Loading...
HomeMy WebLinkAboutWPO202100007 Calculations 2021-01-27BROOKHILL STORMWATER MANAGEMENT CALCULATIONS PACKET (Blocks 16-17) Date of Calculations JANUARY 21, 2020 PREPARED BY: COLLINS 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations Soils Mapping (Source: NRCS Web Soil Survey Online Database) Soils Table (Source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003) Map Unit Map Uni[ Name percent of Percent Symbol AOI 16 Codorus silt 2.6% loam, 0 to 2 percent slopes, occasionally flooded 27B Elioak loam, 2 24.7% to 7 percent slopes 27C Elioak loam, 7 20.5% to 15 percent slopes 28133 Elioak clay 0.2% loam, 15 to 25 percent slopes, severely eroded 34B Glenelg loam, 2 8.5% to 7 percent slopes 34C Glenelg loam, 7 9.2% to 15 percent slopes 34D Glenelg loam, 3.0% 15 to 25 percent slopes 39D Hazel loam, 15 25.9% to 25 percent slopes 39E Hazel loam, 25 3.5% to 45 percent slopes 95 Hatboro silt 2.0% loam, 0 to 2 percent slopes, occasionally flooded Totals for Area of 100.00% Interest Note: The soils' properties witin this development are predominantly (96%+/-) composed of hydrologic soil group type B soils. Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) Pbr�rr O tpOaQ Plop � 2 Terrain Pshwoo°e /4 � a T15 O1n,le9e W°v ` a i330° o � �i1 m p c 0 Y 30 0 m 0 I c o e`N ��ao o`Qo1n c Polo Q` o°°°s Ra c 7�e95aw` 0 o at N 4 2, °c CO 000 0.4km d.2mi .v l:an ehrnnt POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90 % CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, VOlume 2, Version 3 IRDSbased precipitation frequency estimates with 90% confidence Intervals (In inches)' Avaa9e nxen Fleml (yeas) �� oo© 10 25 60 100 200 ® 10W 244r 3.00 (2.693.38) 3.63 1 (3.26-4.09) 4,64 1 (4.155.21) 5A8 1 (4.896.15) 6.74 1 (5.97-7.53) 7.81 (6.87-9.71) 8.99 (7.85-10.0) 10.3 (8.89-11.4) 12.3 (10.4-13.6) 135 1 (113-15.5) }}\ §; ]{ w§@a!a ) R!a@mam!@a§@ u \ / o | - .J3; Jo ! ! .]l.Jl.7l J! . ! ! ! ])|])| ]!|])|]!|])| f _ !!!2!! ! !kf£lf7kf£!f )\ U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (T,) or Travel Time (Tj Project: Brookhill Location: Blocks 16-17 Check One: Present X Developed X Check One: T, X T, Segment ID Sheet Flow: (Applicable to T, only) 1 Surface description (Table 3-I) 2 Manning's roughness coeff., o (Table 3-1 3 Flow length, L (total L < 100) (ft) 4 Two-year 24-hour rainfall, P,(in.) 5 Land slope, s (ft/ft) 6 Compute T,= (0.007(n•L)0a) / Pi 3 sa Shallow Concentrated Flow: ] Surface description (paved or unpaved) 8 Flow Length, L (ft) 9 Watercourse slope, s(R/ft) 10 Average velocity, V (Figure 3-I) (ft/s) 11 T,=L/3600•V Channel Flow: 12 Cress sectional Now area, a (ft) 13 Wetted perimeter, P„ (ft) 14 Hydraulic radius, r= a/P„ (it) 15 Channel Slope, s (ft/ft) 16 Manning's Roughness Coeff, n 17 V= ( 1A9rV3s05 ] / n 18 Flow length, L (R) 19 T� I / 3600•V 20 Watershed or subarea T, or T, (Add T, in steps 6, 31 and 19) Note: The shoretest SCS Tc is 0.10 hm. Designed By: FGM, PE Checked By: SRC, PE Through subarea n/a FL-ENG-21A O6/04 Date: 12/23/2020 Date: 12/23/2020 DAA DAA DAA DAB DAB DAB DAC CAC (Pre-Dev.) (Post-Dev.) (Final Buildout) (Pre-Dev.) (Port-Dev.) (Final Buildout) (Pre-Dev.) (Post-Dev.) Dense Dense Dense Dense Dense Dense Dense Dense Grass Grass Grass Grass Grass Grass Grass Grass 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 100 100 100 100 100 IN 100 60 3.63 3.63 3.0 3.63 3.63 3.63 3.63 3.63 0.07 0.16 0.16 0.04 O.OS O.OS 0.09 0.25 0.135 1 0.10 0.10 0.17 OAS O.1S 0.12 0.05 Unpaved Unpaved Unpaved Unpaved Unpaved 650 I1S0 100 100 75 0.14 0.07 0.05 O.OS 0.20 6.3 4.3 3.6 3.6 7.2 0.029 0.07 0.01 0.01 0.00 o PJ o WJ o+ o+ 2 m+ m+ x x x x w n a n a a E E o c o `o ,n `o 0 6 rn 0 6 rn o. o. _ a - o. n p r p ve S o S a S o e S e A m A a a .. .. 0.16 1 0.12 1 0.12 1 0.24 1 0.17 1 0.17 1 0.13 1 0.10 !< f, !< ) s � � § Channel & Flood Protection Calculations 9 VAC 25-870-66 (Point ofAnalysis'A') 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: Under no condition shall Q Developed be greater than Q Pre -Developed nor shall Q Developed be required to be less than that calculated in the equation: Q Allowed < (Q Forest * RV Forest ) I RV Developed Q Allowed Where: QForest = CN Forest= S Forest RV Forest= CN Post -Developed= S Post -Developed = RV Post -Developed = Q Developed Q Developed < 0.15 cfs 0.94 cfs (From Worksheet 4 Watershed Summary) 55 (From Worksheet 4 Watershed Summary) 8.18 (From SCS TR-55 eq. 2-4) 0.19 in. (From SCS TR-55 eq. 2-3) 80 (From Worksheet 4 Watershed Summary) 2.54 (From SCS TR-55 eq. 2-4) 1.23 in. (From SCS TR-55 eq. 2-3) = 0.15 cfs (For Proposed Watershed) = 0.15 Cfs (For Final Buildout Watershed) Section B.4 Limits of Analysis The analysis