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Home My WebLink AboutAppendix 1-SOBO Lofts-Site Plan Design Report SITE PLAN DESIGN REPORT WATER, SEWER, AND STORM DRAINAGE IMPROVEMENTS SOBO MIXED USE BUILDING BOZEMAN, MONTANA December 2016 Prepared by: TD&H ENGINEERING 234 E. BABCOCK, SUITE 3 BOZEMAN, MT 59715 Project No. B16-070 12/19/16 2 Purpose and Introduction The purpose of this report is to explain how water, sanitary sewer, and storm drainage improvements will be designed to meet City of Bozeman Design Standards and provide service to the proposed development. This report will provide information on the design of the above mentioned infrastructure. The proposed development is a redevelopment of approximately 0.65 acres near downtown Bozeman. Currently, the site consists of one residence (716 West Babcock) and the vacated Pizza Hut building (718 West Babcock). The proposed improvements consist of demolishing the existing site and constructing one mixed-use building with 42 1-bedroom apartments and 3,000 square feet of retail space. In addition to the structure, this project includes new sidewalks, two exterior parking lots, and parking on the buildings ground level. This design report describes how new connections to the existing infrastructure will accommodate this development. Water The project site has two existing water services extending off W. Babcock Street. These services will be abandoned and plugged at the main. A new domestic water service (4-inch, to be verified by mechanical engineer) and fire service (6-inch, to be verified by sprinkler designer) will be extended to the building. Water and fire services will be installed per the City of Bozeman Design Standards and Modifications to Montana Public Works Standard Specifications (MPWSS). Construction of new water main is not anticipated with this project. The anticipated demands for the project are summarized in Table 1 and calculations are provided in the Appendix. Table 1. Estimated Water Demands Average Day Max Day Peak Hour Demand 15,826 gpd 36,400 gpd 33.0 gpm Sanitary Sewer The project site has three existing sewer services extending off the alley south of the site. These services will be capped and abandoned in place. A new sewer service (4-inch) will be extended to structure and connect to the existing main in W. Babcock Street. The sewer service will be installed per the City of Bozeman Design Standards and Modifications to MPWSS. Construction of new sewer main is not anticipated with this project. The anticipated demands for the project are summarized in Table 2 and calculations are provided in the Appendix. Table 2. Estimated Sewer Demands Average Day Peak Hour Demand 8,745 gpd 25.9 gpm 3 Storm Drainage The proposed site development includes buildings, asphalt, and concrete. The small site will be primarily covered in hardscape. To accommodate existing and increased storm runoff from the site, a below grade retention structure is proposed. The retention structure will include 36-inch diameter perforated corrugate metal pipe. It is anticipated the pipe will be located or tied directly into native gravel. Site runoff from the lower parking lot and commercial space roof will be retained while runoff from the larger residential roof will discharge directly to the City storm drain system. The roof drains will be sized for the 25- year design flow and in accordance with the Uniform Plumbing Code, whichever is more restrictive. Post vs. pre-development was analyzed using a 10-year design storm. As a result of the proposed retention ponds, the post development runoff is equal to the pre development runoff even though the proposed residential building runoff will discharge offsite undetained. The retention pipe was sized per the City of Bozeman Design Criteria, utilizing a 10-year, 2- hour storm and the rational method. Once retained, water from the 10-year, 2-hour storm will be contained and allowed to infiltrate through the perforated pipe and into the native gravel. The 100-year storm overflow path will convey water directly to adjacent streets. Calculations are included in the Appendix. 