WSP00945

• File Number: 8442.400
• Description: Missouri Basin - Pick Sloan Project - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/28/1985
• Author: DoI, BoR
• Title: Lake Andes - Wagner Unit Planning Report / draft Enviromental Statement
• Water Supply Pro - Doc Type: Report/Study

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Unit of Lake Andes National Wildlife Refuge and Red Lake as part of the
mitigation plan. (See Mitigation section.) Water will not be required
every year. Owens Bay, a 240-acre marsh, would require approximately 720
to 1,500 acre-feet, and Red Lake, a 500-acre marsh, about 1,500 to
3,000 acre-feet. The volumes were determined by providing for a 3-foot
depth and allowing for 39 inches of annual evaporation. The water for both
areas would be needed during the spring and/or fall, and not during the
peak irrigation season. In addition, delivery could be scheduled so that
both facilities would not require water at the same time. A maximum demand
of 4,500 acre-feet would be required anyone season. Since the-supplemen-
tal water will be furnished on an as-needed basis, it is not possible to
predict the average annual diversion. Therefore it was assumed that the
average use would be one-half the maximum demand or 2,250 acre-feet. (See
Table 5.)

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Additional water (maximum of 450 acre-feet) will be provided to 330 acres

of existing wetlands. This volume was based on filling the basin to an

18-inch depth. The average annual water requirement would be

250 acre-feet. The water would be of Lake Francis Case quality and would

be provided via turnouts. Operational wastes will be used when practical.

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The fish rearing pond on Lake Francis Case will not require a diversion

from Lake Francis Case. The pond will be filled in the spring by natural

runoff in the drainage to North Bay arm.

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Shortages.--Irrigation shortages would be very .rare and cause only minor
impact to crop production.

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The proposed operation of Lake Francis Case would maintain an elevation of

1335 or higher through the end of August. Drawdown during September would

occur only during years when navigation season had to be reduced to

6 months or less. If drawdown did occur in September, the average annual

shortage would be 6.7 perc'ent during the years when drawdown occur. This

reduced season would occur only after 3 years of severe drought. An analy-

sis showed that the chances of 3 years of low flows (such as 1934-36)

occurring consecutively are about 1 percent, or a lOO-year event.

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