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HomeMy WebLinkAboutWPO202100034 Calculations 2023-01-10VICTORIAN HEIGHTS VSMP STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations December 22, 2022 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 Si " . . !Database) Soils Table (Source: NRCS Web Soil Survey Online Database) Note: The soils' properties witin this development are predominantly composed of hydrologic group type B soils. Albemarle County, Virginia (VA003) Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent of AOI Symbol 27B Elioak loam, 2 to 7 6.8% percent slopes 27C Elioak loam, 7 to 37.2% 15 percent slopes 39D Hazel loam, 15 to 8.9% 25 percent slopes 65B Fairview sandy 47.2% loam, 2 to 7 percent slopes Totals for Area of 100.00yo Interest Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, VOIUtile 2, Version 3 PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)t Average recurrence interval (years) t 2 5 70 25 50 700 200 500 7000 24hr (2.70-3.37) (3.264.08) (4.15-5.21) (/.89b.1/) (5.97-7.52) (6.87-8.70) (7.85-10.0) (8.89-11.4) (10.a13.6) (11.6-15.4) 0-3. 3.63 4.64 5.48 6.-T 7.81 8.-1 10.3 722 .6-1 Map v 0 Tertam a or E 3 0 o a) Select location Move crosshair or double click b) Clkk on stedon icon ❑ Shaw stations on map Location information: South h h„ Name: Charlottesville. Virginia, USA' oe a Latitude: 38.0975° RSoutFork River �'a e Longitude:-78,46850 Reservolr a4�s y Elevation: 500.6 it I 90 O� Ce MFd lip ° u e x P^ ya W o.6e g n r- + 3 R e 200 v g0 4 I--� A Source,-ESRI Maps aWtt s °of "Source: USGS POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Ada. 14, Volume 2, Version 3 Pre -Development Site Flow Hydrographs The following inflow hydrographs reflect the pre -development onsite concentrated flow from Subareas A, B, C, and G. 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) DA A 0.10 0.10 0.41 0.0012 (Pre-Dev.) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.09 12.0 0.36 12.1 0.88 12.2 0.55 12.3 0.25 12.4 0.21 12.5 0.19 12.6 0.16 12.7 0.14 12.8 0.13 13.0 0.11 13.2 0.10 13.4 0.09 13.6 0.09 13.8 0.08 14.0 0.07 14.3 0.07 14.6 0.07 15.0 0.06 15.5 0.06 16.0 0.05 16.5 0.05 17.0 0.05 17.5 0.04 18.0 0.04 19.0 0.04 20.0 0.03 22.0 0.03 26.0 0.00 6 5 4 3 2 1 a SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A) 0 5 10 15 20 25 30 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 (mil -in) DA A 0.10 0.10 0.34 0.0021 (Pre-Dev.) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.D0 11.0 0.00 11.3 0.D0 11.6 0.D0 11.9 0.26 12.0 0.99 12.1 1.81 12.2 1.04 12.3 0.45 12.4 0.36 12.5 0.32 12.6 0.27 12.7 0.23 12.8 0.21 13.0 0.19 13.2 0.17 13.4 0.15 13.6 0.14 13.8 0.13 14.0 0.12 14.3 0.11 14.6 0.11 15.0 0.10 15.5 0.09 16.0 0.08 16.5 0.07 17.0 0.07 17.5 0.07 18.0 0.06 19.0 0.06 20.0 0.05 22.0 0.05 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A) Worksheet Sb (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 A 0.10 0.10 0.23 0.0055 (Pre-Dev.) Hydrograph Time(hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.05 11.3 0.07 11.6 0.10 11.9 1.19 12.0 3.26 12.1 5.26 12.2 3.06 12.3 1.19 12.4 0.89 12.5 0.77 12.6 0.65 12.7 0.55 12.8 0.49 13.0 0.43 13.2 0.38 13.4 0.34 13.6 0.31 13.8 0.29 14.0 0.26 14.3 0.24 14.6 0.22 15.0 0.20 15.5 0.18 16.0 0.16 16.5 0.15 17.0 0.14 17.5 0.14 18.0 0.13 19.0 0.11 20.0 0.10 22.0 0.09 26.0 0.D0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A) 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 B 0.10 0.10 0.37 0.0004 (Pre-Dev.) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.D0 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.04 12.0 0.16 12.1 0.33 12.2 0.19 12.3 0.09 12.4 0.07 12.5 0.06 12.6 0.05 12.7 0.05 12.8 0.04 13.0 0.04 13.2 0.03 13.4 0.03 13.6 0.03 13.8 0.03 14.0 0.02 14.3 0.02 14.6 0.02 15.0 0.02 15.5 0.02 16.0 0.02 16.5 0.01 17.0 0.01 17.5 0.01 18.0 0.01 19.0 0.01 20.0 0.01 22.0 0.01 26.0 0.D0 6 6 4 3 2 1 0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA B) 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 B 0.10 0.10 0.31 0.0007 (Pre-Dev.) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.D0 11.0 0.00 11.3 0.D0 11.6 0.D0 11.9 0.07 12.0 0.26 12.1 0.53 12.2 0.32 12.3 0.14 12.4 0.11 12.5 0.10 12.6 0.09 12.7 0.07 12.8 0.07 13.0 0.06 13.2 0.05 13.4 0.05 13.6 0.05 13.8 0.04 14.0 0.04 14.3 0.04 14.6 0.03 15.0 0.03 15.5 0.03 16.0 0.03 16.5 0.02 17.0 0.02 17.5 0.02 18.0 0.02 19.0 0.02 20.0 0.02 22.0 0.01 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA B) 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 B 0.10 0.10 0.20 0.0016 (Pre-Dev.) Hydrograph Time(hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.02 11.3 0.03 11.6 0.04 11.9 0.40 12.0 0.99 12.1 1.59 12.2 0.94 12.3 0.36 12.4 0.26 12.5 0.22 12.6 0.19 12.7 0.16 12.8 0.14 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 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA B) Worksheet Sb (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am;Q (mi2-in) DA C 0.13 0.13 0.48 0.0002 (Pre-Dev) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.D0 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.D0 12.0 0.02 12.1 0.08 12.2 0.07 12.3 0.04 12.4 0.03 12.5 0.03 12.6 0.02 12.7 0.02 12.8 0.02 13.0 0.02 13.2 0.02 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 0.01 