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HomeMy WebLinkAboutWPO202200040 Calculations 2023-03-10BROOKHILL STORMWATER MANAGEMENT CALCULATIONS PACKET (WPO 202200040- Archer Avenue Extension) Date of Calculations AUGUST 22, 2022 Revised on March 3, 2023 iCOTT/R. C'bLLINS'Z Lic. No. 035791 ,:t:. 3/3/23 PREPARED BY: COLLINS FmG-IIiFERING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations for Archer Avenue's Extension Soils Mapping & Table for Archer Avenue's Extension (Source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003) Map Unit Symbol Map Unit Name Percent of A0t 27B Elioak loam, 2 21.3% to 7 percent slopes 27C Elioak loam, 7 31.0% to 15 percent slopes 34C Glenelg loam, 15.9% 7 to 15 percent slopes 34D Glenelg loam, 2.2% 15 to 25 percent slopes 39D Hazel loam, 15 29.7% to 25 percent slopes Totals for Area of 100.0% Interest Note: Soils' properties witin this development are predominantly composed of hydrologic type B soils. Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) 1 U Map v CO 129211. AshWo ode/Rva ... nSyY°d° Y E\\. °t 3\V C C n Y L m 600ft POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, Volume 2, Version 3 PDS-based precipitation frequency estimates with 90 % confidence intervals in Inches)' Aver rawaence inlawal oy m) ouraean OOO 10 25 ® 100 200 ® 1000 24-0r 2 9eJ0.3D (3:5408) (4-14520) (41".14) (54S.751) (68"sg) (7W.99) (8.87-11.4) (104136) (11615.4) x a 0 i 0 in a w W � N U II a � w � w a tpp O A �D O N N 'N 6 N VI m Ol N 3 � o Z o " u x U y O m N Of m 0 0 b O N O O ? Q 6 4 T eNl vNl vmi 6 O vNi v O m 0 a N � O O b e~i N O Vml e~I O Imfl n O (,� m �O N Of �D VI m tD Vl m tD VI « o c - W O 6 d c O O a O c Z u m 2 E C o 0- w 4 -6 u > C y L C a a � w u wt; o 0 0 0 0 0 0 0 E w .- .- �. .- « .- « c w w ` C o o u a o 0 u a o 0 u a o 0 u ti C y u m a y u m a y u m a w u a a i 0 ¢ 0 0¢ 0 0 0¢ 0 0 0¢ 0 0 0 « O U. O O O O O O O `w '2 O_ c c O_ c c o_ c c O_ c o a Z a 2 a Z a Z a E ' a 3 o a 3 0 m 3 0 m 3 0 E 3 3 E 9 3 E 9 3 E 9 3 0 o a ax ,v L w c m an w n m� C O m O N m m v v v o v o n o o c O O O p O D 0 O O` U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (T,) or Travel Time (Tt) Project: Brookhill Location: Archer Ave. Extension Check One: Present X Developed X Check One: T, X Tt Segment ID: Sheet Flow: (Applicable to T. only) 1 Surface description (Table 3-1) 2 Manning's roughness coeff., n (Table 3-1 3 Flow length, L (total L < 100) (k) 4 Two-year 24-hour rainfall, P,(in.) 5 Land slope, s [fit/fit) 6 Compute Tt= [0.007(n-L)a.e] / Pi .s s.e Designed By: FGM, PE Checked By: SRC, PE Through subarea n/a FL-ENG-21A 06/04 Date: 8/22/2022 Date: 8/22/2022 DA4A DA48 DA4A DA4B (Pre-Dev.) (Pre-Dev.) (Post-Dev.) (Post-Dev.) Woods (Light Woods (Light Dense Dense Underbrush) Underbrush) Grass Grass 0.4 0.4 0.24 0.24 100 100 35 90 3.62 3.62 3.62 3.62 0.23 0.13 0.46 0.09 0.13 0.16 0.03 0.11 Shallow Concentrated Flow: 7 Surface description (paved or unpaved) Unpaved Unpaved 8 Flow Length, L (fit) 75 65 9 Watercourse slope, s (ft/ft) 0.15 0.17 10 Average velocity, V (Figure 3-1) (ft/s) 6.3 6.8 11 Tt=L/3600'V 0.00 0.00 Channel Flow: 12 Cross sectional flow area, a (ft) 13 Wetted perimeter, Pw (fit) 14 Hydraulic radius, r = a/Pw (k) 15 Channel Slope, s (ft/ft) 16 Manning's Roughness Coeff, n 17V=[1.49r"'s"j/n 18 Flow length, L (ft) 19 Tt= L/3600•V 20 Watershed