terminates at the onsite subarea since subsection B.3.a is met. 9 VAC 25-870-66 (Point of Analysis W) 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.: Concentrated stormwater flow to stormwater conveyance systems that currently experience localized flooding [i.e. the floodplain] during the 10-year 24-hour storm event shall confine the postdevelopment peak flow rate from the 10-year 24-hour storm event within the stormwater conveyance system [i.e. the detention facilities] to avoid the localized flooding. Detention of stormwater or downstream improvements may be incorporated into the approved land -disturbing activity to meet this criterion." Please note, the detention facilities contain the 10-yr design storm, herby satisifying this critei 10-yr 24-hr SCS Design Storm's Peak WSE = 371.46 ft (For Proposed Plan) 10-yr 24-hr SCS Design Storm's Peak WSE = 371.56 ft (For Final Buildout) SWM Facility Top of Dam Elevation = 373.00 ft Section C.3 Limits of Analysis "...Stormwater conveyance systems shall be analyzed for compliance with flood protection criteria to a point where" either a, b or c are met. Section C.3.c.: "The stormwater conveyance system [i.e. the facilities' outfall] enters a mapped floodplain or other flood -prone area, adopted by ordinance, of any locality." 9 VAC 25-870-66 (Point ofAnalysis'B') 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: Under no condition shall Q Developed be greater than Q Pre -Developed nor shall Q Developed be required to be less than that calculated in the equation: Q Allowed < (Q Forest * RV Forest ) I RV Developed Q Allowed Where: QForest = CN Forest= S Forest RV Forest= CN Post -Developed= S Post -Developed = RV Post -Developed = Q Developed Q Developed < 0.24 cfs 1.43 cfs (From Worksheet 4 Watershed Summary) 55 (From Worksheet 4 Watershed Summary) 8.18 (From SCS TR-55 eq. 2-4) 0.19 in. (From SCS TR-55 eq. 2-3) 79 (From Worksheet 4 Watershed Summary) 2.68 (From SCS TR-55 eq. 2-4) 1.18 in. (From SCS TR-55 eq. 2-3) = 0.19 cfs (For Proposed Watershed) = 0.24 cfs (For Final Buildout Watershed) Section B.4 Limits of Analysis The analysis terminates at the onsite subarea since subsection B.3.a is met. 9 VAC 25-870-66 (Point of Analysis W) 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.: Concentrated stormwater flow to stormwater conveyance systems that currently experience localized flooding [i.e. the floodplain] during the 10-year 24-hour storm event shall confine the postdevelopment peak flow rate from the 10-year 24-hour storm event within the stormwater conveyance system [i.e. the wet pond] to avoid the localized flooding. Detention of stormwater or downstream improvements may be incorporated into the approved land - disturbing activity to meet this criterion." Please note, the wet pond contains the 10-yr design storm, herby satisifying this criterion. 10-yr 24-hr SCS Design Storm's Peak WSE = 369.59 ft (For Proposed Plan) 10-yr 24-hr SCS Design Storm's Peak WSE = 370.32 ft (For Final Buildout) SWM Facility Top of Dam Elevation = 372.00 ft Section C.3 Limits of Analysis "...Stormwater conveyance systems shall be analyzed for compliance with flood protection criteria to a point where" either a, b or c are met. Section C.3.c.: "The stormwater conveyance system [i.e. the wet pond's outfall] enters a mapped floodplain or other flood -prone area, adopted by ordinance, of any locality." 9 VAC 25-870-66 (Point ofAnalysis'C') 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.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-yr 24-hour design storm's peak flow rate is not erosive in the concrete storm sewer and cross sections A (manmade channel), B (manmade channel) and C (manmade double 60"x60" concrete box culverts in stream's bed). This conclusion is logical since the storm sewer, manmade channels and manmade box culverts were designed for storms in excess of the 2-year design storm and were recently approved with adequacies. Section B.4.a. Limits of Analysis Stormwater conveyance systems shall be analyzed for compliance with channel protection criteria to a point where, based on land area, the site's contributing drainage area is less than or equal to 1.0% of the total watershed area. Note, post -development subarea C's contributing drainage area is less than 1% of the overall watershed draining to cross section C (the double 60"x60" concrete box culverts). 