C I D.A.D I D.A.E I TOTAL - RUNOFF REDUCTION VOLUME ACHIEVED(ft') 6,978 0 0 0 0 6,978 TP LOAD AVAILABLE FOR REMOVAL(Ib/yr) 5.48 1.64 0.00 0.00 0.00 7.12 TP LOAD REDUCTION ACHIEVED(Ib/yr) 4.93 0.00 0.00 o.aa 0.00 4.93 TP LOAD REMAINING(Ib/yr) 0.55 II 1.64 I 0.00 I 0.00 II 0.00 I 2.20 NITROGEN LOAD REDUCTION ACHIEVED)Ib/yr)II 36.03 II 0.00 I 0-.0() -1M1 0.00 I� --- Total Phosphorus FINAL POST-DEVELOPMENT TP LOAD(Ib/yr) 9.05 TP LOAD REDUCTION REQUIRED)Ib/yr) 5.52 I MEMIIIIIM= IIIMIWIA.W.ml.TP LOADR PLOAOR ACHIEVEDMANING (Ibyyr) 4.12S{I = TP LOAD REMAINING(Ib/yr): 4.12 REMAINING TP LOAD REDUCTION REQUIRED(Ib/yr): 0.59 Total Nitrogen(For Information Purposes) POST-DEVELOPMENT LOAD(Ib/yr) 64.75 --- NITROGEN LOAD REDUCTION ACHIEVED Ir) 36.03 --- REMAINING POST-DEVELOPMENT NITROGEN LOAD(Ib/yr) 28.72 --- --IIII1.1111. SCS TR-55 Calculations Soils Mapping (Source: NRCS Web Soil Survey Online Database) Itik, �� c r. ' l, E , N: ‘...,,i,,z„ , ,. ,, ,), , , <A 1 . le„,.?„ ,, ,.. , W , ..i tai ,41 Soils Table (Source: NRCS Web Soil Survey Online Database) Map Unit Legend 1, Albemarle County,Virginia (VA003) Albemarle County, Virginia (VA003) Map Unit Map Unit Name Acres Percent of Symbol in AOI AOI 2C Albemarle fine 0.2 2.5% sandy loam, 7 to 15 percent slopes 21B Culpeper fine 3.6 42.2% sandy loam, 2 to 7 percent slopes 39D Hazel loam, 15 4.8 55.4% to 25 percent slopes Totals for Area of 8.6 100.0% Interest Note:The soils' properties for this development are predominantly composed of hydrologic type B. L Map -I H Terrain Rio - -U=In I y°7bys Rc g0refo„.. , w n p\; 4 0 i Dece Cliff ,p ,8,a` �`a 21 0n-i o a`` bOOft e, 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 Average recurrence interval(years) Lhua4ar I 1 11 2 11 5 11 10 11 25 11 50 11 100 11 200 11 500 11 1000 24-hr 3.03 3.66 4.68 5.53 6.80 7.89 9.09 10.4 12.4 14.1 (2.72-340) (3.29-411) {4.19-5.25) (4.94-6.19) (6.03-7.59) (6.94-8.78) (7.93-10.1) (.899-11.5) (10.5-13.7) {11.8-15.6) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Dunlora Phases I&II Designed By: KKW&FGM Date: 3/7/2018 Location: Dunlora Drive and Rio Road Checked By:SRC Date: 3/7/2018 Check One: Present X Developed 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 0.41 40.2 (Present) B Woods in Good Condition 55 1.99 109.5 62 6.18 Lawns in Good Condition 61 1.59 97.0 DA'A' Impervious Areas 98 2.14 209.7 (Developed) B Woods in Good Condition 55 0.00 0.0 81 2.37 Lawns in Good Condition 61 1.85 112.9 DA'B' Impervious Areas 98 0.00 0.0 (Present) B Woods in Good Condition 55 0.55 30.3 58 7.28 Lawns in Good Condition 61 0.50 30.5 Impervious Areas 98 0.68 66.6 DA'B' (Developed) B Woods in Good Condition 55 0.00 0.0 85 1.77 Lawns in Good Condition 61 0.37 22.6 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 3.03 3.66 5.53 n/a Runoff,Q-inches 0.40 0.68 1.76 DA'A'(Present) Runoff,Q-inches 1.33 1.83 3.44 DA'A'(Developed) Runoff,Q-inches 0.28 0.51 1.46 DA'B'(Present) Runoff,Q-inches 1.61 2.15 3.86 DA'B'(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(Ta)or Travel Time(Ti) Project: