PROJ00515

• Contract/PO #: FS0019X
• Contractor Name: Turkey Creek Snowball Creek Project CWRPDA 1985
• Contract Type: Loan
• Water District: 0
• County: Archuleta
• Loan Projects - Doc Type: Feasibility Study

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Evaporation losses have been estimated from published data ( USGS,
19~5). For' the 87 surface acres of the full reservoir the annual
evaporation would be 70 acre-feet, with the major portions occurring during
the summer. Net seepage loss would occur primarily in the dam and abutment
area, and would be recoverable for use downstream. Volume will vary with
reservoir elevation, and based on measurements at similar dams may average
at the maximum 40 gallons per minute or 65 acre-feet per year. The effect
of either of these losses on the net water supply is negligible. When the
allowable project diversions through Snowball Ditch exceeded the reservoir
capacity, the excess water was designated as spill from the reservoir.
Diversions through Snowball Ditch for project purposes will be limited to
those required to fill the reservoir.

Three different circumstances were examined by the operation study:

1. Snowball Reservoir was used to meet the entire demand by Pagosa
Springs.

2 . Diversions on the San Juan River were used to meet the Pagosa
Springs demand, and any shortage was made up by water from
Snowball Reservoir.

3. Snowball Reservoir was used to meet the Pagosa Springs demand
during most years, and the San Juan River diversions were used to
make up the shortage in "dry" years.

The model was run for a series of reservoir sizes to determine the
size necessary to provide a full supply during the critical historic period
of record (1977-1978). When Snowball Reservoir is used to meet the entire
Pagosa Springs demand a capacity of 2,900 acre-feet is adequate. Using
Snowball Reservoir to supplement San Juan River diversions requires a
reservoir capacity of 1,200 acre-feet. Allowing the use of San Juan River
diversions to supplement water from Snowball Reservoir in "dry" years
results in a required reservoir capacity of 2,700 acre-feet. A copy of the
final printout is in Appendix D. Tables 3.5, 3.6, and 3.7 show the monthly
virgin flows at the Snowball Ditch diversion; available monthly inflows to

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