or subarea T. or Tt (Add Tt in steps 6,11 and 19) Note: The shoretest SCS Tc is 0.10 hrs. c c c 0 o o + c 0 .2 Y LL v w C N v w+ a 4 C 1� C� 0 in n n 0 o a N m v 0.00 0.07 0.01 0.13 1 0.16 1 0.10 1 0.12 0 ry O L O u mlQ M v a n 0 v v O d c m O C p .O-i ry N C O ry O c a m � m e1 S p l0 N N O e1 O r r M m L vi O O V 1O a om a �+ m a d � T a ry l0 e^i O ei L J O O 3 a M O O N a N o r• �O of O N Vf ei L 6 o n N ry N l0 M M n V n n Vl 'O « T W 0 u 3 eel S m V VI M ei a � lO O1 VI lO L o n ry l0 l0 O VI V ei v` « L `O u 3 o n a V Y`O V C \ � ' W E r' L a U a a u C J a a y 6 p0 0 Ma OC,O O 1° L 'Y-i u E m m Q d O 3 « N U A t J cd a Q a j O c N a a a .0 a 6 a r-O « E � c c m a pis �u°�mJa ar ri I of I v vi 6 r: a of 3 3 0 r 3 0 ..1 F j 9 VAC 25-870-66 Channel & Flood Protection Analysis 9 VAC 25-870-66 (Point of Analysis #1) 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." NOTE: The two-year 24-hour storm event is not erosive in the manmade storm sewer & riprap lined outlet protection. 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: Contributing Drainage Area (DA 4A) = 0.70 ac. Overall Drainage Area (to Culvert) = 79.20 ac. (See Road Plan Sheet 11 for Culvert Drainage Area Map) Percent of Contributing DA to Overall DA = 0.9 % 9 VAC 25-870-66 (Point of Analysis #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.a: The point of discharge (i.e. the storm sewer), "confines the postdevelopment peak flow rate from the 10-year 24-hour storm event within the stormwater conveyance system to avoid the localized flooding." NOTE: The proposed storm sewer's 10-year HGL does not overtop the inlets and is therefore considered to be contained within the system. See Road Plan sheet 10 for HGL computations. Section C.3.a Limits of Analysis The flood protection analysis terminates at the site outfall because this is where the "site's contributing drainage area is less than or equal to 1.0% of the total watershed area draining to a point of analysis in the downstream stormwater conveyance system" 9 VAC 25-870-66 (Point of Analysis #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.l.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 :S I.F. * (Q Pre -Developed * RV Pre -Developed ) / RV Developed Q Allowed Where: QPre-Developed — CN Pre -Developed = S Pre -Developed = RV Pre -Developed = CN Post -Developed — S Post -Developed — RV Post -Developed — I.F. = Q Developed < 0.09 cfs Section B.4 Limits of Analysis 0.37 cfs (From Worksheet 4 Watershed Summary) 60 (From Worksheet 4 Watershed Summary) 6.78 (From SCS TR-55 eq. 2-4) 0.32 in. (From SCS TR-55 eq. 2-3) 77 (From Worksheet 4 Watershed Summary) 2.98 (From SCS TR-55 eq. 2-4) 1.07 in. (From SCS TR-55 eq. 2-3) 0.80 (Factor of Safety) 0.09 cfs The analysis terminates at the onsite subarea since subsection B.3.a is met. 9 VAC 25-870-66 (Point of Analysis #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.b.: The point of discharge (the site outfall), "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 4B Peak Flow Rate = 3.09 cfs 10-Year, 24-Hour Post -Development Subarea 4B Peak Flow Rate = 2.79 cfs Section C.3 Limits of Analysis The flood protection analysis terminates at the subarea since subsection C.2.b is met. In addition to the 9VAC25-870-66 compliances shown previously at points of analyses #1 and #2, compliance is also met for the