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HomeMy WebLinkAbout010 - Appendix H - Water Sewer Storm Design Report JOB NO. B20-069 MONTANA | WASHINGTON | IDAHO | NORTH DAKOTA | PENNSYLVANIA AUGUST 2023 406.586.0277 tdhengineering.com 234 East Babcock Street Suite 3 Bozeman, MT 59715 CLIENT ENGINEER Intrinsik Architecture 106 E. Babcock Street, Suite 1A Bozeman, MT 59715 TD&H Engineering 234 East Babcock Street, Suite 3 Bozeman, MT 59715 Engineer: Cody Croskey, PE 112 EAST MAIN MIXED-USE BUILDING BOZEMAN, MONTANA BASIS OF DESIGN REPORT Image courtesy of Intrinsik Architecture 8/22/2023 112 EAST MAIN MIXED-USE BUILDING ENGINEERING DESIGN REPORT AUGUST 2023 Purpose and Introduction The purpose of this report is to explain how water, sanitary sewer, and storm drainage improvements will be designed to meet the City of Bozeman requirements and Montana Public Works Standard Specifications (MPWSS) to provide service to a new mixed-use building in downtown Bozeman, Montana. The project is located at 112 E. Main Street in downtown Bozeman between the intersections of S. Black and S. Bozeman Avenues. The new building will be located on the same approximately 56,000 S.F. parcel as the National Building which is generally comprised of lots 1-4 and lots 13-20 in Block B of the Original Townsite of Bozeman. The site is within the Downtown zoning district B-3 and is currently developed and mostly hardscaped with the existing US Bank office building and a shared parking lot and alley. Proposed redevelopment includes the demolition of the US Bank budling and construction of a new multi-story mixed-use building with ground-floor retail and residential/office spaces above. Some shared parking lot improvements are proposed to accommodate a larger dumpster enclosure and a patio open space south of the new building. The site will be nearly 100% covered by the new building with new water and sewer services connecting to the existing main lines in Main Street and roof drains connecting into an existing storm drain line in the alley to the south. Design Report Water The US Bank Building has a single live water service connection entering through the basement of the adjacent National Building. This service is proposed to be abandoned where it leaves the National Building basement, and a new service connection will be made in Main Street. The estimated existing domestic water demands being removed with the existing building are summarized in Table 1 below with supporting assumptions and calculations provided in Appendix A in accordance with C.O.B. DSSP Section V.A.4 and the 2017 Water Facility Plan. Table 1: Estimated Existing Water Demands (Being Removed) Average Day Max. Day Peak Hour Existing Building Demand -(268) gpd -(0.4) gpm -(0.6) gpm The new mixed-use building will replace the existing uses with 7 new dwelling units, 6,010 S.F. of ground floor undesignated commercial/retail space, and 6,075 S.F of office space. The new estimated domestic water demands for the project are summarized in Table 2 below with supporting assumptions and calculations provided in Appendix A in accordance with C.O.B. DSSP Section V.A.4 and the 2017 Water Facility Plan. Table 2: Estimated New Water Demands Average Day Max. Day Peak Hour New Building Demand 2,939 gpd 4.7 gpm 6.1 gpm Irrigation at the site will be limited to roof-top planter features and ground level planting beds that will also be supplied from the building’s public water supply. The new building will be equipped with fire sprinklers and the fire flow requirement for the new building is 1,500 gpm based on building size and construction type as determined following International Fire Code Appendix B criteria. A new 2-inch domestic water service and 4-inch fire service line will be extended to the new building from the existing 6-inch