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HomeMy WebLinkAbout006 Civil Stormwater Design Report   Stormwater Design Report  Page 1  02/20/2023  TABLE OF CONTENTS  Overview .........................................................................................................................................  2  Existing Conditions ........................................................................................................................... 2  Proposed Stormwater Improvements ............................................................................................. 2    APPENDIX  Appendix A ........................................................................................................  Drainage Basin Map  Appendix B ............................................................... Drainage Basin & Storage Facility Calculations  Appendix C ............ Excerpts from: “Blackwood Groves Subd. Phase 2 Stormwater Design Report”                                            Stormwater Design Report  Page 2  02/20/2023  OVERVIEW  The purpose of this report is to detail the stormwater design for the two proposed multi‐family residential  developments on Lot 1, Block 14 of Blackwood Groves Subdivision. These projects have been prepared as  two separate site plans known as The Cottages at Blackwood Groves and the Arbor Houses at Blackwood  Groves project. The Cottages project involves the construction of 36 cottage‐style residences, 8 carriage‐ style garage units with apartments above them, and 1 community amenity building, while the Arbor  Houses project involves the construction of two 10‐plex apartment buildings.  Block 14 is surrounded on 4 sides by newly constructed city standard streets, with Canter Avenue to the  west, Victoria Street to the north, Winterthur Avenue to the east, and Blackwood Road to the south.  Lot  1 is 4.587 acres and encompasses the western portion and the majority of Block 14. A linear park spans  the entire eastern side of the Block along Winterthur Avenue.    EXISTING CONDITIONS  Except for the utilities (water, sewer, gas, electric) stubbed into the Block, the project site is currently  vacant. The site currently slopes from south to north at ~1%‐2%. The seasonal high groundwater elevation  on the site was estimated to be at ~3‐3.3’ below existing grade based on the groundwater monitoring  results provided in the subdivision stormwater report by C&H Engineering.   PROPOSED STORMWATER IMPROVEMENTS  The stormwater improvements for the subdivision infrastructure were designed to accommodate runoff  from the project site. Based on the calculations in Appendix B of this report, the inlets and storm pipes in  the streets adjacent to the project site can accommodate the runoff from the 25‐year storm event, while  the subdivision ponds can accommodate the runoff volume from the 10‐year 2‐hour storm event. The  subdivision ponds were also designed with weirs in the outlet structures to retain the 0.5” runoff  reduction volume from the drainage areas contributing to the ponds. Therefore, the proposed design does  not include any stormwater retention or treatment facilities on the project site. Instead, grading, and a  series of grassed swales, inlets, piping, and chases are proposed to help convey runoff from the site to the  stormwater infrastructure in the adjacent city streets.  The project site was partially included in 3 separate drainage basins with the subdivision stormwater  design. Drainage Basin 9B includes most of the eastern and northern portions of the site (and the adjacent  linear park) and drains to an inlet on Victoria Street at the north end of the site. Drainage Basin 9B2  includes the western portion of the site, which drains to an inlet on Canter Avenue at the northwest corner  of the site. Drainage Basin 1F includes the southernmost portion of the site, which drains to Blackwood  Road and on to an inlet in Canter Avenue in the southwest portion of the site. Drainage Basins 9B and 9B2  ultimately drain to Detention Pond 9 in the northwest corner of the subdivision. Drainage Basin 1F drains  to Detention Pond 1 on the western side of the subdivision.   The areas and runoff coefficients for the portions of the project site that are proposed to drain to DB 9B,  9B2, and 1F are slightly different than what was proposed in the subdivision stormwater design report.  Therefore, using the Rational Method, the calculations in Appendix B provide new areas, runoff  coefficients, and flow rates for these areas, and incorporate them into the subdivision pond sizing  calculations to show that adequate capacity exists in the subdivision ponds for the revised areas.      Stormwater Design Report  Page 3  02/20/2023  The overland flow portion of the time of concentrations for these drainage basins each originated on the  project site as well. Now that the proposed design for the project site is complete, these TOC paths were  revised to show the actual overland flow paths for each drainage basin. The channel flow TOC values were  also adjusted to match the location where the revised overland flow paths entered the street gutters.   Summary tables showing these revised values are included below for reference. The green values  represent values that were improved because of the revisions, while the red values represent values that  were impacted or increased.    