disconnected sheet flow runoff along the roadway's embankments via 9VAC25-870-66 section D. As depicted in the following sheet, the embankments' disconnected sheet flows are decreased (48% reduction) with the proposed roadway. This is a result of the roadway's drainage being captured and directed away from the embankments via the proposed storm sewer. In addition to the reduction in disconnected sheet flow, the groundcover in the proposed roadway's embankments will remain pervious (grass) in the post -development state. The one exception to this grass groundcover is where pervious riprap is proposed to further limit the risk of erosion. In summary, the embankments' sheet flows meet 9VAC25-870-66 Section D requirements through the above stated reduction in sheet flow volumes and the continued presence of a pervious groundcover. This design will reduce the potential erosion, sedimentation, flooding and impacts to down -gradient properties and resources. SCS TR-55 Hydrographs Worksheet Sb (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) DA 4A (Pre-Dev.) 0.13 0.13 0.53 0.0002 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 0.02 12.1 0.12 12.2 0.09 12.3 0.04 12.4 0.04 12.5 0.04 12.6 0.03 12.7 0.03 12.8 0.02 13.0 0.02 13.2 0.02 13.4 0.02 13.6 0.02 13.8 0.02 14.0 0.02 14.3 0.01 14.6 0.01 15.0 0.01 15.5 0.01 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 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 -0.02 SCS TR-55 Pre -Development Unit Hydrograph (DA 4A) 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 Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (mi2-in) DA 4A(Pre-Dev.) 0.13 0.13 0.44 0.0004 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 0.03 12.1 0.24 12.2 0.17 12.3 0.09 12.4 0.08 12.5 0.07 12.6 0.06 12.7 0.05 12.8 0.05 13.0 0.04 13.2 0.04 13.4 0.04 13.6 0.03 13.8 0.03 14.0 0.03 14.3 0.03 14.6 0.03 15.0 0.03 15.5 0.02 16.0 0.02 16.5 0.02 17.0 0.02 17.5 0.02 18.0 0.02 19.0 0.02 20.0 0.01 22.0 0.01 26.0 0.00 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.0 SCS TR-55 Pre -Development Unit Hydrograph (DA 4A) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (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 (mi2-in) DA 4A(Pre-Dev.) 0.13 0.13 0.29 0.0014 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 0.21 12.0 0.79 12.1 1.29 12.2 0.72 12.3 0.30 12.4 0.24 12.5 0.21 12.6 0.17 12.7 0.15 12.8 0.13 13.0 0.12 13.2 0.11 13.4 0.10 13.6 0.09 13.8 0.08 14.0 0.07 14.3 0.07 14.6 0.06 15.0 0.06 15.5 0.05 16.0 0.05 16.5 0.04 17.0 0.04 17.5 0.04 18.0 0.04 19.0 0.03 20.0 0.03 22.0 0.03 26.0 0.00 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 0.0 SCS TR-55 Pre -Development Unit Hydrograph (DA 4A) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet Sb (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) DA 4B(Pre-Dev.) 0.16 0.16 0.45 0.0007 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 0.05 12.1 0.37 12.2 0.26 12.3 0.13 12.4 0.12 12.5 0.11 12.6 0.09 12.7 0.08 12.8 0.07 13.0 0.07 13.2 0.06 13.4 0.06 13.6 0.05 13.8 0.05 14.0 0.05 14.3 0.04 14.6 0.04 15.0 0.04 15.5 0.03 16.0 0.03 16.5 0.03 17.0 0.03 17.5 0.03 18.0 0.03 19.0 0.02 20.0 0.02 22.0 0.02 26.0 0.00 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.0 SCS TR-55 Pre -Development Unit Hydrograph (DA 413) 5.0 10.0 15.0 20.0 25.0 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 Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (mi2-in) DA 4B(Pre-Dev.) 0.16 0.16 0.37 0.0012 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 0.19 12.0 0.68 12.1 1.13 12.2 0.63 12.3 0.26 12.4 0.21 12.5 0.18 12.6 0.15 12.7 0.13 12.8 0.12 13.0 0.10 13.2 0.09 13.4 0.08 13.6 0.08 13.8 0.07 14.0 0.06 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 0.03 18.0 0.03 19.0 0.03 20.0 0.02 22.0 0.02 26.0 0.00 1.20 1.00 0.80 0.60 0.40 0.20 0.00 0.0 SCS TR-55 Pre -Development Unit Hydrograph (DA 413) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (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 (mi2-in) DA 4B (Pre-Dev.) 0.16 0.16 0.25 0.0033 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 0.51 12.0 1.88 12.1 3.09 12.2 1.73 12.3 0.72 12.4 0.57 12.5 0.49 12.6 0.42 12.7 0.35 12.8 0.32 13.0 0.28 13.2 0.25 13.4 0.23 13.6 0.21 13.8 0.19 14.0 0.18 14.3 0.16 14.6 0.15 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 0.08 20.0 0.07 22.0 0.06 26.0 0.00 3.50 3.00 2.50 2.00 L50 1.00 0.50 0.00 0 SCS TR-55 Pre -Development Unit Hydrograph (DA 413) Worksheet Sb (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) DA 4A (Post-Dev.) 0.10 0.10 0.06 0.0024 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.06 11.3 0.08 11.6 0.13 11.9 0.80 12.0 1.55 12.1 2.42 12.2 1.49 12.3 0.52 12.4 0.35 12.5 0.29 12.6 0.25 12.7 0.21 12.8 0.18 13.0 0.16 13.2 0.14 13.4 0.12 13.6 0.11 13.8 0.10 14.0 0.09 14.3 0.08 14.6 0.08 15.0 0.07 15.5 0.06 16.0 0.06 16.5 0.05 17.0 0.05 17.5 0.05 18.0 0.04 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 (DA 4A) 5.0 10.0 15.0 20.0 25.0 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 Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (mi2-in) DA 4A (Post-Dev.) 0.10 0.10 0.05 0.0030 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.07 11.3 0.10 11.6 0.16 11.9 1.02 12.0 1.97 12.1 3.07 12.2 1.90 12.3 0.66 12.4 0.45 12.5 0.37 12.6 0.32 12.7 0.26 12.8 0.23 13.0 0.20 13.2 0.17 13.4 0.16 13.6 0.14 13.8 0.13 14.0 0.12 14.3 0.10 14.6 0.10 15.0 0.09 15.5 0.08 16.0 0.07 16.5 0.06 17.0 0.06 17.5 0.06 18.0 0.05 19.0 0.05 20.0 0.04 22.0 0.04 26.0 0.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0.0 SCS TR-55 Post -Development Unit Hydrograph (DA 4A) 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (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*Ct (mi2-in) DA 4A(Post-Dev.) 0.10 0.10 0.03 0.0050 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.12 11.3 0.17 11.6 0.27 11.9 1.67 12.0 3.24 12.1 5.06 12.2 3.12 12.3 1.09 12.4 0.74 12.5 0.62 12.6 0.52 12.7 0.43 12.8 0.38 13.0 0.33 13.2 0.29 13.4 0.26 13.6 0.23 13.8 0.21 14.0 0.19 14.3 0.17 14.6 0.16 15.0 0.15 15.5 0.13 16.0 0.12 16.5 0.11 17.0 0.10 17.5 0.10 18.0 0.09 19.0 0.08 20.0 0.07 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 (DA 4A) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Detention Basin 'C' Routing Calculations & Level Spreader'C' Calculations Archer Avenue Extension- Detention Basin 'C' BasinFlow printout INPUT: Basin: Archer Avenue Extension- Detention Basin 'C' 6 Contour Areas Elevation(ft) 436.00 438.00 440.00 442.00 444.00 446.00 Start—Elevation(ft) 6 Outlet Structures Outlet structure 0 Orifice Area(sf) Computed Vol.(cy) 137.00 0.0 392.00 18.8 738.00 60.0 1293.00 134.2 1925.00 252.6 2665.00 421.9 436.00 Vol.(cy) 0.00 name: Barrel- Str. Al area (sf) 3.142 diameter or depth (in) 24.