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HomeMy WebLinkAboutWPO202000037 Calculations 2021-07-19GALAXI E FARM STORMWATER MANAGEMENT CALCULATIONS PACKET (Amendment #1 to WPO 202000037) Date of Calculations JULY 19, 2021 APPROVED by the Albemarle County Community Development Department Date 9/28/2021 File WP0202000037 — Amendment #1 PREPARED BY: ;�., COLLINS ENGINEERING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations Soils Mapping (Source: NRCS Web Soil Survey Online Database) Soils Table (source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003) Map percent of Unit Map Unit flame A0I Symbol 71B Rabun clay loam, 15.3% 2 to 7 percent slopes 72C3 Rabun clay, 7 to 20.9% 15 percent slopes, severely eroded 72D3 Rabun clay, 15 38.2% to 25 percent slopes, severely eroded 79B Meadowville silt 25.6% loam, 2 to 7 percent slopes Totals for Area of 100.00/0 Interest The NRCS web soil survey defines this development's soils as predominantly having a hydrologic group type B. Precipitation Data (Source: NCIAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) Map ❑� Temail L �{ C eO 04 P a 414 *1a I �n �EoN 100m / POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90Ye CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, Volume 2, Version 3 PDS•based precipitation frequency estimates with 90% confidence intervals (in inches)' A"mge rerm iM mal(yens) Ouw6mOOO 70 0® +� ®® ,D6o 24-nr 3.01 (2.733A1) 3.67 (3.3D-4.12) 11 /.70 (4.215.27) 11 555 (4.96521) 11 6.83 (6.06-7.60) 11 7.92 (6.98a.80) 11 9.11 (7.97-1D.1) 11 105 (9.04-11.6) 123 (10.6-13.8) 11 14.2 (11.9A5.7) U.S. Department of Agriculture Natural Resources Conservation Service Project: Galaxie Farm Location: Galaxie Farm Ln. Check One: Present X 1. Runoff curve Number (CN) Developed TR 55 Worksheet 2: Runoff Curve Number and Runoff Designed By: FGM, PE Checked By: SRC, PE FL-ENG-21A 06/04 Date: 7/30/2021 Date: 7/30/2021 Soil name and Cover description CN (weighted) _ Drainage Area hydrologic group (Cover type, treatment, and hydrologic condition; percent CN Area Product of CN x total product/ Calculated Description (Appendix A) impervious; unconnected/ connected impervious area ratio) (Acres) Area total area 'S' Value Impervious Areas 98 0.61 59.8 Onsite DA A Lawns in Good Condition 61 7.04 429.4 (Pre-Dev.) B Exposed / Bare Earth 86 0.00 0.0 64 5.66 Woods in Good Condition 55 0.10 5.5 Impervious Areas 98 3.70 362.2 Onsite DA A Lawns in Good Condition 61 4.05 247.3 (Post-Dev.) e Exposed / Bare Earth 86 0.00 0.0 79 2 72 Woods in Good Condition 55 0.00 0.0 Impervious Areas 98 0.48 47.5 Onsite DA B Lawns in Good Condition 61 0.42 25.4 (Post-Dev.) B Exposed / Bare Earth 86 0.00 0.0 Bl 2.36 Woods in Good Condition 55 0.00 0.0 2. Runoff 1-Year Storm I 2-Year Storm I 10-Year Storm I 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 0.48 0.78 1.94 Onsite DA A (Pre-Dev.) Runoff, Q- inches 1.20 1.67 3.25 Onsite DA A (Post-Dev.) Runoff, Q- inches 1.34 1.84 3.47 Onsite DA B (Post-Dev.) U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (Tt) Project: Galaxie Farm Location: Galaxie Farm Ln. Designed By: FGM, PE Checked By: SRC, PE Check One: Present X Developed X Check One: Tc X Tt Segment ID: Sheet Flow: (Applicable to Tc 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, PZ (in.) 5 Land slope, s (ft/ft) 6 Compute Tt = [0.007(n*L)08] / P20.5 SOA 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 