16.5 0.01 17.0 0.01 17.5 0.01 18.0 0.01 19.0 0.01 20.0 0.D0 22.0 0.D0 26.0 0.D0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA Q 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) DA C 0.13 0.13 0.40 0.0003 (Pre-Dev) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.D0 11.0 0.00 11.3 0.D0 11.6 0.D0 11.9 0.02 12.0 0.08 12.1 0.19 12.2 0.15 12.3 0.08 12.4 0.06 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 0.02 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 0.01 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.D0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA Q 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 C 0.13 0.13 0.26 0.0009 (Pre-Dev) Hydrograph Time(hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.01 11.6 0.01 11.9 0.14 12.0 0.42 12.1 0.74 12.2 0.53 12.3 0.27 12.4 0.18 12.5 0.14 12.6 0.12 12.7 0.10 12.8 0.09 13.0 0.07 13.2 0.07 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 0.02 17.5 0.02 18.0 0.02 19.0 0.02 20.0 0.02 22.0 0.02 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA C) 0 5 10 15 20 25 30 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) DA G 0.10 0.10 0.17 0.0003 (Pre-Dev) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.01 11.6 0.01 11.9 0.08 12.0 0.19 12.1 0.30 12.2 0.18 12.3 0.07 12.4 0.05 12.5 0.04 12.6 0.03 12.7 0.03 12.8 0.03 13.0 0.02 13.2 0.02 13.4 0.02 13.6 0.02 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 0.01 16.5 0.01 17.0 0.01 17.5 0.01 18.0 0.01 19.0 0.01 20.0 0.D0 22.0 0.D0 26.0 0.D0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA G) 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 G 0.10 0.10 0.14 0.0004 (Pre-Dev) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.00 11.0 0.01 11.3 0.01 11.6 0.02 11.9 0.13 12.0 0.27 12.1 0.42 12.2 0.26 12.3 0.09 12.4 0.06 12.5 0.05 12.6 0.05 12.7 0.04 12.8 0.03 13.0 0.03 13.2 0.03 13.4 0.02 13.6 0.02 13.8 0.02 14.0 0.02 14.3 0.02 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.D0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA G) 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 G 0.10 0.10 0.09 0.0004 (Pre-Dev) Hydrograph Time(hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.01 11.3 0.01 11.6 0.02 11.9 0.14 12.0 0.28 12.1 0.43 12.2 0.27 12.3 0.09 12.4 0.06 12.5 0.05 12.6 0.04 12.7 0.04 12.8 0.03 13.0 0.03 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 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA G) 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) DA J 0.21 0.21 0.32 0.0011 (Existing Offsite-Outside LOD) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.04 12.0 0.17 12.1 0.54 12.2 0.74 12.3 0.55 12.4 0.33 12.5 0.23 12.6 0.19 12.7 0.16 12.8 0.13 13.0 0.11 13.2 0.10 13.4 0.09 13.6 0.09 13.8 0.08 14.0 0.07 14.3 0.06 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 6 5 4 3 2 1 0 SCS TR-55 Existing Unit Hydrograph (DA J) 0 5 10 15 20 25 30 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 (mi'-in) DA J 0.21 0.21 0.27 0.0018 (Existing Offsite-Outside LOD) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.00 11.0 0.01 11.3 0.01 11.6 0.01 11.9 0.11 12.0 0.36 12.1 0.97 12.2 1.25 12.3 0.90 12.4 0.52 12.5 0.36 12.6 0.29 12.7 0.23 12.8 0.20 13.0 0.16 13.2 0.14 13.4 0.13 13.6 0.12 13.8 0.11 14.0 0.10 14.3 0.08 14.6 0.08 15.0 0.07 15.5 0.07 16.0 0.06 16.5 0.05 17.0 0.05 17.5 0.05 18.0 0.05 19.0 0.04 20.0 0.04 22.0 0.03 26.0 0.00 6 SCS TR-55 Existing Unit Hydrograph (DAJ) 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 J 0.21 0.21 0.18 0.0041 (Existing Offsite-Outside LOD) Hydrograph Time (hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.06 11.3 0.08 11.6 0.11 11.9 0.55 12.0 1.23 12.1 2.61 12.2 3.07 12.3 2.07 12.4 1.15 12.5 0.78 12.6 0.60 12.7 0.48 12.8 0.41 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 0.10 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 SCS TR-55 Existing Unit Hydrograph (DA J) 0 5 10 15 20 25 30 Site Outflow (DA A + DA B + DA C + DA G + DA J) Hydrograph Time(hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.01 11.6 0.01 11.9 0.25 12.0 0.90 12.1 2.12 12.2 1.72 12.3 1.00 12.4 0.69 12.5 0.55 12.6 0.46 12.7 0.39 12.8 0.35 13.0 0.31 13.2 0.27 13.4 0.25 13.6 0.23 13.8 0.21 14.0 0.20 14.3 0.18 14.6 0.17 15.0 0.16 15.5 0.14 16.0 0.13 16.5 0.12 17.0 0.12 17.5 0.11 18.0 0.11 19.0 0.09 20.0 0.08 22.0 0.08 26.0 0.00 SCS TR-55 Pre -Re Development Unit Hydrograph (ON DA A+B+C+G+J) Site Outflow (DA A + DA B + DA C + DA G + DA J) Hydrograph Time(hrs.) 2-yr Discharges (cfs) 0.0 0.00 11.0 0.01 11.3 0.02 11.6 0.03 11.9 0.58 12.0 1.96 12.1 3.93 12.2 3.01 12.3 1.67 12.4 1.12 12.5 0.89 12.6 0.73 12.7 0.61 12.8 0.54 13.0 0.47 13.2 0.42 13.4 0.38 13.6 0.35 13.8 0.32 14.0 0.29 14.3 0.26 14.6 0.25 15.0 0.23 15.5 0.21 16.0 0.19 16.5 0.17 17.0 0.17 17.5 0.16 18.0 0.15 19.0 0.13 20.0 0.11 22.0 0.11 26.0 0.