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I I I I I I I I I I I I I I I I I I I 1.4 Firefighting Requirements Firefighting demands must be considered in any municipal water system design. Although annual volumes req'Jired for fire purposes are small, the demand may govern the design of parts of the distribution system, treated water storage facilities, and pumping equipment. For the current population of approximately 10,000, the required fire flow is 3100 gpl'l. At the projected population of 35,000, in the year 2028, a fire flow of 5700 gpm is estimated. These fi gures a re based on the recol1l11enda ti ons of the Nati ona 1 Board of Fi re Underwriters. When sizing distribution systems, the typical practice is to assume a coincident draft during the firefighting demand equal to the maximum daily demand. For high value districts, fire flow capacities must be maintained for 10 hou rs; therefore, the requi red flow capaci ti es for 1986 and 2028 are 4.5 mgd and 8.2 mgd, respectively. When added to the maximum daily demand, these capacities are still less than the peak hourly demand. Even though fire flow requirements do not control the sizing of the overall distribution system, they do establish minimum capacities for the extremities of the system. The City of Craig uses population density and hydrant spacing for determining the fire flow capacities of each distribution pipeline. Craig has a Class 5 fire insurance rating from the Insurance Services Offices. The rating is based on a scale from one to ten, with Class 1 being the highest rating possible. 1. 5 SU1II1lary The City's existing diversion system has the capacity to deliver approximately 12.6 mgd which would be sufficient to meet the maximum daily demand for a population of approximately 35,000. This level of water demand has been selected for use in this study. Both existing supplies and the estimated yield from an enlarged Elkhead Lake will be used to satisfy this water requi rement. - 21 -