Dunlora Phases I&II 3/7/2018 Location: Dunlora Drive and Rio Road 3/7/2018 Check One: Present X Developed X Check One: T, X Tt Through subarea n/a DA'A' DA'A' DA'B' DA'B' Segment ID: (Present) (Developed) (Present) (Developed) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass Dense Grass Dense Grass Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 0.24 0.24 0.24 3 Flow length,L(total L<100)(ft) 100 100 100 50 4 Two-year 24-hour rainfall,P2(in.) 3.66 3.66 3.66 3.66 5 Land slope,s(ft/ft) 0.035 0.035 0.16 0.19 6 Compute Tt=[0.007(n*L)°'$]/P2'5 S '4 0.18 0.18 0.10 0.05 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Paved 8 Flow Length,L(ft) 691 87 42 55 9 Watercourse slope,s(ft/ft) 0.09 0.06 0.24 0.02 10 Average velocity,V(Figure 3-1)(ft/s) 4.9 4 8 3 11 TL=L/3600*V 0.04 0.0 0.00 0.01 Channel Flow: 12 Cross sectional flow area,a(ft2) 13 Wetted perimeter,PN,(ft) 14 Hydraulic radius,r=a/PW(ft) 15 Channel Slope,s(ft/ft) 16 Manning's Roughness Coeff,n 17 V=[1.49r2/'3s05]/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) ( 0.22 0.18 I 0.10 I 0.10 I Note:Tc of 0.10 hours is the most conservative SCS TR-55 time of concentration U.S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Dunlora Phases I&II Date: 6/19/2018 Location: Dunlora Drive and Rio Road Date: 6/19/2018 Check One: Present X Developed X Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Drainage Area Description Description Description DA'A' DA'A' DA'B' DA'B' (Present) (Developed) (Present) (Developed) Drainage Area(Am)in miles'= 0.0062 0.0062 0.0016 0.0016 Runoff curve number CN= 62 81 58 85 Time of concentration(Tc)= 0.22 0.18 0.10 0.10 Rainfall distribution type= II II II II Pond and swamp areas spread 0 0 0 0 throughout the watershed= 2.Frequency-years 1 2 10 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-inches 3.03 3.66 5.53 3.03 3.66 5.53 3.03 3.66 5.53 3.03 3.66 5.53 4.Initial Abstraction,la-inches 1.24 1.24 1.24 0.47 0.47 0.47 1.46 1.46 1.46 0.35 0.35 0.35 5.Compute la/P 0.41 0.34 0.22 0.16 0.13 0.09 0.48 0.40 0.26 0.12 0.10 0.06 6.Unit peak discharge,Qu-csm/in 625 650 725 800 800 850 775 800 975 1000 1000 1000 7.Runoff,Qfrom Worksheet 2-inches 0.40 0.68 1.76 1.33 1.83 3.44 0.28 0.51 1.46 1.61 2.15 3.86 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed through SWM Routed through SWM where Qp=Qu Am Q Fp 1.57 2.77 7.96 Facility 0.36 0.67 2.34 Facility Note:Qu of 1000 csm/inch is the most conservative SCS TR-55 Qu. Outflow -,t, s :(1-Yogur Storm Event) a .al. .z Post-Development DA'A' 1.57 cfs 0.70 cfs DA'B' 0.36 0.48 cfs Total= 1.93 cfs 1.18 cfs Outflow Summary: (2-Year Storm Event) Pre-Develbpment Post-Development DA'A' 2.77 cfs 1.15 cfs DA'B' 0.67 0.55 cfs Total= 3.44 cfs 1.70 cfs Outflow S mmary: (10 Year Storm Event) Pre-Development Post-Development DA'A' 7.96 cfs 7.42 cfs DA'B' 2.34 2.24 cfs Total= 10.30 cfs 9.66 cfs Watershed Summary Pre-Development Post-Development DA'A' 3.99 ac. 3.99 ac. DA'B' 1.05 ac. 1.05 ac. Total= 5.04 ac. 5.04 ac. Subarea A Routing Calculations enCOCOLLINSEN .GiNSE. PNG 200 GARRETT ST, SUITE K CHARLOTTESVILLE VA 22902 434.293.3719 PH 434.293.2813 FX www.col fins-engineering.corn May 30, 2017 Emily Cox County of Albemarle Department of Community Development 401 McIntire Road Charlottesville, VA 22902 Dunlora Park Pond Riser Narrative The Dunlora Park pond riser was updated in field from a 24"to a 48"riser. A comparison of the approved and installed (proposed) designs follows, demonstrating water quantity compliance for the installed riser: Approved Proposed: Riser Rim: 409.67 409.95 Low-flow Orifice: (2) 2.5-inch orifices at 402.00 (2) 2.5-inch orifices at 402.00 Mid-flow Orifice: (7) 3-inch orifices at 408.64 Riser Size: 24" 48" The revised pond routing holds all other inputs constant and changes the 24"riser to a 48"riser, raises the rim to 409.95 (0.28'), and provides (7)new 3"mid-flow orifices at 408.64. The one- year flow(channel adequacy) is unchanged, and the two- and ten-year flows remain below pre- development requirements. The 100-year storm is provided one-foot of freeboard. Approved Watershed Summary Pre-Development Post-Development 1-year 2-year 10-year 1-year 2-year 10-year C N Aaca, Flow, Flow, Flow, N Aa�a' Flow, Flow, Flow, cfs cfs cfs cfs cfs cfs DA'A' 62 4.17 2.41 2.88 7.70 80 4.17 0.70 0.72 6.76 Watershed Summary(Revised) Pre-Development Post-Development C Area, 1-year 2-year 10-year Area, 1-year 2-year 10-year Flow, Flow, Flow, CN Flow, Flow, Flow, N ac. cfs cfs cfs ac' cfs cfs cfs DA'A' 62 4.17 2.41 2.88 7.70 80 4.17 0.70 1.15 7.42 The approved and revised routings follow. Please contact me if you have any questions or require any further information. Sincerely, Kaitlyn Walthall, PE Approved Routing Calculations Basin A- Detention Cell BasinFlow printout INPUT: Basin: Basin A- Detention Cell Routing 6 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 402.00 81.00 0.0 404.00 717.00 25.7 406.00 1845.00 117.3 408.00 3096.00 298.3 410.00 4450.00 576.3 412.00 5906.00 958.6 Start_Elevation(ft) 402.00 Vol. (cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Riser area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 409.670 multiple 1 discharge into riser Outlet structure 1 Weir name: Emergency Spillway length (ft) 33.000 side angle 75.500 coefficient 3.300 invert (ft) 410.670 multiple 1 discharge through dam Outlet structure 2 Orifice name: Low-Flow Orifice area (sf) 0.034 diameter or depth (in) 2.500 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 402.000 multiple 2 Page 1 Basin A- Detention Cell discharge into riser Outlet structure 3 Orifice name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 401.000 multiple 1 discharge out of riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 7.612 peak time (hrs) 11.970 volume (cy) 916.526 Hydrograph 1 SCS name: 2 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 8.357 peak time (hrs) 11.970 volume (cy) 1006.233 Hydrograph 2 SCS Page 2 Basin A- Detention Cell name: 10 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 15.921 peak time (hrs) 11.970 volume (cy) 