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HomeMy WebLinkAboutWPO201600034 Calculations WPO VSMP 2016-04-29 GREENLOFT FARM FINAL VSMP STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations APRIL 29, 2016 Revised on OCTOBER 21, 2016 PREPARED BY: COLLINS 200 GARRETT STREET,SUITE K CHARLOTTESVILLE,VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com STORMWATER MANAGEMENT NARRATIVE OVERALL: This project utilizes Engineering Site Design (ESD) techniques outlined in the 2013 Draft VSMH. The use of these ESD techniques,the vast acreage left undisturbed and the clustered low-impact development proposed results in minimal environmental impacts. STORMWATER QUALITY: The considerable amount of acreage being preserved,and prohibited from disturbances and future development, results in this clustered development's water quality compliance. The preservation of over 45 acres of forested open space within the parcel's 148+acre limits yields a minimum phosphorus load reduction requirement of 0 pounds per year. STORMWATER QUANTITY: Subareas A and C are detained via proposed detention facilities.These facilities are not required to adhere to DEQ's Post-Construction Virginia Stormwater BMP Clearinghouse's requirements due to the site's previously noted water quality compliance through preservation. These facilities include a multi-stage riser, barrel and an emergency spillway and detain the 1-year and 2-year storm events below pre-development conditions.The routing of these facilities, and the final stormwater management analysis, can be viewed within this report. ENGINEERING SITE DESIGN PARCTICES IMPLEMENTED This development utilizes environmental site design (ESD)techniques and practices in accordance with the July 2013 draft VSMH.The stormwater management design concept was integrated early in the site planning and design of this development. This is evident in the alignment of the roads horizontally and vertically to reduce grading impacts and the low-impact fashion of the clustered development. More detailed examples of ESD techniques and practices proposed are as follows: ESD practice#1: The proposed preservation of undisturbed natural areas This is accomplished through an easement dedication of the stream buffer. This is also achieved through the significant preserved open spaces proposed to remain undisturbed outside the limits of disturbance,and that are prohibited from future development. Please note the subdivision plat and erosion and sediment control plans prohibit future disturbances and development of lots within the open spaces shown to be preserved. ESD practice#2:The proposed preservation of riparian buffers This is accomplished through the easement dedication of the stream buffer noted above. ESD practice#3: The proposed preservation or planting of native trees This is accomplished through limiting the proposed disturbances in the erosion and sediment control plan.The limits of disturbance remain outside the limits of existing native trees that are proposed to remain within the stream buffer and preserved open spaces. ESD practice#5: The proposed avoidance of disturbance within steep slopes where possible This development limits disturbances to the Albemarle County defined critical slopes. This is evident is the detention facilities'grading and the alignments of the roads and lots. ESD practice#6: The proposed design fits the terrain This development limits lot grading, has minimal disturbances with the proposed roads and places the detention facilities in existing low areas outside of