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HomeMy WebLinkAboutWPO201900027 Calculations 2020-10-08PLEASANT GREEN- CONNECTOR ROAD STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations OCTOBER 2, 2020 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 lei Soils Table (Source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003) Map Unit Map Unit Name percent of Symbol cen 01 7B Braddock loam, 13.0% 2 to 7 percent slopes 17 Craigsville loam, 51.9% 0 to 2 percent slopes, frequently flooded 37D3 Hayesville clay 35.1% loam, 15 to 25 percent slopes, severely eroded 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 A. Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) Map Terrain �K yo 0 % Bn7n S7 ) Jeremiah �n o n P 0or9am" < ? v! noq o D C � a) 6 ar0a'nrn Bran s Rn 100m Jarman. Gap Rd J"d, POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, Volume 2, Version 3 I PDS-based precipitation frequency estimates with 90 % confidence intervals (in inches)' I 3.08 3.72 C74 5.59 6.84 7.97 9.09 10A 12.3 140 24.Ir (2.77-344) 1 (3.354.16) 1 (4.255.30) 1 (5.005.24) 1 (6.08-7.62) 1 (6.9".80) 1 (7.90.10.1) 1 (8.W11.5) 1 (10.5-13.7) 1 (11.7-15.6) U.S. Department of Agriculture Natural Resources Conservation Service Project: Pleasant Green- Connector Rd. Location: Orchard Dr. Connection 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: 10/2/2020 Date: 10/2/2020 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 ASoils Impervious Areas 98 0.00 0.0 DAA (Conservatively Woods 55 0.15 8.3 55 8.18 (Pre-Dev.) Analyzed as B Soils) Lawns 61 0.00 0.0 ASoils Impervious Areas 98 0.75 73.9 DAA (Conservatively Woods 55 0.00 0.0 86 1.58 (Post-Dev.) Analyzed as B Soils) I Lawns 1 61 1 0.35 1 21.1 2. Runoff 1-Year Storm 2-Year Storm 10-Year Storm I Drainage Area Description Frequency -years 1 2 10 n a Rainfall, P (24 hour)- inches 3.08 3.72 5.59 n/a Runoff, Q-inches 0.22 1 0.42 1 1.29 IDAA (Pre-Dev.) Runoff, Q- inches 1.76 1 2.33 1 4.06 1 DA A (Post-Dev.) U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (T j or Travel Time (TJ Project: Pleasant Green- Connector Rd. Location: Orchard Dr. Connection Check One: Present X Developed X Check One: T, X T, Sheet Flow: (Applicable to T, only) Designed By: FGM, PE Checked By: SRC, PE Through subarea n/a Segment ID: 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 T, _ [0.007(n*L)"] / P2" SIA 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= [ 1.49r2/3S05 ] / n 18 Flow length, L (ft) 19 T,= L / 3600*V 20 Watershed orsubareaT,orT, (Add Tt in steps 6, 11 and 19) Note: The shoretest SCS Tc is 0.10 hrs. FL-ENG-21A 06/04 Date: 10/2/2020 Date: 10/2/2020 DAA DAA (Pre-Dev.) (Post-Dev.) Woods- Light Dense Underbrush Grass 0.4 0.24 90 25 3.72 3.72 0.111 0.280 0.15 0.03 0.15 1 0.10 U.S. Department of Agriculture Natural Resources Conservation Service Project: Location: TR 55 Worksheet 4: Graphical Peak Discharge Method Pleasant Green- Connector Rd. Orchard Dr. Connection Check One: Present X Developed X Designed By: FGM, PE Date: 10/2/2020 Checked By: SRC, PE Date: 10/2/2020 1. Data Drainage Area Description Drainage Area Description Drainage Area Description DA A (Pre-Dev.) DA A (Post-Dev.) Drainage Area (Am) in milesz = 0.0002 0.0017 Runoff curve number CN= 55 86 Time of concentration (Tc)= 0.15 0.10 Rainfall distribution type= II II Pond and swamp areas spread throughout the watershed= 0 0 2. Frequency -years 1 2 10 1 2 10 3. Rainfall, P (24 hour)- inches 3.08 3.72 5.59 3.08 3.72 5.59 4. Initial Abstraction, la- inches 1.64 1.64 1.64 0.32 0.32 0.32 5. Compute la/P 0.53 0.44 0.29 0.10 0.08 0.06 6. Unit peak discharge, Qu- csm/in 425 600 825 975 975 1000 7. Runoff, Qfrom Worksheet 2- inches 0.22 0.42 1.29 1.76 2.33 4.06 8. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 9. Peak Discharge, Qp- cfs where Qp=Qu Am Q Fp See SCS Unit Hydrographs See Bioretention Basin Routings WATERSHED SUMMARY CN ac. cfs cfs cfs A (Pre -Dev.) 55 0.15 0.03 0.05 0.16 6A(Post-Dev.) 86 1.10 1.94 2.98 5.53 Channel and Flood Protection Computations 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.l.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." 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;" 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.a.: The point of discharge "confines the postdevelopment peak flow rate from the 10-year 24- hour storm event within the stormwater conveyance system to avoid the localized flooding." Section C.3.c Limits of Analysis The flood protection analysis terminates at the site outfall because, "the stormwater conveyance system enters a mapped floodplain." Pre -Development Inflow Hydrographs (Pre-Dev. 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 (mi2-in) DAA (Pre-Dev.) 0.15 0.15 0.53 0.000051 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 0.00 12.0 0.00 12.1 0.03 12.2 0.02 12.3 0.01 12.4 0.01 12.5 0.01 12.6 0.01 12.7 0.01 12.8 0.01 13.0 0.01 13.2 0.00 13.4 0.00 13.6 0.00 13.8 0.00 14.0 0.00 14.3 0.00 14.6 0.00 15.0 0.00 15.5 0.00 16.0 0.00 16.5 0.00 17.0 0.00 17.5 0.00 18.0 0.00 19.0 0.00 20.0 0.00 22.0 0.00 26.0 0.00 0.03 0.03 0.02 0.02 0.01 0.01 0.00 a.a -0.01 SCS TR-55 Pre -Development Unit Hydrograph (DA A) 5.0 10.0 15.0 20.0 25.0 30.0 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 (mi2-in) DAA (Pre-Dev.) 0.15 0.15 0.44 0.000 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 0.00 12.0 0.01 12.1 0.05 12.2 0.04 12.3 0.02 12.4 0.02 12.5 0.02 12.6 0.01 12.7 0.01 12.8 0.01 13.0 0.01 13.2 0.01 13.4 0.01 13.6 0.01 13.8 0.01 14.0 0.01 14.3 0.01 14.6 0.01 15.0 0.01 15.5 0.01 16.0 0.00 16.5 0.00 17.0 0.00 17.5 0.00 18.0 0.00 19.0 0.00 20.0 0.00 22.0 0.00 26.0 0.00 0.06 0.05 0.04 0.03 0.02 0.01 0.00 0.0 SCS TR-55 Pre -Development Unit Hydrograph (DA A) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 51b (Modified for Clarity): Basic watershed Data 10-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 (mil -in) DAA (Pre-Dev.) 0.15 0.15 0.29 0.0003 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 0.00 12.0 0.02 12.1 0.16 12.2 0.11 12.3 0.06 12.4 0.05 12.5 0.05 12.6 0.04 12.7 0.04 12.8 0.03 13.0 0.03 13.2 0.03 13.4 0.03 13.6 0.02 13.8 0.02 14.0 0.02 14.3 0.02 14.6 0.02 15.0 0.02 15.5 0.02 16.0 0.01 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 0.19 0.16 0.14 0.12 0.10 0.09 0.06 0.04 0.02 0.00 0 SCS TR-55 Pre -Development Unit Hydrograph (DA A) Post -Development Routing Calculations (Confirms confinement of Post -Development Subarea A's 10-yr Storm) Bioretention Basin Routings BasinFlow printout INPUT: Basin: Bioretention Basin Routings 8 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 691.50 1542.00 0.0 692.00 1542.00 28.6 693.00 1542.00 85.7 694.00 1542.00 142.8 695.00 1551.00 200.1 696.00 1651.00 259.3 697.00 2398.00 333.9 698.00 3308.00 439.1 Start—Elevation(ft) 3 Outlet Structures Outlet structure 0 Orifice 696.00 Vol.