water main in East Main Street. Final service sizing will be verified by the mechanical engineer in accordance with the Uniform Plumbing Code and actual fixture unit counts. The services will be type-k copper and class 51 ductile iron and be installed per the City of Bozeman Design Standards and Modifications to Montana Public Works Standard Specifications (MPWSS). No new water main extensions are anticipated with this project as a 6” water main is looped around the development within Main Street. Fire hydrant flow reports were provided by the City Engineering Department for the nearest existing fire hydrants to confirm the existing 6” water main has adequate capacity to convey the maximum day plus fire flow demand for the proposed development in accordance with C.O.B. DSSP Section V.A.4. The existing water distribution system for this area was modeled using Bentley’s WaterCAD software. The water modeling indicates that the maximum day domestic demand of 4.7 gpm plus 1,500 gpm fire flow is more than available in the 6” water main adjacent to the project without dropping below a 20 psi residual pressure or exceeding 15 ft per second velocities in the water mains. The results from the water modeling analysis are provided in Appendix A. Sewer The US Bank building has at least one live sewer service connection that is believed to exit at the northeast corner of the building toward Main Street, but there may also be connections entering through the basement of the adjacent National Building. All exiting services will be abandoned during building demolition and a new service connection will be made in Main Street. The estimated sewer demands being removed with the existing building are summarized in Table 3 below with supporting assumptions and calculations provided in Appendix B in accordance with C.O.B. DSSP Section V.B and the 2015 Wastewater Facilities Plan. Table 3: Estimated Existing Sewer Demands (Being Removed) Average Day (gpd) Peak Hour (gpm) Existing Building Demand -(357) - Lot Infiltration -(29) - Total Sewer Demand -(386) -(1.21) The new mixed-use building will replace the existing uses with 7 new dwelling units, 6,010 S.F. of ground floor undesignated commercial/retail space, and 6,075 S.F of office space. The new estimated domestic sewer demands for the project are summarized in Table 4 below with supporting assumptions and calculations provided in Appendix B in accordance with C.O.B. DSSP Section V.B and the 2015 Wastewater Facilities Plan. Table 4: Estimated New Sewer Demands Average Day (gpd) Peak Hour (gpm) New Building Demand 1,811 - Lot Infiltration 29 - Total Sewer Demand 1,840 5.55 A new 6-inch sewer service is proposed to extend from the new building to the existing 8-inch sewer main in East Main Street. Final service sizing for this project will be verified by the mechanical engineer in accordance with the Uniform Plumbing Code and actual fixture unit counts. The new 6-inch sewer service line will be SDR-26 PVC and will be installed per the City of Bozeman Design Standards and Modifications to Montana Public Works Standard Specifications (MPWSS). Storm Drainage Existing Conditions: The existing project site is currently developed and nearly completely impervious with existing buildings, asphalt/concrete pavement, and a few small landscaped areas behind the US Bank building. Runoff is currently collected and conveyed by an existing storm drain pipe in the alley to the storm sewer main line in S. Black Avenue. The runoff is then routed through an existing treatment unit in N. Black Avenue on the north side of Main Street before making its way to the Bozeman Creek outfall at N. Rouse Avenue. Stormwater Quantity: The proposed redevelopment includes a new multi-story building, building entry and patio improvements at the south end, and parking lot