1916.892 Hydrograph 3 SCS name: 100 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 30.997 peak time (hrs) 11.970 volume (cy) 3732.026 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1 yr 24hr SCS Method Storm Event inflow (cfs) 7.612 at 11.96 (hrs) discharge (cfs) 0.699 at 12.44 (hrs) water level (ft) 408.644 at 12.56 (hrs) storage (cy) 377.012 Hydrograph 1 Routing Summary of Peaks: 2 yr 24hr SCS Method Storm Event inflow (cfs) 8.357 at 11.96 (hrs) discharge (cfs) 0.717 at 12.50 (hrs) water level (ft) 408.979 at 12.60 (hrs) storage (cy) 421.913 Page 3 Basin A- Detention Cell Hydrograph 2 Routing Summary of Peaks: 10 yr 24hr SCS Method Storm Event inflow (cfs) 15.921 at 11.96 (hrs) discharge (cfs) 6.762 at 12.12 (hrs) water level (ft) 410.666 at 12.12 (hrs) storage (cy) 691.674 Hydrograph 3 Routing Summary of Peaks: 100 yr 24hr SCS Method Storm Event inflow (cfs) 30.997 at 11.96 (hrs) discharge (cfs) 30.312 at 11.98 (hrs) water level (ft) 410.996 at 11.98 (hrs) storage (cy) 753.095 Mon Sep 19 10:52:51 EDT 2016 Page 4 Proposed Routing Calculations Basin A- Detention Cell-48 riser field update BasinFlow printout INPUT: Basin: Basin A- Detention Cell Routing 6 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 402.00 81.00 0.0 404.00 717.00 25.7 406.00 1845.00 117.3 408.00 3096.00 298.3 410.00 4450.00 576.3 412.00 5906.00 958.6 Start_Elevation(ft) 402.00 Vol.(cy) 0.00 5 Outlet Structures Outlet structure 0 Orifice name: Riser area (sf) 12.566 diameter or depth (in) 48.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 409.950 multiple 1 discharge into riser Outlet structure 1 Weir name: Emergency Spillway length (ft) 33.000 side angle 75.500 coefficient 3.300 invert (ft) 410.670 multiple 1 discharge through dam Outlet structure 2 Orifice name: Low-Flow Orifice area (sf) 0.034 diameter or depth (in) 2.500 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 402.000 multiple 2 Page 1 Basin A- Detention Cell-48 riser field update discharge into riser Outlet structure 3 Orifice name: Mid-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 408.640 multiple 7 discharge into riser Outlet structure 4 Orifice name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 401.000 multiple 1 discharge out of riser 4 Inflow Hydrographs Hydrograph 0 SCS name: 1 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 7.612 peak time (hrs) 11.970 volume (cy) 916.526 Hydrograph 1 SCS name: 2 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 Type 2 rainfall, P (in) 3.700 Page 2 Basin A- Detention Cell-48 riser field update 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) 8.357 peak time (hrs) 11.970 volume (cy) 1006.233 Hydrograph 2 SCS name: 10 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 15.921 peak time (hrs) 11.970 volume (cy) 1916.892 Hydrograph 3 SCS name: 100 yr 24hr SCS Method Storm Event Area (acres) 4.170 CN 80.000 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) 30.997 peak time (hrs) 11.970 volume (cy) 3732.026 OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1 