PROJ00436

• Contract/PO #: C153669
• Contractor Name: Windsor Reservoir and Canal Company
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: EIA
• Loan Projects - Doc Type: Feasibility Study

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B.7. Big Windsor Reservoir

Big Windsor Reservoir is filled out of the Larimer and Weld Canal and can divert up to 650 cfs
into the reservoir. Discharges of up to 200 cfs are delivered into the New Cache LaPoudre Ditch
No.2. This water is traded for river water in the Eaton Ditch which may be taken out of
Horsetooth Reservoir.

C. FIRM YIELD

The firm or safe yield of a reservoir is generally defined as "the maximum quantity of water which can be
guaranteed during a critical dry period". The safe yield of the reservoirs was not evaluated by analysis of
the available flow of water in the Cache La Poudre River as this is beyond the scope of this report. The
dry years of 1951 through 1956 were not included in the analysis as good records were not available from
the State Engineer on this period of time and because the water in the Poudre River Basin has changed
since that time due to the Windy Gap Project. It was evaluated only by review of the water record from
1974 through 1994.

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From a review of Figure IV-I through IV-5, it can be seen that most of the reservoirs have been filled to
near capacity most years and significantly drawn down during most of the years. For the twenty years of
record shown the reservoirs have been filled to within five feet of the maximum capacity as itemized
below.

Big Windsor Reservoir
Cobb Lake
Douglas Reservoir
Reservoir NO.8
Reservoir No.8 Annex

95 % of the years
42 % of the years
90 % of the years
90 % of the years
90 % of the years

The lowest storage levels for all the reservoirs was for the years 1974 through 1994 is in 1977. The safe
yield of the reservoirs was considered to be the storage for 1977 as this was the most recent dry period with
the lowest water storage in all six reservoirs. Releases from the reservoirs was not used to determine the
firm yield as the records are not as detailed and are not as complete as the storage levels in the reservoirs.

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Table IV-2 is a summary of the fill levels for the six reservoirs for 1977. As shown in the table, the total
storage for 1977 for all six reservoirs is 30,200 acre-feet. For purposes of this report, this is considered
to be the FIRM YIELD for the storage reservoirs owned by the Windsor Reservoir & Canal Company.

D. WATER QUALITY

The water quality in the WR&C system is of relatively good quality, especially for irrigation purposes.
The water supplying these reservoirs is mostly runoff from the mountains and from the plains and is of
good quality. No major pollution sources are upstream of these reservoirs other than some cattle feed lots.
These are relatively small and scattered, however, and most of the runoff is from timberland, pasture land,
and farm land. Some silt load is expected, as for any plains reservoir, but is not expected to be severe.

Page IV-S
WR&C Feasibility Study

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