stream buffers and floodplain areas. This development also maintains the general drainage patterns and does not excessively reroute runoff. ESD practice#7: The proposed development is located in less sensitive areas This development avoids disturbances to the more environmentally sensitive areas, inclusive of the critical slopes, intermittent stream and stream buffers. ESD practice#8: Reduced limits of disturbances This project clusters its development, as is evident in the lot layout and roadways'grading plan. This development also provides significant open spaces that are proposed to remain undisturbed outside the limits of disturbance. ESD practice#9: Proposed use of open space This project clusters its development and utilizes open space outside of the limits of the right-of-way and lots.The cluster development strategy yields extensive open spaces in excess of 30%. r ESD practice#10: Creative development design The clustered development with significant open spaces, coupled with the road design resulting in limited lot grading, provides for a creative development designed with limited disturbances in a low impact fashion consistent with chapter 6 of the 2013 VSMH draft. ESD practice#11: Reduced roadway widths and lengths The proposed plan utilizes the shortest widths allowed by Albemarle County Fire and Rescue.Also, the plan minimizes the lengths of roadways by having a cul-de-sac for lot frontage, and does not propose single frontage lots. Meaning, all roadways have lots on either side of the road, hereby minimizing roadway lengths. ESD practice#12: Reduced impervious footprints In accordance with ESD practice#10,the roadway impervious areas were minimized to the fullest extent possible. ESD practice#13: Reduced parking footprints This development provides off street parking, and in many cases will provide homes with built-in attached garages, hereby reducing the parking footprints. ESD practice#17: Use of buffers& undisturbed filter areas The natural site features of undisturbed vegetated areas throughout the parcel's limits reduce runoff. These areas also provide infiltration and stormwater filtering of pollutants, sediment recycling nutrients,and maximize on-site storage of stormwater. ESD practice#18: Creative site grading, berming and terracing The proposed detention facilities'grading utilizes berming in existing lot areas to minimize grading disturbances for their installation. ESD practice#19: Use of natural drainage ways& vegetated swales instead of storm sewers and curb & gutter The proposed plan utilizes vegetative grass-lined roadside swales in lieu of curb and gutter to convey the roads' runoff. Storm sewer are proposed in select areas,where required. The use of existing drainage ways is also incorporated into the design. ESD practice#20: Drain runoff to pervious areas The proposed grading plan and VRRM water quality calculations allow for the rear portions of specific lots to drain away from the road towards pervious areas being preserved & left undisturbed. This allows for groundwater recharge and recycling of nutrients. DEQ Virginia Runoff Reduction Method Water Quality Calculations Virginia Runoff Reduction Method New Development Worksheet-v2.8 -June 2014 To be used w/2011 BMP Standards and Specifications Site Data Project Name:Greenloft Farm VSMP Plan Date: 10/21/16 data input cells calculation cells constant values 1. Post-Development Project&Land Cover Information Constants Annual Rainfall(inches) 43 Target Rainfall Event(inches) 1.00 Phosphorus EMC(mg/L) 0.26 Nitrogen EMC(mg/L)r 