9 VAC 25-870-66 (Point of Analysis'C') 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.: Concentrated stormwater flow to stormwater conveyance systems that currently experience localized flooding [i.e. the floodplain] during the 10-year 24-hour storm event shall confine the postdevelopment peak flow rate from the 10-year 24-hour storm event within the stormwater conveyance system [i.e. the storm sewer] to avoid the localized flooding." Please note, the storm sewer's hydraulic grade line calculations have been provided showing the peak back water elevations do not overtop the inlets, herby satisifying this requirement. This is consistent with logic since storm sewer systems are designed for the 10-year storm events. Section C.3 Limits of Analysis "...Stormwater conveyance systems shall be analyzed for compliance with flood protection criteria to a point where" either a, b or c are met. Section C.3.c.: "The stormwater conveyance system [i.e. the downstream storm sewer] enters a mapped floodplain or other flood -prone area, adopted by ordinance, of any locality." Dry Detention Basin 'A' & Underground Detention System Combined Routing Calculations (Subarea A- Proposed Development) BH Blocks 16-17 UGD System- Subarea A Proposed Plan BasinFlow printout INPUT: Basin: Brookhill Blocks 16-17- Subarea A Proposed Plan 13 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 361.00 9.00 0.0 362.00 1285.00 17.3 363.00 1875.00 75.5 364.00 2384.00 154.2 365.00 2863.00 251.2 366.00 3334.00 365.8 367.00 3802.00 497.9 368.00 4083.00 643.9 369.00 4303.00 799.2 370.00 4377.00 959.9 371.00 3683.00 1109.0 372.00 4248.00 1255.7 373.00 4855.00 1424.2 Start-Elevation(ft) 361.00 Vol.(cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Low -Flow Orifice area (sf) 0.012 diameter or depth (in) 1.500 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 361.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Barrel area (sf) 4.909 diameter or depth (in) 30.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 361.000 multiple 1 discharge out of riser Page 1 BH Blocks 16-17 UGD System- Subarea A Proposed Plan Outlet structure 2 Weir name: Riser diameter (in) 60.000 side angle 0.000 coefficient 3.300 invert (ft) 370.750 multiple 1 discharge into riser transition at (ft) 1.519 orifice coef. 0.500 orifice area (sf) 19.635 Outlet structure 3 Weir name: Emergency Spillway length (ft) 30.000 side angle 75.964 coefficient 3.000 invert (ft) 371.750 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr 24-hr SCS Design Storm Area (acres) 7.250 CN 80.000 Type 2 rainfall, P (in) 3.090 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 11.725 peak time (hrs) 11.922 volume (cy) 1283.474 Page 2 BH Blocks 16-17 UGD System- Subarea A Proposed Plan Hydrograph 1 SCS name: 2-yr 24-hr SCS Design Storm Area (acres) 7.250 CN 80.000 Type 2 rainfall, P (in) 3.630 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 15.482 peak time (hrs) 11.922 volume (cy) 1694.668 Hydrograph 2 SCS name: 10-yr 24-hr SCS Design Storm Area (acres) 7.250 CN 80.000 Type 2 rainfall, P (in) 5.780 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 31.881 peak time (hrs) 11.922 volume (cy) 3489.768 Hydrograph 3 SCS name: 100-yr 24-hr SCS Design Storm Area (acres) 7.250 CN 80.000 Type 2 rainfall, P (in) 8.990 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 58.352 peak time (hrs) 11.922 volume (cy) 6387.391 Page 3 BH Blocks 16-17 UGD System- Subarea A Proposed Plan 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 Design Storm 11.705 at 11.92 (hrs) 0.148 at 18.10 (hrs) 370.054 at 19.18 (hrs) 968.591 Peaks: 2-yr 24-hr SCS Design Storm 15.455 at 11.92 (hrs) 0.459 at 12.44 (hrs) 370.783 at 12.44 (hrs) 1078.742 Peaks: 10-yr 24-hr SCS Design Storm 31.825 at 11.92 (hrs) 30.813 at 11.94 (hrs) 371.455 at 11.94 (hrs) 1173.083 Peaks: 100-yr 24-hr 58.250 at 58.293 at 371.812 at 1226.524 Mon Dec 14 16:12:46 EST 2020 SCS Design Storm 11.92 (hrs) 11.94 (hrs) 11.94 (hrs) Page 4 Dry Detention Basin 'A' & Underground Detention System Combined Routing Calculations (Subarea A- Final Buildout) BH Blocks 16-17 UGD System- Subarea A Final Buildout BasinFlow printout INPUT: Basin: Brookhill Blocks 16-17- Subarea A Final Buildout 13 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 361.00 9.00 0.0 362.00 1285.00 17.3 363.00 1875.00 75.5 364.00 2384.00 154.2 365.00 2863.00 251.2 366.00 3334.00 365.8 367.00 3802.00 497.9 368.00 4083.00 643.9 369.00 4303.00 799.2 370.00 4377.00 959.9 371.00 3683.00 1109.0 372.00 4248.00 1255.7 373.00 4855.00 1424.2 Start-Elevation(ft) 361.00 Vol.(cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Low -Flow Orifice area (sf) 0.012 diameter or depth (in) 1.500 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 361.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Barrel area (sf) 4.909 diameter or depth (in) 30.