yr 24hr SCS Method Storm Event inflow (cfs) 7.612 at 11.96 (hrs) Page 3 Basin A- Detention Cell-48 riser field update discharge (cfs) 0.699 at 12.46 (hrs) water level (ft) 408.636 at 12.54 (hrs) storage (cy) 376.003 Hydrograph 1 Routing Summary of Peaks: 2 yr 24hr SCS Method Storm Event inflow (cfs) 8.357 at 11.96 (hrs) discharge (cfs) 1.150 at 12.38 (hrs) water level (ft) 408.867 at 12.38 (hrs) storage (cy) 406.506 Hydrograph 2 Routing Summary of Peaks: 10 yr 24hr SCS Method Storm Event inflow (cfs) 15.921 at 11.96 (hrs) discharge (cfs) 7.415 at 12.12 (hrs) water level (ft) 410.608 at 12.12 (hrs) storage (cy) 681.170 Hydrograph 3 Routing Summary of Peaks: 100 yr 24hr SCS Method Storm Event inflow (cfs) 30.997 at 11.96 (hrs) discharge (cfs) 30.245 at 11.98 (hrs) water level (ft) 410.954 at 11.98 (hrs) storage (cy) 745.211 Thu May 18 16:48:11 EDT 2017 Page 4 1 1'WIDE FOREBAYTOP OF AM i \ ELEV 424.00'Who'WID FOREEIAY SPILLWAY CRE T — ELEV.=423.o0' 430 \ 430 FORE3AY W/2:1 P•OPOSEI LEVEL II BIOFILT R CELL SIDE SLOPES'. CLEANOUT,5: , SURFACE ELEV.= 22.00' DETAIL PROPOSED ADDTRIONA \ GRADE INFORMATION.( YP.) o'WIDE A'2MORED SPILLWAY CREST ELEV.=423.o0',CREST to 425 I 12"ABOVE BIOFILTER TOP 425 I LAYER,CREATING A MAXIMUM PONDING D PTH OF2 2"(TOP OF i •/ y \ NG J 4 4+.00' F OOR EL: FLOOR ELEI _ ._ -i 420 42..00' 422 00' - _-- 1 \ •'OF S I A E AI'I'ROVED SUI __ __ ' 420 EDIA.SIDE SLOP: =- -- _-_-i \ PROPOSED 048'CL.III RCP STANDPIPE w/ EXCAVA ION NEED - NOT B: ___ ---_ TRASHRACKS SHALL H LL SERVE AS THE RISER VERTICAL. -- -- \i STRUCTURE. 1 — 3"M NIMUM 'EA GRAVEL LAYER 3 j N = RISER RIM ELEV=409.95' 1 N N SEVEN(7)03"MID-FLOW',ORIFICE E LEV.=405.64' 415 12"MINI UM GRAVEL SUM' •`� •`�� • TWO(2) 02.5"LOW-FLOW ORIFICE ELEV.=402'415 L....L._Aline In I 12" ELEV. 14.75' \ PROPOSED 33'WIDE GRASS PROPOSED LEV:L 2 (MIN. 1I PTH) I LINE0 EMERGENCY SPILLWAY BIORETENTION B'SIN W/55:1 SIDE 5_OPES CREST 6"SCHE PULE 40 PERFORA ED PVC UNDERDRAINS,10' ELEVATION=41o.6T MAXI UM SPACING WIT CLEANOUTS,SHALL BE \ (8'TOP OF DAM ELEV.=412.00') 410 INST'LLED THROUGHO TTHE BIOFILTER IN THE 410 LOW.R S I UNE LAYER. NL)ERURAINS SHALL BE SLOPED TO DRAIN TO TH: RISER STRUCTURE OR TO \ N DAYLIG T INTO THE DETE TION CELL&SHA_L HAVE A 12"5 ONE SUMP LOCA D BELOW THE INVERT OF _ - -- ., ----- ..-....-------- THE UND:RDRAINS. EX STING 405 GRADE 405 I 1PROPOSED VDOT EC-1 CLASS \ r Al OUTLET PROTEC-ION w/ GEOTEXTILE FILTER FABRIC \ UNDERLAYMENT(L=8',W1=4.5', FLOOR EL:V.= j W2=9.5';D=1.4'MIN.) 40 .00' 400 j 400 TO PREVENT FLOTATION THE RI ER BASEr - 10 ... AND BARREL CONNECTION SH•LL BE FIRMLY EMBEDDED 6"INTO A REINFORCED 18"THICK CONCRETE FOUNDATION THAT 15 PROPOSED 015' CL.III RCP BARREL 4'X 4',AND IS BURIED BELOW THE LIMITS (75LF,S=1.33%; 395 PRO'ILE SCALES OF THE BASIN GRADING. INV.IN=4o1.00',INV.OUTT400.o0') 395 .,_5. (U) 1'=50' (M) 392 392 M OO c O O ON00 I NQ1 0 trONen N N N rl 0 10+00 10+50 11+00 11+50 12+00 12+50 13+00 13+25 Subarea B Routing Calculations Subarea B Routing Calculations UGD with Narrative BasinFlow printout