1.86 Target Phosphorus Target Load(lb/acre/yr) 0.41 J I 0.90 Land Cover (acres) 'A soils B Soils C Soils D Soils Totals Forest/Open Space(acres)--undisturbed, protected forest/open space or reforested land 0.00 45.48 0.00 0.00 45.48 Managed Turf(acres)--disturbed,graded for yards or other turf to be mowed/managed 0.00 17.80 81.39 0.00 99.19 Impervious Cover(acres) 0.00 1.93 2.16 0.00 4.09 Total 148.76 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 Forest/Open Space Cover(acres) 45.48 Weighted Rv(forest) 0.03 %Forest 31% Managed Turf Cover(acres) 99.19 Weighted Rv(turf) 0.22 %Managed Turf 67% Impervious Cover(acres) 4.09 ~ Rv(impervious) 0.95 - %Impervious 3% Total Site Area(acres) 148.76 Site Rv 0.18 - Post-Development Treatment Volume(acre-ft) 2.23 Post-Development Treatment Volume(cubic _- feet) 96,978 Post_Development Load(TP)(Ib/yr) 60.93 Post_Development Load(TN)(Ib/yr)r 435.891 Total Load(TP)Reduction Required(Ib/yr) -0.06 Site Results D.A.A D.A.B D.A.C D.A.D D.A.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 0.00 0.00 0.00 0.00 0.00 OK. TURF AREA TREATED 0.00 0.00 0.00 0.00 0.00 OK. AREA CHECK OK. OK. OK. OK. OK. Phosphorus - i TOTAL TREATMENT VOLUME(c7) 96,978 TOTAL PHOSPHORUS LOAD REDUCTION REQUIRED(LB/YEAR) -0.06 • RUNOFF REDUCTION(ct) 0 PHOSPHORUS LOAD REDUCTION ACHIEVED(LB/YR) 0.00 • ADJUSTED POST-DEVELOPMENT PHOSPHORUS LOAD(TP)(Ib/yr) 80.93 • REMAINING PHOSPHORUS LOAD REDUCTION(LB/YR)NEEDEDICONGRATULATIONSII YOU EXCEEDED THE TARGET REDUCTION BY 0.1 LBIYEARIE Nitrogen,for information purposes) TOTAL TREATMENT VOLUME(ct)1 98,978 RUNOFF REDUCTION(ct) 0 NITROGEN LOAD REDUCTION ACHIEVED(LB/YR) 0.00 ADJUSTED POST-DEVELOPMENT NITROGEN LOAD(TN)(Ib/yr)1 435.891 SCS TR-55 Calculations (The soils' properties witin the parcel's limits are predominantly composed of hydrologic types B&C.) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Dudley Mountain Designed By: FGM,PE Date: 10/21/2016 Location: Dudley Mountain Road Checked By:SRC,PE Date: 10/21/2016 Check One: Present X Developed X 1.Runoff curve Number(CN) Soil name and Cover description CN(weighted) Drainage Area Area Product of Calculated e hydrologic group (Cover type,treatment,and hydrologic condition;percent CN total product/ Description (Acres) CN x Area p ct/ 'S'Value (Appendix A) impervious;unconnected/connected impervious area ratio) total area DA A Impervious Areas 98 0.00 0.0 (Present) C Woods in Good Condition(Approx.1/2 of pre-development watershe 70 9.27 648.9 72.0 3.89 Lawns in Good Condition(Approx.1/2 of pre-development watershed 74 9.28 686.7 DAB Impervious Areas 98 0.00 0.0 (Present) C Woods in Good Condition(Approx.1/4 of pre-development watershe 70 1.07 74.9 73.0 3.70 Lawns in Good Condition(Approx.3/4 of pre-development watershed 74 3.23 239.0 DAC&D Impervious Areas 98 0.00 0.0 (Present) 8 Woods in Good Condition(Approx.3/4 of pre-development watershe 55 75.82 4170.0 56.5 7.70 Lawns in Good Condition(Approx.1/4 of pre-development watershed 61 25.27 1541.6 DA E Impervious Areas 98 0.00 0.0 (Present) C Woods in Good Condition(Approx.1/2 of pre-development watershe 70 11.43 800.1 72.0 3.89 Lawns in Good Condition(Approx.1/2 of pre-development watershed 74 11.43 845.8 OAA Impervious Areas 98 1.18 115.4 (Developed) C Woods in Good Condition(Approx.1/2 of areas not impervious) 70 10.27 718.9 73.4 3.62 Lawns in Good Condition(Approx.1/2 of areas not impervious) 74 10.27 760.0 DAB Impervious Areas 98 0.26 25.9 (Developed) C Woods in Good Condition(Approx.1/4 of pm-development watershe 70 0.75 52.5 75.0 3.33 Lawns in Good