4 Appendix Overall Project Areas Hard Gravel Landscaped Total Hard Gravel Unimproved Weighted Surfaces Area Area Area Coeff. Coeff. Coeff. Average C (sf) (sf) (sf) (sf) C C C CAVG Existing 12550.49 0.00 15761.19 28311.68 0.9 0.8 0.1 0.45 Proposed 24776.22 0.00 3535.46 28311.68 0.9 0.8 0.1 0.80 Total Lot Area 28312.00 sf Total Lot Area 0.650 acres Basin A, Retention Area (North Parking Lot and North Building Roof) Hard Gravel Landscaped Total Hard Gravel Unimproved Weighted Surfaces Area Area Area Coeff. Coeff. Coeff. Average C (sf) (sf) (sf) (sf) C C C CAVG Proposed 6801.00 0.00 380.00 7181.00 0.9 0.8 0.1 0.86 Total Lot Area 7181.00 sf Total Lot Area 0.165 acres Basin B, Areas Directly Discharging from Site Hard Gravel Landscaped Total Hard Gravel Unimproved Weighted Surfaces Area Area Area Coeff. Coeff. Coeff. Average C (sf) (sf) (sf) (sf) C C C CAVG Proposed 17974.00 0.00 3156.08 21130.08 0.9 0.8 0.1 0.78 Total Lot Area 21130.08 sf Total Lot Area 0.485 acres SOBO MIXED USE BUILDING C Value Determination J:\2016\B16-070 718 West Babcock\DOCUMENTS\DESIGN REPORT\Storm Drain Calcs.xls TD&H Storm Drain CalculationsProject: SOBO MIXED USE BUILDING10-year flow calculationsTc*Tc* 10 yr FlowSlope Distance Ct1Slope k Velocity Distancet2Velocity Distancet3Total C Area TotaliQ% ft min % fps ft min fps ft min min ac min in/hr cfsPre development5.20 139 0.59 6.49 1.00 0.619 2.03 0 0.00 3 0 0.00 6.49 0.45 0.65 6.49 2.717 0.80Basin B1.00 50 0.50 7.93 1.00 0.491 1.61 160 1.66 3 0 0.00 9.59 0.78 0.49 9.59 2.108 0.80Estimate average flow of 3 fpsFHWA HEC 22, Eqn 3-4Cf = 1.0 for 10-year storm eventK=0.457 Grassed Water Way (Roadside Ditch)K=0.619 Paved AreaK=0.491 Unpaved shallow concentrated flowTIME OF CONCENTRATION10 YEAR FLOW CALCOverland FlowShallow FlowPipe Flow3111871/fcSD)CC.(.T-=AiCQ=65.1064.0-=cTiSkV=28.3 TD&H Storm Drain CalculationsProject: SOBO MIXED USE BUILDING25-year flow calculationsTc*Tc* 10 yr FlowSlope Distance Ct1Slope k Velocity Distancet2Velocity Distancet3Total C Area TotaliQ% ft min % fps ft min fps ft min min ac min in/hr cfsCommerical Downspout2.00 137 0.90 1.91 1.00 0.619 2.03 0 0.00 3 0 0.00 1.91 0.90 0.076 1.91 7.081 0.48Residential Downspout2.00 177 0.90 2.17 1.00 0.619 2.03 0 0.00 3 0 0.00 2.17 0.90 0.285 2.17 6.524 1.67Estimate average flow of 3 fpsFHWA HEC 22, Eqn 3-4Cf = 1.1 for 25-year storm eventK=0.457 Grassed Water Way (Roadside Ditch)K=0.619 Paved AreaK=0.491 Unpaved shallow concentrated flowTIME OF CONCENTRATION25 YEAR FLOW CALCOverland FlowShallow FlowPipe Flow3111871/fcSD)CC.(.T-=AiCQ=64.2578.0-=cTiSkV=28.3 SOBO MIXED USE BUILDING Commercial Downspout Sizing Input Values d = 0.50 ft y = 0.465 ft Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ) 5.21 rad 2*arccos(1-y/(d/2)) Area (A) 0.19 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P) 1.30 ft 0.5Θd Hydraulic Radius (R ) 0.15 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T) 0.26 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n = 0.013 (For PVC per COB Design Standards) S0 =0.02 ft/ft Q = 0.86 cfs 1.49/n*A*R2/3*S0 0.5 V = 4.50 ft/s J:\2016\B16-070 718 West Babcock\DOCUMENTS\DESIGN REPORT\Storm Drain Calcs.xls 4 OF 6 SOBO MIXED USE BUILDING Residential Downspout Sizing Input Values d = 0.67 ft y = 0.623 ft Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ) 5.21 rad 2*arccos(1-y/(d/2)) Area (A) 0.34 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P) 1.75 ft 0.5Θd Hydraulic Radius (R ) 0.20 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T) 0.34 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n = 0.013 (For PVC per COB Design Standards) S0 =0.02 ft/ft Q = 1.87 cfs 1.49/n*A*R2/3*S0 0.5 V = 5.46 ft/s J:\2016\B16-070 718 West Babcock\DOCUMENTS\DESIGN REPORT\Storm Drain Calcs.xls 5 OF 6 10-yr C Area 2-hr Q V Length ac (i) in/hr cfs cf 36" Culvert Basin A 0.86 0.16 0.41 0.058 417 59 SOBO MIXED USE BUILDING Retention Calculations - 10-Year, 2 hr Event AiCQ=QV•=7200 J:\2016\B16-070 718 West Babcock\DOCUMENTS\DESIGN REPORT\Storm Drain Calcs.xls Preliminary Design Report Update Updated 12/19/16, units increased to 42 1-bedroom units with 3,000 sf of Commercial. 42 42 15,065.4 15,826 15,826 15,826 36,400 659.4 11 11 33 42 7,985 7,985 8,745 0.08862 0.08862 No Change, 4.3 8,647.18 37,280 25.9 SOBO MIXED USE BUILDING Sewer Capacity Check Input Values d = 0.33 ft y = 0.11 ft Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ) 2.46 rad 2*arccos(1-y/(d/2)) Area (A) 0.02 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P) 0.41 ft 0.5Θd Hydraulic Radius (R ) 0.06 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T) 0.31 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n = 0.013 (For PVC per COB Design Standards) S0 =0.02 ft/ft Q = 0.06 cfs 1.49/n*A*R2/3*S0 0.5 28 gpm V = 2.52 ft/s J:\2016\B16-070 718 West Babcock\DOCUMENTS\DESIGN REPORT\Sewer Capacity Check.xls 1 OF 1 SHEETDESIGNED BY:QUALITY CHECK:JOB NO.FIELDBOOKDRAWN BY:DATE:B16-070 BASEMONTANAWASHINGTONIDAHO GREAT FALLS-BOZEMAN-KALISPELL-SHELBY REV DATELEWISTONSPOKANE Engineering tdhengineering.com NORTH DAKOTAWATFORD CITY REVISION 718 WEST BOZEMAN BOZEMAN, MONTANA STORM WATER BASINS B16-07012-14-16.DWGC1.1MMN1KLSBASIN ABASIN BCOMMERCIALROOFRESIDENTIALROOFJ:\2016\B16-070 718 West Babcock\CADD\CIVIL\DWG\B16-070 Base.dwg, 12/19/2016 11:03:51 AM, MMN1