Tt = 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 ] / n 18 Flow length, L (ft) 19 Tt= L/ 3600*V 20 Watershed or subarea Tc or Tt (Add Tt in steps 6, 11 and 19) Note: The shoretest SCS Tc is 0.10 hrs. Date: 7/30/2021 Date: 7/30/2021 Through subarea n/a Onsite DA A Onsite DA A Onsite DA B (Pre-Dev.) (Post-Dev.) (Post-Dev.) Short Short Short Grass Grass Grass 0.15 0.15 0.15 100 100 75 3.67 3.67 3.67 0.06 0.06 0.12 0.10 0.10 0.06 Unpaved Unpaved 425 100 0.09 0.10 4.8 5.2 0.02 0.01 3 c ai c 3 c Oi c M C CLO ` LL C h0 ` N N b0 C N N toC E c v c E c v U m a)C m a) U @ O0 U M 00 o s o fl s o ti o 0 o a v o o Q (Uono " 'n E �m " 'a E L M L 0.00 0.00 0.12 1 0.11 10.10 U.S. Department of Agriculture Natural Resources Conservation Service Project: Location: Galaxie Farm Galaxie Farm Ln. TR 55 Worksheet 4: Graphical Peak Discharge Method Check One: Present X Developed X Designed By: FGM, PE Checked By: SRC, PE Date Date 7/30/2021 7/30/2021 1. Data Drainage Area Description Drainage Area Description Drainage Area Description Onsite DA A (Pre-Dev.) Onsite DA A (Post-Dev.) Onsite DA B (Post-Dev.) Drainage Area (Am) in milesz = 0.0121 0.0121 0.0014 Runoff curve number CN= 64 79 81 Time of concentration (Tc)= 0.12 0.11 0.10 Rainfall distribution type= II II 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 1.13 1.13 1.13 0.54 0.54 0.54 0.47 0.47 0.47 5. Compute la/P 0.37 0.31 0.20 0.18 0.15 0.10 0.16 0.13 0.09 6. Unit peak discharge, Qu- csm/in 775 875 925 950 975 1000 Out of Bounds 7. Runoff, Qfrom Worksheet 2- inches 0.48 0.78 1.94 1.20 1.67 3.25 1.34 1.84 3.47 8. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 1 1 1 1 1 9. Peak Discharge, Qp- cfs where Qp=Qu Am Q Fp See SCS Unit Hydrographs (Worksheet 5b) See Routing Calculations For Peak Outflov See SCS Unit Hydrographs I (Worksheet 5b) Channel and Flood Protection Computations (For Onsite Subareas A & B) 9 VAC 25-870-66 Section B: Channel Protection (Onsite Subarea A, Site Outfall #1) "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 (Calcuated) 51. F. * (Q Pre -Developed * (RV Pre -Developed ) ) / (RV Developed) Q Allowed (Calcuated) < Where: Q Pre -Developed = CN Pre -Developed — 5 Pre -Developed RV Pre -Developed CN Post -Developed— S Post -Developed — RV Post -Developed I.F. _ Q Developed 1.75 cfs 5.44 cfs (From Worksheet 4 Watershed Summary) 64 (From Worksheet 4 Watershed Summary) 5.66 (From SCS TR-55 eq. 2-4) 0.48 in. (From SCS TR-55 eq. 2-3) 79 (From Worksheet 4 Watershed Summary) 2.72 (From SCS TR-55 eq. 2-4) 1.20 in. (From SCS TR-55 eq. 2-3) 0.80 (Factor of Safety) = 1.46 cfs Section B.4 Limits of Analysis The analysis terminates at the detention faclity since "...subsection 3 of this subsection is utilized to show compliance with the channel protection criteria..." 9 VAC 25-870-66 (Onsite Subarea A, Site Outfall #1) 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 (the SWM facility), "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 Subarea A Peak Flow Rate = 21.93 cfs 10-Year, 24-Hour Post -Development Subarea A Peak Flow Rate = 20.93 cfs Section C.3 Limits of Analysis The flood protection analysis terminates at the SWM facility since subsection C.2.b is met. 9 VAC 25-870-66 (Onsite Subarea B, Site Outfall #2) 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.i.a. "The manmade stormwater conveyance system shall convey the postdevelopment