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 432.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Barrel- Str. AS to 6" HOPE area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 430.000 multiple 1 discharge out of riser Outlet structure 2 Orifice name: Low -Flow Orifice area (sf) 0.010 diameter or depth (in) 1.330 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 436.000 multiple 1 discharge into riser Page 1 Archer Avenue Extension- Detention Basin 'C' Outlet structure 3 Orifice name: Mid -Flow Orifice area (sf) 0.545 diameter or depth (in) 10.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 441.150 multiple 1 discharge into riser Outlet structure 4 Weir name: diameter (in) side angle coefficient invert (ft) multiple discharge transition at (ft) orifice coef. orifice area (sf) Outlet structure 5 Weir name: length (ft) side angle coefficient invert (ft) multiple discharge 4 Inflow Hydrographs Hydrograph 0 SCS Riser - into riser 1.215 0.500 12.566 Emergency Spillway 8.000 0.000 3.300 444.500 1 through dam name: 1-yr 24-hr TR-55 SCS Method Design Storm Area (acres) 1.360 CN 77.000 Type 2 rainfall, P (in) 3.000 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) 1.787 peak time (hrs) 11.922 volume (cy) 195.663 Page 2 Hydrograph 1 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 2 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 3 SCS Archer Avenue Extension- Detention Basin 'C' 2-yr 24-hr TR-55 SCS Method Design Storm 1.360 77.000 2 3.620 0.1200 0.0200 30.000 1.00 true 2.537 11.922 277.732 10-yr 24-hr TR-55 1.360 77.000 2 5.470 0.1200 0.0200 30.000 1.00 true 5.041 11.922 551.850 name: 100-yr 24-hr TR-55 Area (acres) 1.360 CN 77.000 Type 2 rainfall, P (in) 8.970 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) 10.299 peak time (hrs) 11.922 volume (cy) 1127.368 SCS Method Design Storm SCS Method Design Storm Page 3 Archer Avenue Extension- Detention Basin 'C' OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 1 Routing Summary of Peaks: inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 2 Routing Summary of Peaks inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 3 Routing Summary of Peaks: inflow (cfs) discharge (cfs) water level (ft) storage (cy) 1-yr 24-hr TR-55 SCS Method Design Storm 1.784 at 11.92 (hrs) 0.087 at 12.24 (hrs) 441.113 at 12.54 (hrs) 96.205 2-yr 24-hr TR-55 SCS Method Design Storm 2.533 at 11.92 (hrs) 1.036 at 12.08 (hrs) 441.688 at 12.08 (hrs) 119.859 10-yr 24-hr TR-55 SCS Method Design Storm 5.033 at 11.92 (hrs) 2.785 at 12.06 (hrs) 443.070 at 12.06 (hrs) 191.770 100-yr 24-hr TR-55 SCS Method Design Storm 10.281 at 11.92 (hrs) 9.819 at 11.94 (hrs) 443.789 at 11.94 (hrs) 237.902 Mon Sep 12 10:17:13 EDT 2022 Page 4 LEVEL SPREADER'C' DESIGN Per VSMH Chpt. 11, Section 11.5.3: Step 1 Area = (Eqn 11.11) Tv= Qa= (From Worksheet 2) CN = 1.36 ac. 2,594 cf 0.53 watershed inches 77 Step 2 Tc = 0.12 hrs Step 3 la = 0.60 la/P= 0.60 q "= 350 csm/in A= 0.002 miz q PT,= 0.4 cfs NOTES: q PT.is the Treatment Volume peak discharge, or the peak flow rate for the 1-inch rainfall event. The level spreader receives this Treatment Volume runoff via a separate pipe outfall. Per the VA DEC? Specification #2, page 14, the Level Spreader should be designed per the following: "13 feet of Level Spreader length per every 1 cubic foot per