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HomeMy WebLinkAboutWPO202000055 Calculations 2021-10-20WHITE GABLES VSMP STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations September 8, 2021 APPROVED Gr' by the Albemarle County SCOTT R. INS'Z Community Devel ent Department Date ppLJ No. 35791 File wPOZOZ0000ss o� 9/08/21 ZONAL PREPARED BY: COLLINS ENGINEEPIMM 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations )atabase) Soils Table (Source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003'. Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent of AOI Symbol 14B Chester loam, 2 8.9% to 7 percent slopes 19B Minnieville loam, 55.1% 2 to 7 percent slopes 36B Hayesville loam, 2 15.8% to 7 percent slopes 36C Hayesville loam, 7 20.2% to 15 percent slopes Totals for Area of 100.0% Interest Note: The soils' properties witin this development are predominantly composed of hydrologic group type B soils. Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) +- O Terrain 3 Eight yyoods < n N S L a o _u 4 t a 3 o enrid0e P Ce ar(( qd I iy a s_3 )�Y Rtl Bellair 1oa�n 300tt 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)l Average rtanence interval years) ol�l� 0 251 50 100 200 I5011 1000 24M 3.04 3.fi7 4.fi9 5.55 6.82 7.90 9.11 10A 12.4 14.1 (2.73J.40) 1 (3.314.11) 1 (4.21-S25) 1 (4.96-6.14) 11 (&06-7s7) 11 (6.974175) 1 (7.96-10.1) 1 (9.02-11.S) 1 (10.6-13.7) 1 (11.8-15.5) Channel and Flood Protection Calculations Project: Location: U.S. Department of Agriculture Natural Resources Conservation Service White Gables White Gables Lane Check One: Present X Developed 1. Runoff curve Number (CN) TR 55 Worksheet 2: Runoff Curve Number and Runoff Designed By: LMW, PE Checked By: SRC, PE FL-ENG-21A 06/04 Date: 9/15/2020 Date: 9/15/2020 Cover description CN (weighted) _Calculated Drainage Area Soil name and hydrologic (Cover type, treatment, and hydrologic condition; percent CN Area Product of CN x total product/ 'S' Description group (Appendix A) (Acres) Area Value impervious; unconnected/ connected impervious area ratio) total area Impervious Areas 98 0.11 10.3 DAA B Lawns in Good Condition (25%+/-) 61 1.40 85.4 63 5.89 (Pre-Dev.) Woods/Grass Combination 58 0.20 11.6 DAA(SWALE) Impervious Areas 98 0.39 38.2 (Post-Dev) B Lawns in Good Condition 61 0.19 11.6 85 1.76 Woods/Grass Combination 58 1 0.00 1 0.0 Impervious Areas 98 0.65 63.7 DAB (Post-Dev) B Lawns in Good Condition 61 0.48 29.3 82 2.15 Woods/Grass Combination 58 0.00 0.0 2. Runoff 1-Year Storm I 2-Year Storm I 10-Year Storm Drainage Area Description Frequency -years 1 2 10 n/a Rainfall, P (24 hour)- inches 3.04 3.67 5.55 n/a Runoff, Q-inches 0.45 0.74 1.86 DA A(Pre-Dev.) Runoff, Q-inches 1.62 2.17 3.88 DA A(SWALE)(Post-Dev) Runoff, Q- inches 1.43 1.95 3.60 DA B(Post-Dev) U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (T,) Project: White Gables Location: White Gables Lane Check One: Present X Developed X Check One: Tc X T, Segment ID Sheet Flow: (Applicable to Tc only) Designed By: Date: Checked By: Date: n/a DA A DA A (SWALE) DA B (Pre-Dev.) (Post-Dev) (Post-Dev) 1 Surface description (Table 3-1) Grass -dense Grass -dense Grass -dense 2 Manning's roughness