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A+B+C+G+i) Site Outflow (DA A + DA B + DA C + DA G + DA J) Hydrograph Time(hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.14 11.3 0.19 11.6 0.29 11.9 2.42 12.0 6.18 12.1 10.63 12.2 7.86 12.3 3.97 12.4 2.55 12.5 1.96 12.6 1.60 12.7 1.32 12.8 1.16 13.0 0.99 13.2 0.86 13.4 0.78 13.6 0.71 13.8 0.65 14.0 0.59 14.3 0.53 14.6 0.50 15.0 0.46 15.5 0.41 16.0 0.37 16.5 0.33 17.0 0.32 17.5 0.30 18.0 0.29 19.0 0.25 20.0 0.21 22.0 0.20 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DAA+B+C+G+i) Channel and Flood Protection Calculations The following calculations shows how Subarea A meets Channel and Flood Protection requirements, while also demonstrating how offsite upland flow from Subarea J is taken into account in the calculations for the routings and outflow hydrographs. Project: Location: U.S. Department of Agriculture Natural Resources Conservation Service Victorian Heights Berkmar Drive Check One: Present X 1. Runoff curve Number (CN) Developed 7R 55 Worksheet 2: Runoff Curve Number and Runoff Designed By: UMW, PE Checked By: SRC, PE FL-ENG-21A 06/04 Date: 12/22/2022 Date: 12/22/2022 Cover description CN (weighted) _Calculated'S' Drainage Area Soil name and hydrologic (Cover type, treatment, and hydrologic condition; percent CN Area Product of CN x total product/ Description group (AppendixA) (Acres) Area Value impervious; unconnected/ connected impervious area ratio) total area DAA Impervious Areas 98 0.17 16.7 B Lawns in Good Condition (25%+/-) 61 0.22 13.4 62 6.22 (Pre-Dev.) Woods Grass Good Condition 58 1.65 95.7 Impervious Areas 98 0.05 5.3 DA B (Pre-Dev.) B Lawns in Good Condition (25%+/-) 61 0.42 25.6 64 5.55 Woods Grass Good Condition 58 0.07 4.1 Impervious Areas 98 0.00 0.0 DAC (Pre-Dev) B Lawns in Good Condition 61 0.02 1.2 58 7.20 Woods Grass Good Condition 58 0.37 21.5 DAG Impervious Areas 98 0.08 7.8 (Pre-Dev) B Lawns in Good Condition 61 0.08 4.9 80 2.58 Woods Grass Good Condition 58 0.00 0.0 CAA Impervious Areas 98 3.02 295.6 (Post-Dev) B Lawns in Good Condition 61 1.50 91.5 86 1.67 Woods Grass Good Condition 58 0.00 0.0 DA1 Impervious Areas 98 0.21 20.6 (Existing Offsite- B Lawns in Good Condition 61 1.00 61.0 67 4.83 Outside LOD) Woods Grass Good Condition 58 0.00 0.0 2. Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency -years 1 2 10 n/a Rainfall, P(24 hour) -inches 3.00 3.63 5.48 n/a Runoff, Q-inches 0.39 0.66 1.72 DA A(Pre-Dev.) Runoff, Q-inches 0.48 0.79 1.92 DA B(Pre-Dev) Runoff, Q- inches 0.28 0.51 1.45 DA C(Pre-Dev) Runoff, Q- inches 1.22 1.70 3.27 DA G(Pre-Dev) Runoff, Q-inches 1.64 2.19 3.89 DA A(Post-Dev) Runoff, Q-inches 0.60 0.95 2.18 DA J(Existing Offsite-Outside LOD) U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (T,) or Travel Time (Tt) Project: Victorian Heights Location: Berkmar Drive Check One: Present X Developed Check One: T, X T, Sheet Flow: (Applicable to T, only) X 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, P,(in.) 5 Land slope, s (ft/ft) 6 Compute Tt = [0.007(n*!_ ° 81 / Pi S s°.a Shallow Concentrated Flow Designed By: Checked By: n/a FL-ENG-21A 06/04 Date: 12/22/2022 Date: 12/22/2022 DA A DA B DA C DA A 1 (Pre-Dev.) (Pre-Dev.) (Pre-Dev) (Post-Dev) (Existingng - D) LO Outside LOD) Smooth Smooth Smooth Surface Surface Woods -Light Surface Grass -dense 0.011 0.011 0.4 0.011 0.24 27 25 50 100 54 3.63 3.63 3.63 3.63 3.63 0.02 0.02 0.06 0.01 0.02 0.01 0.01 0.12 0.03 0.14 7 Surface description (paved or unpaved) Unpaved Unpaved Unpaved Paved Unpaved 8 Flow Length, L (ft) 494 265 290 161 690 9 Watercourse slope, s (ft/ft) 0.06 0.17 0.19 0.03 0.03 10 Average velocity, V (Figure 3-1) (ft/s) 4.0 6.5 7.0 1.3 2.7 11 T,=L/3600*V 0.03 0.01 0.01 0.03 0.07 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 17V=[1.49r/Y']/n 18 Flow length, L (ft) 19 T,= L / 3600*V 20 Watershed or subarea Tc or Tt (Add T, in steps 6, 11 and 19) 7F -- 0.10 1 0.10 1 0.13 1 0.10 1 0.21 Natural Resources Conservation Service TR SS Graphical Peak Discharge Method Project: Victorian Heights Designed By: 0 Date: 12/22/2022 Location: Berkmar Drive Checked By: 0 Date: 12/22/2022 Check One: Presen% DewX 1. Data Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description DAA (Pre-Dev.) DAB (Pre-Dev.) DAC (Pre-Dev) DAG (Pre-Dev) DAA (Post-Dev) DAJ (Existing Offsite-Outside LOD) Drainage Area(Am) in miles2= 0.0032 0.0009 0.0006 0.0003 0.0071 OA019 Runoff curve number CN= 62 64 58 80 86 67 Time of concentration(Tc)= 0.10 0.10 0.13 0.10 0.10 0.21 Rainfall distribution type= Type 11 Type II Type II Type 11 Type II Type II Pond and swamp areas spread throughout the watershed= 0 0 0 0 0 0 2. Frequency -years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3. Rainfall, P(24 hour) -inches 3.00 3.63 SAS 3.00 3.63 SAS 3.00 3.63 SAS 3.00 3.63 SAS 3.D0 3.2 SAS 3.00 3.0 SAS 4. Initial Abstraction, la -inches 1.24 1.24 1.24 1.11 1.11 1.11 1.44 1.44 1.44 0.52 0.52 O.S2 0.33 0.33 0.33 0.97 0.97 0.97 S. Compute la/ P 0.41 0.34 0.23 0.37 0.31 0.20 0.48 0.40 0.26 0.17 0.14 0.09 0.11 0.09 0.06 0.32 0.27 0.18 6. Unit peak Discharge, Qu-amfin Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows ]. Runoff, Q from Worksheet 2-inches 0.39 0.66 1.72 0.48 0.79 1.92 0.28 0.51 1.45 1.22 1.70 3.27 0.28 0.51 1.45 0.60 0.95 2.18 S. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9. Peak Discharge, Qp-cfs where Qp=Qu Am QFp 0.88 1.81 5.26 0.33 0.53 1.59 0.08 0.19 0.74 0.30 0.42 0.43 Routed through Underground Detention Basin O.J4 1.25 3.OJ WATERSHED SUMMARY FOR CHANNEL PROTECTION Area, 1-year Flow, CN ac. cts FDA A+B+C+G(Pre-Dev) 63 3.13 1.59 CN Area, ar. DA A (Post-Dev) 86 4.52 Area, 1-year Flow, CN ac. cts DA J (Edsting Offske Outside LOD) 67 1.21 0.74 WATERSHED SUMMARY FOR FLOOD PROTECTION Area, 10-year Flow, CN ac. cts DAA+B+C+G+1(Pre-Dev) 64 4.34 10.63 DAA+1(Post-Dev) 82 5.73 10.59 9 VAC 25-870-66 Section B: Channel Protection Utilizing a 1-inch Orifice "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 8.3 "... 