second (cfs) of inflow for discharges to a Vegetated Filter Strip or Conserved Open Space consisting of native grasses or thick ground cover." The proposed vegetated filter strip located below subarea 4B's'Detention Basin C' will predominantly consist of native grasses and will have a thick ground cover. Therefore a 13' per 1 cfs design is applicable to 'Level Spreader C'. Site Specific LS length -to -Flow Ratio = 13 ft per 1 cfs Min. Level Spreader C Design Length= 5 ft Notes: Max. LS Length = 130 ft Min. LS Length = 13 ft Proposed LS Length = 13 ft Worksheet for Str. A3 Treatment Volume Capacity Check Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Roughness Coefficient 0.010 Channel Slope 0.035 ft/ft Diameter 6.0 in Discharge 0.40 cis Results Normal Depth 2.2 in Flow Area 0.1 ft2 Wetted Perimeter 0.7 ft Hydraulic Radius 1.2 in Top Width 0.48 ft Critical Depth 3.9 in Percent Full 37.1 % Critical Slope 0.005 ft/ft Velocity 6.03 ft/s Velocity Head 0.57 ft Specific Energy 0.75 ft Froude Number 2.872 Maximum Discharge 1.47 cis Discharge Full 1.36 cis Slope Full 0.003 ft/ft Flow Type Supercritical GVF Input Data Downstream Depth 0.0 in Length 0.0 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.0 in Profile Description N/A Profile Headloss 0.00 ft Average End Depth Over Rise 0.0 % Normal Depth Over Rise 37.1 % Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 2.2 in Critical Depth 3.9 in Channel Slope 0.035 ft/ft Critical Slope 0.005 ft/ft Bentley Systems, InC. Haestatl Methods Solution FlowMasler Detention Basin C- Barrel TW Analysis.fm8 Center [10.03.00.031 3/2/2023 27 Siemon Company Drive Suite 200 W Page 1 of 1 Watertown, CT 06795 USA +1-203-755-1666 Riprap Outlet Protection Calculations & Structure A1's Tailwater Analysis 4n,C-T ' 2o'TFCTZ fQ Qoc) - I,%a cF5 (rXCccz MZN, 10-YaOvsz&� ol;alo,j'1 1© cis (6KCQC*S �00-yf, oEsssr� 3 00 � (tzP AAQ stz � ,; O�eTK �� scoN� (d sr uLw 3� 1.5 x d5o i f3�T Nc�r LESS TKOW 6u N�cE; lea 4tRTg 3,��-3� MZN. R6mNaEt+K1Ew Abe RzeaRp SzzC = e': C��riE��aE Vi:�JvT CL, Ak Sn= O.�`� ANO A C>ECr'rM of hTCNE aF �$" �S (ta"> O,Bxl.$) Voat cL, RS 1992 3.18 jaa; •aziS de.adL8 OSp MUM ----- __ _ _--_-- = _= __°==___=-__ _- Source: USDA-SCS Plate 3.18-3 Le III - 164 1992 3.18 PIPE OUTLET CONDITIONS A A 'IPE OUTLET TO FIAT .REA WITH NO DEFINED 'HANNEL I a d 7- SECTION A -A FILTER CLOTH KEY IN 6'-9"; RECOMMENDED FOR ENTIRE PERIMETER f 3do (MIN.) 'IPE OUTLET TO WELL IEFINED CHANNEL I d SECTION A —A FILTER CLOTH KEY IN 6"-9% RECOMMENDED FOR ENTIRE PERIMETER NOTES: 1. APRON LINING MAY BE RIPRAP, GROUTED RIPRAP, GABION BASKET, OR CONCRETE. 2. La IS THE LENGTH OF THE RIPRAP APRON AS CALCULATED USING PLATES 3.16-3 AND 3.16-4. 3. d = 1.5 TIMES THE MAXIMUM STONE DIAMETER, BUT NOT LESS THAN 6 INCHES. Source: Va. DSWC Plate 3.18-1 III - 157 Worksheet for Str. Al Tailwater Analysis Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Roughness Coefficient 0.010 Channel Slope 0.115 ft/ft Diameter 24.0 in Discharge 9.82 cis Results Normal Depth 5.1 in Flow Area 0.5 ft2 Wetted Perimeter 1.9 ft Hydraulic Radius 3.0 in Top Width 1.64 ft Critical Depth 13.5 in Percent Full 21.2 % Critical Slope 0.003 ft/ft Velocity 20.18 ft/s Velocity Head 6.33 ft Specific Energy 6.75 ft Froude Number 6.522 Maximum Discharge 107.09 cis Discharge Full 99.55 cis Slope Full 0.001 ft/ft Flow Type Supercritical