coeff., n (Table 3-1) 0.24 0.24 0.24 3 Flow length, L (total L < 100) (ft) 100 90 100 4 Two-year 24-hour rainfall, P2(in.) 3.67 3.67 3.67 5 Land slope, s (ft/ft) 0.02 0.01 0.02 6 Compute T, = [0.007(n'L)0"8] / Pz .5 5 .4 0.22 0.27 0.22 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) 11 T, = L / 3600`V 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) 11 T, = L / 3600`V Channel Flow: 12 Cross sectional flow area, a (ft) 13 Wetted perimeter, Pw (ft) 14 Hydraulic radius, r = a/Pw (ft) 15 Channel Slope, s (ft/ft) 16 Manning's Roughness Coeff, n 17 V= [ 1.49r2/3s0"5 j / n 18 Flow length, L (ft) 19 T,= L / 3600'V 20 Watershed or subarea Tc or T, (Add T, in steps 6, 11 and 19) Paved Paved Unpaved 42 28 25 0.03 0.05 0.04 3.5 4.5 3.6 0.00 0.00 0.00 Unpaved Paved 316 170 0.06 0.06 4.0 5.9 0.02 0.01 N N O! Gl n a a a C C 3 3 0 0 LL LL O! Gl C C c c m m U U 0 0 0 0 0.24 0.28 0.23 Sub -Area or Reach Identifier SUBAREAS PRE DEV REACHES OUTLET Albemarle ZONE-2 NOAA-D County, Virginia Watershed Peak Table Peak Flow by Rainfall Return Period 2-Yr 10-Yr 1-Yr (cfs) (cfs) (cfs) 1.39 3.91 1.39 3.91 0.73 0.73 WinTR-55, Version 1.00.10 Page 1 9/9/2020 4:59:57 PM U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Graphical Peak Discharge Method Project: White Gables Designed By: 0 Date: 9/8/2021 Location: White Gables Lane Checked By: 0 Date: 9/8/2021 Check One: Present X Developed X 1. Data Drainage Area Description Drainage Area Description Drainage Area Description DAA (Pre-Dev.) DAA(SWALE) (Post-Dev) DAB (Post-Dev) Drainage Area (Am) in miles 0.0027 0.0009 0.0018 Runoff curve number CN= 63 85 82 Time of concentration (Tc)= 0.24 0.28 0.25 Rainfall distribution type= Type II 1 Type II Type II Pond and swamp areas spread throughout the watershed= 0 0 0 2. Frequency -years 1 2 10 1 2 10 1 2 10 3. Rainfall, P (24 hour)- inches 3.04 3.67 5.55 3.04 3.67 5.55 3.04 3.67 5.55 4. Initial Abstraction, la- inches 1.18 1.18 1.18 0.35 0.35 0.35 0.43 0.43 0.43 5. Compute la/P 0.39 0.32 0.21 0.12 0.10 0.06 0.14 0.12 0.08 6. Peak Discharge, Qp-cfs0.73 where Qp=Qu Am Q Fp 39 F 3.91 Routed through Dry Swale 'A' & Detention Basin'B' Routed Through Detention Basin'B' WATERSHED SUMMARY CN Area, ac. 1-year Flow, cfs 2-year Flow, cfs 10-year Flow, cfs DA A (Pre-Dev) 63 1.71 0.73 1.39 3.91 CN Area, 1-year Flow, 2-year Flow, 10-year Flow, DA A & B (Post-Dev) 84 1.71 0.17 1.29 2.69 NOTE: Sub-Area'A' is routed through Dry Swale'A' and then through Detention Basin'B'. Sub -Area B is routed through Detention Basin 'B' 9 VAC 25-870-66 Section B: Channel Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet the criteria in subdivision 1, 2 or 3 of this subsection..." Section B.1: Manmade stormwater conveyance systems "When stormwater from a development is discharged to a manmade stormwater conveyance system, following the land -disturbing activity, either..." a. or b. shall be met: Section B.1.b. "The peak discharge requirements for concentrated stormwater flow to natural stormwater conveyance systems in subdivision 3 of this subsection shall be met." Section B.3 "... the maximum peak flow rate from the one-year 24-hour storm following the land -disturbing activity shall be calculated either.." a. or b." Section B.3.a. In accordance with the following methodology: Q Allowed !