PROJ00273

• Contract/PO #: C153368
• Contractor Name: Cache LaPoudre Water Development Study
• Water District: 0
• County: Larimer
• Bill Number: SB 81-439
• Loan Projects - Doc Type: Feasibility Study

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ished greatly to a period of lower flows during the years from 1924 through
1980.

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b.

Transbasin Imports

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The plot of the annual imports of Laramie, Michigan, and
Colorado River Basin water to the upper basin is shown in Figure 111-3. The
total annual imports increased rapidly from zero in 1894 to a peak of 68,000
acre-feet in 1938. Then imports decreased drastically and rapidly to a much
lower level in 1940. The lower levels were due to decreased facility capacity
caused by reduced maintenance of these facilities. The average of all trans-
basin imports to the headwaters of the Cache la Poudre River Basin has been
only 37,000 acre-feet per year since 1953, when the Colorado-Big Thompson
Project first imported water to the Cache la Poudre system. The Colorado-Big
Thompson Project has imported, on the average, 89,300 acre-feet per year into
the lower basin for the period 1953 through 1981 as shown in Figure 111-4.

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c.

Major Upstream Diversions

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An estimate of the total annual recorded flows from the four
major diversions in the upper basin which divert water from the upper basin
above the mouth of the canyon are shown in Figure 111-5. The diversions into
the irrigation canals are recorded only during the irrigation season. In some
years a minor amount of unrecorded flow is diverted to storage in lower basin
reservoirs outside the irrigation season. This winter diversion is minor in
comparison to the total annual flow.

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d.

Consumptive Uses

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The major man-made consumptive uses of water in the upper basin
which affect the recorded streamflows are due to the evaporation from reser-
voirs and irrigation along the floodplains and terraces. It is estimated that
the increased consumptive use due to man-made lakes and irrigation i.n the
upper basin is less than 5,000 acre-feet per year, which is considered to be
minor in comparison to annual flows,

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e.

Effects of Regulation

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Effects on the annual strearnflows due to upper basin reservoir
regulation were estimated through an analysis of available reservoir operation
records. The analysis of major upper basin reservoir regulation records
demonstrated their use to be one of retaining spring runoffs and imported
waters for use later in the irrigation season. Therefore, the effect on the
measured annual streamflow due to such regulation was determined to be minor.

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3. Derivation of Annual. Rative Plows

An estimate of the annual native flow at the mouth of the canyon was
made by adjusting the recorded streamflow by adding the measured amount di-
verted from the upper basin via the North Poudre Canal, North Poudre Supply
Canal, Poudre Valley Canal, and the Fort Collins Pipeline and subtracting the

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III-2

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