modifications to add a larger dumpster enclosure and landscaped islands. Runoff flow rates and volumes will not be increased as a result of the site redevelopment since the total impervious area will remain the same or slightly less than existing (see the stormwater runoff calculations provided in Appendix C). The new building and area drains will also continue to direct runoff to the storm drain line that exists in the alley where it is currently discharging. Therefore, no on-site stormwater detention or retention facilities are required to limit flows to the predevelopment runoff rates per C.O.B DSSP Section II.C. Stormwater Quality: Runoff from this site will continue to be discharged to an existing hydrodynamic separating treatment unit in N. Black Avenue at the same flow rate and volume as the existing development. This is expected to meet the 80% TSS removal offsite treatment criteria with no additional on-site treatment required or feasible. Conveyance: The existing inlet and 8-inch storm drain pipe in the alley will be replaced and upsized with 15-inch pipe out to its connection point in S. Black Avenue to improve conveyance. This pipe is already being partially replaced as part of the National Building project to the west. A pipe conveyance calculation demonstrating capacity for the 25-yr storm event from this development is provided in Appendix C. APPENDIX A Water Calculations 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 Existing Water Demand Calculation Domestic Water Demand - Existing Building: Commercial Use: Retail =15,554 sf 0.357 acres Commercial Flow =268 GPD 750 gal/acre/day per Table 3.5, 2017 Water Facility Plan Peak Hour Demand: Average Day Demand =268 GPD (All Uses) Average Day Demand =0.2 gpm (GPD / 1,440 minutes) Maximum Day Demand =0.4 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =0.6 gpm (Ave. Day x Peaking Factor = 3) 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 New Water Demand Calculation Domestic Water Demand - New Building: Residential Use: Residential Units =7 units People =15.2 people (2.17 people/unit) Residential Flow =2,582 GPD (170 gpcd)(Per COB Design Standards) Commercial Use: Commercial Mixed Use =12,085 sf 0.277 acres Commercial Flow =357 GPD 1,285 gal/acre/day per Table 3.9, 2017 Water Facility Plan Peak Hour Demand: Average Day Demand =2,939 GPD (All Uses) Average Day Demand =2.0 gpm (GPD / 1,440 minutes) Maximum Day Demand =4.7 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =6.1 gpm (Ave. Day x Peaking Factor = 3) Fire Flow Requirement - New Building: IBC Construction Type =All Types (Up to 51,500 SF w/ sprinklers per IFC Appendix B) Fire Flow Calculation Area =10,161 sf Automatic Fire Sprinkler System =Yes Fire Sprinkler System Type =NFPA 13R Required Fire Flow =1,500 gpm (per IFC Appendix B) (Per COB 2015 Wastewater Facilities Plan) CITY OF BOZEMAN Fire Flow Request Form PHONE (406) 582-3200 FAX (406) 582-3201 Date June 30, 2023 Location Main Street (S. Black & S. Bozeman Ave.) Pressure Zone HGL 5125 (S) GIS Hydrant ID# 73, 88, 201 Adjacent Main Size 6-inch CI, 6-inch CI, 8-inch DI Model Scenario Maximum Day Demand, Steady State, Fire Flow Reference 2017 Water Facility Plan Update1 Hydrant Curves An Excel Spreadsheet with hydrant curves has been provided for the requested location Requested Location via the Bozeman Infrastructure Viewer2 If you have questions or need further information feel free to email. Data Disclaimer: Water distribution information is calculated using hydraulic modeling software and is subject to variation. Actual field conditions may vary. This information is provided to the requestor for evaluation purposes only, without warranty of any kind, including, but not limited to any expressed or implied warranty arising by contract, stature, or law. In no event