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 361.000 multiple 1 discharge out of riser Page 1 BH Blocks 16-17 UGD System- Subarea A Final Buildout Outlet structure 2 Weir name: Riser diameter (in) 60.000 side angle 0.000 coefficient 3.300 invert (ft) 370.750 multiple 1 discharge into riser transition at (ft) 1.519 orifice coef. 0.500 orifice area (sf) 19.635 Outlet structure 3 Weir name: Emergency Spillway length (ft) 30.000 side angle 75.964 coefficient 3.000 invert (ft) 371.750 multiple 1 discharge through dam 4 Inflow Hydrographs Hydrograph 0 SCS name: 1-yr 24-hr SCS Design Storm Area (acres) 8.550 CN 81.000 Type 2 rainfall, P (in) 3.090 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 14.511 peak time (hrs) 11.922 volume (cy) 1588.442 Page 2 BH Blocks 16-17 UGD System- Subarea A Final Buildout Hydrograph 1 SCS name: 2-yr 24-hr SCS Design Storm Area (acres) 8.550 CN 81.000 Type 2 rainfall, P (in) 3.630 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 19.037 peak time (hrs) 11.922 volume (cy) 2083.852 Hydrograph 2 SCS name: 10-yr 24-hr SCS Design Storm Area (acres) 8.550 CN 81.000 Type 2 rainfall, P (in) 5.780 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 38.651 peak time (hrs) 11.922 volume (cy) 4230.903 Hydrograph 3 SCS name: 100-yr 24-hr SCS Design Storm Area (acres) 8.550 CN 81.000 Type 2 rainfall, P (in) 8.990 time of conc. (hrs) 0.1200 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 70.104 peak time (hrs) 11.922 volume (cy) 7673.803 Page 3 BH Blocks 16-17 UGD System- Subarea A Final Buildout 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 Design Storm 14.486 at 11.92 (hrs) 0.153 at 12.70 (hrs) 370.746 at 12.98 (hrs) 1073.578 Peaks: 2-yr 24-hr SCS Design Storm 19.004 at 11.92 (hrs) 10.695 at 12.04 (hrs) 371.096 at 12.04 (hrs) 1122.129 Peaks: 10-yr 24-hr SCS Design Storm 38.584 at 11.92 (hrs) 37.608 at 11.94 (hrs) 371.555 at 11.94 (hrs) 1187.849 Peaks: 100-yr 24-hr 69.981 at 69.417 at 371.948 at 1247.586 Mon Dec 14 16:12:28 EST 2020 SCS Design Storm 11.92 (hrs) 11.94 (hrs) 11.94 (hrs) Page 4 Level Spreader 'A' Calculations LEVEL SPREADER 'A' DESIGN (Full Buildout) Per VSMH Chpt. 11, Section 11.5.3 Step 1 Area = 8.55 ac. (Eqn 11.11) Tv= 18,840 cf Q,= 0.61 watershed inches (From Worksheet 2) CN = 81 Step 2 Tc = 0.12 hrs Step 3 la = 0.47 la/P= 0.47 q "= 550 csm/in A= 0.013 miz q PT ,= 4.5 cfs Note, q PT, is the Treatment Volume peak discharge, or the peak flow rate for the 1-inch rainfall event. Per the VA DEQ Specification #2, page 14, the Level Spreader should be designed per the following: "Where the Conserved Open Space is a mix of grass and forest (or re -forested), establish the Level Spreader length by computing a weighted average of the lengths required for each vegetation type." 75%+/- Native Grasses/groundcover below tree canopy at a LS length of 13 ft per 1 cfs 25%+/- Forest Litter/groundcover below tree canopy at a LS length of 40 ft per 1 cfs Site Specific / Weighted Average LS length = 19.8 ft per 1 cfs LS'B' Design Length= 88 ft Note: Max. LS Length = 130 ft Min. LS Length = 13 ft Level II Wet Pond Routing Calculations (Subarea B- Proposed Development) BH Blocks 16-17 Level II Wet Pond- Subarea B Proposed Plan BasinFlow printout INPUT: Basin: BH Blocks 16-17 Level II Wet Pond- Subarea B Proposed Plan 8 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 360.00 4332.00 0.0 362.00 7286.00 425.6 364.00 11535.00 1116.7 365.00 14463.00 1597.1 366.00 19279.00 2219.8 368.00 26749.00 3917.0 370.00 34696.00 6186.4 372.00 43302.00 9069.3 Start—Elevation(ft) 4 Outlet Structures Outlet structure 0 Orifice 366.00 Vol.(cy) 2219.80 name: Proposed Barrel area (sf) 7.069 diameter or depth (in) 36.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 360.000 multiple 1 discharge out of riser Outlet structure 1 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) 366.000 multiple 1 discharge into riser Page 1 BH Blocks 16-17 Level II Wet Pond- Subarea B Proposed Plan Outlet structure 2 Weir name: diameter (in) side angle coefficient invert (ft) multiple discharge transition at (ft) orifice coef. orifice area (sf) Outlet structure 3 Weir name: length (ft) side angle coefficient invert (ft) multiple discharge 4 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) Proposed Riser 60.000 0.000 3.300 369.250 1 into riser 1.519 0.500 19.635 Proposed Emergency Spillway 50.000 75.960 3.300 370.250 1 through dam 1-yr SCS TR-55 24-hr Design Storm 13.390 78.000 2 3.000 0.1700 0.0200 30.000 1.00 true 17.106 11.961 2030.279 Page 2 BH Blocks 16-17 Level II Wet Pond- Subarea B Proposed Plan Hydrograph 1 SCS name: 2-yr SCS TR-55 24-hr Design Storm Area (acres) 13.390 CN 78.000 Type 2 rainfall, P (in) 3.630 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 24.198 