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HomeMy WebLinkAbout16 - Design Report - Armory Hotel - Water, Sewer, Stormwater DESIGN REPORT WATER, SEWER & STO►RMWATER MANAGEMENT Armory Hotel Prepared for: Venue Architects LLP 13 S. Willson Suite Two, Bozeman, MT 59715 Prepared by: C&H Engineering and Surveying, Inc. 1091 Stoneridge Drive, Bozeman, MT 59718 (406) 587-1115 rs- ,, a 4 0ES Project Number: 13025 JUNE 2013 INTRODUCTION The Armory Hotel is a proposed 8-story hotel located at 24 W. Mendenhall Street. The 0.44-acre development is situated in the northwest quarter of Section 7,Township 2 South,Range 6 East of P.M.M., Gallatin County, Montana. This project will require connection to existing City of Bozeman(COB)water,sanitary sewer,and storm sewer syestems. WATER SYSTEM LAYOUT The hotel is proposed to tap into the existing 6-inch water main running in W. Mendenhall Street and will be serviced by a 4-inch domestic water service line and a 6-inch fire water line. There are no proposed main extensions or improvements associated with this project. The COB currently has plans to replace the 6-inch water main with a new 8-inch main. For conservative purposes,this hydraulic model is based on the existing 6-inch main. A WaterCAD analysis is enclosed analyzing the existing main to determine if adequate pressures are available. The existing system is modeled as a pump with characteristics matching data measured by the COB Water Department. Water Demand MKK Engineers designed the mechanical systems for the hotel and determined that the peak domestic flow demand for the hotel is 208 gpm. The required fire flow demand for the 6-inch fire line was calculated to be 750 gpm by Sprinkler Technology Design. Available Pressure The COB measured fire hydrant pressures for hydrant#84 at the intersection of E. Lamme Street and N. Black Avenue on August 30, 2012. The COB indicated that these pressures would be representative of conditions in the W. Mendenhall water main. The measured pressures and discharge are as follows: Design Report-Page 2 of 6 Hydrant 484: Static= 130 psi Pitot= 110 psi(Hydrant#85) Residual= 126 psi Discharge= 1,760 gpm HYDRAULIC ANALYSIS A water distribution model was created using WaterCAD Version 6.5 for demand forecasting and describing domestic and fire protection requirements. In order to model the system, each junction node of the system was assessed a demand based on its service area. Junction nodes were added representing the connection points for the domestic and fire service lines. Two additional junctions were added to represent existing fire hydrant connections at the intersections of N. Tracy and N. Willson Avenues with W. Mendenhall. The 4-inch domestic service line is the only junction assigned a base demand which is the peak 208 gpm demand imposed by the hotel. All other junctions were assigned fire flow constraints to ensure these requirements would be satisfied under peak flow conditions. The measured flow/pressure information was used to develop relationships between static head and flow to represent existing conditions in the W. Mendenhall main. This relationship was used in the model by simulation of pumps at the assumed start of the model at the intersection of W. Mendenhall and N. Tracy Avenue. The pumps are connected to reservoirs which act as a source of water. The elevations of the reservoirs are fixed at the elevation of the pumps, which is also equivalent to the elevation of the start point. The reservoir does not create any head on the system, the head is generated entirely by the pumps. The input data and the pump curve are included in Appendix A. DISTRIBUTION MAIN The 8-inch water main does provide adequate capacity with regards to the hotel's peak demand. The flows and pressures within the system for the peak demands were generated with the Design Report-Page 3 of 6 WaterCAD program and can be found in Appendix A. The capacity of the system to meet fire flow requirements was tested by running a steady state fire flow analysis for all junctions at fire hydrant or line locations. This includes a conservative fire flow demand of 1,000 gpm for the 6-inch hotel fire line, and assumed a 2,500-gpm demand at the existing fire hydrant connections. The residual pressures at all junctions were required to remain above 20 psi. The model shows that all hydrant junctions satisfy fire flow constraints, while providing service to the hotel at peak hour. The results of the analysis at peak flow is provided in Appendix A. SEWER SYSTEM A 6-inch sewer service line is proposed to be installed out of the northeast corner of the hotel. The service line will connect with the existing 6-inch sewer main running in Mendenhall Street. There are no proposed main extensions or improvements associated with this project. The COB is currently planning a sewer improvement project on the existing main which will result in a new inside diameter of 5.7 inches, a manning's n of 0.010 and slope of 0.76% (email communication from Bob Murray and Dustin Johnson,COB). A recent flow monitoring program conducted by COB determined that the existing peak flow for the 6-inch main is 6 gpm. The anticipated peak flow for the Armory Hotel, including a peaking factor, is 208 gpm. Therefore, the peak total flow in the main is expected to be 214 gprn after hotel construction. The capacity of a 5.7-inch main is checked using Manning's Equation: Qffiil=(1.486/n)AeS"2 Mannimes n =0.010 for sewer liner S=Slope=0.0076 fl/ft A=area=(3.14/4)d 2=(3.14/4)(5.7/12)2=0.1772 ft2 P=perimeter=(3.14)d=(3.14)(5.7/12)= 1.4923 ft R=hydraulic radius=A/P=0.34907/2.0944=0.1188 fl Design Report-Page 4 of 6 RM=0.2416 ft S"2=0.0872 ft/ft Qfuii=(1.486/0.010)(0.1772)(0.2416)(0.0872) =0.5546 cfs (249 gpm) Based on these calculations,the peak flow through the sewer is anticipated to be 86%of capacity (q/Qf„1i). The COB has indicated that the 5.7-inch line will be adequate to handle the additional flows and will not need to be upgraded (email communication from Bob Murray and Dustin Johnson,COB). STORM SEWER SYSTEM All stormwater runoff generated on the hotel roof will be conveyed via an 8-inch storm service line to the existing 27-inch storm sewer main located in the alley behind the south end of the property.No additional impervious areas are proposed with the project;therefore runoff volumes will remain the same as before the development. The peak stormwater runoff rate and volume are calculated as follows: The time of concentration(TC) is calculated as the flow time from the most hydraulically remote point in the drainage to the proposed discharge point. The TC is then used to calculate the peak stormwater release rate. The COB's Design Standards and Specifications Policy (DSSP) require that storm sewer facilities be designed to handle a 25-year storm event. Therefore, the peak stormwater release rate is calculated for a 25- year storm event. Flow line length= 139 ft Slope=2.00% TC=2 mins,0.033 hrs(Figure 1-1,DSSP) I2s=Intensity(25-yr freq.)=0.78(TC)(A''4)=6.9222 in/hr Q25=CIA=(0.95)(6.9222 in/hr)(0.377 acres)=2.4792 cfs The capacity of the existing 27-inch vitrified clay main is checked using Manning's Equation: Design Report-Page 5 of 6 Qf,n=(1.486/n)AR2'3S"n Manning's n =0.013 for vitrified clay(Chow, 1959) S=minimum slope=0.004 ft/ft A=area=(3.14/4)d 2=(3.14/4)(27/12)2=3.9761 ft' P=perimeter=(3.14)d=(3.14)(27/12)=7.0686 ft R=hydraulic radius=A/P=3.9761/7.0686=0.5625 ft W13=0.6814 ft S1J2=0.0633 ft/ft Qfon=(1.486/0.013)(3.9761)(0.6814)(0.0633) = 19.6037 cfs q/Qf„»=2.4792 cfs/ 19.6037 cfs=0.1265= 12.65% Based on these calculations the peak flow from the hotel project for a 25-year storm would occupy 12.65% of the existing 27-inch main in the alley, which shows the existing main is capable of handling the flows from the hotel. 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