PROJ00441

• Contract/PO #: C153459
• Contractor Name: Loveland, City of
• Water District: 0
• County: Larimer
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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9.0 EVALUATION OF SYSTEM YIELD (TASK 7)

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The computer simulations using the models developed as part of Task 6 and
described in the previous section produced a 1,000-year synthetic record of
water availability from each of the City's four major water supply sources
on a monthly basis. The models also compared the total available supply to
the City's monthly demand to identify periods of surplus or deficit. As
described earlier in Section 2.1, use of a long-term synthetic record as
opposed to specific "design" droughts permits examination of a wide range
of drought sequences. By operating the models using the 1,000 year
synthetic records, it was possible to generate a large number of surplus
and/or deficit periods which could then be evaluated in terms of
probability of occurrence, magnitude, and duration. Table 9-1 presents a
summary of deficits encountered in the seven growth scenarios investigated.
The results demonstrate that significant deficits, in terms of number,
duration, and magnitude will not occur until the demand on the City Supply
system exceeds 14,000 ac-ft/yr.

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The reliability of the City'S total water supply was determined by
calculating the probability of failure to meet demand at any time during
the 1,000-year record. The system yield will, of course, vary over time in
response to the sequence of droughts encountered. Deficits (or in the
cases where deficits do not occur, surpluses) were ranked by magnitude for
each scenario and assigned recurrence intervals based on that ranking. For
example, the largest deficit of record was assigned a rank of 1 and a
recurrence interval of 1000 years (1000 divided by 1), the second largest
was assigned a rank of 2 and a recurrence interval of 500 years (1000
divided by 2), and so on. In order to evaluate system yield, the surplus
or deficit resulting from typical drought conditions at the 25-, 50-, 100-
and 200-year recurrence intervals were determined in this fashion and are
summarized in Table 9-2, with more detailed data presented in Tables 9-3
through 9-9.

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9-1