peak time (hrs) 11.961 volume (cy) 2872.050 Hydrograph 2 SCS name: 10-yr SCS TR-55 24-hr Design Storm Area (acres) 13.390 CN 78.000 Type 2 rainfall, P (in) 5.480 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 47.335 peak time (hrs) 11.961 volume (cy) 5618.145 Hydrograph 3 SCS name: 100-yr SCS TR-55 24-hr Design Storm Area (acres) 13.390 CN 78.000 Type 2 rainfall, P (in) 8.990 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 95.661 peak time (hrs) 11.961 volume (cy) 11353.889 Page 3 BH Blocks 16-17 Level II Wet Pond- Subarea B Proposed Plan OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS TR-55 24-hr Design Storm inflow (cfs) 17.104 at 11.96 (hrs) discharge (cfs) 0.187 at 18.72 (hrs) water level (ft) 367.973 at 21.40 (hrs) storage (cy) 3890.621 Hydrograph 1 Routing Summary of Peaks: 2-yr SCS TR-55 24-hr Design Storm inflow (cfs) 24.196 at 11.96 (hrs) discharge (cfs) 0.221 at 22.44 (hrs) water level (ft) 368.710 at 23.96 (hrs) storage (cy) 4655.688 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS TR-55 24-hr Design Storm inflow (cfs) 47.331 at 11.96 (hrs) discharge (cfs) 10.653 at 12.20 (hrs) water level (ft) 369.593 at 12.20 (hrs) storage (cy) 5675.818 Hydrograph 3 Routing Summary of Peaks: 100-yr SCS TR-55 24-hr Design Storm inflow (cfs) 95.652 at 11.96 (hrs) discharge (cfs) 82.177 at 12.02 (hrs) water level (ft) 370.444 at 12.02 (hrs) storage (cy) 6771.820 Thu Dec 17 13:24:39 EST 2020 Page 4 Level II Wet Pond Routing Calculations (Subarea B- Final Buildout) BH Blocks 16-17 Level II Wet Pond- Subarea B Final Buildout BasinFlow printout INPUT: Basin: BH Blocks 16-17 Level II Wet Pond- Subarea B Final Buildout 8 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 360.00 4332.00 0.0 362.00 7286.00 425.6 364.00 11535.00 1116.7 365.00 14463.00 1597.1 366.00 19279.00 2219.8 368.00 26749.00 3917.0 370.00 34696.00 6186.4 372.00 43302.00 9069.3 Start—Elevation(ft) 4 Outlet Structures Outlet structure 0 Orifice 366.00 Vol.(cy) 2219.80 name: Proposed Barrel area (sf) 7.069 diameter or depth (in) 36.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 360.000 multiple 1 discharge out of riser Outlet structure 1 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) 366.000 multiple 1 discharge into riser Page 1 BH Blocks 16-17 Level II Wet Pond- Subarea B Final Buildout Outlet structure 2 Weir name: diameter (in) side angle coefficient invert (ft) multiple discharge transition at (ft) orifice coef. orifice area (sf) Outlet structure 3 Weir name: length (ft) side angle coefficient invert (ft) multiple discharge 4 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) Proposed Riser 60.000 0.000 3.300 369.250 1 into riser 1.519 0.500 19.635 Proposed Emergency Spillway 50.000 75.960 3.300 370.250 1 through dam 1-yr SCS TR-55 24-hr Design Storm 21.190 81.000 2 3.000 0.1700 0.0200 30.000 1.00 true 31.499 11.961 3738.536 Page 2 BH Blocks 16-17 Level II Wet Pond- Subarea B Final Buildout Hydrograph 1 SCS name: 2-yr SCS TR-55 24-hr Design Storm Area (acres) 21.190 CN 81.000 Type 2 rainfall, P (in) 3.630 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 43.511 peak time (hrs) 11.961 volume (cy) 5164.282 Hydrograph 2 SCS name: 10-yr SCS TR-55 24-hr Design Storm Area (acres) 21.190 CN 81.000 Type 2 rainfall, P (in) 5.480 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 81.850 peak time (hrs) 11.961 volume (cy) 9714.661 Hydrograph 3 SCS name: 100-yr SCS TR-55 24-hr Design Storm Area (acres) 21.190 CN 81.000 Type 2 rainfall, P (in) 8.990 time of conc. (hrs) 0.1700 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 160.229 peak time (hrs) 11.961 volume (cy) 19017.454 Page 3 BH Blocks 16-17 Level II Wet Pond- Subarea B Final Buildout OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: 1-yr SCS TR-55 24-hr Design Storm inflow (cfs) 31.496 at 11.96 (hrs) discharge (cfs) 0.238 at 14.66 (hrs) water level (ft) 369.137 at 15.70 (hrs) storage (cy) 5135.101 Hydrograph 1 Routing Summary of Peaks: 2-yr SCS TR-55 24-hr Design Storm inflow (cfs) 43.507 at 11.96 (hrs) discharge (cfs) 5.967 at 12.34 (hrs) water level (ft) 369.480 at 12.34 (hrs) storage (cy) 5539.047 Hydrograph 2 Routing Summary of Peaks: 10-yr SCS TR-55 24-hr Design Storm inflow (cfs) 81.842 at 11.96 (hrs) discharge (cfs) 60.448 at 12.04 (hrs) water level (ft) 370.318 at 12.04 (hrs) storage (cy) 6602.824 Hydrograph 3 Routing Summary of Peaks: 100-yr SCS TR-55 24-hr Design Storm inflow (cfs) 160.214 at 11.96 (hrs) discharge (cfs) 150.088 at 12.00 (hrs) water level (ft) 370.769 at 12.00 (hrs) storage (cy) 7219.984 Thu Dec 17 13:24:14 EST 2020 Page 4 Subarea C's Analysis of the Storm Sewer's Hydraulic Grade Lines and Cross Sections