peak flow rate from the two-year 24-hour storm event without causing erosion of the system." Note, the 2-year 24-hour storm event is not erosive on the concrete pipes and in the riprap lined outlet protection located within Cow Branch. Section B.4 Limits of Analysis "stormwater conveyance systems shall be analyzed for compliance with channel protection criteria to a point where either.." a. or b. are met Section B.4.a. "Based on land area, the site's contributing drainage area is less than or equal to 1.0% of the total watershed area;" Note, the analysis terminates at the point of analysis (i.e. the location in Cow Branch where manmade riprap improvements are proposed). 9 VAC 25-870-66 (Onsite Subarea B, Site Outfall #2) 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.a: The point of discharge (site outfall #2), "Confines the postdevelopment peak flow rate from the 10-year 24-hour storm event within the stormwater conveyance system [i.e. the storm sewer and riprap] to avoid the localized flooding." 10-Year, 24-Hour Design Storm Peak Back Water Surface Elevation = 464.54 ft Lowest Rim Elevation Envisioned in Storm Sewer System = 470.75 ft (No overtopping Occurs in Structures 12 & 14) Section C.3 Limits of Analysis ....stormwater conveyance systems shall be analyzed for compliance with flood protection criteria to a point where:" a, b or c are met. Section C.3.a.: "The site's contributing drainage area [i.e. Onsite Subarea B] is less than or equal to 1.0% of the total watershed area draining to a paint of analysis in the downstream stormwater conveyance system [i.e. the culverts and riprap];" Pre -Development SCS TR-55 Hydrographs (For Onsite Subarea A) Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) Onsite DA A (Pre-Dev.) 0.12 0.12 0.37 0.0058 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.90 12.0 3.30 12.1 5.44 12.2 3.05 12.3 1.26 12.4 1.00 12.5 0.87 12.6 0.73 12.7 0.62 12.8 0.56 13.0 0.50 13.2 0.44 13.4 0.40 13.6 0.37 13.8 0.34 14.0 0.31 14.3 0.28 14.6 0.27 15.0 0.24 15.5 0.22 16.0 0.20 16.5 0.18 17.0 0.17 17.5 0.16 18.0 0.16 19.0 0.14 20.0 0.12 22.0 0.11 26.0 0.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 -1.00 SCS TR-55 Pre -Development Unit Hydrograph (Onsite DA A) Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) Onsite DA A (Pre-Dev.) 0.12 0.12 0.31 0.0095 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 1.46 12.0 5.40 12.1 8.90 12.2 4.98 12.3 2.06 12.4 1.63 12.5 1.42 12.6 1.20 12.7 1.02 12.8 0.92 13.0 0.82 13.2 0.72 13.4 0.66 13.6 0.60 13.8 0.55 14.0 0.50 14.3 0.46 14.6 0.44 15.0 0.40 15.5 0.36 16.0 0.32 16.5 0.29 17.0 0.29 17.5 0.27 18.0 0.26 19.0 0.23 20.0 0.19 22.0 0.18 26.0 0.00 SCS TR-55 Pre -Development Unit Hydrograph (Onsite DA A) 30.0 Worksheet Sb (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Belov Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (mi2-in) Onsite DA A(Pre-Dev.) 0.12 0.12 0.20 0.0234 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 3.61 12.0 13.31 22.1 21.93 12.2 12.28 12.3 5.09 12.4 4.03 12.5 3.49 12.6 2.95 12.7 2.51 12.8 2.27 13.0 2.02 13.2 1.78 13.4 1.62 13.6 1.48 13.8 1.36 14.0 1.24 14.3 1.12 14.6 1.08 15.0 0.98 15.5 0.89 16.0 0.80 16.5 0.73 17.0 0.70 17.5 0.66 18.0 0.63 19.0 0.56 20.0 0.47 22.0 0.45 26.0 0.00 25.00 20.00 15.00 10.00 5.00 0.00 0 SCS TR-55 Pre -Development Unit Hydrograph (Onsite DA A) Proposed Dry Detention Basin 'A' Routing Calculations (For Onsite Subarea A) Galaxie Farm- Basin Routings BasinFlow printout INPUT: Basin: Galaxie Farm- Basin Routings 7 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 470.00 110.00 0.0 472.00 653.00 25.5 474.00 1658.00 108.2 476.00 3090.00 281.3 478.00 4971.00 577.1 480.00 6216.00 990.6 482.00 8129.00 1520.3 Start—Elevation(ft) 5 Outlet Structures Outlet structure 0 Orifice 470.00 Vol.