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 6.3.a. In accordance with the following methodology: Q Allowed < I.F. * (Q Pre -Developed + (RV Pre -Developed) ) I (RV Developed ) + Q Pre -Developed Offsite Q Allowed < 1.06 cfs Where: QPre-Developed= CN Pre -Developed= S Pre -Developed = RV Pre -Developed — CN Post -Developed= S Post -Developed = RV Port -Developed= I.F. = Q Pre -Developed Offsite = Q Developed 1.59 cfs (From TR-55) 63 (From Curve Number Summary) 5.98 (From SCS TR-55 eq. 2-4) 0.42 in. (From SCS TR-55 eq. 2-3) 86 (From Curve Number Summary) 1.67 (From SCS TR-55 eq. 2-4) 1.64 in. (From SCS TR-55 eq. 2-3) 0.80 (Factor of Safety) 0.74 cfs (From TR-55) = 1.03 cfs Section B.4 Limits of Analysis The analysis terminates at Post -Development Subarea A since subsection B.3.a is met. 9 VAC 25-870-66 Section C: Flood Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and hydraulic methodologies:" Section C.2.b.: The point of discharge (Detention Basin B's 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 Subareas A, B, C, G & 1 Peak Flow Rate = 10.63 cfs 10-Year, 24-Hour Post -Development Subarea A & J Peak Flow Rate = 10.59 cfs Section C.3 Limits of Analysis The flood protection analysis terminates at Subarea A since subsection C.2.b is met. Post -Development Detention Basin Routings and Outflow Hydrographs The following routing calculations and outflow hydrographs reflect the post -development attenuation in Subarea A from the proposed underground detention facility. Post -Development DA A Inflow Hydrograph Time (hrs) Inflow (cfs) 0.0 0.00 0.5 0.08 1.0 0.08 1.5 0.09 2.0 0.09 2.5 0.09 3.0 0.10 3.5 0.10 4.0 0.11 4.5 0.11 5.0 0.12 5.5 0.12 6.0 0.14 6.5 0.14 7.0 0.15 7.5 0.16 8.0 0.17 8.5 0.20 9.0 0.24 9.5 0.24 10.0 0.29 10.5 0.38 11.0 0.53 11.3 0.71 11.6 1.67 11.9 9.49 12.0 7.59 12.1 2.53 12.2 1.37 12.3 1.12 12.4 0.95 12.5 0.78 12.6 0.66 12.7 0.61 12.8 0.57 13.0 0.49 13.2 0.43 13.4 0.40 13.6 0.35 13.8 0.32 14.0 0.29 14.3 0.27 14.6 0.25 15.0 0.23 15.5 0.20 16.0 0.18 16.5 0.17 17.0 0.16 17.5 0.15 18.0 0.14 19.0 0.12 20.0 0.10 22.0 0.09 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 Inflow Hydrograph (1-yr Design Storm) Post -Development DA A Inflow Hydrograph Time (hrs) Inflow (cfs) 0.0 0.00 0.5 0.10 1.0 0.11 1.5 0.11 2.0 0.12 2.5 0.12 3.0 0.13 3.5 0.13 4.0 0.14 4.5 0.15 5.0 0.16 5.5 0.16 6.0 0.18 6.5 0.18 7.0 0.20 7.5 0.21 8.0 0.22 8.5 0.26 9.0 0.32 9.5 0.32 10.0 0.39 10.5 0.51 11.0 0.70 11.3 0.95 11.6 2.22 11.9 12.64 12.0 10.11 12.1 3.37 12.2 1.83 12.3 1.49 12.4 1.27 12.5 1.03 12.6 0.88 12.7 0.82 12.8 0.76 13.0 0.65 13.2 0.57 13.4 0.53 13.6 0.47 13.8 0.43 14.0 0.39 14.3 0.36 14.6 0.34 15.0 0.31 15.5 0.27 16.0 0.23 16.5 0.22 17.0 0.21 17.5 0.20 18.0 0.18 19.0 0.15 20.0 0.13 22.0 0.12 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 -2.0 Inflow Hydrograph (2-yr Design Storm) Post -Development DA A Inflow Hydrograph Time(hrs) Inflow(cfs) 0.0 0.00 0.5 0.18 1.0 0.20 1.5 0.20 2.0 0.21 2.5 0.22 3.0 0.23 3.5 0.24 4.0 0.25 4.5 0.27 5.0 0.29 5.5 0.29 6.0 0.32 6.5 0.33 7.0 0.36 7.5 0.38 8.0 0.39 8.5 0.46 9.0 0.56 9.5 0.57 10.0 0.69 10.5 0.90 11.0 1.24 11.3 1.68 11.6 3.93 11.9 22.36 12.0 20.13 12.1 5.97 12.2 3.24 12.3 2.64 12.4 2.25 12.5 1.83 12.6 1.55 12.7 1.44 12.8 1.34 13.0 1.16 13.2 1.01 13.4 0.93 13.6 0.83 13.8 0.76 14.0 0.69 14.3 0.63 14.6 0.59 15.0 0.54 15.5 0.48 16.0 0.41 16.5 0.39 17.0 0.37 17.5 0.35 18.0 0.32 19.0 0.27 20.0 0.24 22.0 0.21 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 25.00 20.00 15.00 10.00 5.00 o.W -s.W Inflow Hydrograph (10-yr Design Storm) Post -Development DA A + J Inflow Hydrograph (To Underground Detention) Time (hrs) Inflow (cfs) 0.0 0.00 11.0 0.53 11.3 0.71 11.6 1.67 11.9 9.53 12.0 7.77 12.1 3.07 12.2 2.11 12.3 1.67 12.4 1.28 12.5 1.01 12.6 0.84 12.7 0.77 12.8 0.70 13.0 0.60 13.2 0.53 13.4 0.49 13.6 0.44 13.8 0.40 14.0 0.36 14.3 0.33 14.6 0.31 15.0 0.29 15.5 0.26 16.0 0.22 16.5 0.21 17.0 0.20 17.5 0.19 18.0 0.18 19.0 0.15 20.0 0.13 22.0 0.12 26.0 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 Inflow Hydrograph (1-yr Design Storm) Post -Development DA A + J Inflow Hydrograph (7o Underground Detention) Time (hrs) Inflow (cfs) 0.0 0.00 11.0 0.71 11.3 0.96 11.6 2.23 11.9 12.75 12.0 10.47 12.1 4.35 12.2 3.07 12.3 2.40 12.4 1.79 12.5 1.40 12.6 1.16 12.7 1.05 12.8 0.95 13.0 0.82 13.2 0.71 13.4 0.65 13.6 0.58 13.8 0.53 14.0 0.48 14.3 0.44 14.6 0.41 15.0 0.38 15.5 0.34 16.0 0.29 16.5 0.28 17.0 0.26 17.5 0.25 18.0 0.23 19.0 0.19 20.0 0.17 22.0 0.15 26.0 0.00 Inflow Hydrograph (2-yr Design Storm) Post -Development DA A + J Inflow Hydrograph (To Underground Detention) Time (hrs) Inflow (cfs) 0.0 0.00 11.0 1.29 11.3 1.76 11.6 4.04 11.9 22.91 12.0 21.36 12.1 8.57 12.2 6.30 12.3 4.71 12.4 3.40 12.5 2.61 12.6 2.15 12.7 1.93 12.8 1.74 13.0 1.49 13.2 1.30 13.4 1.19 13.6 1.06 13.8 0.97 14.0 0.88 14.3 0.80 14.6 0.75 15.0 0.68 15.5 0.61 16.0 0.53 16.5 0.50 17.0 0.47 17.5 0.45 18.0 0.41 19.0 0.35 20.0 0.30 22.0 0.27 26.0 0.