A. B & C (For Subarea C's Channel & Flood Protection Compliance) Subarea C's Storm Sewer This analysis shows the 10-year hydraulic grade lines do not overtop the inlets, hereby confirming the 10-year design storm is confined within the stormwater conveyance system. fi W M M M N M M M M P4 � a W e o a o 0 00 M M M M M z ON M p a s a a a a a a w a' xi o O a z M a r a N a CD a o r ao h r M W - O V r - N O O O O O O O O O O ID o O O O� t0 M O O O N N p O O O O O O O W =a O O O O O O O O N � e v ao ry o O o 0 0 r M N o O N �p Vl r N1 M r try O� O - Ji O O O O O O O O I I O M N o W V V1 M V1 �O Vl r N1 - O O O O O O O O O O O O O O O O O O O O O O O O O W N V1 r N1 ON ON M V Vl V �O V , P a G W 3 w M M o o ^ m o o ao M v M M M a a 0 � z Q z F Subarea C's Cross Section A This analysis shows the 2-yr design flow is not erosive on the channel. Per the VESCH's Table 5-14 entitled Permissible Velocities for Grass -Lined Channels shown on page V-120, the maximum allowable velocity for fescue grass is 5 ft/s. This analysis also shows the 30-year design storm is contained within its banks. Please note, this channel was recently designed, reviewed and approved in the Brookhill Road Improvement Plan for State Route 643 Polo Grounds Road, Stella Lane and Archer Avenue (sheet C-309), further depicting its adequacies. Cross Section A- 2yr Design Storm Complex Channnel- X-Section A (2-yr design storm) Input: Slope Flow (given) line x y n 0 0.000 1.000 0.030 (first n value not used) 1 5.000 0.000 0.030 2 7.000 0.000 0.030 3 12.000 1.000 0.030 Output: Depth 0.419 (y) ( 0.419) Channel bed segment output: line Q v 1 1.02 2.32 2 3.12 3.72 3 1.02 2.32 Thu Dec 17 12:23:53 EST 2020 A P 0.44 2.14 0.84 2.00 0.44 2.14 Page 1 Cross Section A- 10yr Design Storm Complex Channnel- X-Section A (10-yr design storm) Input: Slope 0.018 Flow (given) 10.290 line x y n 0 0.000 1.000 0.030 (first n value not used) 1 5.000 0.000 0.030 2 7.000 0.000 0.030 3 12.000 1.000 0.030 Output: Depth 0.583 (y) ( 0.583) Channel bed segment output: line Q v 1 2.44 2.88 2 5.40 4.64 3 2.44 2.88 Thu Dec 17 12:24:19 EST 2020 A P 0.85 2.97 1.17 2.00 0.85 2.97 Page 1 Subarea Cs Cross Section B This analysis shows the 2-yr design flow is not erosive on the channel. Per the VESCH's Table 5-14 entitled Permissible Velocities for Grass -Lined Channels shown on page V-120, the maximum allowable velocity for fescue grass is 5 ft/s. This analysis also shows the 30-year design storm is contained within its banks. Please note, this channel was recently designed, reviewed and approved in the Brookhill Road Improvement Plan for State Route 643 Polo Grounds Road, Stella Lane and Archer Avenue (sheet C-309), further depicting its adequacies. Cross Section B- 2yr Design Storm Complex Channnel- X-Section B (2-yr design storm) Input: Slope Flow (given) Output: 0.012 5.160 line x y n 0 0.000 1.000 0.030 (first n value not used) 1 5.000 0.000 0.030 2 7.000 0.000 0.030 3 12.000 1.000 0.030 Depth 0.463 (y) ( 0.463) Channel bed segment output line Q v 1 1.08 2.02 2 3.00 3.25 3 1.08 2.02 Thu Dec 17 12:24:42 EST 2020 A P 0.53 2.36 0.93 2.00 0.53 2.36 Page 1 Cross Section B- 10yr Design Storm Complex Channnel- X-Section B (10-yr design storm) Input: Slope 0.012 Flow (given) 10.290 line x y n 0 0.000 1.000 0.030 (first n value not used) 1 5.000 0.000 0.030 2 7.000 0.000 0.030 3 12.000 1.000 0.030 Output: Depth 0.640 (y) ( 0.640) Channel bed segment output: line Q v 1 2.57 2.51 2 5.16 4.03 3 2.57 2.51 Thu Dec 17 12:24:59 EST 2020 A P 1.02 3.26 1.28 2.00 1.02 3.26 Page 1 Subarea C's Cross Section C The 2-yr design flow is nonerosive on the concrete in the 60"x60" double box culverts, and the 10-yr design flow does not overtop Polo Grounds Road. Please note, this channel was recently designed, reviewed and approved in the Brookhill Road Improvement Plan for State Route 643 Polo Grounds Road, Stella Lane and Archer Avenue (sheet C-810), further depicting the channel's adequacies. Please see the excerpts below from the approved Brookhill Road Improvement Plan for State Route 643 Polo Grounds Road, Stella Lane and Archer Avenue (sheet C-810): PROPOSED CONDITIONS: IN THE PROPOSED CONDITION THE EXISTING CULVERT WILL BE UPSIZED TO A DUAL 5'X5' BOX CULVERT WHICH CAN ADEQUATELY CONVEY THE 10 YEAR RUNOFF OF 599 CFS WITH A Hwld VALUE OF 1.34 AT MAXIMUM ELEVATION OF 348.75, WHICH IS 2.75' BELOW THE PROPOSED ROAD GRADE OF ±351.50. HOWEVER, SINCE THE REQUIRED PEDESTRIAN TUNNEL THAT IS LOCATED APPROXIMATELY 110' TO THE EAST OF THE CULVERT HAS AN INVERT ELEVATION OF ±444.60 SOME OF THE 10 YEAR STORMWATER RUNOFF WILL BE CONVEYED THROUGH THE PEDESTRIAN TUNNEL IN THE 10 YEAR STORM EVENT. THIS SITUATION