Condition(Approx.3/4 of pre-development watershed 74 2.27 168.0 DA C Impervious Areas 98 1.59 155.9 (Developed) B Woods in Good Condition(Approx.1/2 of areas not impervious) 55 10.00 550.0 60.9 6.41 Lawns in Good Condition(Approx.1/2 of areas not impervious) 61 10.00 610.0 DAD Impervious Areas 98 0.34 33.7 (Developed) 8 Woods in Good Condition(Approx.3/4 of of areas not impervious) 55 59.30 3261.5 56.7 7.64 Lawns in Good Condition(Approx.1/4 of of areas not impervious) 61 19.76 1205.4 DA E Impervious Areas 98 0.72 70.4 (Developed) C Woods in Good Condition(Approx.1/2 of areas not impervious) 70 10.04 702.8 72.9 3.72 Lawns in Good Condition(Approx.1/2 of areas not impervious) 74 10.04 743.0 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 1.12 1.25 2.67 DA A(Present) Runoff,Q-inches 1.18 1.32 2.76 DAB(Present) Runoff,Q-inches 0.40 0.47 1.40 DA C&D(Present) Runoff,Q-inches 1.12 1.25 2.67 DA E(Present) Runoff,Q-inches 1.20 1.34 2.80 DA A(Developed) Runoff,Q-inches 1.30 1.45 2.95 DA 8(Developed) Runoff,Q-inches 0.57 0.66 1.74 DA C(Developed) Runoff,Q-inches 0.40 0.48 1.42 DAD(Developed) Runoff,Q-inches 1.17 1.31 2.75 DA E(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(T d or Travel Time(T,) Project: Dudley Mountain Designed By: FGM,PE Date: 10/21/2016 Location: Dudley Mountain Road Checked By: SRC,PE Date: 10/21/2016 Check One: Present X Developed X Check One: T, X T, Through subarea n/a DAA DAB DAC&D DAE DAA DAB DAC DAD DA E Segment ID: (Present) (Present) (Present) (Present) (Developed) (Developed) (Developed) (Developed) (Developed) Sheet Flow:(Applicable to T ,only) Woods-Light Dense Woods-Light Woods-Light Woods-Light 1 Surface description(Table 3-1) Underbrush Grass Underbrush Dense Grass Underbrush Dense Grass Dense Grass Underbrush Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.4 0.4 0.4 0.24 0.4 0.4 0.24 0.4 0.24 3 Flow length,L(total L <100)(ft) 100 100 100 100 100 100 100 100 100 4 Two-year 24-hour rainfall,P 2(in.) 3.7 3.7 3.7 3.7 3.7 3.7 3.7 3.7 3.7 5 Land slope,s(ft/ft) 0.04 0.07 0.07 0.05 0.04 0.10 0.02 0.07 0.05 6 Compute T,=(0.007(n'L)08)/Pz s s" 0.25 I 0.20 I 0.20 I 0.15 I 0.25 I 0.17 I 0.22 I 0.20 I 0.15 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved Unpaved Unpaved Unpaved Unpaved Unpaved Unpaved Unpaved Unpaved 8 Flow Length,L(ft) 1015 935 920 900 785 725 140 920 900 9 Watercourse slope,s(ft/ft) 0.128 0.070 0.177 0.107 0.143 0.077 0.100 0.177 0.107 10 Average velocity,V(Figure 3-1)(ft/s) 5.8 4.3 6.8 5.4 6.1 4.4 5.2 6.8 5.4 11 T,=L/3600•V I 0.05 I 0.06 I 0.04 I 0.05 I 0.04 I 0.05 I 0.01 I 0.04 I 0.05 I Channel Flow: 12 Cross sectional flow area,a(ft 2) c� o .. o x o r o N 13 Wetted perimeter,P.(ft) - c _ u A .. o c p 14 Hydraulic radius,r=a/P„(ft) `c ` `c rd E rd E 15 Channel Slope,s(ft/ft) Fl t c' fl m u w 16 Manning's Roughness Coeff,n `o'^ °v e'^ c`^ ° v3 os o S v c N o 5 -c 17 V=(1.49r s' j/n ^ `o - m 2 18 Flow length,L(ft) -+ .a,4,''?'-, .. 19 T,=L/3600•V I I 0.05 I 0.04 I I I 0.04 I 0.05 I 0.04 20 Watershed or subarea T,or T, (Add T,in steps 6,11 and 19) 0.30 I 0.26 I 0.29 I 0.24 I 0.29 I 0.22 I 0.27 I 0.29 I 0.24 • U.S.Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4:Graphical Peak Discharge Method Project Dudley Mountain Designed By:FGM,PE Date: 10/21/2016 Location: Dudley Mountain Road Checked By:SRC,PE Date: 10/21/2016 Check One: Present S Developed % Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area 1.Data Description Description Description Description Description Description Description Description Description DAA DAB DAC&D DAE DAA DAB DAC DAD DAE (Present) (Present) (Present) (Present) (Developed) (Developed) (Developed) (Developed) (Developed) Drainage Area(Am)in mild= 0.0290 0.0067 0.1580 0.0357 0.0339 0.0051 0.0337 01241 0.0325 Runoff curve number CN= 72.0 73.0 56.5 72.0 73.4 75.0 60.9 56.7 72.9 Time of concentration(Tc). 