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 Inflow Hydrograph (10-yr Design Storm) BasinFlow printout INPUT: Basin: 0 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 3 Storage Pipes Storage pipe 0 name: 120" HOPE 1 diameter (in) 120.000 length (ft) 118.000 invert (ft) 506.565 angle 0.287 volume (cy) 343.248 Storage pipe 1 name: 120" HOPE 2 diameter (in) 120.000 length (ft) 118.000 invert (ft) 506.500 angle 0.287 volume (cy) 343.248 Storage pipe 2 name: 120" HOPE 3 diameter (in) 120.000 length (ft) 131.000 invert (ft) 506.500 angle 0.287 volume (cy) 381.064 Start—Elevation(ft) 506.50 Vol.(cy) 5 Outlet Structures Outlet structure 0 Orifice name: BARREL area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 506.400 multiple 1 discharge out of riser Outlet structure 1 Orifice 11=111 name: LOW-RISE ORIFICE area (sf) 0.099 diameter or depth (in) 4.250 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 506.500 multiple 1 discharge into riser Outlet structure 2 Orifice name: EMERGENCY BYPASS PIPE area diameter or depth width for rect. coeffi invert mul discharge Outlet structure 3 Orifice (sf) 1.227 (in) 15.000 (in) 0.000 -ient 0.600 (ft) 515.000 tiple 1 out of riser name: MID -RISE ORIFICE area (sf) 0.889 diameter or depth (in) 8.000 width for rect. (in) 16.000 coefficient 0.600 invert (ft) 511.500 multiple 1 discharge into riser Outlet structure 4 Orifice name: OVERFLOW WEIR area (sf) 1.469 diameter or depth (in) 16.410 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 516.000 multiple 1 discharge into riser 3 Inflow Hydrographs Hydrograph 0 Curve name: 1 YR UGD A INFLOW time incr (minlhrs) 0.02 time limit (minlhrs) 30.00 file: Q:\Projects\202196 - Victorian Heights\Calculations\SWM\3rd Sub\1 YR UGD A.txt volume (cy) 1312.29 routed true time in hours true Hydrograph 1 Curve name: 2 YR UGD A INFLOW time incr (minlhrs) 0.02 time limit (minlhrs) 30.00 file: Q:\Projects\202196 Sub\2 YR UGD A.txt volume (cy) 1762.31 routed true time in hours true Hydrograph 2 Curve name: 10 YR UGD A INFLOW time incr (minlhrs) 0.02 time limit (minlhrs) 30.00 file: Q:\Projects\202196 Sub\10 YR UGD A.txt volume (cy) 3259.04 routed true time in hours true OUTPUT: Routing Method: storage -indication - Victorian Heights\Calculations\SWM\3rd - Victorian Heights\Calculations\SWM\3rd Hydrograph 0 Routing Summary of Peaks: 1 YR UGD A INFLOW inflow (cfs) 9.527 at 11.90 (hrs) discharge (cfs) 1.033 at 12.42 (hrs) water level (ft) 511.426 at 12.48 (hrs) storage (cy) 479.112 Hydrograph 1 Routing Summary of Peaks: 2 YR UGD A INFLOW inflow (cfs) 12.749 at 11.90 (hrs) discharge (cfs) 3.954 at 12.14 (hrs) water level (ft) 512.272 at 12.14 (hrs) storage (cy) 593.894 Hydrograph 2 Routing Summary of Peaks: 10 YR UGD A INFLOW inflow (cfs) 22.914 at 11.90 (hrs) discharge (cfs) 10.588 at 12.08 (hrs) water level (ft) 516.178 at 12.08 (hrs) storage (cy) 1037.337 Post -Development Site Flow Hydrographs The following hydrographs reflect the post -development flow from the site by adding the hydrographs for Subarea A (from detention routings) and Subarea J (offsite upstream flow that runs through site). Post -Development DA A+J Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.49 11.3 0.50 11.6 0.57 11.9 0.85 12.0 0.95 12.1 1.00 12.2 1.02 12.3 1.03 12.4 1.03 12.5 1.03 12.6 1.03 12.7 1.03 12.8 1.03 13.0 1.02 13.2 1.01 13.4 1.00 13.6 0.99 13.8 0.97 14.0 0.96 14.3 0.94 14.6 0.92 15.0 0.89 15.5 0.84 16.0 0.80 16.5 0.76 17.0 0.71 17.5 0.66 18.0 0.61 19.0 0.49 20.0 0.37 22.0 0.23 26.0 0.00 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Outflow Hydrograph (1-yr Design Storm) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Post -Development DA A+l Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.57 11.3 0.59 11.6 0.66 11.9 0.97 12.0 1.95 12.1 3.95 12.2 3.86 12.3 3.52 12.4 3.04 12.5 2.27 12.6 1.94 12.7 1.69 12.8 1.49 13.0 1.22 13.2 1.06 13.4 1.04 13.6 1.03 13.8 1.02 14.0 1.01 14.3 0.99 14.6 0.97 15.0 0.94 15.5 0.91 16.0 0.87 16.5 0.83 17.0 0.79 17.5 0.75 18.0 0.70 19.0 0.60 20.0 0.49 22.0 0.31 26.0 0.00 27.0 0.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 -0.50 Outflow Hydrograph (2-yr Design Storm) Post -Development DA A+J Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.85 11.3 0.87 11.6 0.95 11.9 7.31 12.0 9.56 12.1 10.59 12.2 9.77 12.3 9.10 12.4 8.34 12.5 7.53 12.6 6.70 12.7 5.88 12.8 5.07 13.0 3.50 13.2 2.07 13.4 1.65 13.6 1.39 13.8 1.21 14.0 1.10 14.3 1.04 14.6 1.03 15.0 1.02 15.5 1.00 16.0 0.97 16.5 0.95 17.0 0.92 17.5 0.89 18.0 0.86 19.0 0.80 20.0 0.72 22.0 0.56 26.0 0.00 27.0 0.30 30.0 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 Outflow Hydrograph (10-yr Design Storm) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 STORM SEWER COMPUTATIONS For outfall from UGD to existing pipe 10 YEAR STORM SEWER COMPUTATIONS Design Storm Year= 10 FOMT OOWNSiREAM STRUC VRE DRAM AREA RUNOFF COEFF. CA MLE! IIAM RAM FALL RUNOFF Q MVERi ELEVATION$ LENGTH SLOFE CIA CAPA- C. VEL FLOW IIFM REMARK$ MCR ACCUM ACRES C MM MPS CFS. UP. LOWER FEEF FLFT. MCHES CFS. FPS. SEC DGD 0.00 0.90 0.00 0.00 5.00 6.67 10.5 4 506.48 505.71 35.00 0.0220 18 16.9 10.1 3.5 4 0.00 0.90 0.00 0.00 5.06 6.65 10.5 3 505.61 503.96 92.08 0.0179 18 15.2 9.2 10.0 3 0.00 0.90 0.00 0.00 5.22 6.59 10.5 2 503.86 500.29 63.54 0.0562 18 27.0 14.3 4.5 2 0.00 0.90 0.00 0.00 5.30 6.57 10.5 1 500.19 496.36 40.80 0.0939 18 34.9 17.1 2.4 1 0.00 0.90 0.00 0.00 5.34 6.56 10.5 OITI' 496.11 485.74 103.41 0.1003 18 33.3 16.6 6.2 Hydraulic Grade Line Calculation Design Year: 10 Project: Victorian Heights Job #: 202196 Prepared by: LMW, PE W= STATION OU TWATER SURFACE ELEV Da Q. ZW Se H, N CnONLOSS ................................................................... 