Block 14 Drainage Basin Summary Drainage Basin Original Revised Per Block 14 Design Area (Ac) Weighted C-Value Time of Conc. (min.) 25-year Runoff Rate (cfs) Area (Ac) Weighted C-Value Time of Conc. (min.) 25-year Runoff Rate (cfs) 9B / 9BA 4.14 0.58 23.87 3.39 3.95 0.59 22.22 3.44 9B2 1.67 0.63 15.03 2.01 1.78 0.77 19.93 2.17 1F 0.8 0.72 6.9 1.81 0.88 0.69 11.54 1.35   Pond Summary Sheet Pond Original Revised Per Block 14 Design Provided Storage Volume (ft3) Contributing Area (ac) Weighted C-Value Required Storage Volume (ft3) Contributing Area (ac) Weighted C-Value Required Storage Volume (ft3) 9 22.48 0.66 54,249 22.41 0.65 52,267 57,340 1 18.87 0.61 29,471 18.90 0.61 29,418 34,978     Similarly, the revised 25‐year runoff rates for these three drainage basins were calculated and used to  confirm that adequate capacity exists in the downstream subdivision storm sewer pipes for the revised  runoff rates from these drainage basins. The original pipe capacity calculations from C&H Engineering’s  design report for the subdivision are redlined in Appendix C to show the revised runoff rates. A summary  table of these revised rates is included below for reference. The green values represent pipe flow rates  that were reduced because of the revisions, while the red values represent pipe flow rates that increased.  The revisions to the flow rates were extremely minor, and ultimately resulted in only a 0.20 cfs increase  in flow in the downstream pipes. After comparing these results to the pipe capacities provided in C&H  Engineering’s report, all downstream pipe segments have adequate capacity to accommodate the revised  flow rates.           Stormwater Design Report  Page 4  02/20/2023  Subdivision Pipe Capacity Summary Pipe # Contributing Pipes Original Pipe Flow Rate (cfs) Revised Pipe Flow Rate (cfs) (Per Block 14) Provided Pipe Capacity (cfs) 9A 9B2 5.32 5.49 22.44 9B / 9BA 9C 7.69 7.75 10.14 9B2 N/A 2.01 2.17 16.34 9C N/A 4.31 4.31 4.34 9D 9B, 9C 8.43 8.49 14.69 9D2 9A, 9B, 9B2, 9C, 9D, 9I, 9I2 17.66 17.88 18.26 9E 9A, 9B, 9B2, 9C, 9D, 9D2, 9I, 9I2, 9G 23.64 23.86 26.74 9F 9A, 9B, 9B2, 9C, 9D, 9D2, 9E, 9I, 9I2, 9G 24.23 24.45 27.23 9G N/A 1.42 1.42 7.49 9I 9I2 3.90 3.90 27.49 1F N/A 1.81 1.35 7.51 1H 2.15 1.69 5.01 *Original Pipe Flow Rates & Provided Pipe Capacities as listed in Subdivision Design Report    A portion of the interior of the site will be drained by on‐site piping and inlets and will flow to the existing  storm inlet located in Victoria Street. Sub‐Basin 9B‐A (a portion of Basin 9B) was created to size the  internal piping for the site for the 25‐year runoff. Conservatively, the time required for flow within the on‐ site pipes was not included within the time of concentration. Instead, the time of concentration for  overland flow to the most upstream inlet was applied to the entire contributing area to Sub‐Basin 9B‐A to  calculate peak runoff. The proposed 8” PVC storm pipes have been sized to adequately convey this runoff.  Supporting Calculations are included in Appendix B.     Appendix A Drainage Basin Map 8''ST8''ST8''ST8''ST8''ST8''ST 8''ST 8''ST 8''STLOT 1 199,809 SF (14.46) (14.00) (9.09) (19.24) (22.53) (21.48) (19.35) VICTORIA STREET WINTERTHUR AVENUECANTER AVENUEBLACKWOOD ROAD DRAINAGE BASIN 9B (2.45 AC) DRAINAGE BASIN 9B2 (1.78 AC) EX. ST INLET EX ST INLET PIPE 9B2 EX ST INLET PIPE 9B PIPE 9C PIPE 1F (14.20) (18.78)50 2050 195018501750165015501450135012 50225021 502050195018501750165015501450135012 50115010 5010 5011 5016 5014501450 1 4 5 0 1 25011 5010 501150125012 50125013 50155 01 7 50 1 8 5019501 9 502 0 50 2 1 50205020502050195018 5018 5019 50205016501650 16 50165014 5014 5013 5013 5013 5012 5011 5012 5011501 1 501 2 50155014 5016 5015 50155014 (20.15) 5014 501550145015501450145013501450125014 5 0 1 3 5012 5015 5015 5 0 1 6 5016 50165016501750175016 5019 5021 5020 5019 5018 5019 5017 5017 5015 501250135012 5012 501550155015 501750185018 502 1 5020 5019 502050195018 50 2 1 5021501550145015 BLDG #1 BLDG #2 ELECELECELECELECCOCO DS DS DS DS DS DS DS DS DS DS DS DS DS DSDS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DSDS DSDS DSDS DRAINAGE BASIN 1F (0.88 AC) SUB-DRAINAGE BASIN 9B-A (1.51 AC) 0 30'60' SCALE 1" = 30' N REVISIONS DATENO.DESC. DRAINAGE BASIN MAP BOZEMAN, MONTANA BLOCK 14 CIVIL SITE PLAN COTTAGES AT BLACKWOOD GROVES FIGURE 1 PROJECT NO: DATE: 22002 February 20, 2023 LEGEND DRAINAGE BASIN BOUNDARY DRAINAGE BASIN COVER TYPE - PERVIOUS STORM MANHOLE STORM INLET STORM CATCH BASIN STORM POND / SWALE SYMBOL DESCRIPTION DRAINAGE BASIN COVER TYPE - IMPERVIOUS DRAINAGE BASIN COVER TYPE - ROOF DRAINAGE BASIN COVER TYPE - STREET R.O.W. TIME OF CONCENTRATION PATH SUB BASIN 9B-A TIME OF CONCENTRATION Appendix B Drainage Basin & Storage Facility Calculations Basis for Calculations Time of Concentration (Ttotal) (minutes) Rainfall Intensity (I) (in/hr) Ttotal = To + Tc Rainfall Frequency Equation To = Time of Concentration for Overland Flow 10 year I = 0.64(X-.65) Pervious 11 year I = 0.78(X-.64) Whereas:100 year I = 1.01(X-.67) To = 1.87 (1.1-CCf)D1/2 Tc = L/V/60 Whereas: (Sb)1/3 X = Storm Duration (hr) C = Runoff Coefficient L = Length of Channel (ft) = Ttotal / 60 Cf = Frequency Adjustment Factor V = Mean Velocity (ft/sec) D = Length of Basin (ft)V = 1.486 Sb = Slope of Basin (%) n n = Manning's Coefficient R = Hydraulic Radius (ft) Hydraulic Radius = Area (ft2) / Wetted Perimeter (ft)Integral Curb & Gutter 0.136 Sc = Slope of Channel (ft/ft) Rational Method Peak Runoff (Q) Q = CIA Drainage Basin Area (Ac.) C-Value Tc (25-yr)Peak Flow (cfs) 9B / 9BA 3.95 0.59 22.22 3.44 9B2 1.78 0.77 19.93 2.17 1F 0.88 0.69 11.54 1.35 R2/3(Sc)1/2 Drainage Basin Time of Concentration and Peak Runoff Calculations Drainage Basin Summary Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coefficient (C) A (Ac) x C ROW - Local 9B 31,547 0.72 0.76 0.5504 Impervious 9B 11,936 0.27 0.95 0.2603 Roof 9B 21,437 0.49 0.95 0.4675 Pervious 9B 20,738 0.48 0.20 0.0952 Park - Pervious 9B 18,286 0.42 0.20 0.0840 Park - Impervious 9B 2,613 0.06 0.95 0.0570 Total 106,556 2.45 1.5144 Weighted C:0.62 10 25 100 Cf - Frequency Adjustment Factor 1 1.1 1.25 C - Runoff Coefficient (Overland Flow) 0.2 9B / 9BA 0.2 0.22 0.25 D - Length of Basin (ft) 221 Sb - Slope of Basin (%)2.1000 To - Time of Conc. - Overland (min.)19.54 19.1 18.45 L - Length of Channel (ft) 401 n - Manning's Coefficient 0.013 R - Hydraulic Radius(ft) 0.136 Sc - Slope of Channel (ft/ft)0.005 V - Velocity (ft/sec) 2.14 2.14 2.14 Tc - Time of Conc. - Channel (min.)3.12 3.12 3.12 Time of Concentration (Ttotal) 22.66 22.22 21.57 X - Storm Duration (hr) 0.38 0.37 0.36 I - Intensity (in/hr) 1.21 1.47 2.00 Q - Peak Runoff (cfs) 1.83 2.23 3.04 Required Gutter Capacity (cfs): 2.23 Provided Gutter Capacity (cfs):3.39 (Per C&H Phase 1 Stormwater Design Report) Rainfall Frequency (yr) Contributing Area & Runoff Coefficient Tabulation Drainage Basin: 9B Time of Concentration & Runoff Rate Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coefficient (C)A (Ac) x C Impervious 9B-A 9,845 0.23 0.95 0.2147 Roof 9B-A 20,332 0.47 0.95 0.4434 Pervious 9B-A 35,535 0.82 0.20 0.1632 Total 65,712 1.51 0.8213 Weighted C:0.54 10 25 100 Cf - Frequency Adjustment Factor 1 1.1 1.25 C - Runoff Coefficient (Overland Flow) 0.2 C * Cf 0.2 0.22 0.25 D - Length of Basin (ft) 223 Sb - Slope of Basin (%)2.5000 9B / 9BA 18.52 18.11 17.49 L - Length of Channel (ft) 1 n - Manning's Coefficient 0.013 R - Hydraulic Radius(ft) 0.136 Sc - Slope of Channel (ft/ft)0.1 V - Velocity (ft/sec) 9.56 9.56 9.56 Tc - Time of Conc. - Channel (min.)000 Time of Concentration (Ttotal) 18.52 18.11 17.49 X - Storm Duration (hr) 0.31 0.30 0.29 I - Intensity (in/hr) 1.37 1.68 2.31 Q - Peak Runoff (cfs) 1.13 1.38 1.89 Pipe Capacity Pipe Pipe Size (in) Flow Depth - d (in) Slope (ft/ft) Manning's n Flow (CFS) On-Site 8" PVC 8 7.50 0.0118 0.013 1.41 Sub-Drainage Basin: 9B-A Contributing Area & Runoff Coefficient Tabulation Time of Concentration & Runoff Rate Rainfall Frequency (yr) Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coefficient (C) A (Ac) x C ROW - Local 9B 31,547 0.72 0.76 0.5504 Impervious 9B 11,936 0.27 0.95 0.2603 Roof 9B 21,437 0.49 0.95 0.4675 Pervious 9B 20,738 0.48 0.20 0.0952 Park - Pervious 9B 18,286 0.42 0.20 0.0840 Park - Impervious 9B 2,613 0.06 0.95 0.0570 Impervious 9B-A 9,845 0.23 0.95 0.2147 Roof 9B-A 20,332 0.47 0.95 0.4434 Pervious 9B-A 35,535 0.82 0.20 0.1632 Total 172,268 3.95 2.3357 Weighted C:0.59 10 25 100 Cf - Frequency Adjustment Factor 1 1.1 1.25 C - Runoff Coefficient (Overland Flow) 0.2 C * Cf 0.2 0.22 0.25 D - Length of Basin (ft) 221 Sb - Slope of Basin (%)2.1000 To - Time of Conc. - Overland (min.)19.54 19.1 18.45 L - Length of Channel (ft) 401 n - Manning's Coefficient 0.013 R - Hydraulic Radius(ft) 0.136 Sc - Slope of Channel (ft/ft)0.005 V - Velocity (ft/sec) 2.14 2.14 2.14 Tc - Time of Conc. - Channel (min.)3.12 3.12 3.12 Time of Concentration (Ttotal) 22.66 22.22 21.57 X - Storm Duration (hr) 0.38 0.37 0.36 I - Intensity (in/hr) 1.21 1.47 2.00 Q - Peak Runoff (cfs) 2.81 3.44 4.68 Drainage Basin: 9B / 9B-A Contributing Area & Runoff Coefficient Tabulation Time of Concentration & Runoff Rate 9B / 9BA Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coefficient (C) A (Ac) x C ROW - Local 9B2 15,281 0.35 0.76 0.2666 Impervious 9B2 24,493 0.56 0.95 0.5342 Roof 9B2 23,203 0.53 0.95 0.5060 Pervious 9B2 14,657 0.34 0.20 0.0673 Total 77,634 1.78 1.3741 Weighted C:0.77 10 25 100 Cf - Frequency Adjustment Factor 1 1.1 1.25 C - Runoff Coefficient (Overland Flow) 0.2 C * Cf 0.2 0.22 0.25 D - Length of Basin (ft) 213 Sb - Slope of Basin (%)2.0000 To - Time of Conc. - Overland (min.)19.5 19.06 18.41 L - Length of Channel (ft) 196 n - Manning's Coefficient 0.013 R - Hydraulic Radius(ft) 0.136 Sc - Slope of Channel (ft/ft)0.0155 V - Velocity (ft/sec) 3.76 3.76 3.76 Tc - Time of Conc. - Channel (min.)0.87 0.87 0.87 Time of Concentration (Ttotal) 20.37 19.93 19.28 X - Storm Duration (hr) 0.34 0.33 0.32 I - Intensity (in/hr) 1.29 1.58 2.16 Q - Peak Runoff (cfs) 1.77 2.17 2.97 Required Gutter Capacity (cfs): 2.17 Provided Gutter Capacity (cfs):3.39 (Per C&H Phase 1 Stormwater Design Report) 9B / 9BA Drainage Basin: 9B2 Contributing Area & Runoff Coefficient Tabulation Time of Concentration & Runoff Rate Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coefficient (C) A (Ac) x C ROW - Collector 1F 19,007 0.44 0.70 0.3054 ROW - Local 1F 1,542 0.04 0.76 0.0269 Impervious 1F 2,006 0.05 0.95 0.0438 Roof 1F 8,967 0.21 0.95 0.1956 Pervious 1F 6,645 0.15 0.20 0.0305 Total 38,168 0.88 0.6022 Weighted C:0.69 10 10 100 Cf - Frequency Adjustment Factor 1 1.1 1.25 C - Runoff Coefficient (Overland Flow) 0.34 C * Cf 0.34 0.37 0.43 D - Length of Basin (ft) 60 Sb - Slope of Basin (%)1.2000 To - Time of Conc. - Overland (min.)10.36 9.9 9.2 L - Length of Channel (ft) 265 n - Manning's Coefficient 0.013 R - Hydraulic Radius(ft) 0.136 Sc - Slope of Channel (ft/ft)0.008 V - Velocity (ft/sec) 2.7 2.7 2.7 Tc - Time of Conc. - Channel (min.)1.64 1.64 1.64 Time of Concentration (Ttotal) 12.00 11.54 10.84 X - Storm Duration (hr) 0.20 0.19 0.18 I - Intensity (in/hr) 1.82 2.24 3.18 Q - Peak Runoff (cfs) 1.1 1.35 1.91 Required Gutter Capacity (cfs): 1.35 Provided Gutter Capacity (cfs):2.63 (Per C&H Phase 2 Stormwater Design Report) 9B / 9BA Drainage Basin: 1F Contributing Area & Runoff Coefficient