WAS MODELED IN HYDRAFLOW HYDROGRAPHS USING MULTISTAGE CULVERTS AND THE CALCULATED 10 YEAR HEADWATER ELEVATION IS 346.18. THE ASSOCIATED FLOW THROUGH THE DUAL 5'X5' BOX CULVERT AND PEDESTRIAN TUNNEL WITH A HEADWATER ELEVATION OF 406.16 AT 445 CFS AND 154 CFS RESPECTIVELY. BOTH THE ONE AND TWO YEAR STORM EVENTS PASS THROUGH THE DUAL BOX CULVERT WITHOUT ENTERING THE PEDESTRIAN TUNNEL. PROP. GRADE ABOVE SANITARY PROP. DUAL M W`LL•W W W"W `W-10 YEAR WSE.tt348'.18)• .WWWW W `W W W W 4YEARW$E:(&1 1)— PROP. Riprap Lined Outlet Protection Calculations OLITLC-T ?ROTrcCrlo(,J '�:)6SYGrj 'uwa«t�wci�t. %04-16-17 �a ta�f�O ,� SvgAar�A R T}+E Fasewc rr CALCVASt kl coNSER Arx. .LY ASS,.ME T4-\E LcvEL SH�ta "RS Low-Fc�w Qx(�E zs cLoa6Co ANQ ALL Rw.m^ 35 ILov--rcra •co Tx€ P,�Z,.wtre-f 4�`TFM.L �quY+.�r ('AoT�`-cr;I..aN s Q\e = 3o.a\ c-rs �ea�e b PLF N7 q+ c, - 31.0 ccs (F2NAL B.aLo� T� Qcaemw 40 CVS 76 QER i�.A�E 3.\$-1 , `pE�TH of STdJi, d = 1, 5 x STcr+� 'pIAMC-ZCR, 43N'�' Nfit -LOSS 'CFtAAI '�- Ps.@G- a.ntFALL 51YAM6 T6R :. 3O" K TW � '/d Q3✓�HETE Q PER VESC% �LwrE 3.18-4 Viso a a" 1 awEven dsp Mz,.ran.w CECnnnMC t4G F3 fy' LA a x wirh` A nv,, &CCC�Ah IANXO c1s�-&"y vOaC GLWSs A\, )c�e--t sTcw,* as PRcPcs*O (4jo° 0A) i4p.EFek 6'H1: FsuAL CYCSYG' J zS vOa[ C L. Ay CC-1 kiL'WAP wat-H P- a* "R cr va C3. aoaJ n FS FiL( ii fxgi4c wuAaLmA , Ri.OPAp -M %t IrLAT, Q, LNw6 Apv �AAW'c V--z 1Yt-(5 of TS' (,Ar PxnE c--,-r4L� ao+n 6t.7' C,nt EAw ovr o-tLG�+ 4aa'� rrac+v�. K 5uDA2 p Q P" io.Gr9 oc's (TACP*sd,a %AN) Q,o= 501.53 afs �Frwt�L rj uXLu�e�C F� G'o crs X ?IOE Qp.TFALL'Z)2AW,T64' %7(" TW TcvvC- # Pia VEstN 3,\8 -'1 dam° 0.3' , He A MiN. 0.�wnn�A,O En d + 611 iF+ CL, RS, FcC'1 SON Lp, = ' w, = `Y (3 lA. W a' I d.2" 0. + OA LA) 13* o SS \JWV CL.Pa.$C-C--% RiP➢.AP WL M A 174OYtl GP F%cvz11 FASAXIL u r�eaLA4A h� , RXQaAQ Tt, 16E fLA'r I a3' a OTC+ hW NA`6 %hXaMS °. 9' (ae W10r, ov`tPAu) ANp \dale (kr ENO OV QNOrLfgl 9w tr<zoN). 1992 3.18 F Source: USDA-SCS Plate 3.18-4 III - 165 Virginia Runoff Reduction Method Water Quality Calculations (For the Proposed Plan) This analysis is for the proposed plan and shows its water quality compliance. Please note, the level II wet pond and the level spreader were designed for the more stringent final buildout's higher treatment volumes. The final buildout's higher treatment volumes can be viewed in the next section entitled ' '. WQVirgiM RunWReM MeM New Oeve em Comptl eSpreodSM1eel-Vendee 3A 02%18MP Standards and SpNncations C110130ra1r RMP S6n&WssM SpecOcalbns Pm)mn Name: B.AHill Blocks 16-1)(Proposed nanl am.inpm®nr Date: 12/33/3@0 amvuerryn specipmriomlin: 3013 Draft 55tlsaSpecs elaNrian Mls (Site Information Project (Treatment Volume and Loads) Inoev¢uavavduerl Constants m pnN l 1.00 regmmarl O.z6 geoulImgR) (TN)EMC(m/Il I.B6 v as IIL/a,r,,M OA1 11 tun t el, lacncd 090 .re C,nswc•Cmrer(:rer) va Weiphrai Pvlturertl 003 %Forert <% ManapaTuh Cwerlareal G.OS Wm%Maa Rv lWhl O.M %Manages Tutl s5M Im em.o.r Coaer laoerl v.xo Rv lm M.-) 0.95 %Iemn — al% `+ra nti (as—) i125 u.zo Runes f Coeffidems IRVI T emvauma Iwo-fll uaoB in Volume(se.s ReD 4R658 Wb d(lh/W) 31M .._.__Wall.. � ..._.... z1310 Jt 000000000 00 000 00 00 00 00 �00 Ili!!!!!! 1111111111111111 111111111 go go 11 go go I111 go go 11 go go I111 I A go { go Ill loll A Al 1loll t q 11111111111 oil 11111111 oil )� IF � )1111111 {� I � )III 1111 oil MINE 11 111 11 1 111 MINE 11 111 11 1 111 MINE 11 111 11 1 111 ; u W U M M ]L m x H yy d w p �p W O O O O O 6 O m Q .i Q O O O O O Y Q p O O O O '888SSY � g g $ c 0000co QQ,oS u W O p C Q O O O O O O O O O O Y O Q p O [86 O O m O' O m O O o w m g O O N a a i N m N m Y m q' p^ ti N N m m m u o O O p d Z m O o p to in of Y O a y d of d ry p O f! O m d S ry i M 3 6 y~j O O M M M M O Ol N N M M N N O N N ti N ti N f W W Qi Li 6 0 0 0 Q Q W Z L a W OW V� W a Q Q A N w 7 x> Q a0�>? C 7 OS�O Q� W? C F? m F rc Q OL N _ J Q Q f f W 1 UO Q Q UC Wz w WOWCC U z y z j £ 100. > FaF O 200 F FFag R E F Zz O W F 02 O d O W O m p w O W 6 Q H C >> O O A D O L p 0 0 M Y.O J Or OJOj O „LL„6�iu ' f W Q f f f W 0 O z F OO z O z OD Ols O N 1' f_ z_ C O z Q Z z O z ' Q W o � W � C Q C i Runoff Volume and Curve Number Calculations Enter design storm rainfall depths (in): 1-year storm 2-year storm 10-year storm 3.fi9 sae -_ We AGAAAMN14 parp jeIowmes.raw.gor/Mr/Pfrk/J -- "Notes (see below): - -- 11] The curve numbers and runoff volumes computed in this spreaim sbeet for each drainage area are limited in their applicability for tletemm�m g and tleonstrrtirg compliance with water quanuty requirements. See VRRM User's Guide and Documentation for acc iuonal information. [2] Runoff Volume RIV) bar preandpast- development