INPUT: Basin: Dunlora Phase II Subarea 'B' Routing - Underground Detention 0 Contour Areas Elevation(ft) Area(sf) Computed Vol. (cy) 1 Storage Pipes Storage pipe 0 name: Underground Detention diameter (in) 120.000 length (ft) 60.000 invert (ft) 439.750 angle 0.287 volume (cy) 174.533 Start_Elevation(ft) 439.75 Vol. (cy) 0.00 6 Outlet Structures Outlet structure 0 Orifice name: Low-Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 439.750 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 445.250 multiple 2 discharge into riser Page 1 Subarea B Routing Calculations UGD with Narrative Outlet structure 2 Orifice name: High-Flow Orifices area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 445.920 multiple 2 discharge into riser Outlet structure 3 Orifice name: Emergency Spillway Simulation area (sf) 6.827 diameter or depth (in) 35.380 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 448.330 multiple 1 discharge into riser Outlet structure 4 Weir name: Access Riser diameter (in) 48.000 side angle 0.000 coefficient 3.000 invert (ft) 454.000 multiple 1 discharge into riser Outlet structure 5 Orifice name: Barrel area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 439.750 multiple 1 discharge out of riser Page 2 Subarea B Routing Calculations UGD with Narrative 3 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr 24-hr Peak SCS TR-55 Storm Event Area (acres) 1.050 CN 85.000 Type 2 rainfall, P (in) 3.030 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) 2.150 peak time (hrs) 11.917 volume (cy) 227.599 Hydrograph 1 SCS name: 2-yr 24-hr Peak SCS TR-55 Storm Event Area (acres) 1.050 CN 85.000 Type 2 rainfall, P (in) 3.660 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) 2.873 peak time (hrs) 11.917 volume (cy) 304.174 Hydrograph 2 SCS name: 10-yr 24-hr Peak SCS TR-55 Storm Event Area (acres) 1.050 CN 85.000 Type 2 rainfall, P (in) 5.530 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) 5.144 peak time (hrs) 11.917 volume (cy) 544.616 Page 3 Subarea B Routing Calculations UGD with Narrative OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-yr 24-hr Peak SCS TR-55 Storm Event inflow (cfs) 2.140 at 11.92 (hrs) discharge (cfs) 0.480 at 12.12 (hrs) water level (ft) 443.996 at 12.12 (hrs) storage (cy) 67.272 Hydrograph 1 Routing Summary of Peaks: 2-yr 24-hr Peak SCS TR-55 Storm Event inflow (cfs) 2.860 at 11.92 (hrs) discharge (cfs) 0.553 at 12.14 (hrs) water level (ft) 445.277 at 12.14 (hrs) storage (cy) 95.633 Hydrograph 2 Routing Summary of Peaks: 10-yr 24-hr Peak SCS TR-55 Storm Event inflow (cfs) 5.120 at 11.92 (hrs) discharge (cfs) 2.237 at 12.06 (hrs) water level (ft) 448.364 at 12.06 (hrs) storage (cy) 157.542 Tue Jun 19 11:05:19 EDT 2018 Notes: The previous design met 9VAC25-870-66 requirements. This design proposed a 108" pipe with a "low-flow" orifice set near the pipe's crown. This is a problematic design prone to standing water, advanced degradation of the pipe, increased likelihood of joint and subsurface failure and presents an unhealthy breeding