Tabulation Time of Concentration & Runoff Rate Design Rainfall Frequency (year): 10 Storage Method: Detention Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Outlet Structure Pervious Facility Type: Pond C = Runoff Coefficient Facility Make/Model: N/A I = Rainfall Intensity (in/hr): (I = 0.64x-0.65) A = Drainage Basin (acres) Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coe. (C)A (Ac) x C ROW - Local 1A 18,698 0.43 0.76 0.3262 ROW - Collector 1A 1,253 0.03 0.70 0.0201 ROW - Local 1B 25,176 0.58 0.76 0.4393 ROW - Collector 1B 18,906 0.43 0.70 0.3038 ROW - Alley 1B 1,309 0.03 0.80 0.0240 Residential - Low-Med 1B 3,540 0.08 0.35 0.0284 Residential - Dense 1B 21,122 0.48 0.75 0.3637 Park 1B 18,365 0.42 0.20 0.0843 OS 1B 2,231 0.05 0.20 0.0102 ROW - Local 1C 56,157 1.29 0.76 0.9798 Residential - Dense 1C 77,210 1.77 0.75 1.3294 Park 1C 13,889 0.32 0.20 0.0638 OS 1C 7,940 0.18 0.20 0.0365 ROW - Local 1D 39,731 0.91 0.76 0.6932 ROW - Collector 1D 3,503 0.08 0.70 0.0563 Residential - Dense 1D 183,260 4.21 0.75 3.1553 ROW - Local 1E 5,325 0.12 0.76 0.0929 ROW - Collector 1E 53,409 1.23 0.70 0.8583 ROW - Alley 1E 6,491 0.15 0.80 0.1192 Residential - Low-Med 1E 32,456 0.75 0.35 0.2608 Residential - Dense 1E 10,390 0.24 0.75 0.1789 Park 1E 29,708 0.68 0.20 0.1364 OS 1E 6,639 0.15 0.20 0.0305 ROW - Collector 1F 19,007 0.44 0.70 0.3054 ROW - Local 1F 1,542 0.04 0.80 0.0283 Roof 1F 8,967 0.21 0.95 0.1956 (Adjusted Per Block 14 Design) Pervious 1F 6,645 0.15 0.20 0.0305 (Adjusted Per Block 14 Design) ROW - Collector 1G 23,719 0.54 0.70 0.3812 ROW - Local 1H 2,190 0.05 0.76 0.0382 Park 1I 41,311 0.95 0.20 0.1897 OS 1I 49,170 1.13 0.20 0.2258 Residential - Dense 1I 33,991 0.78 0.75 0.5852 Totals 823,250 18.90 11.5711 Weighted C:0.61 Storage Facility Calculations Pond 1 Basis For Calculations Storage Facility Information Contributing Area & Runoff Coefficient Tabulation Pre-Development Discharge Rate (cfs) =0.97 (Per C&H Phase 1 Stormwater Design Report) Rainfall Intensity (in/hr) (I = 0.64x-0.65) Runoff Rate (cfs) (Q = CIA) Runoff Volume (ft3) (=Q- (Storm Duration x 60)) Discharge Volume (ft3) Required Detention Volume (ft3) (= Runoff Volume - Infiltration Volume) 0.24 2.79 45,132 15,714 29,417.8 0.24 2.78 45,190 15,772 29,418.1 0.24 2.77 45,249 15,830 29,418.2 0.24 2.77 45,307 15,889 29,418.1 0.24 2.76 45,365 15,947 29,417.9 0.24 2.75 45,423 16,005 29,417.6 0.24 2.75 45,480 16,063 29,417.2 0.24 2.74 45,538 16,121 29,416.6 0.24 2.73 45,595 16,180 29,415.8 0.24 2.73 45,653 16,238 29,415.0 0.24 2.72 45,710 16,296 29,414.0 0.23 2.71 45,767 16,354 29,412.8 Required Detention Volume (ft3):29,418 Provided Detention Volume (ft3):34,978 (Per C&H Phase 1 Stormwater Design Report) 281 275 276 277 278 279 280 274 Required Detention Volume Storm Duration (min) 270 271 272 273 Design Rainfall Frequency (year): 10 Storage Method: Detention Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Outlet Structure Pervious Facility Type: Pond C = Runoff Coefficient Facility Make/Model: N/A I = Rainfall Intensity (in/hr): (I = 0.64x-0.65)   A = Drainage Basin (acres) Land Use Drainage Basin Number Contributing Area (sf) Contributing Area (Ac) Runoff Coe. (C)A (Ac) x C ROW - Local 9A 14,613 0.34 0.76 0.2550 Residential - Dense 9A 62,824 1.44 0.75 1.0817 ROW - Local 9B 31,547 0.72 0.76 0.5504 Impervious 9B / 9BA 21,781 0.50 0.95 0.4750 (Adjusted Per Block 14 Design) Roof 9B / 9BA 41,769 0.96 0.95 0.9109 (Adjusted Per Block 14 Design) Pervious 9B / 9BA 56,272 1.29 0.20 0.2584 (Adjusted Per Block 14 Design) Park - Pervious 9B 18,286 0.42 0.20 0.0840 (Adjusted Per Block 14 Design) Park - Impervious 9B 2,613 0.06 0.95 0.0570 (Adjusted Per Block 14 Design) Impervious 9B2 24,493 0.56 0.95 0.5342 (Adjusted Per Block 14 Design) Roof 9B2 23,203 0.53 0.95 0.5060 (Adjusted Per Block 14 Design) Pervious 9B2 14,657 0.34 0.20 0.0673 (Adjusted Per Block 14 Design) ROW - Local 9B2 15,281 0.35 0.76 0.2666 ROW - Local 9C 22,307 0.51 0.76 0.3892 Commercial 9C 26,505 0.61 0.95 0.5780 Residential - Dense (Reduced C) 9C 45,055 1.03 0.40 0.4137 ROW - Local 9D 12,697 0.29 0.76 0.2215 Residential - Dense 9D 11,619 0.27 0.40 0.1067 OS 9D 3,357 0.08 0.20 0.0154 ROW - Local 9E 21,527 0.49 0.76 0.3756 Residential - Dense 9E 102,610 2.36 0.75 1.7667 ROW - Local 9F 7,859 0.18 0.76 0.1371 ROW - Local 9G 9,046 0.21 0.76 0.1578 OS 9G 13,120 0.30 0.20 0.0602 Park 9G 4,251 0.10 0.20 0.0195 Residential - Dense 9G 35,478 0.81 0.75 0.6108 ROW - Local 9H 17,977 0.41 0.76 0.3136 Residential - Low-Med 9H 20,009 0.46 0.35 0.1608 ROW - Local 9I 11,917 0.27 0.76 0.2079 Residential - Dense 9I 33,798 0.78 0.75 0.5819 ROW - Collector 9I2 35,815 0.82 0.70 0.5755 ROW - Collector 9J 41,138 0.94 0.70 0.6611 ROW - Local 9K 5,714 0.13 0.76 0.0997 Residential - Low-Med 9K 12,487 0.29 0.35 0.1003 Residential - Dense 9L 103,406 2.37 0.75 1.7804 OS 9L 50,963 1.17 0.20 0.2340 Totals 975,992 22.41 14.6141 Weighted C:0.65 Storage Facility InformationBasis For Calculations Storage Facility Calculations Pond 9 Contributing Area & Runoff Coefficient Tabulation Pre-Development Discharge Rate (cfs) =0.65 (Per C&H Phase 1 Stormwater Design Report) Rainfall Intensity (in/hr) (I = 0.64x-0.65) Runoff Rate (cfs) (Q = CIA) Runoff Volume (ft3) (=Q- (Storm Duration x 60)) Discharge Volume (ft3) Required Detention Volume (ft3) (= Runoff Volume - Infiltration Volume) 0.13 1.87 80,151 27,885 52,266.1 0.13 1.87 80,190 27,924 52,266.3 0.13 1.86 80,229 27,963 52,266.5 0.13 1.86 80,269 28,002 52,266.6 0.13 1.86 80,308 28,041 52,266.7 0.13 1.86 80,347 28,080 52,266.8 0.13 1.86 80,386 28,119 52,266.8 0.13 1.86 80,425 