0.30 0.26 0.29 0.24 0.29 0.22 0.27 0.29 0.24 Rainfall distribution type= II II II II II II 11 II II Pond and swamp areas spread 0 0 0 0 0 0 0 throughout the watershed. 2.Frequency-years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3.Rainfall,P(24 hour)-Inches 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 3.5 3.7 5.6 4.Initial Abstraction,la.inches 0.78 0.78 0.78 0.74 0.74 0.74 1.54 1.54 1.54 0.78 0.78 0.78 0.72 0.72 0.72 0.67 0.67 0.67 1.28 1.28 1.28 1.53 1.53 1.53 0.74 0.74 0.74 5.Compute la/P 0.22 0.21 0.14 0.21 0.20 0.13 0.44 0.42 0.27 0.22 0.21 0.14 0.21 0.20 0.13 0.19 0.18 0.12 0.37 0.35 0.23 0.44 0.41 0.27 0.21 0.20 0.13 6.Unit peak discharge,Qu-wn/in 625 625 650 675 675 700 425 450 600 700 700 725 625 625 650 725 725 750 525 550 650 400 450 600 700 700 725 7.Runoff,Q from Worksheet 2-inches 1.12 1.25 2.67 1.18 1.32 2.76 0.40 0.47 1.40 1.12 1.25 2.67 1.20 1.34 2.80 1.30 1.45 2.95 0.57 0.66 1.74 0.40 0.48 1.42 1.17 1.31 2.75 8.Pond and Swamp adjustment factor,Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9.Peak Discharge,Qp-cfs Routed Through The Routed Through The where Op.C1u Am Q Fp 20.31 22.71 50.29 5.35 5.97 12.98 26.70 33.64 132.86 28.03 31.35 69.13 Detention Basin 4.85 5.38 11.34 Detention Basin 20.06 26.82 105.34 26.70 29.79 64.81 WATERSHED SUMMARY Pre-Development Post-Development 1-year Flow, 2-year Flow, 1-year Flow, 2-year Flow, CN Area,ac. cfs ds CN Area,ac. cfs cfs DA 51' 72.0 18.55 20.31 22.71 73.4 21.72 2.19 6.45 DA II' 73.0 4.30 5.35 5.97 75.0 3.28 4.85 5.38 DA'C 56.5 101.09 26.70 33.64 60.9 21.59 0.52 0.56 DA Tr 56.7 79.40 20.06 26.82 DA'E' 72.0 22.86 28.03 31.35 72.9 20.80 26.70 29.79 Total= 146.80 80.39 93.67 Total= 146.80 54.31 69.00 Detention Basin A BasinFlow printout INPUT: Basin: Detention Basin A 8 Contour Areas Elevation(ft) Area(sf) Computed vol .(cy) 590.00 2494.00 0.0 592.00 3374.00 216.5 594.00 4363.00 502.3 596.00 5464.00 865.5 598.00 6679.00 1314.5 600.00 8011.00 1857.8 602.00 9450.00 2503.8 602.50 9825.00 2682.2 Start_Elevation(ft) 590.00 vol . (cy) 0.00 5 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) 589.250 multiple 1 discharge out of riser outlet structure 1 weir name: Riser Top diameter (in) 42.000 side angle 0.000 coefficient 3.300 invert (ft) 599.750 multiple 1 discharge into riser transition at (ft) 1.063 orifice coef. 0.500 orifice area (sf) 9.621 outlet structure 2 Weir name: Emergency Spillway length (ft) 45.000 side angle 75.960 coefficient 3.300 invert (ft) 600.750 multiple 1 discharge through dam Outlet structure 3 Orifice name: Low-Flow Orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 590.000 multiple 1 discharge into riser Page 1 Detention Basin A Outlet structure 4 Orifice name: Mid-Flow Orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 595.000 multiple 1 discharge into riser 3 Inflow Hydrographs Hydrograph 0 SCS name: 1-Year 24 hr peak SCS Method Design Storm Area (acres) 21.720 CN 73.400 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.2900 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 25.006 peak time (hrs) 11.995 volume (cy) 3510.814 Hydrograph 1 SCS name: 2-Year 24 hr peak SCS Method Design Storm Area (acres) 21.720 CN 73.400 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.2900 