regardless of cause, shall the City be liable for any direct, indirect, special, punitive or consequential damages of any kind whether such damages arise under contract, tort, strict liability or inequity. HOME OF MONTANA STATE UNIVERSITY GATEWAY TO YELLOWSTONE PARK 1 https://www.bozeman.net/home/showpublisheddocument/4977/636420174896170000 2 https://gisweb.bozeman.net/Html5Viewer/?viewer=infrastructure GIS Hydrant # Available Flow (gpm)Residual Pressure (psi)73 0 127.3 200 126.88 400 126.21 600 125.3 800 124.19 1,000.00 122.86 1,200.00 121.33 1,400.00 119.61 1,600.00 117.69 1,800.00 115.6 2,000.00 113.31 2,200.00 110.85 2,400.00 108.21 2,600.00 105.39 2,800.00 102.4 3,000.00 99.24 3,200.00 95.91 3,400.00 92.4 3,600.00 88.73 3,800.00 84.89 4,000.00 80.88 4,200.00 76.7 4,400.00 72.36 4,600.00 67.85 4,800.00 63.18 5,000.00 58.35 5,200.00 53.36 5,400.00 48.22 5,600.00 42.91 5,800.00 37.45 6,000.00 31.79 6,200.00 25.98 6,400.00 20.01 6,600.00 13.88 6,800.00 7.6 7,000.00 1.17 7,034.72 0.03 Hydrant Curve 0 20 40 60 80 100 120 140 0 1000 2000 3000 4000 5000 6000 7000 8000Residual Pressure (psi)Available Flow (gpm) Hydrant Curve 73 Data Disclaimer: Water distribution information is calculated using hydraulic modeling software and is subject to variation. Actual field conditions may vary. This information is provided to the requestor for evaluation purposes only, without warranty of any kind, including, but not limited to any expressed or implied warranty arising by contract, stature, or law. In no event regardless of cause, shall the City be liable for any direct, indirect, special, punitive or consequential damages of any kind whether such damages arise under contract, tort, strict liability or inequity. GIS Hydrant # Available Flow (gpm)Residual Pressure (psi)88 0 127.62 200 126.89 400 125.47 600 123.39 800 120.71 1,000.00 117.45 1,200.00 113.62 1,400.00 109.25 1,600.00 104.33 1,800.00 98.9 2,000.00 92.94 2,200.00 86.48 2,400.00 79.52 2,600.00 72.06 2,800.00 64.12 3,000.00 55.69 3,200.00 46.77 3,400.00 37.38 3,600.00 27.52 3,800.00 17.2 4,000.00 6.4 Hydrant Curve 0 20 40 60 80 100 120 140 0 500 1000 1500 2000 2500 3000 3500 4000 4500Residual Pressure (psi)Available Flow (gpm) Hydrant Curve 88 GIS Hydrant # Available Flow (gpm)Residual Pressure (psi)201 0 127.35 200 127.01 400 126.63 600 126.17 800 125.63 1,000.00 125.01 1,200.00 124.33 1,400.00 123.58 1,600.00 122.77 1,800.00 121.89 2,000.00 120.95 2,200.00 119.94 2,400.00 118.88 2,600.00 117.75 2,800.00 116.56 3,000.00 115.31 3,200.00 114 3,400.00 112.64 3,600.00 111.21 3,800.00 109.72 4,000.00 108.17 4,200.00 106.56 4,400.00 104.89 4,600.00 103.16 4,800.00 101.38 5,000.00 99.53 5,200.00 97.63 5,400.00 95.68 5,600.00 93.67 5,800.00 91.6 6,000.00 89.47 6,200.00 87.26 6,400.00 84.99 6,600.00 82.66 6,800.00 80.28 7,000.00 77.85 7,200.00 75.36 7,400.00 72.81 7,600.00 70.2 7,800.00 67.55 8,000.00 64.84 8,200.00 62.07 8,400.00 59.25 8,600.00 56.37 8,800.00 53.44 9,000.00 50.45 9,200.00 47.42 9,400.00 44.33 9,600.00 41.18 9,800.00 37.98 10,000.00 34.73 10,200.00 31.41 10,400.00 28.05 10,600.00 24.64 10,800.00 21.17 11,000.00 17.65 11,200.00 14.08 11,400.00 10.45 11,600.00 6.78 11,800.00 3.05 11,961.02 0 Hydrant Curve 0 20 40 60 80 100 120 140 0 2000 4000 6000 8000 10000 12000 14000Residual Pressure (psi)Available Flow (gpm) Hydrant Curve 201 Data Disclaimer: Water distribution information is calculated using hydraulic modeling software and is subject to variation. Actual field conditions may vary. This information is provided to the requestor for evaluation purposes only, without warranty of any kind, including, but not limited to any expressed or implied warranty arising by contract, stature, or law. In no event regardless of cause, shall the City be liable for any direct, indirect, special, punitive or consequential damages