(cy) 259.34 name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 691.500 multiple 1 discharge out of riser Outlet structure 1 Weir name: Riser diameter (in) 48.000 side angle 0.000 coefficient 3.300 invert (ft) 696.500 multiple 1 discharge into riser transition at (ft) 1.215 orifice coef. 0.500 orifice area (sf) 12.566 Page 1 Outlet structure 2 Weir name: length (ft) side angle coefficient invert (ft) multiple discharge transition at (ft) orifice coef. orifice area (sf) 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) Bioretention Basin Routings Emergency Spillway- 20.000 75.960 3.300 697.000 1 into riser 0.764 0.500 12.566 Set 12" Above Bio Mix 1-yr 24-hr SCS TR-55 Design Storm 1.100 86.000 2 3.080 0.1000 0.0200 30.000 1.00 true 2.416 11.917 255.827 Page 2 Bioretention Basin Routings Hydrograph 1 SCS name: 2-yr 24-hr SCS TR-55 Design Storm Area (acres) 1.100 CN 86.000 Type 2 rainfall, P (in) 3.720 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 3.202 peak time (hrs) 11.917 volume (cy) 339.017 Hydrograph 2 SCS name: 10-yr 24-hr SCS TR-55 Design Storm Area (acres) 1.100 CN 86.000 Type 2 rainfall, P (in) 5.590 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 5.613 peak time (hrs) 11.917 volume (cy) 594.185 Hydrograph 3 SCS name: 100-yr 24-hr SCS TR-55 Design Storm Area (acres) 1.100 CN 86.000 Type 2 rainfall, P (in) 9.090 time of conc. (hrs) 0.1000 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 10.317 peak time (hrs) 11.917 volume (cy) 1092.270 Page 3 Bioretention Basin Routings OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: 1-yr 24-hr SCS TR-55 Design Storm inflow (cfs) 2.405 at 11.92 (hrs) discharge (cfs) 1.937 at 11.94 (hrs) water level (ft) 696.630 at 11.94 (hrs) storage (cy) 303.037 Hydrograph 1 Routing Summary of Peaks: 2-yr 24-hr SCS TR-55 Design Storm inflow (cfs) 3.187 at 11.92 (hrs) discharge (cfs) 2.980 at 11.94 (hrs) water level (ft) 696.673 at 11.94 (hrs) storage (cy) 306.427 Hydrograph 2 Routing Summary of Peaks: 10-yr 24-hr SCS TR-55 Design Storm inflow (cfs) 5.586 at 11.92 (hrs) discharge (cfs) 5.526 at 11.94 (hrs) water level (ft) 696.761 at 11.94 (hrs) storage (cy) 313.511 Hydrograph 3 Routing Summary of Peaks: 100-yr 24-hr SCS TR-55 Design Storm inflow (cfs) 10.269 at 11.92 (hrs) discharge (cfs) 10.653 at 11.92 (hrs) water level (ft) 696.904 at 11.92 (hrs) storage (cy) 325.517 Tue Sep 29 16:25:37 EDT 2020 Page 4 Riprap Lined Outlet Protection Calculations Below the Triple Box Culvert �J�iN RU Ir ��ANVA-(..�.SC{•,�a,2., 3. 3•y (=NI, � 7S ovt L<"AA*ft3t�,ci'�Gi iZ Sl-tNl1. tjF 11yE9 l0 D%TE0.MZ'"E Ttl� FXS�'c NT Or d+Cltit \,i bi.E R YCiv R�Vii Il laU ?,�IPr P�ry CALCi, - TIoIa5 DC-S36tj 1 AV, 'R-� (VSEtow\ RRG f2oM FiMA FLoao 3NsvwpNcC S�uD`I=5\oo3CQ 000Ct Xec�WL-t 6aw.ny, . P�EAJs� A"() SLC FnTACFto "fJEEC RAS A t+ ISMS Fa�- 4�cASAnrt CSRCE�v �RoQc�SE✓� CRobi7n�9R�, Sw�� 6� 2cA`� QSo = 1 3@0 r rs RJR C�OWN+nA&AM Qua, = \, yS0 crs SELcioN �' 3 a, a �3o cr5 /♦txn p�A�Yis 4CQ JVc�'\ 'DARx/JAGE MAWAL SELT-bN S-3.