28,158 52,266.8 0.13 1.85 80,464 28,197 52,266.8 0.13 1.85 80,503 28,236 52,266.7 0.13 1.85 80,542 28,275 52,266.6 0.13 1.85 80,580 28,314 52,266.5 Required Detention Volume (ft3):52,267 Provided Detention Volume (ft3):57,340 (Per C&H Phase 1 Stormwater Design Report) 716 717 718 719 720 721 722 723 724 725 726 715 Required Detention Volume Storm Duration (min) Appendix C Excerpts from: “Blackwood Groves Subdivision, Phase 2 Stormwater Design Report” By C&H Engineering and Surveying, Inc. REQ'D PIPE CAPACITY DA 1F 1.81 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 1F Project:Blackwood Groves Subdivision Phase 2 INPUT D= 15 inches d= 14.07 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0056 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 6.28 7.51 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 1.38 (Per revised 1F runoff rate - See Appendix B) REQ'D PIPE CAPACITY Pipe 1F + DA 1H 2.15 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 1H Project:Blackwood Groves Subdivision Phase 2 INPUT D=15 inches d= 14.07 inches Mannings Formula n=0.013 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0052 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 4.19 5.01 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 1.72 (Per revised 1F runoff rate - See Appendix B) POND 1 - DETENTION REQUIRED VOLUME 1. Calculate Area and Weighted C Factor (Post-Development) Contributing Area DA C Area (ft 2 )C * Area ROW - Local 1A 0.76 18698 14257 ROW - Collector 1A 0.70 1253 877 ROW - Local 1B 0.76 25176 19134 ROW - Collector 1B 0.70 18906 13234 ROW - Alley 1B 0.80 1309 1047 Residential - Low-Med 1B 0.35 3540 1239 Residential - Dense 1B 0.75 21122 15842 Park 1B 0.20 18365 3673 OS 1B 0.20 2231 446 ROW - Local 1C 0.76 56157 42679 Residential - Dense 1C 0.75 77210 57907 Park 1C 0.20 13889 2778 OS 1C 0.20 7940 1588 ROW - Local 1D 0.76 39731 30196 ROW - Collector 1D 0.70 3503 2452 Residential - Dense 1D 0.75 183260 137445 ROW - Local 1E 0.76 5325 4047 ROW - Collector 1E 0.70 53409 37387 Row - Alley 1E 0.80 6491 5193 Residential - Low-Med 1E 0.35 32456 11360 Residential - Dense 1E 0.75 10390 7793 Park 1E 0.20 29708 5942 OS 1E 0.20 6639 1328 ROW - Collector 1F 0.70 19007 13305 ROW - Local 1F 0.80 1542 1234 Residential - Dense 1F 0.75 14423 10818 ROW - Collector 1G 0.70 23719 16604 ROW - Local 1H 0.76 2190 1664 Park 1I 0.20 41311 8262 OS 1I 0.20 49170 9834 Residential - Dense 1I 0.75 33991 25493 Total 822064 505057 A = Area (acres)18.87 C = Weighted C Factor 0.61 2. Pre-Development Conditions Pre-Development Drainage Area Name = EX 1 Pre-Development Drainage Area Size = 7.80 (acres) Pre Development Tc =62 (minutes) Pre-Development Runoff Rate (Total) =0.97 (cfs) 5. Calculate Required Pond Volume Total Area (acres) =18.87 acres Weighted C =0.61 Discharge Rate (cfs) =0.97 cfs (Equal to Pre-Development Runoff Rate) Duration(min) Duration(hrs) Intensity (in/hr)Qin (cfs)Runoff Volume Release Volume Required Storage (ft3) 268 4.47 0.24 2.81 45,105 15,636 29,470 269 4.48 0.24 2.80 45,164 15,694 29,470 270 4.50 0.24 2.79 45,223 15,752 29,471 271 4.52 0.24 2.78 45,282 15,811 29,471 272 4.53 0.24 2.78 45,340 15,869 29,471 273 4.55 0.24 2.77 45,398 15,927 29,471 274 4.57 0.24 2.76 45,456 15,986 29,471 275 4.58 0.24 2.76 45,514 16,044 29,470 276 4.60 0.24 2.75 45,572 16,102 29,470 277 4.62 0.24 2.75 45,630 16,161 29,469 PROVIDED VOLUME (ft3)34,978 OUTLET STRUCTURE SLOT Q=CLH3/2 Q = Discharge (cfs)0.97 C = Weir Coefficient 3.33 (per COB Design Standards) H = Head (ft)1.5 L = Horizontal Length (ft)0.16 L = Slot Width (inches)1.9 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Basin Contributing Area Area (ft2 ) Hardscape 454,192 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.55 0.05 + 0.9*I I = Percent impervious cover (decimal)0.55 decimal A = Entire drainage area 18.87 acres RRV = Runoff Reduction Volume 0.430 acre-ft RRV = Runoff Reduction Volume 18,745 cubic feet DRAINAGE AREA # 9A 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 14613 11106 Residential - Dense 0.75 62824 47118 Total 77437 58224 A = Area (acres)1.78 C = Weighted C Factor 0.75 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.00 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.75 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 276 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)8.54 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0144 L = length of gutter (ft)279 V = mean velocity (ft/s)3.60 Tc Gutter Flow (minutes) =1.29 Tc Total =9.84 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.75 (calculated above) I = 0.78 Tc-0.64 (in/hr)2.48 (25-yr storm) A = area (acres)1.78 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)3.32 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0144 Q = PROVIDED GUTTER CAPACITY (cfs)4.46 REQ'D PIPE CAPACITY DA 9A + Pipe 9B2 5.32 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9A Project:Blackwood Groves Phase 1 INPUT D= 15 inches d= 14.07 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.05 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 18.77 22.44 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 5.53 (Per revised 9B2 runoff rate - See Appendix B) DRAINAGE AREA # 9B 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 31547 23976 Residential - Dense 0.60 127749 76649 Park 0.20 20901 4180 Total 180197 104805 A = Area (acres)4.14 C = Weighted C Factor 0.58 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 0.75 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.60 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 598 