of any kind whether such damages arise under contract, tort, strict liability or inequity. Scenario: Base ©2017 HERE © 2017 Microsoft Corporation Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203-755-16667/10/2023 WaterCAD [10.04.00.108]Bentley Systems, Inc. Haestad Methods Solution CenterB22-044 FIRE FLOW.wtg Fire Flow Node FlexTable: Fire Flow Results Table Pipe w/ Maximum Velocity Velocity of Maximum Pipe (ft/s) Junction w/ Minimum Pressure (System) Pressure (Calculated System Lower Limit) (psi) Pressure (System Lower Limit) (psi) Junction w/ Minimum Pressure (Zone) Pressure (Calculated Residual) (psi) Pressure (Residual Lower Limit) (psi) Flow (Total Available) (gpm) Fire Flow (Available) (gpm) Label PIPE-1315.00J-255120J-2553202,4412,441J-2 PIPE-915.00J-245320J-2452201,8501,850J-6 PIPE-1315.00J-225120J-2254202,3932,393J-7 PIPE-1015.00J-255120J-2551202,3502,350J-10 PIPE-1215.00J-104920J-1050202,8142,814J-11 PIPE-1115.00J-255420J-2554201,3221,322J-13 PIPE-515.00J-255120J-2550202,3502,350J-14 PIPE-215.00J-194920J-1949202,7912,791J-15 PIPE-915.00122 E MAIN4720122 E MAIN45202,3732,372112 E MAIN PIPE-615.00112 E MAIN4620112 E MAIN44202,5182,517122 E MAIN PIPE-415.00J-255420J-2553201,3221,322J-19 PIPE-1315.00J-225120J-2251202,4132,413J-20 PIPE-1315.00J-225120J-2251202,4132,413J-21 PIPE-1315.00J-255120J-2551202,4122,412J-22 PIPE-1315.00J-255120J-2551202,4282,428J-23 PIPE-1315.00J-255120J-2551202,4282,428J-24 PIPE-1315.00J-245120J-2451202,4282,428J-25 Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203-755-16667/10/2023 WaterCAD [10.04.00.108]Bentley Systems, Inc. Haestad Methods Solution CenterB22-044 FIRE FLOW.wtg APPENDIX B Sewer Calculations 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 Existing Sewer Demand Calculation Average Day Sewer Demand - Existing Building: Commercial Use: Retail =15,554 sf 0.357 acres Commercial Flow =357 GPD 1,000 gal/acre/day per Table 2-12 2015 Wastewater Facilities Plan Infiltration: Property Size =0.19 acres Infiltration Flow =29 GPD (150 gpd/acre per COB Design Standards) Total Existing Average Day Demand: 386 GPD (residential + commercial + infiltration) Total Existing Peak Sewer Flow: Average Day Demand =386 GPD (residential + commercial) P =0.0060 (population/1,000) Peaking Factor =4.43 Peak Sewer Demand =1,712 GPD (avg. day demand)*(peaking factor) + Infiltration Flow =29 GPD (not peaked) Total Peak Flow =1,741 GPD (residential + commercial + infiltration) Peak Sewer Flow =1.21 GPM (peak flow)/(24 hrs/day)/(60 min/hr) 𝑄𝑚𝑎𝑥 𝑄𝑎𝑣𝑔 =18 +𝑠ℎ𝑛𝑠𝑠𝑎𝑛𝑑𝑠 𝑛𝑑 𝑛𝑑𝑛𝑛𝑙𝑑1/2 4 +𝑠ℎ𝑛𝑠𝑠𝑎𝑛𝑑𝑠 𝑛𝑑 𝑛𝑑𝑛𝑛𝑙𝑑1/2 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 New Sewer Demand Calculation Average Day Sewer Demand : Residential Use: Residential Units =7 units Population =15.2 people (2.17 people/unit) Residential Flow =978 GPD (64.4 gpcd) Commercial Use: Commercial Mixed Use =12,085 sf 0.277 acres Commercial Flow =832 GPD 3,000 gal/acre/day per Table 2-13, Zone B3, 2015 Wastewater Facilities Plan Infiltration: Property Size =0.19 acres Infiltration Flow =29 GPD (150 gpd/acre per COB Design Standards) Total Development Average Day Demand: 1,840 GPD (residential + commercial + infiltration) Total Development Peak Sewer Flow: Average Day Demand =1,811 GPD (residential + commercial) P =0.0152 (population/1,000) Peaking Factor =4.40 Peak Sewer Demand =7,958 GPD (avg. day demand)*(peaking factor) + Infiltration Flow =29 GPD (not peaked) Total Peak Flow =7,987 GPD (residential + commercial + infiltration) Peak Sewer Flow =5.55 GPM (peak flow)/(24 hrs/day)/(60 min/hr) Values per C.O.B. 2015 Wastewater Facilities Plan 𝑄𝑚𝑎𝑥 𝑄𝑎𝑣𝑔 =18 +𝑠ℎ𝑛𝑠𝑠𝑎𝑛𝑑𝑠 𝑛𝑑 𝑛𝑑𝑛𝑛𝑙𝑑1/2 4 +𝑠ℎ𝑛𝑠𝑠𝑎𝑛𝑑𝑠 𝑛𝑑 𝑛𝑑𝑛𝑛𝑙𝑑1/2 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 6" Sewer Service Pipe Capacity Input Values d =0.50 ft =6" y =0.375 ft =75% Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ)4.19 