GVF Input Data Downstream Depth 0.0 in Length 0.0 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.0 in Profile Description N/A Profile Headloss 0.00 ft Average End Depth Over Rise 0.0 % Normal Depth Over Rise 21.2 % Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 5.1 in Critical Depth 13.5 in Channel Slope 0.115 ft/ft Critical Slope 0.003 ft/ft Bentley Systems, Inc. Haestad Methods Solution FlowMaster Detention Basin 4- Barrel TW Analysis.fm8 Center [10.03.00.031 9/12/2022 27 Siemon Company Ddw; Suite 200 W Page 1 of 1 Watertown, CT 06795 USA +1-203-755-1666 Virginia Runoff Reduction Method Water Quality Calculations Mp WgiNa RunoffPemrObn Melhol DeveAWwnr Campo Spread[beer-Versdon3b r,=l chi SaMWNp" SpatlMebn[ OO 2013 DraX Base StardstlasY 3peaMulbna F_—RDleet Xanre: Braokhill- Archer Avenue Exenmen tlane inpN allz pare: B/33/3033 Bmp Dezipn 5pafh[Niwrztirt: 3013OraX 3ttls8Specs ukulv[bnal6 ISIte Information Post -Development Project (Treatment Volume and Wads) lantltme. lanes) •sei% asei% csa[ Dsa[ FaeNDmrspae l•aa-aaemnree, DAO rer[.ale RBo orerame.�� n laser- .vaaeab yr aN.ewmaree za seasessescarespe" 09g OYl 3m Constants Rama[oelfcienes (Ra) all pnrberi i pbiB 1 BSai[ [Sri[ OSeil[ m llneberl 1.00 rerUpKI, se, iRp3 LLpa Op5 u17ri M[Img/o O.M A15 Rap LL33 Ol5 Tats,genlRp EMCyry/LI I.B6 R95 R95 R95 R95 ae IW..Ml aAa P"sererrmreekmbm 0.90 breY/ ,Spas( ,laves) -- I ]n I=Vasere I p.1180 %ForK Q( 1aW Rb/p) 3]3 kenasar�.rmaa,laoe4 1pv.tB weymea mlamp %Meriegetlruf R% Inpervbrat lavc5) 0.9] Rv(impem—) 0.95 %Imlerviou )8% I; e e eee e e e e e e e e e e e e a e e e e e a e e e sa e e a e i eee eee e e e e e e a e e e e e e e e a F[� {g{e fi3! e e e e e e e e e e e e l�Y A 'v � 8 6 9 a e a e e e e e 9 e e 'a 4}'� fe e e eei eei eee e e e e e e a e e e e e a e e m g�4A Sag f�( E . � a!i d e � i dg' Fs! a € !� {� ,I 1 {1 11 !11 )1 loll } l )� l ) ) M ...` , ..� r 1-1 0OOOF a SSSSS]L G H,5 a S S S S S Y Q R 06 0 O r- a6SSSS0 a SS S � o 66 o c c 0 C o 0 0 Q E 0 u 0 666660 rya V p Q a p pS O O p S Na0 W O O O e+mN N CD N Q Q OS p p SSSY p p 1A _N CD y V Q\\\ \\\\ T T d I.L a: N L �y V a> C W O W c O W W Q Q Qa W a s a i Q aaa __ N O aai Y N s r LL r W G d OO > J W Q Q W v Z Q W t a Q Q Q Q W Z Q W a L Q Q(] Q W Q Q N O ` W r f¢ ¢ C •O O W R W C s m Q d F W Z Q 6 Q W~ YI W W $' L~ W W L Z= Q W �¢ Z C 6 Z 1 f Z p. Z Q Z K d. Z O Y W �. Z V' O K a $ Z E m O 2 O R O g O O Q 0 EWGZ p O f LL�oa� a >�yo J G �`oGGoG mD J f O N F Z e g g m J 00 O W Z �Q s 3 O4S 3 �'ss N O LL s F W O f f F N W Q K Z LL V m O N z Z_ Y f_ 6 O Z < Z Z Z uy 7 LO+ Q d H i K C C 7 K Runoff Volume and Curve Number Calculations Enter design storm rainfall depths (in(: 1 arsmrm i rnorm 1 rstmm 3.m 3.A, 3AT 1¢e NOM A[Im 14OilNJ/hacnws.nmagdAtlq/pfdyl/ •Notes (ra a lselow): 111 The curve numbers and mnaR volumes computed in this spreatlsMet Mr each drainW area are limited in their applicability for detemmming and demonstrating compliance with water quantity requirements. see VRIIM User's Rude and Documentation for a dda,,n,l,nMrm,t,,n, pl Runoff Volume (pifor pre- antl Rest development drainage areas must be in volumetric units le.g., acni or cubic hell when using the Energy Balance Equaton. Runoff measured in watershed- intlees and shown inthe spreadsheet as RV(walersh ckinch) can only he used in the Energy Balance Equation when