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)22.15 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0083 L = length of gutter (ft)245 V = mean velocity (ft/s)2.37 Tc Gutter Flow (minutes) =1.72 Tc Total =23.87 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.58 (calculated above) I = 0.78 Tc-0.64 (in/hr)1.41 (25-yr storm) A = area (acres)4.14 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)3.39 (assuming no carry flow) 3.31 (Per revised 9B runoff rate - See Appendix A) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0083 Q = PROVIDED GUTTER CAPACITY (cfs)3.39 REQ'D PIPE CAPACITY DA 9B+Pipe 9C 7.69 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9B Project:Blackwood Groves Phase 1 INPUT D= 15 inches d= 14.07 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0102 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 8.48 10.14 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 7.62 (Per revised 9B runoff rate - See Appendix B) DRAINAGE AREA # 9B2 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 15281 11614 Residential - Dense 0.60 57621 34573 Total 72902 46186 A = Area (acres)1.67 C = Weighted C Factor 0.63 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 0.75 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.60 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 210 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)13.12 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0155 L = length of gutter (ft)370 V = mean velocity (ft/s)3.24 Tc Gutter Flow (minutes) =1.91 Tc Total =15.03 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.63 (calculated above) I = 0.78 Tc-0.64 (in/hr)1.89 (25-yr storm) A = area (acres)1.67 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)2.01 (assuming no carry flow) 2.21(Per revised 9B2 runoff rate - See Appendix A) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0083 Q = PROVIDED GUTTER CAPACITY (cfs)3.39 REQ'D PIPE CAPACITY DA 9B2 2.01 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9B2 Project:Blackwood Groves Phase 1 INPUT D= 15 inches d= 14.07 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0265 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 13.67 16.34 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 2.21 (Per revised 9B2 runoff rate - See Appendix B) DRAINAGE AREA # 9C 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 22307 16953 Commercial 0.95 26505 25180 Residential - Dense 0.75 45055 33791 Total 93867 75924 A = Area (acres)2.15 C = Weighted C Factor 0.81 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.00 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.75 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 304 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)8.97 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0144 L = length of gutter (ft)165 V = mean velocity (ft/s)2.92 Tc Gutter Flow (minutes) =0.94 Tc Total =9.91 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.81 (calculated above) I = 0.78 Tc-0.64 (in/hr)2.47 (25-yr storm) A = area (acres)2.15 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)4.31 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0144 Q = PROVIDED GUTTER CAPACITY (cfs)5.80 REQ'D PIPE CAPACITY DA 9C 4.31 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9C Project:Blackwood Groves Subdivision Phase 1 INPUT D= 12 inches d= 11.26 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.006 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 0.77 2.64 0.29 5.67 4.34 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D DRAINAGE AREA # 9D 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area Residential - Dense 0.40 11619 4647 OS 0.20 3357 671 ROW - Local 0.76 12697 9649 Total 27672 14968 A = Area (acres)0.64 C = Weighted C Factor 0.54 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.50 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.40 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 108 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)11.20 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0075 L = length of gutter (ft)157 V = mean velocity (ft/s)2.60 Tc Gutter Flow (minutes) =1.01 Tc Total =12.21 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.54 (calculated above) I = 0.78 Tc-0.64 (in/hr)2.16 (25-yr storm) A = area (acres) 0.64 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)0.74 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0075 Q = PROVIDED GUTTER CAPACITY (cfs)3.22 REQ'D PIPE CAPACITY Pipe 9B + DA 9D 8.43 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9D Project:Blackwood Groves Phase 1 INPUT D= 18 inches d= 16.88 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0081 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.72 3.96 0.44 8.53 14.69 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 8.36 (Per revised 9B runoff rate - See Appendix A) REQ'D PIPE CAPACITY Pipe 9D + Pipe 9I + Pipe 9A 17.66 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe: Pipe 9D2 Project: Blackwood Groves Phase 1 INPUT D=21 inches d= 19.70 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0055 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 2.34 4.62 0.51 7.79 18.26 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 17.79 (Per revised 9B& 9B2 runoff rates - See Appendix B) Pipe 9D2 DRAINAGE AREA # 9E 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 21527 16360 Residential - Dense 0.75 102610 76958 Total 124137 93318 A = Area (acres)2.85 C = Weighted C Factor 0.75 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.00 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.75 