rad 2*arccos(1-y/(d/2)) Area (A)0.16 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P)1.05 ft 0.5Θd Hydraulic Radius (R )0.15 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T)0.43 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n =0.013 (per COB Design Standards) S0 =0.0104 ft/ft (min. 1/8" per foot for 6" services) Q =0.52 cfs Q = 1.49/n*A*R2/3*S00.5 Q =235.00 gpm Q gpm = (Q cfs)(7.48 gal/ft3)(60 sec/min) V =3.31 ft/s V = Q/A Results A 6" diameter sewer service at the min. 1/8" per foot slope flowing 75% full has the capacity for 235.00 gpm. J:\2020\B20-069 US Bank Site in Downtown Bozeman\DOCUMENTS\REPORTS\112 E. Main Design Report\Parts\112 E. Main Water & Sewer Calcs.xls 1 OF 1 Appendix C Storm Water Calculations UPUPDESIGNED BY:QUALITY CHECK:JOB NO.FIELDBOOKDRAWN BY:DATE:112 E. MAIN SW BASINSREV DATE NOT FORCONSTRUCTION REVISION 112 EAST MAIN MIXED-USE BUILDING BOZEMAN, MONTANA STORM DRAINAGE BASIN MAP B20-06908.22.23.DWGFIGURE1CJCEngineering 234 E. BABCOCK ST., SUITE 3 • BOZEMAN, MONTANA 59715 406.586.0277 • tdhengineering.com E. MAIN STREETS. BLACK AVE.THENATIONALBUILDINGBASIN-1 (112 E. MAIN IMPROVEMENTS):PRE:POST:CAVE = 0.86CAVE = 0.85I10 = 0.41I10 = 0.41A = 0.35 ACA = 0.35 ACQ10 = 0.97 CFSQ10 = 0.96 CFSQ25 = 1.26 CFSQ25 = 1.25 CFSJ:\2020\B20-069 US Bank Site in Downtown Bozeman\CADD\CIVIL\DWG\CAD 2023.08.14 112 E Main SP\112 E. Main SW Basins.dwg, 8/22/2023 5:21:50 PM, CJC TD&H Stormwater Calculations Project: 112 East Main Street Mixed-Use Building Date: 08.22.23 Runoff Calculations "C" 0.9 0.8 0.3 0.1 Pre vs. Post-Development Runoff Coefficient: Total Area (SF)Total Area (Acres) Hardscape Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite "C" Pre 15,226 0.35 14,434 0 0 792 0.86 Post 15,226 0.35 14,258 0 0 968 0.85 Time of Concentration: Tc* Slope Distance t1 Slope Velocity Distance t2 Velocity Distance t 3 Total %ft min %fps ft min fps ft min min Pre 5.00 Post 5.00 * Tc minimum of 5 minutes FHWA HEC 22, Eqn 3-4 Estimate average flow of 3.0 fps K=0.457 Grassed Water Way (Roadside Ditch) K=0.619 Paved Area Cf = 1.0 for 10-year storm event K=0.491 Unpaved shallow concentrated flow Tc*Tc*10 yr Flow C Area Total Total i Q ac min hour in/hr cfs Pre 0.86 0.35 5.00 0.083 3.218 0.97 Post 0.85 0.35 5.00 0.083 3.218 0.96 * Tc minimum of 5 minutes Tc*Tc*25 yr Flow C(Cf)Area Total Total i Q ac min hour in/hr cfs Pre 0.94 0.35 5.00 0.083 3.826 1.26 Post 0.93 0.35 5.00 0.083 3.826 1.25 * Tc minimum of 5 minutes 10-Year Runoff Flow Rate: Overland Flow Shallow Flow/Gutter Flow Pipe Flow C k Roof Drain Tc < 5 Minutes 25-Year Runoff Flow Rate: Rational Formula "C" Values Per MTDEQ 8: Hardscape Area Gravel Area Unimproved Area Lawn/landscape Description Existing Building, South Entry and Modified Parking Existing Building, South Entry and Modified Parking Roof Drain Tc < 5 Minutes 31 11871 / f i S D)CC.(.T −= AiCQ= SkV=28.3 𝑖25 =0.78 ⋅𝑇𝑐−.64 𝑖10 =0.64 ⋅𝑇𝑐−.65 AiCQ= 𝐶𝑓= 1.10 (25-yr) 112 East Main Street Mixed-Use Building 112 E. Main Street Date: 08.22.23 15" Storm Pipe Capacity Input Values d =1.25 ft =15" y =1.175 ft =94% Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ)5.29 rad 2*arccos(1-y/(d/2)) Area (A)1.20 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P)3.31 ft 0.5Θd Hydraulic Radius (R )0.36 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T)0.59 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n =0.013 (per COB Design Standards) S0 =0.0050 ft/ft Q =4.93 cfs Q = 1.49/n*A*R2/3*S00.5 Q =2211.09 gpm Q gpm = (Q cfs)(7.48 gal/ft3)(60 sec/min) V =4.12 ft/s V = Q/A Results A 15" diameter storm pipe at a min. 0.5% slope flowing 94% full has the capacity to convey 4.93 CFS. J:\2020\B20-069 US Bank Site in Downtown Bozeman\DOCUMENTS\REPORTS\112 E. Main Design Report\Parts\112 E. Main Storm Water Calcs.xls 1 OF 1