5.2. SR 08-08-2011 - Laserfiche WebLink

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Trunk Watermain System Requirements To evaluate the trunk water distribution system required for all three scenarios, the provided low pressure zone water model was utilized. The water demands from each scenario were entered into the City's existing low pressure zone model to determine a sufficient trunk watermain pipe size that will provide the development with sufficient pressures and fire flows on the peak water demand day. Typically, it is recommended that a public water supply system provide water pressures between 40 and 80 psi and available fire flows of over 1,000 gpm for residential areas and over 3,000 gpm for non-residential areas in the trunk watermain on the peak day. Fire flow recommendations can be decreased if buildings within the development are required to be sprinkled for fire suppression purposes. It is recommended for the purposes of this study that minimum fire flows are 2,000 gpm with the assumption that fire suppression will be required for all multi-family and commercial buildings Based on the low pressure zone water model, trunk watermain will be required to be extended within the study area to provide sufficient fire flow. It is recommended that a 16-inch diameter watermain is extended south from the existing 16-inch diameter watermain within the TH 10 right-of-way at 171St Avenue. The 16-inch diameter watermain should be extended through the west portion of the development ideally within aCity-owned right-of-way. It could then be downsized to a 12-inch diameter on the east side of TH 10 within the 165th Avenue right-of--way. The 12-inch diameter watermain should then be looped within the eastern portion of the development and connected to the existing 16-inch watermain within 171St Avenue. The remaining looping could be accomplished with 8-inch diameter watermain as shown on the attached Figure 13-2. With the above described watermain extension, the following are the pressures and available fire flows that can be expected according to the low pressure zone water model provided by Elfering and Associates: Table 13-2. Anticipated Peak Day Pressure and Fire Flows Scenario Anticipated Pressure (psi) Anticipated Available Fire Flow (gpm) Scenario 1 57 - 62 2,500 - 2,750 Scenario 2 57 - 61 2,250 - 2,500 Scenario 3 53 - 57 2,000 - 2,100 Water Use Mitigation Plan • The water demand information as presented in this AUAR will be provided to the Elk River Municipal Utilities to confirm the water supply, storage, and distribution systems are adequate as the existing water system model provided to us from Elfering and Associates, consultant to the Elk River Municipal Utilities, was incomplete. The City's water system is a split pressure zone system with the proposed development site located on the low pressure zone side. The water system model provided was for the low pressure system only and does not take into account the PRV interactions of the two pressure zones. City of Elk River Draft Alternative Urban Areawide Review July 2011 Page 36 of 84