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 27.869 peak time (hrs) 11.995 volume (cy) 3912.797 Hydrograph 2 scs name: 100-Year 24 hr peak scs Method Design Storm Area (acres) 21.720 CN 73.400 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.2900 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 121.454 peak time (hrs) 11.995 volume (cy) 17052.242 Page 2 • Detention Basin A OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24 hr peak SCS Method Design Storm inflow (cfs) 24.996 at 12.00 (hrs) discharge (cfs) 2.191 at 12.60 (hrs) water level (ft) 599.701 at 12.66 (hrs) storage (cy) 1770.342 Hydrograph 1 Routing Summary of Peaks: 2-Year 24 hr peak SCS Method Design Storm inflow (cfs) 27.858 at 12.00 (hrs) discharge (cfs) 6.445 at 12.36 (hrs) water level (ft) 599.988 at 12.36 (hrs) storage (cy) 1854.173 Hydrograph 2 Routing Summary of Peaks: 100-Year 24 hr peak SCS Method Design Storm inflow (cfs) 121.408 at 12.00 (hrs) discharge (cfs) 119.903 at 12.02 (hrs) water level (ft) 601.473 at 12.02 (hrs) storage (cy) 2323.002 Thu Oct 20 12:11:12 EDT 2016 Page 3 Detention Basin C BasinFlow printout INPUT: Basin: Detention Basin C 6 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 557.00 3623.00 0.0 558.00 4233.00 145.3 560.00 5573.00 507.4 562.00 7107.00 975.9 564.00 8772.00 1562.9 566.00 10540.00 2277.2 Start_Elevation(ft) 557.00 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) 556.460 multiple 1 discharge out of riser Outlet structure 1 weir name: Riser Top diameter (in) 36.000 side angle 0.000 coefficient 3.300 invert (ft) 562.750 multiple 1 discharge into riser transition at (ft) 0.912 orifice coef. 0.500 orifice area (sf) 7.069 Outlet structure 2 weir name: Emergency Spillway length (ft) 75.000 side angle 75.960 coefficient 3.300 invert (ft) 564.000 multiple 1 discharge through dam outlet structure 3 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) 557.000 multiple 1 discharge into riser Page 1 Detention Basin C 3 Inflow Hydrographs Hydrograph 0 sCS name: 1-Year 24 hr peak SCS Method Design Storm Area (acres) 21.590 CN 60.900 Type 2 rainfall , P (in) 3.500 time of conc. (hrs) 0.2700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 12.101 peak time (hrs) 11.994 volume (cy) 1648.602 Hydrograph 1 SCS name: 2-Year 24 hr peak SCS Method Design Storm Area (acres) 21.590 CN 60.900 Type 2 rainfall , P (in) 3.700 time of conc. (hrs) 0.2700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 14.058 peak time (hrs) 11.994 volume (cy) 1915.279 Hydrograph 2 SCS name: 100-Year 24 hr peak SCS Method Design Storm Area (acres) 21.590 CN 60.900 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.2700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 91.328 peak time (hrs) 11.994 volume (cy) 12442.232 Page 2 Detention Basin C OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 1-Year 24 hr peak SCS Method Design Storm inflow (cfs) 12.074 at 12.00 (hrs) discharge (cfs) 0.524 at 13.70 (hrs) water level (ft) 562.038 at 13.88 (hrs) storage (cy) 985.925 Hydrograph 1 Routing Summary of Peaks: 2-Year 24 hr peak SCS Method Design Storm inflow (cfs) 14.027 at 12.00 (hrs) discharge (cfs) 0.555 at 13.24 (hrs) water level (ft) 562.641 at 13.48 (hrs) storage (cy) 1150.741 Hydrograph 2 Routing Summary of Peaks: 100-Year 24 hr peak SCS Method Design Storm inflow (cfs) 91.126 at 12.00 (hrs) discharge (cfs) 90.654 at 12.02 (hrs) water level (ft) 564.432 at 12.02 (hrs) storage (cy) 1706.231 Thu Oct 20 11:42:46 EDT 2016 Page 3 ef1W-t • VAc as-ar10. -‘6 4/Q5116 c_FtAppc,. 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