-a• 6 q ALLj" iS UVdD TQ OETER ENE S�`cSt6N 1 WGt \G1' 1dA0. "E '�C2 7H-,E ATTRLKCM MANnr,N(-' ON / Vto = 3 .vb wis -VH.1s eo s�avAr� c { \BALES 71-+ 100wNiSaCAtA -?EAk I0--Y2 Lbw AT lttl� RAoPgEv) CLtLUCO-1 CAOSSSnG. ++AS A MAxzN�M a�ctL�~r vELoLa2y �F t� `tlS Fwk- ?I-�S:C1 VpO -cr) TCnhL. HkLok ,"c C(pVt, i 4 �S GRtiAte-,1 A -QC b itJSTALLAt'ToN :S 9-[6ZU22C30, niPLv�O"C E c-I, C Ars 1 TCe� C� (Zs e2R5� Complex Channnel Input: Slope 0.008 Flow (given) 820.000 line x y n 0 218.000 691.100 1 220.000 690.900 2 225.000 687.100 3 260.000 687.100 4 270.000 690.000 Output: Depth 2.608 (y) ( 689.708) Channel bed segment output 0.030 (first n value not used) 0.030 0.030 0.030 0.030 line Q V A P 1 0.00 0.00 0.00 0.00 2 19.68 4.40 4.47 4.31 3 741.87 8.13 91.28 35.00 4 58.45 4.98 11.73 9.36 Fri Sep 25 14:07:58 EDT 2020 file: ///P/...lanNSMP%20Plan-%20Connector%20Road/Calculations/SWM1s[%20Submittal/Culvert%20Crossing-%20Riprap%20Design.tKt[9/25/2020 2:14:27 PMl HEC RAS Analysis for the Pleasant Green Proposed Crossing (i.e. The Proposed Connector Road Crossing) HEC RAS Analysis for Pleasant Green Proposed Crossing Crozet, VA Prepared for Collins Engineering April 1, 2019 Revised: June 6, 2019 BACKGROUND The proposed project is located along the northeast side of Powells Creek between Jarmans Gap Road and Cling Lane in Crozet, Virginia. The proposed development, known as Pleasant Green, includes an entrance road that crosses the regulatory floodplain (FEMA Zone AE) of Powells Creek from Orchard Drive in the vicinity of FEMA cross section "G" (FEMA Map: 51003CO229D). A hydraulic analysis was conducted to assess the impacts of this proposed stream crossing on the Base Flood Elevations upstream of the crossing. A prior hydraulic analysis of this reach was completed in May 2017 by Dominion Engineering for the then proposed West Glen Subdivision - which included a similar crossing in the vicinity of FEMA cross section "I". HYDROLOGY Peak flows for Powells Creek have been estimated by FEMA and are presented within Table 3 of Flood Insurance Study #51003CV000C, for Albemarle County, VA. No further hydrologic calculations were conducted for this analysis. HYDRAULICS A HEC-RAS (version 5.0.6) hydraulic model was developed, for both existing and proposed conditions, to assess impacts to the (100-year) base flood elevations and floodplain extents for Powells Creek immediately upstream of the proposed Pleasant Green crossing. Dominion Engineering's previous existing condition ("effective") model was used as the basis for this new model. The following model components were used in this analysis. Cross Sections Aterrain model built with updated topographic survey data provided by Dominion Engineering (2017) was used to provide elevation data for the HEC RAS model. FEMA cross section data was revised accordingly for cross sections F — M. For this analysis, cross section G was replaced with 6 new sections (G1, G2, G3, G4, G5, G6) to adequately model the proposed crossing. Manning's Roughness (n) values were set at 0.08 within the channel and 0.06 for overbank conditions, as referenced in Table 4 of FEMA Flood Insurance Study #51003CV000C. Culverts Three (3) 8'H x 10'W concrete box culverts were modeled for proposed conditions. Culverts were countersunk 6-8" and modeled with a natural bottom and roughness value of 0.03. Channel roughness values immediately upstream and downstream of the culverts were also set at 0.03 to account for proposed inlet and outlet protection. Culverts were modeled as Inlet Controlled. Ineffective flow areas were set upstream and downstream of the proposed crossing, in accordance with HEC RAS guidance. Flows A steady flow model using a subcritical flow regime was used for this analysis. Flow data was unchanged from Dominion Engineering's model. Flow values are as follows: Reach RS 10 YR 50 YR 100 YR FLOODWAY 500 YR POWELLS CREEK 4182.66 750 1200 1370 