� I.F. * (Q Pre -Developed * [RV Pre -Developed I ) / (RV Developed ) Q Allowed < 0.17 cfs Where: QPre-Developed= 0.73 cfs (FromTR-55) CN Pre -Developed= 63 (From Curve Number Summary) S Pre -Developed — 5.89 (From SCS TR-55 eq. 2-4) RV Pre -Developed— 0.45 in. (From SCS TR-55 eq. 2-3) CN Post -Developed— 84 (From Curve Number Summary) S Post -Developed — 1.98 (From SCS TR-55 eq. 2-4) RV Post -Developed= 1.51 in. (From SCS TR-55 eq. 2-3) I.F. = 0.80 (Factor of Safety) Q Developed = 0.17 cfs* *WITH A LOW FLOW ORIFICE OF 1.75" Section B.4 Limits of Analysis The analysis terminates at Post -Development Subarea B since subsection B.3.a is met. 9 VAC 25-870-66 Section C: Flood Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and hydraulic methodologies:" Section C.2.b.: The point of discharge (Detention Basin B's Cutfall), "releases a postdevelopment peak flow rate for the 10-year 24-hour storm event that is less than the predevelopment peak flow rate from the 10-year 24-hour storm event. Downstream stormwater conveyance systems do not require any additional analysis to show compliance with flood protection criteria if this option is utilized." 10-Year, 24-Hour Pre -Development Subareas A-D Peak Flow Rate = 3.91 cfs 10-Year, 24-Hour Post -Development Subareas A-C Peak Flow Rate = 2.69 cfs Section C.3 Limits of Analysis The flood protection analysis terminates at Subarea B since subsection C.2.b is met. Proposed Outlet Protection Calculations OUTLET PROTECTION INTO DRY SWALE'A' PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER d>6" Q10= 2.08 CFS Qdesign= 3.5 CFS PER VESCH PLATE 3.18-4 d50= 0.1 FT La= 4 FT w1= 3*DO= w2= DO + 0.41-a= FINAL DESIGN (MIN. DISCHARGE FOR 12" DIAMETER PIPE) 2.5 FT 2.5 FT NOTE: VDOT CLASS Al STONE HAS A MEAN d50=O.9 FT AND EXCEEDS 0.5 FT OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO THE EXISTING GROUND A MINIMUM OF 9" AT THE ENDS & ALONG THE PERIMETER. EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS Al STONE WITH THE FOLLOWING DIMENSIONS: La= 4 FT w1= 2.5 FT w2= 3 FT DEPTH= 1.5 FT DEPTH (d) >_ 1.5 X 0.9' DEPTH (d) >_ 1.35' OUTLET PROTECTION INTO DETENTION BASIN 'B' PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER d>_6" Q10= 5.66 CFS Qdesign= 6 CFS PER VESCH PLATE 3.18-4 d50= 0.3 FT La= 18 FT w1= 3*DO= 3 FT w2= DO + 0.41-a= 2.72 FT NOTE: VDOT CLASS Al STONE HAS A MEAN d50=O.9 FT AND EXCEEDS 0.5 FT FINAL DESIGN OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO La= 33.5 FT (EXTENDED TO RISER TO PREVENT CLOGGING) w1= 3 FT w2= 3 FT DEPTH= 1.5 FT DEPTH (d) >_ 1.5 X 0.9' DEPTH (d) >_ 1.35' LEVEL SPREADER CALCULATIONS Q10 = 2.69 CFS PER VESCH TABLE 3.21-A DEPTH = 0.5 FT WIDTH OF LOW SIDE SLOPE = 6 FT LENGTH = 10 FT USE RIGID LIP FOR PERMANENT INSTALLATION Post -Development Dry Swale 'A' Routings and Outflow Hydrographs The following routing calculations and outflow hydrographs reflect the post -development attenuation in Subarea A from the proposed Dry Swale 'A' BasinFlow printout INPUT: Basin: 3 Contour Areas Elevation(ft) 600.00 601.00 602.00 Start—Elevation(ft) 3 Outlet Structures Outlet structure 0 Orifice Area(sf) Computed Vol.