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I I I I I I I I I I I I I I I I I I I 3.0 WATER SUPPLY 3 . 1 GENERAL Turkey Creek is a tributary of the San Juan River. It has a drainage area of 28 square miles, and varies in elevation from 7,500 feet at its mouth to 12,000 feet at its headwaters. The tributary area above the point of diversion of the Snowball Ditch is 19.4 square miles. There are no published records of streamflow measurements. Based on field observation during the 1984 and 1985 seasons it is estimated that spring runoff flows frequently exceed 200 cfs, and winter flows are on the order of five to ten cfs. Average historical diversions from Turkey Creek of approximately 5,000 to 6,000 acre-feet annually are reflected in the water commissioner's records for the Snowball and Cummings Ditches. The Turkey Creek Reconnaissance Study (Western Engineers, Inc., 1985) presented an analysis of water supplies at both the mouth of Turkey Creek and at the diversion point of the Snowball Ditch. This feasibility phase of the study considers only the Snowball site alternative. 3.2 PERIOD OF ANALYSIS The hydrologic period from 1960 through 1980 has been used as the period of analysis for this study. This period was selected because first, average flows in the San Juan Basin were below the average for the total period of record; second, the lowest year of record (1977) is included; and third, the gage established on the middle fork of the Piedra River in 1969 could be used directly in the correlation analysis. Figure 3.1 shows a plot of recorded annual discharges for the Navajo River at Edith (drainage area 172 square ~i1es) from 1930 to 1980. It also shows annual discharges for the East Fork of the San Juan (drainage area 86.9 square miles) since 1935, and it shows the calculated flows in Turkey Creek from 1960 to 1980 (plotted to a separate scale). Several items are worthy of note: 3-1