1370 2010 2040 2050 POWELLS CREEK 3384.41 770 1230 140D 1400 POWELLS CREEK 2959.02 780 1240 1410 1410 1430 1430 1450 1450 1460 1460 POWELLS CREEK 2559.86 790 1260 2070 POWELLS CREEK 1979.71 800 1280 2090 POWELLS CREEK 1651.13 810 1290 2100 POWELLS CREEK 908.45 820 1320 840 1340 11480 1480 2130 POWELLS CREEK 202.38 11510 11510 2160 RESULTS The results of this model estimate a maximum rise of 2.59' in 100-year flood elevations immediately upstream of the proposed crossing. The model also indicates a small rise downstream of the proposed crossing — due to a modeled hydraulic jump as flows rapidly decrease in velocity from geometry expansion and high downstream channel roughness (0.08). Impacts to the extents of the 100-year floodplain are displayed on the design plans. HEC RAS output table, flood profiles, and cross sections have been provided in Appendix A of this memo. APPENDIX A Cross Section River Sta Profile Plan Q Total W.S. Elev W.S.E. Rise Vel Chnl Top Width (cfs) (ft) (ft) NO (ft) m 4182.66 100 YR Proposed 1370 769.02 0.00 7.76 166.87 m 4182.66 100 YR Existing 1370 769.02 7.76 166.87 L4 3932.07 100 YR Proposed 1370 765.97 0.00 2.05 206.54 L4 3932.07 100 YR Existing 1370 765.97 2.05 206.54 L3 3891.62 100 YR Proposed 1370 765.68 0.00 4.57 166.44 L3 3891.62 100 YR Existing 1370 765.68 4.57 166.44 EX. CULVERT - CLING LANE 3861.37 Culvert L2 3831.12 100 YR Proposed 1370 761.23 0.00 7.69 136.93 L2 3831.12 100 YR Existing 1370 761.23 7.69 136.93 Ll 3791.09 100 YR Proposed 1370 759.93 0.00 5.7 164.91 Ll 3791.09 100 YR Existing 1370 759.93 5.7 164.89 L 3384.41 100 YR Proposed 1400 747.97 0.00 7.96 118.84 L 3384.41 100 YR Existing 1400 747.97 7.95 118.84 K 2959.02 100 YR Proposedl 1410 737.63 1 0.00 6.31 1 119.09 K 2959.02 100 YR Existing 1410 737.63 6.31 119.08 1 2559.86 100 YR Proposed 1430 727.79 0.00 7.35 153.27 1 2559.86 100 YR Existing 1430 727.79 7.35 153.27 1 1979.71 100 YR Proposed 1450 714.42 0.00 6.5 102.6 1 1979.71 100 YR Existing 1450 714.42 6.5 102.6 H 1651.13 100 YR Proposed 1460 708.4 0.00 5.92 130.07 H 1651.13 100 YR Existing 1460 708.4 5.92 130.08 G6 1159.5 100 YR Proposed 1460 695.93 0.00 7.26 194.41 G6 1159.5 100 YR Existing 1460 695.93 7.26 194.41 G5 1057.41 100 YR I Proposedl 1460 694.87 1 1.61 6.07 1 315.68 G5 1057.41 100 YR Existing 1460 693.26 4.52 229.04 G4 1021.3 100 YR Proposed 1460 694.82 2.59 4.92 310.2 G4 1021.3 100 YR Existing 1460 692.23 4.56 189.38 PROPOSED CROSSING 966.8 Culvert G3 908.45 100 YR Proposed 1480 690.91 0.25 10.12 1 229.3 G3 908.45 100 YR Existing 1480 690.66 2.92 219.1 G2 835.86 100 YR Proposed 1480 690.45 0.61 5.18 251.09 G2 835.86 100 YR Existing 1480 689.84 4.23 238.2 Gl 562.24 100 YR Proposed 1480 683.57 0.00 6.62 225.94 Gl 562.24 1 100 YR Existing 1480 683.57 6.67 226.08 F 202.38 100 YR I Proposedl 1510 1 678.4 1 0.00 1 4.65 1 154.37 F 202.38 1 100YR I Existing 1 1510 1 678.4 1 1 4.65 1 154.37 Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 �OWELLS CREEK POWELLS CREEK ST' 780 760 740 x c 720 a'> w 700 Z g 2 J Z Q U' U' m 2 680 O O K Z O Z O O O O> Z H H H U H H H H H H H J H W W W W W W W W 0) CO CO 0 W m W CO m m W V) m CO CO O Co m m Co Co a) mm a Co m m Co �� a X X X of of 660 0 1000 2600 3000 4000 Main Channel Distance (R) Legend WS 100 YR - Existing WS 100 YR -Proposed Ground POWELLS CREEK S 9182.6d 932.0Z, D384.4 T q 2959.02 N 2559.84 C,p F 1979.7t 1651.11 1159.6 D08.44 D35.8$ 562.24 �02.3$ Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION M .06 )i*.08 _L 06� 771 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION L4 .06.08fi 06 _ 774 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION L3 .06 + .08 .06 _ 772 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 EXISTING CULVERT AT CLING LANE .06.08)i( .06 _ 774 Legend WS 100 YR - Existing Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 EXISTING CULVERT AT CLING LANE .06 + .08 )i( .06 _ 774 Legend WS 100 YR - Existing Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION L2 .06 + .08 )i( .06 _ 772 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION L1 .06 .08 )L 06 J 77z Legend WS 100 YR -Proposed WS 100 YR - Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION L .06.08 .06 _ 765 Legend WS 100 YR - Existing WS 100 YR - Proposed Ground • Bank Sta 760 755 +K c 0 ? 111 750 745 740 0 50 100 150 200 250 Station (R) Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION K .06 )i .08 .06� 750 Legend WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION J .06 _I_ .08-+—.06---� 750 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION 1 .06 ��.08� .06 ' 740 735 730 725 iK c 0 v lL 720 715 710 705 0 100 200 300 400 Station (R) Legend WS 100 YR -Proposed WS 100 YR - Existing. Ground • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION H .06 .OBfi .06 740 735 730 725 +K c 720 v w 715 710 705 700 0 100 200 300 400 500 Station (R) Legend WS 100 YR - Existing WS 100 YR -Proposed Ground • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G6 .06 )i.08 .06� 708 706 704 702 +K c 700 v w 698 696 694 692 0 100 200 300 400 560 Station (R) Legend WS 100 YR - Existing WS 100 YR -Proposed Ground • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G5 .06 )F.03 it .06 ' 715 710 705 c 700 v w 695 690 685 0 100 200 300 400 500 600 Station (R) Legend WS 100 YR -Proposed WS 100 YR - Existing. Ground • Ineff • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G4 .06 ��.03)1" .06 ' 715 710 705 +K c 700 v w 695 690 685 0 100 200 300 400 500 600 Station (R) Legend WS 100 YR -Proposed WS 100 YR - Existing. Ground • Ineff • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 PROPOSED CROSSING .06 ��.03.06' 715 Legend WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 PROPOSED CROSSING .06 ��.03 -L 06 J 710 Legend WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G3 .06 .03 .06 ' 705 700 +K c 695 u w 690 685 0 100 200 300 400 500 600 Station (R) Legend WS 100 YR -Proposed WS 100 YR - Existing. Ground • Ineff • Bank Sta Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G2 .06 )i( .OBfi .06 _ 702 Legend WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION G1 .06 '' .08�.06� 694 Legend WS 100 YR - Existing WS 100 YR -Proposed Pleasant Green Plan: 1) Existing 3/27/2019 2) Proposed 3/28/2019 CROSS SECTION F .06 )i.08� .06 ' 700 Legend WS 100 YR - Existing WS 100 YR -Proposed Water Quality Calculations for the Proposed Plan, Using the DEQ Virginia Runoff Reduction Method for New Developments NOTEWORTH WATER QUALITY ITEMS: 1. Water quality compliance is met through the use of a level II bioretention basin. 2. The VRRM water quality boundary is defined by the ESC boundary for this plan's limits of disturbance (i.e. the disturbed areas not previously permitted and accounted for). 