(cy) 27.00 0.0 289.00 5.0 819.00 24.7 name: riser outlet area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 599.900 multiple 1 discharge out of riser Outlet structure 1 Orifice name: name area (sf) 0.267 diameter or depth (in) 7.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 600.000 multiple 1 discharge into riser Outlet structure 2 Weir name: name diameter (in) 12.000 side angle 0.000 coefficient 3.300 invert (ft) 601.900 multiple 1 discharge into riser 3 Inflow Hydrographs Hydrograph 0 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 1 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 2 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) OUTPUT: 1 yr 2 2 yr 2 10 yr Pi 3.040 0.2800 0.0200 30.000 1.00 true 0.911 11.991 126.319 3.670 0.2800 0.0200 30.000 1.00 true 1.217 11.991 168.648 5.550 0.2800 0.0200 30.000 1.00 true 2.180 11.991 302.201 Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: 1 yr inflow (cfs) 0.911 at 12.00 (hrs) discharge (cfs) 0.879 at 12.04 (hrs) water level (ft) 600.759 at 12.04 (hrs) storage (cy) 2.817 Hydrograph 1 Routing Summary of Peaks: 2 yr inflow (cfs) 1.216 at 12.00 (hrs) discharge (cfs) 1.116 at 12.06 (hrs) water level (ft) 601.044 at 12.06 (hrs) storage (cy) 5.476 Hydrograph 2 Routing Summary of Peaks: 10 yr inflow (cfs) 2.179 at 12.00 (hrs) discharge (cfs) 1.649 at 12.12 (hrs) water level (ft) 601.911 at 12.12 (hrs) storage (cy) 22.081 Fri May 14 13:58:44 EDT 2021 Post -Development DA A Outflow Hydrograph From Dry Swale Routings 0.0 0.00 0.5 0.00 1.0 0.01 1.5 0.01 2.0 0.01 2.5 0.01 3.0 0.01 3.5 0.01 4.0 0.01 4.5 0.01 5.0 0.01 5.5 0.01 6.0 0.01 6.5 0.01 7.0 0.01 7.5 0.01 8.0 0.01 8.5 0.02 9.0 0.02 9.5 0.02 10.0 0.03 10.5 0.04 11.0 0.05 11.3 0.07 11.6 0.13 11.9 0.65 12.0 0.88 12.1 0.84 12.2 0.54 12.3 0.32 12.4 0.21 12.5 0.15 12.6 0.11 12.7 0.09 12.8 0.08 13.0 0.06 13.2 0.05 13.4 0.05 13.6 0.04 13.8 0.03 14.0 0.03 14.3 0.03 14.6 0.02 15.0 0.02 15.5 0.02 16.0 0.02 16.5 0.01 17.0 0.01 17.5 0.01 18.0 0.01 19.0 0.01 20.0 0.01 22.0 0.01 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 1.00 oeo o.aa 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 0 Outflow Hydrograph (1-yr Design Storm) Post -Development DA A Outflow Hydrograph From Dry Swale Routings 0.0 0.00 0.5 0.01 1.0 0.01 1.5 0.01 2.0 0.01 2.5 0.01 3.0 0.01 3.5 0.01 4.0 0.01 4.5 0.01 5.0 0.01 5.5 0.01 6.0 0.01 6.5 0.02 7.0 0.02 7.5 0.02 8.0 0.02 8.5 0.02 9.0 0.03 9.5 0.03 10.0 0.04 10.5 0.05 11.0 0.08 11.3 0.10 11.6 0.18 11.9 0.82 12.1 1.12 12.1 1.10 12.2 0.85 12.3 0.41 12.4 0.29 12.5 0.21 12.6 0.16 12.7 0.13 12.8 0.11 13.0 0.09 13.2 0.07 13.4 0.06 13.6 0.06 13.8 0.05 14.0 0.04 14.3 0.04 14.6 0.04 15.0 0.03 15.5 0.03 16.0 0.02 16.5 0.02 17.0 0.02 17.5 0.02 18.0 0.02 19.0 0.01 20.0 0.01 22.0 0.01 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 0.0 -0.20 Outflow Hydrograph (2-yr Design Storm) 5.0 10.0 15.0 20.0 25.0 30.0 Post -Development DA A Outflow Hydrograph From Dry Swale Routings 0.0 0.00 0.5 0.02 1.0 0.02 1.5 0.02 2.0 0.02 2.5 0.02 3.0 0.02 3.5 0.02 4.0 0.02 4.5 0.03 5.0 0.03 5.5 0.03 6.0 0.03 6.5 0.03 7.0 0.04 7.5 0.04 8.0 0.04 8.5 0.05 9.0 0.06 9.5 0.07 10.0 0.08 10.5 