3.............................................................. ......... V, Ile Qx Vx Q'V V/18 H. ANGLE He IG 13H, 511� FMA 1, H WLET WATERS SURFACE ELEV RM ELEV 486.94 103.41 18 10.49 0.010 1.03 16.6 1.1 1 10.5 17.1 180 4.5 1.59 65 2,50208 5.16 6.71 3.35 4.38 491.32 501.00 497.56 40.80 18 10.49 0,008 0.35 17.1 1.1 2 10.5 14.3 150 3.2 1.11 8 0 2.24 2.92 1.46 1.80 499.36 505.36 501.49 1 63.54 1 18 1 10.49 1 0,008 1 0.54 14.3 0.8 3 10.5 9.2 97 1.3 0.46 0 0 1.25 1.63 0.82 1.36 502.85 523.91 505.16 92.08 18 10.49 0,008 0.78 9.2 0.3 4 10.5 10.1 106 L6 0.55 0 0 0.88 1.15 0.57 1.36 506.52 525.07 506.91 35.00 18 10.49 0,008 0.30 10.1 0.4 UGD i i 1 1 1 1 1 0.00 1 0 0 1 0.39 0.51 1 0.26 0.55 507.46 528.50 Hydraulic Grade Line Page 1 Pre- and Post -Development Sheetflow Volume Computations The following computations demonstrate how post development sheetflow areas D, E, F and H are evaluated to show they do not contribute to downstream erosion or flooding from the pre development areas D, E and F. U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 2: Runoff Curve Number and Runoff FL-ENG-21A 06/04 Project: Victorian Heights Designed By: LMW, PE Date: 2/8/2022 Location: Berkmar Drive Checked By: SRC, PE Date: 2/8/2022 Check One: Present X Developed 1. Runoff curve Number (CN) Drainage Area Soil name and hydrologic Cover description Area Product of CN x CN (weighted) _ Calculated'S' (Cover type, treatment, and hydrologic condition; percent CN total product/ Description group (Appendix A) impervious; unconnected/connected impervious area ratio) (Acres) Area total area Value DAD Impervious Areas 98 0.03 2.9 (Pre-Dev.) B Lawns in Good Condition (25%+/-) 61 0.07 4.3 60 6.62 Sheetflow Woods Grass Good Condition 58 0.55 31.9 DAE Impervious Areas 98 0.02 2.2 (Pre-Dev.) B Lawns in Good Condition (25%+/-) 61 0.07 4.3 59 6.91 Sheetflow Woods Grass Good Condition 58 0.89 51.6 DAF Impervious Areas 98 0.00 0.0 (Pre-Dev.) B Lawns in Good Condition (25%+/-) 61 0.01 0.6 58 7.22 Sheetflow Woods Grass Good Condition 58 0.44 25.5 DAH Impervious Areas 98 0.08 7.6 (Post-Dev.) B Lawns in Good Condition (25%+/-) 61 0.08 5.0 79 2.68 Sheetflow Woods Grass Good Condition 58 0.00 0.0 DAD Impervious Areas 98 0.03 2.9 (Post-Dev.) B Lawns in Good Condition (25%+/-) 61 0.23 14.0 65 5.32 Sheetflow Woods Grass Good Condition 58 0.00 0.0 DAE Impervious Areas 98 0.00 0.0 (Post-Dev.) B Lawns in Good Condition (25%+/-) 61 0.19 11.6 61 6.39 Sheetflow Woods Grass Good Condition 58 0.00 0.0 DA IF Impervious Areas 98 0.00 0.0 (Post-Dev.) B Lawns in Good Condition (25%+/-) 61 0.08 4.9 61 6.39 Sheetflow Woods Grass Good Condition 58 0.00 0.0 2. Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency -years 1 2 10 n/a Rainfall, P (24 hour)- inches 3.00 3.63 5.48 n/a Runoff, Q- inches 0.34 0.60 1.60 DA D(Pre-Dev.)Sheetnow Runoff, Q- inches 0.31 0.55 1.53 DA E(Pre-Dev.)Sheetflaw Runoff, Q- inches 0.28 0.51 1.45 DA F(Pre-Dev.)Sheetflow Runoff, Q-inches 1.18 1.66 3.21 DA H(Post-Dev.)Sheetnow Runoff, Q- inches 0.52 0.83 2.00 DA D(Post-Dev.)Sheetn Runoff, Q- inches 0.37 0.63 1.67 DA E(Post-Dev.)Sheetflow Runoff, Q- inches 0.37 0.63 1.67 DA F(Post-Dev.)Sheelflow Runoff, ches 0.32 0.57 1.56 DA D+E (Pre-Dev.)Sheetflaw Runoff, Q-inches 0.61 1 0.95 1 2.19 IDA H+D+E (Post-Dev.)Sheetflow 9 VAC 25-870-66 Section D: "Increased volumes of sheet flow resulting from pervious or disconnected impervious areas, or from physical spreading of concentrated flow through level spreaders, must be identified and evaluated for potential impacts on down -gradient properties or resources. Increased volumes of sheet flow that will cause or contribute to erosion, sedimentation, or flooding of down gradient properties or resources shall be diverted to a stormwater management facility or a stormwater conveyance system that conveys the runoff without causing down -gradient erosion, sedimentation, or flooding. If all runoff from the site is sheet flow and the conditions of this subsection are met, no further water quantity controls are required." Am (square Volume Q(in) miles) (acre-ft) Pre -Development Onsite DA H Runoff Volume for 2-yr Storm (acre-ft) 0.00 0.00000 0.0000 Post -Development Onsite DA H Runoff Volume for 2-yr Storm (acre-ft) 1.66 0.00025 0.0221 Pre -Development Onsite DA H Runoff Volume for 10-yr Storm (acre-ft) 0.00 0.00000 0.0000 Post -Development Onsite DA H Runoff Volume for 10-yr Storm (acre-ft) 3.21 0.00025 0.0427 There is an increase in onsite sheetflow volume for DA'H', therefore downstream pipes will be evaluated Am (square Volume Q(in) miles) (acre-ft) Pre -Development Onsite DA D Runoff Volume for 2-yr Storm (acre-ft) 0.60 0.00102 0.0323 Post -Development Onsite DA D Runoff Volume for 2-yr Storm (acre-ft) 0.83 0.00041 0.0181 Pre -Development Onsite DA D Runoff