3. The bioretention basin's subarea treats areas outside of this plan's VRRM boundary / ESC limits of disturbance. Inputting the entire biofilter's subarea into the 'Drainage Area A' land cover table would result in a falsely higher phosphorous removal rate for this project's required removal rate since these areas would exceed the inputs in the 'Site' tab that reflect the VRRM boundary / ESC limits of disturbance. To resolve this discrepancy, the 'Drainage Area A' inputs shown in the following calculations only reflect the 'onsite' areas draining to the bioretention basin. In other words, to avoid a falsely high phosphorous removal rate output the areas located within the VRRM boundary / ESC limits of disturbance that fall within subarea A were inputted into the 'Drainage Area A' tab. 4. The methodology described above in #3 is conservative because it yields a smaller phosphorous removal rate provided, enough though in reality it will treat additional upland runoff outside of this plan's VRRM boundary/ ESC limits of disturbance (i.e. it will treat a portion of the roundabout and a portion of existing Orchard Drive that isn't credited in the following calculations). DE0 Virginia Runoff Reduction Method New Development Cumpfbnce Spreadsheet - Version 3.0 02022 BMP Standards and Specifications M 2013 Draft BMP Standards and Specifications project Name: data Input wlls pleasant Green -Connector Road Date: 10/2/2020 mn4ant values BMP Design Speci)icatiom List: 2013 Draft Stds & Specs wlculadon cells Site Information Post -Development Project (Treatment Volume and Loads) Land Cover (acres) ASoils BSoils CSoils DSoils TotaB Forest/Open Space (acres)-- undisturbed, protected brest/olrens oe or reforested land 0.0) Managed Tod (acres) --disturbed, graded for 1.39 a ms or other turf to be mowed/man ed 1.39 Im"miousOmerlacies) 051 0.51 1.90 IfnrrelnM< nual Rainfall (inches) 43 argat Rainfall Event(Inches) 1.00 Focal Phosphorus CrP) EMC(mg/U 0.26 Vocal Nltmgm(TN) EMCImg/U 1.86 aget TP Loa!(lb/aoe/yr) 0.41 Pj(unitma correction factor) 0.90 Forest/Open Space Cover (acres) 0.00 Weighted Rv (forest) 0.00 %Forest 0% Mamged Tud Qwr(acres) 1.39 Weighted Rv (turn 0.15 %Mawged Tud 23% Impervious Cover (acres) 0.51 Rv (Impervious) 0.95 %Impervious 22% Ste Area (acres) 1.% Site Rv 0% Rur�n6fnaHielank IRvI ASoils 1 BSoils 1 CSoils 1 DSoils Forest/Open Space 0.02 0.03 0.04 0.01 Managed Turf 11 0.15 0.20 1 0.22 1 0.25 Impervious Cover 1 0.95 0.95 1 0.95 1 0.95 Treement Volume and Nutrient Loads Treatment Volume 0.0578 acref0 Treatment Volume (cubic fee) 2,516 TP Load(lb/yr) 1.58 TN Used (Ib yr) 11.31 ummam Am n m..m—.r.,.. 5[armwattrBeit Man mem %MIm�RR=RunaH RetluRbn u.a+*w v ry mr rn..^'� nmm rnv.im. amrmv FaNa mn ��. m�+� mM u.a�O1° mMervr n m�mw mm[� 000000000000� 000000000000� �o��000000000� 000000000000� o��000000000� �000000000000� �000000000000� rou.,o�.ow, a,•a,.,am�+,®a„.,oar.l a0w .•oa.l w.w,l ..oal •oa.l .•oar.l —Al Aw.l a] ,'+.1%w.a'Ilnoaal mponn ooto,00 ®m'o,00 ©mmmm omo,00 ooto,00 ommoo ommmm ommmm ooto,00 ooto,00 Site Results (Water Quality Compliance) Area Checks D.A. A DA. 