0.11 11.0 0.15 11.3 0.20 11.6 0.33 11.9 1.21 12.0 1.50 12.1 1.65 12.2 1.58 12.3 1.36 12.4 0.88 12.5 0.38 12.6 0.29 12.7 0.24 12.8 0.21 13.0 0.17 13.2 0.14 13.4 0.13 13.6 0.11 13.8 0.10 14.0 0.09 14.3 0.08 14.6 0.07 15.0 0.07 15.5 0.06 16.0 0.05 16.5 0.04 17.0 0.04 17.5 0.04 18.0 0.03 19.0 0.03 20.0 0.02 22.0 0.02 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 0.0 Outflow Hydrograph (10-yr Design Storm) 5.0 10.0 15.0 20.0 25.0 30.0 Post -Development Detention Basin 'B' Routings and Inflow Hydrographs The following routing calculations and hydrographs reflect the summation of post -development attenuation in Subarea A from the proposed Dry Swale 'A' and the inflow hydrograph of Subarea B. The summation of these hydrographs reflects the inflow hydrograph for proposed Detention Basin ' B' BasinFlow printout INPUT: Basin: 7 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 584.80 5.00 0.0 585.00 412.00 1.1 586.00 780.00 22.9 587.00 1253.00 60.2 588.00 1808.00 116.5 589.00 2423.00 194.6 590.00 3124.00 297.1 Start—Elevation(ft) 585.00 Vol.(cy) 4 Outlet Structures Outlet structure 0 Orifice name: riser outlet area (sf) 0.785 diameter or depth (in) 12.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 583.500 multiple 1 discharge out of riser Outlet structure 1 Orifice name: riser inlet area (sf) 0.017 diameter or depth (in) 1.750 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 584.800 multiple 1 discharge into riser Outlet structure 2 Weir name: RISER TOP diameter (in) 12.000 side angle 0.000 coefficient 3.300 invert (ft) 589.200 multiple 1 discharge into riser 1.14 Outlet structure 3 Weir name: emergency spillway length (ft) 50.000 side angle 0.000 coefficient 3.300 invert (ft) 589.500 multiple 1 discharge through dam Wed Sep 08 11:56:03 EDT 2021 Post -Development DA B Inflow Hydrograph Time (hrs) Inflow (cfs) 0.0 0.00 0.5 0.02 1.0 0.02 1.5 0.02 2.0 0.02 2.5 0.02 3.0 0.02 3.5 0.02 4.0 0.02 4.5 0.02 5.0 0.03 5.5 0.03 6.0 0.03 6.5 0.03 7.0 0.03 7.5 0.03 8.0 0.03 8.5 0.04 9.0 0.05 9.5 0.05 10.0 0.06 10.5 0.08 11.0 0.10 11.3 0.13 11.6 0.21 11.9 1.14 12.0 1.60 12.1 1.41 12.2 0.82 12.3 0.47 12.4 0.32 12.5 0.24 12.6 0.19 12.7 0.15 12.8 0.14 13.0 0.11 13.2 0.10 13.4 0.09 13.6 0.08 13.8 0.07 14.0 0.06 14.3 0.06 14.6 0.05 15.0 0.05 15.5 0.04 16.0 0.04 16.5 0.04 17.0 0.03 17.5 0.03 18.0 0.03 19.0 0.03 20.0 0.02 22.0 0.02 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 1.80 1.60 1.4a 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 0 Inflow Hydrograph (1-yr Design Storm) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.3 11.6 11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 13.0 13.2 13.4 13.6 13.8 14.0 14.3 14.6 15.0 15.5 16.0 16.5 17.0 17.5 18.0 19.0 20.0 22.0 26.0 26.5 27.0 27.5 Post -Development DA B 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.D4 0.D4 0.D4 0.D4 0.05 0.05 0.06 0.07 0.07 0.08 0.10 0.14 0.18 0.29 1.56 2.18 1.92 1.12 0.64 0." 0.33 0.25 0.21 0.19 0.16 0.14 0.12 0.11 0.10 0.09 0.08 0.07 0.07 0.06 0.05 0.05 0.05 0.D4 0.D4 0.03 0.03 0.03 0.00 0.00 0.00 0.00 2.90 2.00 1.90 LM 0.90 0.00 0.90 Inflow Hydrograph (2-yr Design Storm) 30.