PROJ00505

• Contract/PO #: C153419
• Contractor Name: San Miguel Water Conservancy District
• Water District: 0
• County: San Miguel
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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Methods used to estimate water supplies for the Cone Reservoir Enlargement

indicate that additional water is available to the project using original San

Miguel Project water decrees. An average of approximately 1000 additional

acre-feet per year is available to the Cone Reservoir collection ditches. A

maximum of 1,836 acre-feet could have been collected in the wettest year

studied (1983) with practically none (141 acre-feet) available in an extremely

dry year (1977). An operation study to determine the project water supply has

been included in Appendix C. This supply alof'e is not ~ufficient to fully

utilize a 4,000 acre-foot enlargement.

In addition to enhanced collected within the Cone system, members of the

San Miguel Water Conservancy District Board assert that surplus water can be

diverted from the Gurley Ditch to the Cone Reservoir. A 10-year simulation of

historic Gurley Reservoir operation suggests that surplus water has been

available in 5 years (1974 and 1980-1983). The most recent years produced a

surplus of several thousand acre-feet. No record exists to confirm how much of

this surplus was diverted to the Cone Reservoir. With these surplus diversions

from the Gurley Ditch, our simulation indicates that a 4,000 acre-foot

enlargement would be filled in 4 of the 10 years. A more reliabl. water

supply, one defined by an agreement perhaps, could make better use of the

proposed storage enlargement and provide benefits to a greater portion of the

community.

Using methods described in Section 4.3 above, a 10-year yield study for

the Gurley collection system was performed using District-held San Miguel

Project water rights. These rights could yield an average of 7,764 acre-feet

per year. A low of 714 acre-feet would have been obtained in 1977 with over

15,000 acre-feet available in the largest runoff year, 1983. Physical

limitations on the diversion structures and conveyance canals could limit

actual yield. A diurnal fluctuation in flow is usually observed at diversion

points during runoff season. The Naturita Canal (Gurley Reservoir feeder

canal) diverts at numerous tributaries in the Beaver Creek drainage. The

combined flow of all tributaries can exceed the capacity of the ditch at times.

A survey of historic daily records show that the maximum momentary peaks at

each diversion point could exceed the 400 cfs Naturita Canal by about 200 cfs

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