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) 0.51 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED (ac) 0.51 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA (m) 0.59 0.00 0.00 0.00 0.00 OK. MANAGEDTURFAREATREATED(ac) 0.59 0.00 0.00 0.00 0.00 OK. AREA CHECK Site Treatment Volume (ft') 00 Runoff Reduction Volume and TP By Drainage Area D.A. A DA. B D.A. C D.A. D D.A. E TOTAL RUNOFF REDUCTION VOLUME ACHIEVED (ft)Jjj 1,664 0 0 0 0 1,664 TP LOAD AVAILABLE FOR REMOVAL (Ib/yr) 1.31 0.00 0.00 0.00 0.00 1.31 TP LOAD REDUCTION ACHIEVED (Ib/yr) 1.17 0.00 0.00 0.00 0.00 1.17 TP LOAD REMAINING (Ib/yr) 0.13 0.00 0.00 0.00 0.00 0.13 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) 8.59 0.00 0.00 0.00 0.00 8.59 Total Phosphorus FINAL POST -DEVELOPMENT TP LOAD (Ib/yr) 1.58 TP LOAD REDUCTION REQUIRED (Ib/yr)jj 0.80 11 TP LOAD REDUCTION ACHIEVED (Ib/yr) 1 1.17 TP LOAD REMAINING (Ib/yr): 0.41 REMAINING TP LOAD REDUCTION REQUIRED (Ib/yr): 1 0.00 ** ** TARGETTP REDUCTION EXCEEDED By 0.37 LB/YEAR ** Total Nitrogen (For Information Purposes) POST -DEVELOPMENT LOAD(Ib/yr) 11.31 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) 8.59 REMAINING POST -DEVELOPMENT NITROGEN LOAD (Ib/yr) 2.72 Water Quality Calculations for the Proposed Impacts to the Existing, Recorded SWM Forest & Open Space Easement Area NOTEWORTH WATER QUALITY ITEMS: 1. The proposed plan disturbs areas located in a recorded SWM Forest and Open Space easement. The following calculations depict the water quality credit that is associated with the SWM Forest and Open Space easement area being impacted. This credit, which is being removed with this plan, has been added to this project's overall required phosphorous removal rate. 2. The recorded subdivision plat (SUB 201600238) showing the existing SWM Forest and Open Space easement will be abended to vacate this area. DE0 Virginia Runoff Reduction Method New Development Compfbnce Spreadsheet - Version 3.0 02022 BMP Standards and SpeciOceticns M2013 Draft BMP Standards and Specifications ProjectiManne:1 pleasant Green- phosphorous RR Lou Due to SWM Esmt.Impacts data Input calls Date: 1 10/2/2020 constant value BMP Design Speci)icatiom List: 2013 Draft Stds & Specs calculation cells Site Information Post -Development Project (Treatment Volume and Loads) Land Cover (acres) ASoils BSoils CSoils DSoils Totab Forest/Open Space (acres) - undisturbed, protected for esVo ns ce or reforested land 1.02 1.02 Managed Tod (acres) --disturbed, graded for a rds or other turf to be mowed/managed 0.W Imperviouac erlacres) 0.W "Forest/Open Spore areas mustbe Wotestedin accordomewas the Virginia RurmffReducaon Method 1.02 Irnrwmnt< ual - nfall (in <hesl 43 argat Ralnfall Event(Inches) 1.OD Focal phosphorus(TP) EMC(mg/U 0.26 Vocal Nitrogen(TN) EMC(mg/U 1.86 aget TP Load(lb/acre/yr) 0.41 Pj(unitkss correction factor) 0.90 Forest/Open Space Cover (acres) 1.02 Weighted Rv (forest) 0.02 %Forest 100% Managed TurfCover(acres) 0.W Weighted Rv (turn 0.W %Managed Tud 0% Impervious Cover (acres) 0.W Rv (Impervious) 0.95 %Impervious 0% Ste Area (acres) im Site Rv Om Runoff rg% fHA.nte IR.1 ASolls 1 BSolls 1 CSoils 1 DSoils Forest/Open Space 0.02 0.03 0.04 0.01 Managed Turf 11 0.15 0.20 1 0.22 1 0.25 Impervious Cover 1 0.95 0.95 1 0.95 1 0.95 Treatment Volume and Nutrient Loads Treatment Volume 0.W11 (acre-ft) Treatment Volume(cubic fee) 24 TP Load(lb/yr) 0.05 ... TN Used (Ib yr) .. 0.33 Analysis of Temporary ESC Stream Diversion (Note: Design warrants a Type C Diversion) ESC Temporary Stream Diversion Complex Channnel- Analysis for Temporary USC Diversion Input: Slope 0.021 Flow (given) 820.000 line x y n 0 0.000 5.500 0.050 (first n value not used) 1 11.000 0.000 0.050 2 17.000 0.000 0.050 3 28.000 5.500 0.050 Output: Depth 5.223 (Y) ( 5.223) Channel bed segment output: line Q V A P 1 206.84 7.58 27.28 11.68 2 406.31 12.97 31.34 6.00 3 206.84 7.58 27.28 11.68 Wed Sep 30 13:26:08 EDT 2020 Page 1