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.3 11.6 11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 13.0 13.2 13.4 13.6 13.8 14.0 14.3 14.6 15.0 15.5 16.0 16.5 17.0 17.5 18.0 19.0 20.0 22.0 26.0 26.5 27.0 27.5 Post -Development DA B 0.04 0.04 0.05 0.05 0.05 0.05 0.05 0.06 0.06 0.06 0.07 0.07 0.08 0.08 0.08 0.09 0.10 0.12 0.13 0.15 0.19 0.26 0.34 0.54 2.90 3.81 3.57 2.09 1.19 0.81 0.61 0.47 0.39 0.34 0.29 0.25 0.22 0.20 0.18 0.16 0.15 0.14 0.13 0.06 0.06 0.05 0.05 0.05 0.D4 0.D4 0.03 0.03 0.00 0.00 0.00 0.00 4.90 4.Mao 3.90 3.M 2.90 z.M 1.90 M 0s0 0.00 0 30 0.0 Inflow Hydrograph (10-yr Design Storm) 1.0 10.0 150 20.0 25.0 30.0 Post -Development DA A+B Basin Inflow Hydrograph lased on Runoff of DA A+ E 0.0 0.00 0.5 0.02 1.0 0.02 1.5 0.02 2.0 0.02 2.5 0.03 3.0 0.03 3.5 0.03 4.0 0.03 4.5 0.03 5.0 0.03 5.5 0.04 6.0 0.04 6.5 0.04 7.0 0.04 7.5 0.05 8.0 0.05 8.5 0.06 9.0 0.07 9.5 0.07 10.0 0.09 10.5 0.11 11.0 0.16 11.3 0.21 11.6 0.34 11.9 1.80 12.0 2.48 12.1 2.25 12.2 1.37 12.3 0.79 12.4 0.53 12.5 0.39 12.6 0.30 12.7 0.24 12.8 0.21 13.0 0.18 13.2 0.15 13.4 0.13 13.6 0.12 13.8 0.11 14.0 0.09 14.3 0.08 14.6 0.08 15.0 0.07 15.5 0.06 16.0 0.05 16.5 0.05 17.0 0.05 17.5 0.04 18.0 0.04 19.0 0.03 20.0 0.03 22.0 0.02 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 3.00 2.50 zoo 1.50 1.00 0.50 0.00 -0.s0 Inflow Hydrograph (1-yr Design Storm) 1.0 Post -Development DA A+B Basin Inflow Hydrograph lased on Runoff of DA A+ E 0.0 0.00 0.5 0.03 1.0 0.03 1.5 0.03 2.0 0.03 2.5 0.04 3.0 0.04 3.5 0.04 4.0 0.04 4.5 0.04 5.0 0.05 5.5 0.05 6.0 0.05 6.5 0.06 7.0 0.06 7.5 0.06 8.0 0.07 8.5 0.08 9.0 0.09 9.5 0.10 10.0 0.12 10.5 0.16 11.0 0.22 11.3 0.28 11.6 0.47 11.9 2.38 12.0 3.30 12.1 3.02 12.2 1.97 12.3 1.06 12.4 0.72 12.5 0.53 12.6 0.41 12.7 0.34 12.8 0.29 13.0 0.24 13.2 0.21 13.4 0.18 13.6 0.16 13.8 0.15 14.0 0.13 14.3 0.12 14.6 0.11 15.0 0.10 15.5 0.09 16.0 0.07 16.5 0.07 17.0 0.06 17.5 0.06 18.0 0.06 19.0 0.05 20.0 0.04 22.0 0.03 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.aa 0 -0.50 Inflow Hydrograph (2-yr Design Storm) Post -Development DA A+B Basin Inflow Hydrograph lased on Runoff of DA A+ E 0.0 0.00 0.5 0.06 1.0 0.06 1.5 0.06 2.0 0.07 2.5 0.07 3.0 0.07 3.5 0.08 4.0 0.08 4.5 0.09 5.0 0.09 5.5 0.10 6.0 0.10 6.5 0.11 7.0 0.12 7.5 0.12 8.0 0.13 8.5 0.15 9.0 0.18 9.5 0.20 10.0 0.23 10.5 0.30 11.0 0.41 11.3 0.53 11.6 0.86 11.9 4.11 12.0 5.31 12.1 5.22 12.2 3.67 12.3 2.56 12.4 1.69 12.5 0.98 12.6 0.77 12.7 0.63 12.8 0.55 13.0 0.46 13.2 0.40 13.4 0.35 13.6 0.31 13.8 0.28 14.0 0.25 14.3 0.23 14.6 0.21 15.0 0.19 15.5 0.12 16.0 0.10 16.5 0.09 17.0 0.09 17.5 0.08 18.0 0.08 19.0 0.06 20.0 0.05 22.0 0.05 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 0 -1.00 Inflow Hydrograph (10-yr Design Storm) 1.0 Post -Development DA A+B Basin Inflow Hydrograph lased on Runoff of DA A+ E 0.0 0.00 0.5 0.12 1.0 0.12 1.5 0.13 2.0 0.14 2.5 0.14 3.0 0.15 3.5 0.15 4.0 0.16 4.5 0.17 5.0 0.18 5.5 0.19 6.0 0.20 6.5 0.21 7.0 0.22 7.5 0.24 8.0 0.25 8.5 0.29 9.0 0.34 9.5 0.36 10.0 0.43 10.5 0.55 11.0 0.75 11.3 0.98 11.6 1.79 11.9 9.81 12.0 11.61 12.1 8.30 12.2 4.39 12.3 2.66 12.4 1.90 12.5 1.47 12.6 1.17 12.7 1.01 12.8 0.92 13.0 0.78 13.2 0.68 13.4 0.61 13.6 0.55 13.8 0.50 14.0 0.45 14.3 0.41 14.6 0.38 15.0 0.35 15.5 0.31 