(cy) 0.00 name: Barrel area (sf) 1.767 diameter or depth (in) 18.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 469.900 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low -Flow Orifice area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 470.000 multiple 1 discharge into riser Page 1 Galaxie Farm- Basin Routings Outlet structure 2 Orifice name: Mid -Flow Orifices area (sf) 0.785 diameter or depth (in) 12.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 477.330 multiple 5 discharge into riser Outlet structure 3 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 479.500 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Outlet structure 4 Weir name: Emergency Spillway length (ft) 40.000 side angle 75.960 coefficient 3.300 invert (ft) 480.500 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr 24-hr SCS TR-55 Design Storm Area (acres) 7.750 CN 79.000 Type 2 rainfall, P (in) 3.040 time of conc. (hrs) 0.1100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 11.747 peak time (hrs) 11.923 volume (cy) 1267.864 Page 2 Galaxie Farm- Basin Routings Hydrograph 1 SCS name: 2-yr 24-hr SCS TR-55 Design Storm Area (acres) 7.750 CN 79.000 Type 2 rainfall, P (in) 3.670 time of conc. (hrs) 0.1100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 16.390 peak time (hrs) 11.923 volume (cy) 1769.000 Hydrograph 2 SCS name: 10-yr 24-hr SCS TR-55 Design Storm Area (acres) 7.750 CN 79.000 Type 2 rainfall, P (in) 5.550 time of conc. (hrs) 0.1100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 31.644 peak time (hrs) 11.923 volume (cy) 3415.500 Hydrograph 3 SCS name: 100-yr 24-hr SCS TR-55 Design Storm Area (acres) 7.750 CN 79.000 Type 2 rainfall, P (in) 9.130 time of conc. (hrs) 0.1100 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 63.352 peak time (hrs) 11.923 volume (cy) 6837.930 Page 3 Galaxie Farm- Basin Routings OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 1 Routing Summary of inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 2 Routing Summary of inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 3 Routing Summary of inflow (cfs) discharge (cfs) water level (ft) storage (cy) Peaks: 1-yr 24-hr SCS TR-55 Design Storm 11.746 at 11.92 (hrs) 1.455 at 12.22 (hrs) 477.288 at 12.28 (hrs) 455.690 Peaks: 2-yr 24-hr SCS TR-55 Design Storm 16.388 at 11.92 (hrs) 8.385 at 12.06 (hrs) 477.933 at 12.06 (hrs) 564.794 Peaks: 10-yr 24-hr SCS TR-55 Design Storm 31.641 at 11.92 (hrs) 20.929 at 12.04 (hrs) 479.369 at 12.04 (hrs) 850.193 Peaks: 100-yr 24-hr 63.347 at 61.002 at 480.928 at 1218.911 Wed Jul 28 11:18:25 EDT 2021 SCS TR-55 Design Storm 11.92 (hrs) 11.94 (hrs) 11.94 (hrs) Page 4 Post -Development SCS TR-55 Hydrographs (For Onsite Subarea B) Worksheet Sb (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Belov Subarea Tc (hrs.) Tt (hr.) la / P Am»Q (mi2-in) Onsite DA B (Post-Dev.) 0.10 0.10 0.16 0.0019 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.05 SCS TR-55 Post -Development Unit 11.3 0.06 Y g H dro raPh