drainage anew must be in wlumemc units leg., a[mfeet or cubic feet) when using the Energy Ralarce Equation. Runoff measured in watershe6 inches and shown in the spreadsheet as RVlwatershedinch) can only he used in the Energy Balance Equauon when the pre- and postdevelopment drainage areas areepol. Otherwbe lN(watershed inch) be multiplied by the drainage area. [3]Adjusted CNsae, based on notion reduction vdumesm calculated in D.A.tabs. An alternative ON adjustment calculation brV yetoted Roofs is included in OMP specification No. S. --------- -- -- --.must -- Drainage Area Curve Numbers and Runoff Depths* [brine numbers (CN, CNal and runoff depths (RV pe, AwJ are computed with and without reduction proctices. Drainage Area A ASoilz B Soils CSails D Soils Total gun hoes): J.25 ForesVDpen Space- untlkturted, pmte[ted foreshopen spare or reforested! land Area acres LN U.D] 3D UmU.W 55 ID U.D] ]] Run An ReduRion Volume ft 11,L41 Manaretl Too- ii5bnbetl, graded for yards or other turd to be noward/maimbell 1 Area lanes) CN O.W 39 3.5R fil 70 @3 Impervous Cove Arealanes) CN 98 Oow 9R 3ch 98 USA SA 98 - RVD.vdroed (watershed -inch) with no Runoff RetluRion" RVor..mlwd(watefched-Inch/wi[M1 Runoff RetluRion" Atljurtetl CN" 1-year storm 1.25 Bs2 n CNIRA.N 2-year storm 10-year storm 1.T0 3.32 1.91 age --_- 24 3 "See Notes above i DrainageArea B Forest/open Space- undisturbed, pmte[ted mneshoom Prea lanes) spxe or remre[M landLN Manaretl Tm(- to brtbetl,gmtletlmnyams nathentunl prea a[ to be mowetl/man LN fe Impervious Cove Area a[ C RVaw}yad(wmenhed-inch) with no Runoff ReduRion" RVareewe(wOFershed-insh) with Runoff RetluRion" Atljurtetl CN" ASoilz O.W 3c Ogo 39 OUR 98 1-year storm 1.1y 1.19 n B Soils Soils D Soils TOM cam hoes): 13.39 D.OD U.D] U.W Runoff ReduRion 55 ID ]] Volumeft D fil ,0 Po 611 U.D] USo 6c. OSA O.W _-- 9R 98 98 CNlow el 2-year storm 10-year storm 1.br 9.22 7 9.22 n n ',. Kee Notes above ',. ii '. Drain Area Drainpipe C ''� Asoilz B Soils Cs'd Dsoilz Total Area(acion D.00 --____-- ForexVNpen Space inceor rtrsuadeursed, !landrecordedbrexVopen persuaded! Area a [N[re O.W 30 55 o55 O.W 0- ]] 0.uno Volume Volume R': D Managed Tor(-tobe etl,gmtlran sed NS dother turl to be mowetl/man H Nea lanes) CN 39 Oto fil oat O.W a ]a @] a.00 So an CNlu.ad _ 16,Mr storm a.oa a.00 -- 0 --- Impewioos Cover Area(anesl CN 98 aan oao 9B _- RVcey�,p•d (wmrshed-ind/ witM1 na Punaff RetluRion" Pyor..mme(wam[shed-InA) with Runoff RetluRion" Atljurtetl CN" 1,mar storm '2gear storm o.00 oao o.00 o.00 o 0 Kee Notes abave Drainage Area D ASoilz B Soils CSails D Soils Total Area(ame,): DDD mte[tetlforest/open PoresVNpen Spate space or reforested r retiree prea a [N Oyn 30 o55 55 O.W oa aTr ]] Run Sr ReduRlon Volume R': D far to Managed Tor(-tobe med/ono cal NSnother turl to be mowetl/manages Prea lanes) CN Oto 39 fil oel O.O] U.O] @] Impewmo[Cover Nealanesl CN oSoo 98 o. 9B . 98 aSay aSoo 98 CNMaoI 0 1-year storm 2-year storm ID -year storm Ma.•avnpas (wmrshetl-InN) with noPunaff RetluRion" o.00 RVcedeg.d(adrefzhed4mah) with Runoff RetluRion" o.onoao Adjusted Clairo a o Sets Notes above coinage AreaE ASoilz BSoilz CSails DSoilz TOW Ama(2o ): D.DO forest/open Space- undlstorbed, corrected foreet/open since or reforested land o Ss ID n RumNReduNon Voume R : o -Managed Tuff- dinumed graded for yards or other ton to be moves/manages preaa nes cx a.W oao a.W a.W Cover acres W od 9. aa n oSoImprviom CNInw9 1-year storm 2-Year storm 10-year storm -- RVcercpp, (warenhed-ind) With no Runoff RetluRion" o.00 oao a.00 Rv .Nemd(wore[shed-Inch) with Punaff RetluRion" o.n U. a.00 I Atljurtetl Clair o 0 0 ' _ 'See Nate, above , } ] ) ] | ! | ! | k \ ) ) k § t \ ! E \! ) k k )k)� G T 0 I V m O O p o p O O p o p o G O p R p R O q O O O O O 0 O O G p O p O p O p O p O m Li V m c o o$$ d o o$$ 0 0 o?$ 0 0 o O m L G q y O p LA C gg yL q yy�� a T K T K T V Q m 2 ry, L a 0 p L 0 0 c _ 6 V c N ¢ O � T Virginia Runoff Reduction Method Water Quality Calculations (For the Final Buildout) This analysis was used to obtain the more stringent/larger design treatment volumes for the level II wet pond and the level spreader. Since the final buildout of Brookhill will likely introduce additional impervious areas & runoff directed to these two facilities with the construction of the future Block 18, the wet pond and level spreader were overdesigned with this plan to meet the following final buildout's requirements. Please see the previous section entitled 'Virginia Runoff Reduction Method Water Quality Calculations (For the Proposed Plan)' for this plan's water quality compliance. t 10 �1111111111111 oil oil oil oil m q 1 )11 !I )I )1 IN I I I )1 1