16.0 0.27 16.5 0.25 17.0 0.24 17.5 0.22 18.0 0.21 19.0 0.18 20.0 0.15 22.0 0.14 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 -2.00 Inflow Hydrograph (100-yr Design Storm) Post -Development Detention Basin 'B' Routings and Outflow Hydrographs The following routing calculations and outflow hydrographs reflect the post -development attenuation in Subareas A & B from the proposed Detention Basin 'B' Post -Development DA A+B Outflow Hydrograph (From Det. Basin Routings) 0.0 0.03 0.5 0.00 1.0 0.03 1.5 0.03 2.0 0.03 2.5 0.03 3.0 0.04 3.5 0.04 4.0 0.04 4.5 0.04 5.0 0.04 5.5 0.04 6.0 0.04 6.5 0.05 7.0 0.05 7.5 0.05 8.0 0.05 8.5 0.05 9.0 0.06 9.5 0.06 10.0 0.06 10.5 0.07 11.0 0.08 11.3 0.08 11.6 0.09 11.9 0.09 12.0 0.14 12.1 0.14 12.2 0.14 12.3 0.14 12.4 0.14 12.5 0.16 12.6 0.16 12.7 0.16 12.8 0.16 13.0 0.17 13.2 0.17 13.4 0.17 13.6 0.17 13.8 0.17 14.0 0.17 14.3 0.17 14.6 0.16 15.0 0.16 15.5 0.16 16.0 0.16 16.5 0.16 17.0 0.16 17.5 0.15 18.0 0.15 19.0 0.15 20.0 0.14 22.0 0.13 26.0 0.10 26.5 0.09 27.0 0.08 27.5 0.08 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 0.0 Outflow Hydrograph (1-yr Design Storm) 5.0 10.0 15.0 20.0 25.0 30.0 Post -Development DA A+B Outflow Hydrograph (From Det. Basin Routings) 0.0 0.03 0.5 0.00 1.0 0.03 1.5 0.04 2.0 0.04 2.5 0.04 3.0 0.04 3.5 0.05 4.0 0.05 4.5 0.05 5.0 0.05 5.5 0.05 6.0 0.05 6.5 0.06 7.0 0.06 7.5 0.06 8.0 0.06 8.5 0.06 9.0 0.07 9.5 0.07 10.0 0.08 10.5 0.08 11.0 0.09 11.3 0.09 11.6 0.10 11.9 0.10 12.0 0.15 12.1 0.15 12.2 0.15 12.3 0.15 12.4 0.15 12.5 1.29 12.6 1.29 12.7 1.29 12.8 1.29 13.0 0.17 13.2 0.17 13.4 0.17 13.6 0.17 13.8 0.17 14.0 0.17 14.3 0.17 14.6 0.17 15.0 0.17 15.5 0.16 16.0 0.16 16.5 0.16 17.0 0.16 17.5 0.16 18.0 0.16 19.0 0.15 20.0 0.15 22.0 0.14 26.0 0.11 26.5 0.11 27.0 0.10 27.5 0.00 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 0 Outflow Hydrograph (2-yr Design Storm) Post -Development DA A+B Outflow Hydrograph (From Det. Basin Routings) 0.0 0.03 0.5 0.00 1.0 0.04 1.5 0.05 2.0 0.06 2.5 0.06 3.0 0.06 3.5 0.07 4.0 0.07 4.5 0.07 5.0 0.07 5.5 0.07 6.0 0.08 6.5 0.08 7.0 0.08 7.5 0.09 8.0 0.09 8.5 0.09 9.0 0.10 9.5 0.10 10.0 0.11 10.5 0.12 11.0 0.12 11.3 0.12 11.6 0.14 11.9 0.14 12.0 1.55 12.1 1.55 12.2 1.55 12.3 1.55 12.4 1.55 12.5 2.69 12.6 2.69 12.7 2.69 12.8 2.69 13.0 0.16 13.2 0.16 13.4 0.16 13.6 0.17 13.8 0.17 14.0 0.19 14.3 0.19 14.6 0.18 15.0 0.17 15.5 0.17 16.0 0.17 16.5 0.17 17.0 0.16 17.5 0.16 18.0 0.16 19.0 0.16 20.0 0.16 22.0 0.15 26.0 0.12 26.5 0.12 27.0 0.12 27.5 0.00 3.50 2.50 2.00 1.50 1.00 0.50 0.00 0 -0.50 Outflow Hydrograph (10-yr Design Storm) 30.0 Post -Development DA A+B Outflow Hydrograph (From Det. Basin Routings) 0.0 0.03 0.5 0.04 1.0 0.06 1.5 0.07 2.0 0.08 2.5 0.08 3.0 0.09 3.5 0.09 4.0 0.10 4.5 0.10 5.0 0.10 5.5 0.11 6.0 0.11 6.5 0.12 7.0 0.12 7.5 0.12 8.0 0.13 8.5 0.13 9.0 0.14 9.5 0.14 10.0 0.15 10.5 0.15 11.0 0.16 11.3 0.17 11.6 1.21 11.9 9.26 12.0 11.34 12.1 8.59 12.2 3.98 12.3 2.03 12.4 1.69 12.5 1.52 12.6 1.37 12.7 1.17 12.8 1.03 13.0 0.84 13.2 0.72 13.4 0.64 13.6 0.58 13.8 0.53 14.0 0.48 14.3 0.42 14.6 0.37 15.0 0.33 15.5 0.28 16.0 0.23 16.5 0.20 17.0 0.18 17.5 0.17 18.0 0.17 19.0 0.17 20.0 0.17 22.0 0.17 26.0 0.15 26.5 0.15 27.0 0.15 27.5 