Volume for 10-yr Storm (acre-ft) 1.60 0.00102 0.0868 Post -Development Onsite DA D Runoff Volume for 10-yr Storm (acre-ft) 2.00 0.00041 0.0434 There is a decrease in sheetflow volume indicating there is no effect on erosion, sedimentation, or flooding of down gradient properties for DA'D'. Am (square Volume Q(in) miles) (acre-ft) Pre -Development Onsite DA E Runoff Volume for 2-yr Storm (acre-ft) 0.55 0.00154 0.0452 Post -Development Onsite DA E Runoff Volume for 2-yr Storm (acre-ft) 0.63 0.00030 0.0100 Pre -Development Onsite DA E Runoff Volume for 10-yr Storm (acre-ft) 1.53 0.00154 0.1250 Post -Development Onsite DA E Runoff Volume for 10-yr Storm (acre-ft) 1.67 0.00030 0.0264 There is a decrease in sheetflow, volume indicating there is no effect on erosion, sedimentation, or flooding of down gradient properties for DA'E'. Am (square Volume Q(in) miles) (acre-ft) Pre -Development Onsite DA F Runoff Volume for 2-yr Storm (acre-ft) 0.51 0.00070 0.0190 Post -Development Onsite DA F Runoff Volume for 2-yr Storm (acre-ft) 1.45 0.00013 0.0096 Pre -Development Onsite DA F Runoff Volume for 10-yr Storm (acre-ft) 0.63 0.00070 0.0237 Post -Development Onsite DA F Runoff Volume for 10-yr Storm (acre-ft) 1.67 0.00013 0.0111 There is a decrease in sheetflow volume indicating there is no effect on erosion, sedimentation, or flooding of down gradient properties for DA'F'. Am Defining the Limits of Analysis for DA'H' (square Volume Q(in) miles) (acre-ft) Pre -Development Onsite DA D+E Runoff Volume for 2-yr Storm (acre-ft) 0.57 0.00255 0.0775 Post -Development Onsite DA H+D+E Runoff Volume for 2-yr Storm (acre-ft) 0.95 0.00095 0.0483 Pre -Development Onsite DA D+E Runoff Volume for 10-yr Storm (acre-ft) 1.56 0.00255 0.2118 Post -Development Onsite DA H+D+E Runoff Volume for 10-yr Storm (acre-ft) 2.19 0.00095 0.1112 There is a decrease in onsite sheetflow volume for the site at the point where the cumulative drainage areas DA 'H', DA'D' and DA'E' flows into the underground storm sewer system along Berkmar Drive. This will indicate where the pipe analysis of the downstream pipe system can stop. Essentially this means at the point where Post Development DA'H','D', and 'E' meet (Structure EXl) will be the End of Analysis, and one run of storm sewer pipe upstream will be the Limits of Analysis (Structure EX2) for these subareas. Conclusion As shown in the Storm sewer computations for the existing underground storm sewer, the pipe runs from DA'H' (EX4) to the End of Analysis (EX3) are still adequate and contain the 30-year storm even with the increased volume of runoff from DA'H'. These underground pipes are concrete and therefore the increased runoff will not have an effect on erosion of the storm sewer system. Existing Storm Sewer Evaluation The following computations demonstrate how flow from Subarea H is contained in the existing storm sewer system to the End of Analysis for that subarea. 10 YEAR STORM SEWER COMPUTATIONS Design Storm Year= 10 FC. OOWNSiREAM STRUC VSE D. AREA RUNOFF COEFF_ CA INI.E I' TBAE RAPT FALL RUNOFF Q MVERi ELEVATIONS LENGTH SLOFE CIA CAPA- CITY VEL FLOW Tlh® REMARK$ MCR ACCUM ACRES C FRi FRi CFS. UPPER LOWER FEET 1,FT. MCHES CFS. FPS. SEC EX4 0.05 0.55 0.03 0.03 6.00 6.35 0.2 EX3 509.80 509.15 38.70 0.0168 15 8.4 2.6 15.1 EX3 0.90 0.75 0.68 0.70 6.25 6.28 4.4 EX2 508.15 499.60 280.50 0.0305 15 11.3 8.6 32.7 EX2 0.75 0.55 0.41 1.12 6.80 6.12 6.8 EXI 499.45 479.90 393.50 0.0497 15 14.4 11.5 34.1 Hydraulic Grade Line Calculation Design Year: 10 Project: Victorian Heights Job #: 202196 Prepared by: LMW, PE W= STATION OU TWATER SORFACE ELEV Oa Q ZW Se FM N CnONLOSS V, Ile Qx Vx Q'V KQ8 H. ANGLE He IG 13H, ' 5I1� FMA 1, H WLET WATERS SORFACE ELEV RM ELEV 480.90 393.50 15 6.83 0.011 4.40 11.5 0.5 EX2 4.4 8.6 37.9 1.1 0.40 15 0.11448 1.03 1.34 0.67 5.07 485.97 503.94 500.60 280.50 15 4.41 0.005 1.31 8.6 0.3 EX3 0.2 2.6 0.45 0.1 0.04 90 0.07121 0.39 0.51 0.26 1.56 502.16 513.15 510.15 38.70 15 0.17 0.000 0.00 2.6 0.0 EX4 0.00 0 0 0.03 0.03 0.02 0.02 510.17 513.46 Hydraulic Grade Line Page 1 Virginia Runoff Reduction Method Water Quality Calculations (COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF PURCHASING NUTRIENT CREDITS. THE VRRM BOUNDARY IS DEFINED BY THE LIMITS OF DISTURBANCE) Runoff Volume and Curve Number Calculations Ent,, aaegn Oman nlnbu arotb:MP. u," Damage Area Curve Numbers and Rumff Rep[hs' [u•.anurnmrsfa CNatljlaM ry HaaTnr By gel ea ,wiryreawNn eneam,w,eenao„p,aam .o.