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 480 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)12.17 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0152 L = length of gutter (ft)70 V = mean velocity (ft/s)3.70 Tc Gutter Flow (minutes) =0.32 Tc Total =12.48 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.75 (calculated above) I = 0.78 Tc-0.64 (in/hr)2.13 (25-yr storm) A = area (acres)2.85 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)4.56 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0152 Q = PROVIDED GUTTER CAPACITY (cfs)4.58 REQ'D PIPE CAPACITY Pipe 9D2 + Pipe 9G + DA 9E 23.64 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9E Project:Blackwood Groves Phase 1 INPUT D= 21 inches d= 19.70 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0118 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 2.34 4.62 0.51 11.41 26.74 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 23.77 (Per revised 9B& 9B2 runoff rates - See Appendix B) DRAINAGE AREA # 9F 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 7859 5973 Total 7859 5973 A = Area (acres)0.18 C = Weighted C Factor 0.76 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 2.00 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.50 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 15 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)3.16 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0126 L = length of gutter (ft)207 V = mean velocity (ft/s)3.37 Tc Gutter Flow (minutes) =1.03 Tc Total =4.19 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.76 (calculated above) I = 0.78 Tc-0.64 (in/hr)4.29 (25-yr storm) A = area (acres)0.18 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)0.59 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0126 Q = PROVIDED GUTTER CAPACITY (cfs)4.17 REQ'D PIPE CAPACITY Pipe 9E + DA 9F 24.23 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9F Project:Blackwood Groves Phase 1 INPUT D= 24 inches d= 22.51 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.006 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 3.06 5.28 0.58 8.90 27.23 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D 24.36 (Per revised 9B& 9B2 runoff rates - See Appendix B) DRAINAGE AREA # 9G 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 9046 6875 Park 0.20 4251 850 OS 0.20 13120 2624 Residential - Dense 0.60 35478 21287 Total 61894 31636 A = Area (acres)1.42 C = Weighted C Factor 0.51 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.00 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.60 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 270 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)13.52 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0152 L = length of gutter (ft)176 V = mean velocity (ft/s)3.70 Tc Gutter Flow (minutes) =0.79 Tc Total =14.31 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.51 (calculated above) I = 0.78 Tc-0.64 (in/hr)1.95 (25-yr storm) A = area (acres)1.42 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)1.42 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0152 Q = PROVIDED GUTTER CAPACITY (cfs)4.58 REQ'D PIPE CAPACITY DA 9G 1.42 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9G Project:Blackwood Groves Subdivision Phase 1 INPUT D= 12 inches d= 11.26 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.0183 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 0.77 2.64 0.29 9.79 7.49 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D DRAINAGE AREA # 9I 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2 )C * Area ROW - Local 0.76 11917 9057 Residential - Dense 0.75 33798 25348 Total 45714 34405 A = Area (acres)1.05 C = Weighted C Factor 0.75 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%) 1.50 Return (yrs)Cf C = Rational Method Runoff Coefficient 0.75 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft) 169 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)5.84 Tc Gutter Flow Tc = L/V/60 V = (1.486/n)R2/3 S1/2 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0050 L = length of gutter (ft)194 V = mean velocity (ft/s)2.12 Tc Gutter Flow (minutes) =1.53 Tc Total =7.37 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.75 (calculated above) I = 0.78 Tc-0.64 (in/hr)2.99 (25-yr storm) A = area (acres)1.05 (calculated above) Q = REQUIRED GUTTER CAPACITY (cfs)2.36 (assuming no carry flow) PROVIDED GUTTER CAPACITY 1. Calculate Gutter Capacity @ 0.15' Below Top of Curb Q = (1.486/n)AR2/3 S1/2 n = Mannings Coefficient 0.013 A = Area (ft2)1.24 (0.15' below top of curb) P = Wetted perimeter (ft)9.23 (0.15' below top of curb) R = Hydraulic Radius A/P (ft)0.13 (0.15' below top of curb) S = slope (ft/ft)0.0050 Q = PROVIDED GUTTER CAPACITY (cfs)2.63 REQ'D PIPE CAPACITY DA 9I + Pipe 9I2 3.90 cfs MANNING'S EQUATION FOR PIPE FLOW Pipe:Pipe 9I Project:Blackwood Groves Subdivision Phase 1 INPUT D= 15 inches d= 14.07 inches Mannings Formula n= 0.009 mannings T 57.7 degrees Q=(1.486/n)ARh2/3S1/2 S= 0.075 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rh2/3S1/2 n=Manning's roughness coefficient Q=V x A Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 1.20 3.30 0.36 22.99 27.49 PE (<9"dia) 0.015 PE (>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d T D POND 9 - DETENTION REQUIRED VOLUME 1. Calculate Area and Weighted C Factor (Post-Development) Contributing Area DA C Area (ft2)C * Area ROW - Local 9A 0.76 14613 11106 Residential - Dense 9A 0.75 62824 47118 ROW - Local 9B 0.76 31547 23976 Park 9B 0.20 20901 4180 Residential - Dense 9B 0.75 127750 95812 Residential - Dense 9B2 0.60 