HomeMy WebLinkAboutWater Design Report WATER & SEWER DESIGN REPORT
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INTRODUCTION
The Gallatin Valley Mall Re-Development is a project that involves the proposed water main
extension off of an existing 8” water main on the site. This proposed main extension will serve
roughly 4 proposed building sites within the existing mall parking lot. Each site will be
developed for commercial purposes and will be served by a 2” domestic service line and a 4” fire
service line. The project will connect to the municipal water and sewer systems operated by the
City of Bozeman.
WATER SYSTEM LAYOUT
The existing water main in the area utilized for the project is an assumed 8-inch ductile iron pipe
(DIP) located near the southwestern boundary of the subject property. The project was modeled
as one system for the hydraulic analysis. As shown on the schematic site plan, the proposed
water main will extend from the existing 8” DIP main on the south side of the parking lot
northerly into the site and intersecting with the existing 8” DIP main in front of the mall. The
existing 8” DIP main running north-south in the parking lot will be abandoned. It should be
noted that this system will be looped within the existing City of Bozeman infrastructure however
our model is presented as a closed system. Therefore, in reality the actual pressures and flows in
the system are likely to be higher than what is modeled.
WATER DISTRIBUTION SYSTEM SIZING
Demand at each building pad for this model was developed based on estimations by the MEP
engineer and the “Hunter’s Curve” which models the probability of flow as a function of fixture
unit (FU) count. A chart of the “Hunter’s Curve” can be found in Appendix A. For our system
an estimation of 30 FU’s per pad was given, this correlates to a demand of 41 GPM (peak hour
demand).
Based on these calculations and the attached WaterCAD analysis, found in Appendix A, the
existing water distribution system provides adequate pressure and water flow to meet the
required fire demand and the peak hour domestic water demand.
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HYDRAULIC ANALYSIS
The water distribution model was created using WaterCAD Version 10.03.02.75 for demand
forecasting and describing domestic and fire protection requirements. The WaterCAD analysis is
enclosed at the end of the report analyzing the 8-inch water main extensions to be installed with
just Phase 2 of this project. The connection to the existing system was modeled as a pump using
hydrant curves obtained from the City of Bozeman Water Department. Existing COB hydrant
#982 located to the NE of the recently completed Whole Foods building. In the model, the pump
is connected to a reservoir which acts as a source of water. The reservoir does not create any
head on the system; the head is generated entirely by the pumps. The input data and the pump
curves are included at the end of the report. The pump curve table includes all calculations and
equations used in determining flow characteristics at the connection point. A C-factor of 130 was
chosen for ductile iron class 51 pipe. The system was modelled as a steady state hydraulic flow
simulation.
CONCLUSION
The 8-inch class 51 ductile iron water main provides adequate capacity with regards to the Peak
Hour Demands and Fire Flow requirements. The flows and pressures within the system for the
Peak Hour Demands were generated with the WaterCAD program and can be found at the end of
the report.
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 locations and fire service lines. The model
shows that the proposed hydrant and fire service line junctions satisfies fire flow constraints
(residual pressure > 20 psi, flow rate > 1500 gpm), while providing service to the proposed lots
at peak hour. The results of the analysis at peak hourly flow are included in Appendix B.
SEWER SYSTEM
No Sewer main extension is proposed with phase 2 of the Gallatin Valley Mall Re-Development.
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APPENDIX A
WaterCAD Analysis
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Hunter’s Curve Chart and Table, Curve 1 is used for total service water flow estimation.
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