+..oaa OEQ WMinia Bunaff B u&an MCMOE New Deveiapm E Wftnre3geaEiM1eel- C3011BMPBb 2mspa(Iflo 01013 Dra BMP SU dasEs aM 3 peM=Ims P Jo Name: VlMdan HelgM oa@: 12/22/2M B.DO gn Spe[ifirmiam Lis[ 2013 Mah SI&&Spea OnSGnla a,mraliprcne:l 43 awan E.msnnC 1.m TM I �m m+IlmclmW 1.M is rgetm Wea llryeoNV� OA] vllvrma::mnamaeao.l o.m 3.0 0. Virginia Runoff Reduction Method Mrgaheet DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet - Version 3.0 BMP Design Specifications List: 2013 Draft Stds & Specs Site Summary Project Title: Victorian Heights Date: 44539 Total Rainfall= 431nches Site Land Cover Summary A soils BSoils CSoils DSOUS Totals %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 1 0.00 1.90 0.00 0.00 1.90 37 Impervious Cover (acres) 1 0.00 3.23 0.00 0.00 3.23 63 5.13 100 Site Tv and Land Cover Nutrient Loads Site Rv 0.67 Treatment Volume ft 12,518 TP Load (lb/yr) 7.87 TN Load (lb/yr) 56.27 Total TP Load Reduction Required (lb/yr) 5.76 Site Compliance Summary Total Runoff Volume Reduction (ft) 0 Total TP Load Reduction Achieved(lb/yr) 0.00 Total TN Load Reduction Achieved (lb/yr) 0.00 Remaining Post Development TP Load 7.87 (Ib/yr) Remaining TP Load Reduction (lb/yr) 5.76 Required ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Drainage Area Summary D.A. A D.A. B DA. C D.A. D D.A. E Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Impervious Cover (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Total Area (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Drainage Area Compliance Summary DA. A D.A. B DA. C D.A. D DA. E Total TP Load Reduced (lb/vr) 0.00 0.00 0.00 0.00 0.00 0.00 Summary Prior Virginia Runoff Reduction Method Worhsheet TN Load Reduced (lb/yr) 1 0.00 1 0.00 1 0.00 1 0.00 1 0.00 1 0.00 Drainage Area A Summary Land Cover Summary A Soils BSoils CSoils DSoils Total %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 1 0.00 1 0.00 0.00 0.00 0.00 0 Impervious Cover (acres) 1 0.00 1 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Practice Credit Area Cover Credit I s Volume (ft) Upstream to Practice (Ibs) (lb/yr) (Ib/yr) Treatment to be (acres) Area (acres) Practices (Ibs) Employed Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.00 Total TN Load Reduction Achieved in D.A. (lb/yr) 0.00 Drainage Area B Summary Land Cover Summary A Soils BSoils CSoils DSolis Total %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 1 0.00 1 0.00 0.00 0.00 0.00 0 Impervious Cover (acres) 1 0.00 1 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Practice Credit Area Cover Credit I a Volume (Its) Upstream to Practice (Ibs) (lb/yr) (lb/yr) Treatmenttobe (acres) Area (acres) Practices (Ibs) Employed Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. (Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A. (lb/yr) 0.00 Summary Print Virginia Runoff Reduction Method! Worhsheet Drainage Area C Summary Land Cover Summary A Soils BSolls CSolls DSoils Total %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 coo 0 Managed Turf (acres) 1 0.00 1 0.00 0.00 1 0.00 coo I o Impervious Cover (acres) 1 0.00 1 0.00 0.00 1 0.00 coo I o 0.00 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Practice Credit Area Cover Credit I ' Volume (ft) Upstream to Practice (Ihs) (16/yr) (Ih/yr) Treatment tohe (acres) Area(acres) Practices(Ihs) Employed Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. (lh/yr) 0.00 Total TN Load Reduction Achieved in D.A. (lh/yr) 0.00 Drainage Area D Summary Land Cover Summary A Soils B Soils CSolls D Soils Total %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 1 0.00 1 0.00 0.00 1 0.00 0.00 1 0 Impervious Cover (acres) 1 0.00 1 0.00 0.00 1 0.00 0.00 1 0 0.00 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Removed TP Remaining Downstream Practice Credit Area Cover Credit I Volume (ft') Upstream a (lbs) to Practice (Ihs) (16/yr) (Ib/yr) Treatment to be (acres) Area (acres) Practices (Ihs) Employed Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. (lh/yr) 0.00 Total TN Load Reduction Achieved in D.A. (lh/yr) 0.00 Drainage Area E Summary Summary Print Virginia Runoff Reduction Method VVorhsheet Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf (acres) 1 0.00 1 0.00 0.00 1 0.00 0.00 1 0 Impervious Cover (acres) 1 0.00 1 0.00 0.00 1 0.00 0.00 1 0 0.00 BMP Selections Managed Turf Impervious BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Practice Credit Area Cover Credit I a Volume (Tt ( Upstream to Practice (Ihs) (Ih/yr) (Ih/yr) TreEmploydhe (acres) Area (acres) practices (Ihs) Employed Total Impervious Cover Treated (acres) 0.00 Total Turf Area Treated (acres) 0.00 Total TP Load Reduction Achieved in D.A. 0.00 (Ih/yr) Total TN Load Reduction Achieved in D.A. 0.00 (Ih/yr) Runoff Volume and CN Calculations 1-yearstorm 2-yearstorm 10-yearstorm Target Rainfall Event (in) 1 3.00 3.63 SAS Drainage Areas RV & CN Drainage Area A Drainage Area B Drainage Area C Drainage Area D Drainage Area E CN 0 0 0 0 0 RR(f?) 0 0 0 0 0 I -year return period RV wa RR (. -in) 0.00 0.00 0.00 0.00 0.00 RV w RR (wnln) 0.00 0.00 0.00 0.00 0.00 CR adjoined 0 0 0 0 0 2-year return period RV wo RR (.in) 0.00 0.00 0.00 0.00 0.00 RV w RR (wsin) 0.00 0.00 0.00 0.00 0.00 CR adjusted 0 0 0 0 0 30-year return period RVwa RR(we-in) 0.00 0.00 Ow 0.00 0.00 RV w RR iwsin) 0.00 0.00 OAO 0.00 0.00 CR adjusted 0 0 0 0 0 Summary Print OUTFALL PROTECTION COMPUTATIONS OUTLET PROTECTION OUTFALL OF SEDIMENT BASIN PER VESCH PLATE 3.18-1, DEPTH OF STONE (d) = 1.5 x MAX STONE DIAMETER d>_6" Q10= 6.96 CFS Qdesign= 8.6 CFS PER VESCH PLATE 3.18-3 d50= 0.2 FT La= 11 FT w1= 3*DO= 3.75 FT w2= DO + La= 12.25 FT FINAL DESIGN NOTE: VDOT CLASS Al STONE HAS A MEAN d50=O.9 FT AND EXCEEDS 0.5 FT OUTLET PROTECTION TO INCLUDE A FILTER FABRIC UNDERLAYMENT KEYED INTO THE EXISTING GROUND A MINIMUM OF 9" ATTHE ENDS & ALONG THE PERIMETER. EDGES OF FABRIC SHALL OVERLAP A MINIMUM OF 9". STONE TO BE VDOT CLASS Al STONE WITH THE FOLLOWING DIMENSIONS: La= 11 FT w1= 4 FT w2= 13 FT DEPTH= 1.5 FT DEPTH (d) >_ 1.5 X 0.9' DEPTH (d) >_ 1.35'