57621 34573 ROW - Local 9B2 0.76 15281 11614 ROW - Local 9C 0.76 22307 16953 Commercial 9C 0.95 26505 25180 Residential - Dense (Reduced C) 9C 0.40 45055 18022 ROW - Local 9D 0.76 12697 9649 Residential - Dense 9D 0.40 11619 4647 OS 9D 0.20 3357 671 ROW - Local 9E 0.76 21527 16360 Residential - Dense 9E 0.75 102610 76958 ROW - Local 9F 0.76 7859 5973 ROW - Local 9G 0.76 9046 6875 OS 9G 0.20 13120 2624 Park 9G 0.20 4251 850 Residential - Dense 9G 0.75 35478 26609 ROW - Local 9H 0.76 17977 13662 Residential - Low-Med 9H 0.35 20009 7003 ROW - Local 9I 0.76 11917 9057 Residential - Dense 9I 0.75 33798 25348 ROW - Collector 9I2 0.70 35815 25070 ROW - Collector 9J 0.70 41138 28797 ROW - Local 9K 0.76 5714 4343 Residential - Low-Med 9K 0.35 12487 4370 Residential - Dense 9L 0.75 103406 77554 OS 9L 0.20 50963 10193 Total 979189 645148 A = Area (acres) 22.48 C = Weighted C Factor 0.66 2. Pre-Development Conditions Pre-Development Drainage Area Name = EX 2 Pre-Development Drainage Area Size = 92.60 (acres) Pre Development Tc =96 (minutes) Pre-Development Runoff Rate (Total) =8.73 (cfs) Pre-Development Runoff Rate (Pond 8A) =1.88 (cfs) Pre-Development Runoff Rate (Pond 8B) =4.94 (cfs) Pre-Development Runoff Rate (Pond 8C) =1.26 Pre-Development Runoff Rate (Pond 9) =0.65 (cfs) Pre-Development Runoff Rate (Total) =8.73 (cfs) 5. Calculate Required Pond Volume Total Area (acres) =22.48 acres Weighted C =0.66 Discharge Rate (cfs) =0.65 cfs (Equal to Pre-Development Runoff Rate) Duration(min) Duration(hrs) Intensity (in/hr)Qin (cfs)Runoff Volume Release Volume Required Storage (ft3) 733 12.22 0.13 1.86 81,938 27,690 54,248 734 12.23 0.13 1.86 81,977 27,729 54,248 735 12.25 0.13 1.86 82,017 27,768 54,249 736 12.27 0.13 1.86 82,056 27,807 54,249 737 12.28 0.13 1.86 82,095 27,846 54,249 738 12.30 0.13 1.85 82,134 27,885 54,249 739 12.32 0.13 1.85 82,172 27,924 54,248 740 12.33 0.13 1.85 82,211 27,963 54,248 741 12.35 0.12 1.85 82,250 28,002 54,248 742 12.37 0.12 1.85 82,289 28,041 54,248 PROVIDED VOLUME (ft3)57,340 OUTLET STRUCTURE SLOT Q=CLH3/2 Q = Discharge (cfs)0.65 C = Weir Coefficient 3.33 (per COB Design Standards) H = Head (ft)0.75 L = Horizontal Length (ft)0.30 L = Slot Width (inches)3.6 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Basin Contributing Area Area (ft 2 ) Hardscape 599,080 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.60 0.05 + 0.9*I I = Percent impervious cover (decimal)0.61 decimal A = Entire drainage area 22.48 acres RRV = Runoff Reduction Volume 0.563 acre-ft RRV = Runoff Reduction Volume 24505 cubic feet Project Engineer: Project: South Bozeman, Gallatin County, MT Well Information:bgs = below ground surface ags = above ground surface MW-1 MW-2 MW-3 MW-4 MW-5 MW-6 MW-7 MW-8 MW-9 MW-10 MW-11 MW-12 MW-13 MW-14 MW-15 MW-16 MW-17 MW-18 MW-19 MW-20 3.83 3.00 3.08 3.67 1.50 2.42 2.08 3.58 2.92 2.92 3.83 2.92 3.92 3.58 4.08 3.00 3.92 3.50 3.58 2.92 Groundwater Information: MW-1 MW-2 MW-3 MW-4 MW-5 MW-6 MW-7 MW-8 MW-9 MW-10 MW-11 MW-12 MW-13 MW-14 MW-15 MW-16 MW-17 MW-18 MW-19 MW-20 3.34 3.05 3.02 2.78 3.45 1.58 4.24 4.27 2.55 4.13 3.99 4.36 2.25 2.27 2.26 5.50 2.71 2.20 2.97 2.38 3.47 3.18 3.11 2.85 3.49 1.50 4.42 4.42 2.64 4.34 4.31 4.78 2.50 2.32 2.60 6.10 2.85 2.42 3.40 2.77 3.57 3.23 3.13 2.94 4.10 1.64 4.53 4.53 2.67 4.45 4.36 4.90 2.54 2.39 2.65 6.21 2.92 2.74 3.74 2.96 3.75 3.42 3.26 3.18 3.74 1.88 4.72 4.70 2.80 4.59 4.50 5.16 2.84 2.54 2.84 6.32 3.18 3.14 4.07 3.19 3.78 3.63 3.36 3.35 3.81 1.94 4.90 4.98 2.99 4.86 4.56 5.31 3.16 2.83 3.23 DRY 3.79 3.68 4.31 3.49 3.76 3.65 3.41 3.43 3.76 1.91 4.94 5.11 3.09 4.98 4.68 5.48 3.25 2.79 3.30 DRY 4.17 3.91 4.51 3.56 3.94 3.82 3.52 3.45 3.83 2.00 4.90 5.23 3.27 5.08 4.82 5.60 3.42 2.88 3.37 DRY 4.29 4.05 4.67 3.59 3.90 3.68 3.38 3.31 3.75 1.94 4.85 4.93 3.08 5.02 4.86 5.66 3.37 2.88 3.20 DRY 4.22 4.11 4.80 3.48 4.00 3.87 3.55 3.60 4.01 2.24 5.11 5.23 3.44 5.18 4.82 5.65 3.54 3.13 3.46 DRY 4.59 4.31 4.87 3.80 4.09 3.52 3.34 3.33 3.81 2.09 5.06 5.03 3.11 4.99 5.42 5.08 3.34 2.89 3.37 DRY 4.59 4.41 4.47 3.60 4.14 4.09 3.69 3.72 3.92 2.34 5.24 5.42 3.69 5.39 4.95 5.78 3.73 3.34 3.69 DRY 4.87 4.65 5.03 3.89 4.16 4.38 4.13 4.01 4.12 2.49 5.43 5.70 4.06 5.99 5.27 6.24 4.20 3.79 3.99 DRY 5.29 5.19 5.63 4.07 ICE 2.50 2.49 2.03 ICE 0.93 3.43 3.60 2.39 ICE 3.69 3.88 1.38 1.47 1.82 4.04 2.27 0.96 2.07 2.01 1.99 1.95 2.16 1.64 3.00 0.63 3.04 3.29 2.19 3.08 3.07 3.33 0.72 0.72 0.87 3.57 2.10 0.60 1.67 1.28 2.65 2.25 2.37 1.93 3.35 1.03 3.14 3.47 2.29 3.26 3.29 3.60 1.18 1.62 1.57 3.60 2.30 1.20 2.19 1.45 2.94 2.50 2.53 2.17 1.90 1.54 3.32 3.68 2.33 3.53 3.63 3.83 1.56 1.53 1.86 4.13 2.40 1.45 2.47 1.86 3.27 2.97 2.84 2.64 2.35 1.42 3.72 4.30 2.48 3.95 3.92 4.23 2.00 1.67 2.13 4.52 2.68 2.04 3.07 2.38 3.47 3.20 3.00 2.85 2.50 1.52 3.94 4.38 2.59 4.23 4.17 4.61 2.30 2.29 2.42 4.97 2.81 2.55 3.42 2.70 3.57 3.28 3.10 2.98 2.60 1.68 4.13 4.52 2.65 4.39 4.37 4.88 2.53 2.35 2.64 DRY 2.91 2.92 3.85 2.93 3.68 3.38 3.21 3.10 2.70 1.74 4.29 4.68 2.70 4.54 4.57 5.10 2.73 2.43 2.81 DRY 3.12 3.30 4.13 3.17 3.79 3.51 3.32 3.20 2.66 1.89 4.51 4.79 2.81 4.71 4.74 5.32 2.93 2.60 2.97 DRY 3.47 3.56 4.37 3.33 3.92 3.63 3.51 3.38 2.79 1.95 4.79 4.90 2.92 4.89 4.78 5.49 3.08 2.63 3.08 DRY 3.73 4.09 4.57 3.59 5.15.20 4.10.20 4.17.20 4.24.20 5.1.20 5.8.20 Well ID Well Depth (feet-bgs) Top of Well (feet-ags) Ground Elevation 4.6.20 Date 5.10.19 6.10.19 6.17.19 6.20.19 6.28.19 7.12.19 7.26.19 8.9.19 Monitor Well Data Depth to Ground Water (feet-bgs) Project Number: 190390 South Bozeman Groundwater Monitoring Project Location: 8.23.19 3.24.20 5.20.19 5.24.19 5.31.19 5.22.205.29.20