Onsite DA B 11.6 0.10 11.9 0.63 2.00 12.0 1.22 1.80 22.1 1.90 1.60 12.2 1.17 1.40 12.3 0.41 1.20 12.4 0.28 1.00 0.80 12.5 0.23 0.60 12.6 0.20 0.40 - 12.7 0.16 0.20 12.8 0.14 0.00 13.0 0.12 0.0 5.0 10.0 15.0 20.0 25.0 13.2 0.11 13.4 0.10 13.6 0.09 13.8 0.08 14.0 0.07 14.3 0.06 14.6 0.06 15.0 0.05 15.5 0.05 16.0 0.04 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 30.0 Worksheet Sb (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Belov Subarea Tc (hrs.) Tt (hr.) la / P Am»Q (mi2-in) Onsite DA B (Post-Dev.) 0.10 0.10 0.13 0.0026 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.06 11.3 0.09 11.6 0.14 11.9 0.86 12.0 1.67 12.1 2.61 12.2 1.61 12.3 0.56 12.4 0.38 12.5 0.32 12.6 0.27 12.7 0.22 12.8 0.20 13.0 0.17 13.2 0.15 13.4 0.13 13.6 0.12 13.8 0.11 14.0 0.10 14.3 0.09 14.6 0.08 15.0 0.08 15.5 0.07 16.0 0.06 16.5 0.05 17.0 0.05 17.5 0.05 18.0 0.05 19.0 0.04 20.0 0.03 22.0 0.03 26.0 0.00 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0.0 SCS TR-55 Post -Development Unit Hydrograph (Onsite DA B) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet Sb (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Belov Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (mi2-in) Onsite DA B (Post-Dev.) 0.10 0.10 0.09 0.0049 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.12 11.3 0.17 11.6 0.26 11.9 1.63 12.0 3.15 12.1 4.92 12.2 3.04 12.3 1.06 12.4 0.72 12.5 0.60 12.6 0.51 12.7 0.42 12.8 0.37 13.0 0.32 13.2 0.28 13.4 0.25 13.6 0.22 13.8 0.20 14.0 0.19 14.3 0.17 14.6 0.16 15.0 0.14 15.5 0.13 16.0 0.11 16.5 0.10 17.0 0.10 17.5 0.09 18.0 0.09 19.0 0.07 20.0 0.06 22.0 0.06 26.0 0.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (Onsite DA B) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Storm Sewer Analysis 1. For verification of Onsite DA B's channel and flood protection compliance, and 2. For the proposed bypass storm sewer system associated with the ESC plan. Note: For the bypass storm sewer system's contributing drainage area, please see the sheet entitled 'Drainage Plan for the Bypass Storm Sewer' and the section at the back of this report entitled 'Synchronized Hydrographs to the Bypass Storm Sewer'. Storm Sewer Design Sturm Year= 10 POINT DOWNSTREAM STRUCTURE DRAIN AREA RUNOFF COEFF. CA INLET TIME RAIN FALL RUNOFF Q INVERT ELEVATIONS LENGTH SLOPE DIA CAPA- CITY VEL FLOW TIME REMARKS INCR JACCUM ACRES C MIN IN/HR C.F.S. UPPER LOWER FEET FT./FT. INCHES C.F.S. F.P.S. SEC ES-1 15.60 0.55 8.58 8.58 17.00 4.29 45.70 8 484.60 479.50 273.70 0.0186 30 60.6 13.5 20.3 8 1.95 0.40 0.78 9.36 17.34 4.25 49.02 6 479.40 475.75 185.33 0.0197 30 62.4 14.0 13.2 6 1.11 0.35 0.39 9.75 17.56 4.23 50.66 4 475.65 474.74 51.94 0.0175 30 58.8 13.4 3.9 4 21.60 0.25 5.40 15.15 17.62 4.22 50.66 2 474.64 471.30 197.56 0.0169 30 57.8 13.3 14.9 2 0.00 0.45 0.00 18.75 17.87 4.19 70.41 OUT 468.80 468.25 36.02 0.0153 36 89.4 14.0 2.6 14 0.28 090 0.25 0.25 5.00 6.67 4.92 12 464.08 463.32 38.04 0.0200 15 9.9 8.0 4.8 12 0.62 0.50 0.31 0.56 6.00 6.35 4.92 OUT 459.32 458.10 1939 0.0629 l5 17.6 12.2 L6 Collins Engineering 7/28/2021 Page l Design Yen: 10 Hydraulic Grade Line Calculation Project: Galaxie Farm Job #: 202194 Prepared by: FGM, PE INLET OUTLET WATER Do % S, Ht JUNCTION LOSS FINAL INLET WATER RIM STATION SURFACE ELEV ZW V. B- ON Vw Qi VI V,2/2g H; ANGLE He H, 1.3H, .511$ H SURFACE ELEV. ELEV 459.10 19.39 15 4.92 0.005 0.10 4.0 0.1 12 4.92 4.0 19.73 0.2 