the pro- and postArvebpmem cammage areas are equal. Othery ise RVlwalershed inM) murt he multiplied bythe drainage area. pl Adjured CNs art based on runoff reduction volumes as calculated in D.A. tabs. An allemadve CN adjustment calculation for Vegehted Roofs is included in BMV specdnlion No. A Drainage Area Curve Numbers and Runoff Depths" Curve numbers(CN, CNadj) and mwffdepths(RV ) ore computed with and withoutredustmn pmctires. DminageAreaA I ASees BSoils CSoilz DSoils TaGl Area (wues): 0.00 Forest/Open space- undisturbed, mode[ted hard/open space or reforested land Are(acres) ac CN Don 30 EDO ss O.W 70 OlU ]] Runoff Redcll uon Volume A': 0 Managed Tuff-d.q.Ned,MdedbryaMsorother turfmbemawed/man Area acres CN out 39 ERR 61 0.00 74 Dot ED Imperious cover Are", (acres) CN out 9B ERR 9B D.m 9B D. 98 Chlm.a.al 0 1-year storm 2-yearstorm I.,, storm RVywlapad (core aged+mA/ with no Runoff Reductions' am Sm 1 0.00 RVaseene a (Iwmrshed ) with Runoff Reductions' a.m n.m 1 Ono Adjusted Me I to o D 'See Nobes Rome Drainage Area6 ASgils BSoils CSoilz Dsees Total 1,(aves): 1.36 Fornl/Open space- undisturbed, moderated! l foresr/open space or reforested land A(acres) CN D. 3o EDO ss Deed )o D. n Runo as u_on Volume n': 129) Managed Tuff-d.q.Ned,,dedbryaMsorother turf m be maweffin-ged Area(acres) CN D. 39 E. 61 Den J4 O.m BO Impervin., Cover Area acres CN D. 9R 0.59 9R Deed 9s 0.m 9R CNIOA M n 1-year storm 2-year storm Wall storm RV r psatersM1MJiuh) with no Runoff Reduction• 1.m 1.52 3.02 RVp.,.Iepee (Iavrersh4d ) with Runoff Reduction • O.R1 126 2.76 Adjusted CN' R 93 1 74 'See Notes above Drainage AreaC ASails IsSoils CSoils DSoils Totallveafavesr QW Forst Open Space- undisturbed, pmtead bren/o en or reforestedN land Arena[ C 0.. 30 am 55 000 70 0. n owned uns Reduction Volume n': o Manages Turf- remained, Mdea for yams or her turf to be mowed/manages Area acres Call 0.m 39 am 6] O.O] Ja 0.m e0 Impervious Career Area (acres) Call99 0.m am 9a 0.00 9A am 99 Cbl, y, 0 1-year storm 2-year storm IDyear Marro RVoaurelopea (watealMeanMl with no Runoff Redunbn" O.m am am RVOe.elwea (xarerrhetl-0td) with Runoff Redustbne a.m I 0 o.m 0 O.Iw 0 Adjusted CN" *See Notes above Dreinzge Area ASails IsSoils CSoils DSails Total Area paev): OAO Forest/Open Space- undisturbed, protected forest/open space or reforested land prey(acres) Call 0.m 30 am 55 0.00 70 0.m n RYgF Rotation Wunen'. Manages Turf- dirturnea, Mdea for yams or other turf to be mowed/man Area acres I:N 0.m 39 am 61 0.00 70 0.m 90 mpervious Cover Areas (acres) Callcar9R 0.m 0.m o.00 9s 0.m 99 Mils of 0 1-year storm 2-year storm IDyear stormat Wouseepead (uvMnhedJwA/ union no Runoff Redugtbn" 0.m Om 0.m RVwwyr(uoeer9w61wh) said, Runoff Redindinn" am 0.m am Adjusted CN" 0 0 0 "See Ali above Drainage Area ASails Is Sale CSoils DSails Thal Area (acres): 0.00 Forest/Open Space- undisturbed, protected forest/open space or reforested land Area (acres) CN 0.m 30 am 55 O.m JO 0.m D RunoRReaN uon Voluneh 0 Manages Turf-d.n.Ned,MdtldMryaMsor other turf b be nnwed/managed Area (acres) Call 0.m 39 am 61 O.m 10 and 80 Impervious Cocer Area acres CN 0.m 99 am 98 Qm 9B 0.m S. CNwy n 0 1-year storm 2-year storm IDyear storm RVgiuyMO (wMrshMdt[A) with no Runoff Reduetian" 0.m O.m 0.m RVywywa /wvleriwd-0 ) with Runoff Reduction" Mad 0.m 0.m Adjusted Me "See Notes above 0 0