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 0.0 Outflow Hydrograph (100-yr Design Storm) 5.0 10.0 15.0 20.0 25.0 30.0 Virginia Runoff Reduction Method Water Quality Calculations (COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF PURCHASING NUTRIENT CREDITS. THE VRRM BOUNDARY IS DEFINED BY THE LIMITS OF DISTURBANCE) red Vogue, Punaff Red ion MemWRe,.prom lampllan<e SprtaOrFeer-Version 30 Ci ampwna.eeeenaspenwnaa o xma Dem amP s<anaemeena meewmbn. Pori Nere, Gi wm a/x]/mx9 - inem Pro r near lieu No P Iett.,_ a - Site Information -- ____-- _-- Post -Development Project (Treatment Volume and Loads) Enter Total Disturbed Nea(aaesf 2.10 Curate: BMP Deo,n eeiflmfions.13013 WaN an. t Spero No mnacorern..r,:enrereeco,remn J_-.. rnedrdurni �',, __ I � mreiai:memorenenrerear si Pre-aderivaopment Land rarer la=atl asap asaN cane asaie rou. .......... ,e.vape„w.a w=mil--a�n.mea an,mena,m.aa, Po6ttrNopmem land mwr dtrml rooe'Dw pare lxrevl m numeq pm�e.�. b ..woe. aap nm _-. - --- re.a,rme,�.aab w..ae. h- Ori-°am.....a.an. m. .eum..ea ea m..reeet e, 1. tnmmn. do... eoetaaem. larl --- mr6R •I pent, r. 045 pss m-pwm0�e:1 i>olrarlmrra mp=mou. �.e. oss ass ass oss roe �'a a-yeed rear iea .m,.n..aia=w`n Ion rendmr..s r,rn.pmar ....eeoeb -- rm..,0-S ... am — .. a eyroei -- M .°..° .. ...`i...eei a.. --. Ne,smeae.wm —_ —a .a .. rn aemr.snnn�w+.e wmorieuNm«rmarrmw) wra.s«ne ron n..eo..d.p.an aem aa.:� m.—a—.-- po:eoemo.mae. em.n. .mi.e,esi "` �^'•• ass 1--dap=ni"oe-i ..w.,Qi am are rswope,w... w..mmriba,.i are predw..nna arim,.,a de a�ea.�nam...re,es n�e.cn.., w�l rm,aremar) ra,.awwm .n�.eref :sages..° mpe eme.l=,a a.9 a..9 .�.roar'.o.el Moe%I.W . N Tw i>wl a-mp=m..,i ass mt npe i a,.i a�poeN —w—1 am Treatment Volume and pia enl Load Treatment Volume and Nutrient Load o=rrmoduaadatanoem w.o` aaam aorta fe a,a. tI�;>.ass oe.� V.1a.6nae 3,"a ws�n,><, neR LnM1.31 nay LE�o«op 291N pd IMetlM or, m..eiwwr..ppom odiew�.np«�.,.. aep «,R.pR..�ou.,o.,si� p.m p.w o..l +a�ns..nsrnre,su ` tl^^a^'=ommoo.a Tr rsee aeana sn 4 0.l] mmaa uauma Ld] �apmmemne ,.pueeA eardamee"Hudvn iesiv,i<me An—Ime.,.,mp.,.--order— ire w.em..nA.....�w�seo...le�a.m... ee,eammne �m doe ou myme/µal Poet-Dentelopment Requirement for She Area iP loatl Petlue[ion 0.epuiretl Ilb/yrl I.B4 Site Results (Water Quality Compliance) Area Checks O.A.A O.A.B O.A.0 A. D.A.E ARMECK FOREST/OVEN SPACE (a[) am O.W 0.00 i0.00 O.W OK. IMPERWOUS MVER (ac) IMPERVnMCOVERTRENTFD)ac) am 0.00 0.00 0.00 0.00 0.00�M. 0.00 OWOK. OK.. MANAGEDTURFAREA(a[) 0.00 O.00 0.00 00.W OK. MANAGED TURF AREA TREATED(a[) am O.00 0.00 0.00 OK. AREA CHECK OK OK. OK. OK. Site Treatment VOIUme (ffa) 4.028 Runoff Reduction Volume and TP By Drainage Area O.A. A D.AD O.A. E TOTALRUNOFF REDUMM VOLUME ACHIEVED pF) 0 0 0 LOADAVAKABLE FOR REMOVAL (b/1) 0.00 MM0 0.000.0.00 TPIDADREOUCTIONAGVEVED (b/yr) 0.00 0.00 O.W am TP LOAD REMAINING )Ib/yr) 0.00 0.00 O.W am NMWGEN IDAD REDUCTION ACHIEVED(b/yr) am O.W 0.00 0.00 O.W 0.00 Total Phosphorus FINAL POST -DEVELOPMENT TP LOAD Qb/yr) 2.91 TP LOAD REDUCTION REQUIRED pb/yr� 1.60 TPIDADREDUCTIONAODEVED (b/yr) 0.00 W LOAD REMAINING (lb/,): 2.91 REMAINING TP LOAD REDUCTION REQUIRED (lb/yr): 1.80