0.09 0 0 0.15 NA 0.07 0.17 459.27 470.75 464.32 38.04 15 4.92 0.005 0.19 4.0 0.1 14 0.00 170 0 0.06 NA 0.03 0.22 464.54 470.75 470.65 36.02 36 70.41 0.009 0.34 10.0 0.4 2 50.66 10.3 522.9 1.7 0.58 0 0 0.96 N/A 0.48 1.04 471.69 482.00 473.30 197.56 30 50.66 0.013 2.57 10.3 0.4 4 50.66 10.3 522.9 1.7 0.58 154 1.1578 2.15 N/A 1.08 3.64 476.94 482.00 476.94 51.94 30 50.66 0.013 0.68 10.3 0.4 6 49.02 10.0 489.5 1.5 0.54 180 1.08393 2.04 NA 1.02 1.69 478.64 480.00 478.64 185.33 30 49.02 0.012 2.26 10.0 0.4 45.70 9.3 425.5 1.3 0.47 138 0.94217 1.80 NA 0.90 3.16 481.79 484.20 FFS-I 481.79 273.70 30 45.70 0.011 2.90 9.3 0.3 0.00 180 0 0.34 NA 0.17 3.06 484.86 488.50 Collins Engineering Hydraulic Grade Line Page 1 Water Quality Calculations Using the DEQ Virginia Runoff Reduction Method for New Developments (Compliance is met through a nutrient credit purchase.) UrG DErPInln Xun Allearntbn MelFadNewOesaEaMtantrmnWfave 3lrtadaElaat 02011 aMP standards and Speaftatbm Man. DraN BMPshMaNsaM SpaMlotlwu� Pmle«Name' Galati Fame VSMP Mrendment dl Date: ]/30/2021 MP Dedpns ffladena un: 2013 Daft Stds&Spec Site Information Project (Treatment Volume and Loads) CanUants anm,d paimallindesl u ].¢t NNnnE Er.mlirx'n..l ].00 gnrWnJ I... is alNbgen ]NIEMCIm 1 N)EW(m vg«,Pt..ala.o./nl oa9 as vl lunabsan«b'mf«a«I a9a Foren/Opmspautaerlaveil GOO weidnm mrlMreagl Dm a Forx o MerepN In rlwexl ].SB welgM.d. lean den %MenegN Turf FD% ImpeMoux cmer laa-1 5,14 gr l'im mouxl 0e1 %Impervious W% .mwla— �IaeMl 0.5333 Treatment Volume leuble hHl ]3,223 R Load (lb/yr) 10.59 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) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED In) 0.00 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA(ac) 0.00 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA TREATED(ac) 0.00 0.00 0.00 0.00 0.00 OK. AREA CHECK OK. OK. OK. OK. OK. Site Treatment Volume (ft3) 0 Runoff Reduction Volume and TP By Drainage Area D.A. D D.A. E TOTAL RUNOFF REDUCTION VOLUME ACHIEVED (k) 0 0 0 D 0 0 TP LOAD AVAILABLE FOR REMOVAE(Ib/yr) 0.00 0.00 0.00 0.00 0.00 0.00 TP LOAD REDUCTION ACHIEVE 0.00 0.00 0.00 0.00 0.00 0.00 TP LOAD REMAININ 0.00 0.00 0.00 0.00 0.00 000 NITROGEN LOAD REDUCTION ACHIEVE 0.00 0.00 0.00 0.00 0.00E 0.00 Total Phosphorus FINAL POST-DEVELOPMENTTP LOAD (Ib/yr)M TP LOAD REDUCTION REQUIRED (Ib/yr) TP LOAD REDUCTION ACHIEVED (Ib/yr) TP LOAD REMAINING (Ib/yr): REMAINING TP LOAD REDUCTION REQUIRED (Ib/yr): Total Nitrogen (For Information Purposes) POST -DEVELOPMENT LOAD (Ib/yr) NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) REMAINING POST -DEVELOPMENT NITROGEN LOAD (Ib/yr) Synchronized Hydrographs that Contribute to the Bypass Storm Sewer (These hydrographs were generated so that the proposed bypass storm sewer associated with the ESC plan could be sized appropriately. These peak flows are reflected in the storm sewer computations for the bypass storm sewer.) Avinity I Outflow Hydrograph (From Basin's Routings) Time (hrs) Outflow (cfs) 0.0 0.00 0.5 0.00 1.0 0.06 1.5 0.19 2.0 0.35 2.5 0.48 3.0 0.59 3.5 0.68 4.0 0.75 4.5 0.81 5.0 0.87 5.5 0.92 6.0 0.95 6.5 1.18 7.0 1.23 7.5 1.29 8.0 1.36 8.5 1.44 9.0 1.59 9.5 1.77 10.0 1.92 10.5 2.15 11.0 2.49 11.5 3.02 11.9 4.63 12.0 5.51 12.1 17.61 12.2 37.20 12.3 34.03 12.4 26.36 12.5 19.84 13.0 7.02 13.5 5.86 14.0 5.59 14.5 5.28 15.0 4.93 15.5 4.57 16.0 4.20 16.5 3.80 17.0 3.40 17.5 3.02 18.0 2.64 