ground for disease infested mosquitos. To remedy this a low-flow orifice needs to be set at the low point of the underground detention system. When implementing this improved concept, a low-flow orifice diameter of 7/8" is required to meet 9VAC25-870-66 requirements. However a 7/8" low-flow orifice, even with a trashrack, increases the risk of clogging. To resolve this concern the routing calculations above and revised design provide a system with a 3" low-flow orifice. This design is in accordance with the Virginia Stormwater BMP Clearinghouse, where it states "Orifices less than 3 inches in diameter may require extra attention during design to minimize the potential for clogging." Page 4 O N N O l!1 F+ UI N In time h 0.4 0.82 1.24 1.66 2.08 2.5 2.92 3.34 3.76 4.18 4.6 5.02 5.44 5.86 6.28 6.7 7.12 7.54 7.96 8.38 8.8 9.22 9.64 10.06 10.48 10.9 CD 11.32 11.74 12.16 N 12.58 A 13 a 13.42 0 0 13.84 14.26 14.68 15.1 N :. 15.52 0 15.94 16.36 3 16.78 17.2 17.62 18.04 18.46 18.88 19.3 19.72 20.14 20.56 20.98 21.4 21.82 22.24 22.66 23.08 23.5 23.92 _ 1 !. n 0 d F oc (D O 1 N O l!1 N in NJ Ui W in Time(hrs) 0.4 0.82 1.24 1.66 2.08 2.5 2.92 3.34 3.76 4.18 4.6 5.02 5.44 5.86 6.28 6.7 7.12 7.54 7.96 8.38 8.8 9.22 9.64 10.06 10.48 N 10.9 11.32 (DD 11.74 ammo 12.16 N 12.58 0 . 13 u, 13.42 0 13.84 14.26 14.68 15.1 n Vf 15.52 N 15.94 0 16.36 16.78 3 17.2 17.62 18.04 18.46 18.88 19.3 19.72 20.14 20.56 20.98 21.4 21.82 22.24 22.66 23.08 23.5 23.92 I I o 5 n p O N N Time(hrs) 0.4 0.82 1.24 1.66 2.08 2.5 2.92 3.34 3.76 4.18 4.6 5.02 5.44 5.86 6.28 6.7 7.12 7.54 7.96 8.38 8.8 9.22 9.64 10.06 10.48 10.9 [� 11.32 11.74 Jaw fD 12.16 fD 12.58 N N 13 N N 13.42 13.84 14.26 0 14.68 15.1 15.52 N 15.94 VI 16.36 N 16.78 e-f 17.2 0 17.62 3 18.04 18.46 18.88 19.3 19.72 20.14 20.56 20.98 21.4 21.82 22.24 22.66 23.08 23.5 23.92 I I v 5 A ff G ' p„OC1---ZoNJ Ns.J • )14-k-V -TN1 r<(1,040 ANia: E SC F4 611-4(\) S- 6t -\-7 7 -Fee- CiANietv 1-Lo's", ikVE 0,0,1Liz- Cvfati Ego al' 4-to' SaR7. . */ Ovz. %ME 3,1c1-1 --7, wax I s, A k,NAk SC. c-A.cE. K3 - 1, OS scE.Nton0 r gc.)41,tmG Pucre1 to 6t,so: (cos5G.NAtjvc. 11 OVrit LA-1,5s 74.iA I,5 , ;Va. c\So c\scsx cs'" aAQ' AL 7-ccD'i':- k-s.sp.64,-;) Atavalc,or,400./x1--3:,QC TysE. Yv+s A Riprap Outfall Protection- 2 yr Design Storm Complex Channnel Riprap Outfall Protection Calculations- 2 yr. Design Storm Input: Slope 0.280 Flow (given) 0.550 line x y n 0 0.000 1.500 0.050 (first n value not used) 1 4.500 0.000 0.050 2 9.000 1.500 0.050 Output: Depth 0.227 (Y) ( 0.227) Channel bed segment output: line Q V A P 1 0.28 3.56 0.08 0.72 2 0.28 3.56 0.08 0.72 Tue Jun 19 09:30:21 EDT 2018 Page 1 Riprap Outfall Protection- 10 yr Design Storm Complex Channnel Riprap Outfall Protection Calculations- 10 yr. Design Storm Input: Slope 0.280 Flow (given) 2.240 line x y n 0 0.000 1.500 0.050 (first n value not used) 1 4.500 0.000 0.050 2 9.000 1.500 0.050 Output: Depth 0.384 (y) ( 0.384) Channel bed segment output: line Q V A P 1 1.12 5.06 0.22 1.22 2 1.12 5.06 0.22 1.22 Tue Jun 19 09:29:23 EDT 2018 Page 1