18.5 2.29 19.0 1.97 19.5 1.70 20.0 1.45 20.5 1.24 21.0 0.96 21.5 0.93 22.0 0.89 22.5 0.86 23.0 0.82 23.5 0.79 24.0 0.77 24.5 0.55 25.0 0.27 25.5 0.11 26.0 0.03 26.5 0.00 27.0 0.00 27.5 0.00 28.0 0.00 28.5 0.00 29.0 0.00 29.5 0.00 30.0 0.00 30.5 0.00 31.0 0.00 40.00 35.00 30.00 25.00 20.00 15A0 10.00 5.00 am 5.00 Outflow Hydrograph (10-yr Design Storm) Avinity II Outflow Hydrograph (From Basin's Routings) Time (hrs) Outflow (cfs) 0.0 0.00 0.5 0.17 1.0 0.27 1.5 0.33 2.0 0.36 2.5 0.38 3.0 0.40 3.5 0.41 4.0 0.43 4.5 0.44 5.0 0.46 5.5 0.48 6.0 0.50 6.5 0.52 7.0 0.53 7.5 0.55 8.0 0.57 8.5 0.60 9.0 0.63 9.5 0.68 10.0 0.72 10.5 0.78 11.0 0.87 11.5 1.00 11.9 2.10 12.0 2.98 12.1 7.35 12.2 8.50 12.3 8.40 12.4 8.35 12.5 5.10 13.0 3.00 13.5 2.83 14.0 2.61 14.5 2.33 15.0 2.02 15.5 1.63 16.0 1.29 16.5 1.26 17.0 1.23 17.5 1.20 18.0 1.16 18.5 1.13 19.0 1.09 19.5 1.05 20.0 1.00 20.5 0.95 21.0 0.89 21.5 0.84 22.0 0.78 22.5 0.72 23.0 0.65 23.5 0.59 24.0 0.54 24.5 0.43 25.0 0.29 25.5 0.16 26.0 0.06 26.5 0.02 27.0 0.01 27.5 0.00 28.0 0.00 28.5 0.00 29.0 0.00 29.5 0.00 30.0 0.00 30.5 0.00 31.0 0.00 10.00 9.00 am 1.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 Outflow Hydrograph (10-yr Design Storm) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Structure ES-1 Inflow Hydrograph for Overland Runoff (Does not Include Routed Amity I & 11) Time (min.) Inflow (ds) 1.0 2.17 2.0 4.33 3.0 6.50 4.0 &6] 5.0 10.83 6.0 13.00 7.0 15.16 8.0 17.33 9.0 19.50 10.0 21.66 11.0 23.83 12.0 26.00 13.0 28.16 14.0 30.33 15.0 32.49 16.0 34.66 27.0 36.83 18.0 35.53 19.0 34.23 20.0 32.93 21.0 31.64 22.0 30.34 23.0 29.04 24.0 27.75 25.0 26.45 26.0 25.15 27.0 23.85 28.0 22.56 29.0 21.26 30.0 19.96 31.0 18.67 32.0 17.37 33.0 16.07 34.0 14.77 35.0 13.48 36.0 12.18 37.0 10.88 38.0 9.59 39.0 8.29 40.0 6.99 41.0 5.69 42.0 4.40 43.0 3.10 44.0 LED 45.0 0.51 46.0 0.00 47.0 0.00 48.0 0.00 49.0 0.00 50.0 0.00 51.0 0.00 52.0 0.00 53.0 0.00 54.0 0.00 55.0 0.00 56.0 0.00 57.0 0.00 58.0 0.00 59.0 0.00 60.0 0.00 40.00 35.00 30.00 25.00 20.00 ism 30.00 sW 0.00 s 00 Inflow Hydrograph (30-yr Design Storm) Synchronized (Inflow) Unit Hydrograph To Proposed Structure ES-1 This inflow hydrograph sychronizes the Avinity, I outflow hydrograph, the Avinity II outflow hydrograph and the Str. ES-1 inflow hydrograph to determine the peak flow to structure ES-1 (i.e. the upstream point of the bypass storm sewer). Hydrograph Time 10yr Discharges (hrs.) (cfs) 0.0 2.17 0.1 13.00 0.2 26.00 0.3 36.83 0.4 27.75 0.5 20.13 0.6 12.18 0.7 4.40 0.8 0.00 0.9 0.00 1.0 0.33 1.5 0.52 2.0 0.70 2.5 0.86 3.0 0.99 3.5 1.09 4.0 1.18 4.5 1.26 5.0 1.33 5.5 1.40 6.0 1.45 6.5 1.69 7.0 1.77 7.5 1.85 8.0 1.93 8.5 2.03 9.0 2.22 9.5 2.44 10.0 2.64 10.5 2.93 11.0 3.36 11.5 4.02 11.9 6.73 12.0 8.50 12.1 24.96 12.2 45.T0 12.3 42.43 12.4 34.21 12.5 24.94 13.0 10.03 13.5 8.69 14.0 8.20 14.5 7.61 15.0 6.95 15.5 6.20 16.0 5.48 16.5 5.06 17.0 4.63 17.5 4.21 18.0 3.81 18.5 3.41 19.0 3.06 19.5 2.74 20.0 2.45 20.5 2.19 21.0 1.85 21.5 1.12 22.0 1.67 22.5 1.57 23.0 1.48 23.5 1.39 24.0 1.31 24.5 0.98 25.0 0.57 25.5 0.28 26.0 0.09 26.5 0.02 27.0 0.01 27.5 0.01 28.0 0.00 28.5 0.00 29.0 0.00 29.5 0.00 30.0 0.00 30.5 0.00 31.0 0.00 Inflow Unit Hydrograph To Proposed Str. ES-1 5000 -10yroischarges Ira) 1 5 913122125293332414549539616569J3 45.00 40.110 35.00 Structure 4 Inflow Hydrograph (Accounts for Overland Runoff & SWM Facility l0 0446.01) Time (min.) Inflow(cfs) 1.0 1.64 2.0 3.27 3.0 4.91 4.0 6.55 5.0 8.18 6.0 9.82 7.0 11.45 8.0 13.09 9.0 14.73 10.0 16.36 11.0 18.00 12.0 22.17 13.0 21.27 14.0 22.91 15.0 24.54 16.0 23.56 17.0 22.58 18.0 21.60 19.0 20.62 20.0 19.65 21.0 18.67 22.0 17.69 23.0 16.71 24.0 15.73 25.0 14.75 26.0 13.77 27.0 12.79 28.0 11.81 29.0 10.83 30.0 9.85 31.0 8.87 32.0 7.89 33.0 6.91 34.0 5.93 35.0 4.95 36.0 3.97 37.0 2.99 38.0 2.01 39.0 1.03 40.0 0.05 41.0 0.00 42.0 0.00 43.0 0.00 44.0 0.00 45.0 0.00 46.0 0.00 47.0 0.00 48.0 0.00 49.0 0.00 50.0 0.00 51.0 0.00 52.0 0.00 53.0 0.00 54.0 0.00 55.0 0.00 56.0 0.00 57.0 0.00 58.0 0.00 59.0 0.00 60.0 0.00 Inflow Hydrograph (10-yr Design Storm) 0.00 11.0 No MO NOTE: This inflow hydrograph was completed to ensure the proposed bypass pipes 1 & 3 are appropriately sized. The bypass' proposed structure 4 will accept this upland offsite runoff with the developmet of Galaxie Farm. Note, this hydrograph takes Into consideration the overland flow captured by the existing culvert beneath Galaxie Farm Lane and the approved WPO 201200022, SWM Facility ID 0446,01. This SWM facility contains 3 outlet control structures. The primary control (underdrains and a connected riser/barrel system) and the tertiary control (emergency spillway) release runoff to a subarea outside of Galaxie Farm's watershed. The secondary control (a second riser/barrel system) is partially activated during the 10yr design storm and releases runoff to Galaxie Farm's watershed (peak flow of 2.53 cfs at a time of 12.11 hrs. per the asbuilt routings). Synchronized (Inflow) Unit Nydrograph to proposed Structure 4 This inflow hydrogmph Wchronizes the Str. ES-1 hydrograph (which accounts for the Avinity I outflow hydrograph, the Avinity II outflow hydrograph and the structure ES-1's overland flow) and the Str.4 inflow hydrograph (which accounts for the SWM Facility ID 0446.01 and structure 4's overland flaw). This inflow hydrograph does not take into account the minor offsite areas flawing directly to structures 4 & 6. These areas/Flaws are accounted For separately in the storm sewer compuations. fmph Time 30yr Discharges hrs.) (cfs) 0.0 3.80 0.1 22.81 0.2 48.16 0.3 59.41 0.4 43.47 0.5 29.98 0.6 48.18 0.7 4.40 0.8 0.m 0.9 0.W 1.0 0.33 1.5 0.52 2.0 0.70 2.5 0.86 3.0 0.99 3.5 1.09 4.0 1.18 4.5 1.26 5.0 1.33 5.5 1.40 6.0 1,45 6.5 1,69 7.0 1.77 7.5 1.85 8.0 1.93 8.5 2.03 9.0 2.22 9.5 2.44 10.0 2.64 10.5 2.93 11.0 3.36 11.5 4.02 11.9 6.73 12.0 8.50 12.1 24.96 12.2 45.]0 12.3 42.43 12.4 34.71 12.5 24.94 13.0 10.03 13.5 8.69 14.0 8.20 14.5 7.61 15.0 6.95 15.5 6.20 16.0 5.48 16.5 5.06 SZO 4.63 17.5 4.21 18.0 3.81 18.5 3.41 19.0 3.06 19.5 2.74 20.0 2.45 20.5 2.19 21.0 1.85 21.5 1.77 22.0 1.67 22.5 1.57 23.0 1.48 23.5 1.39 24.0 1.31 24.5 0.98 25.0 0.57 25.5 0.28 26.0 0.09 26.5 0.02 27.0 0.01 27.5 0.01 28.0 0.00 28.5 0.00 29.0 0.00 29.5 0.00 30.0 0.00 30.5 0.00 NOTE: Approved WPO 201200022, SWM Facility ID 0446.01, releases a peak flow, of 2.53 ds at a time of 12.11 hrs. (per the asbuih mutings). While this outflow does not synchronize with the adjacent downstream subarea/ inflow hydrograph shown on the previous page, it does synchronize with the Avinity I and Avinity II peak autflaws resulting from the attenuation in these facilities. As a result, the 2.53 ds peak outflow from SWM Facility ID 0446.01 was added to this synchronized hydrograph to ensure its runoff was properly accounted far.