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.15- -16- records on Shrine Pass since 1942 and on Vail Pass since 1952. Table 111-1 shows the April 1 and May 1 values recorded at these locations. .! ! . The cyclic thermal input that occurs in the spring is at least as important as the depth of snowpack. This thermal input determines the snowmelt rate and thus the streamflow discharges. The spring sno~melt accelerates rapidly when the nightime temperatures remain at or above freezing, but any cloud cover temporarily interrupting the therm~l input results in a decrease in the melt rate, and thus, Snowfall Precipitation ~nd SnowPack The Soil Conservation Service has kept snowpack and water content The Shrine Pass station, at 10,500 feet, has an average May 1 snowpack of 55 inches with 19.5 inChes of water content. The average April 1 snQWpack at the Vail Pass station is 55 inches of snow with 17.9 inches of water. The records indicate a maXimum snowpack depth occurs at the Vail Pass station somewhat earlier in the year than at the Shrine Pass station. The reasons for this are many and include elevation, siting and aspect. The Soil Conservation Service has made a statistical analysis using data through 1971.18 The resultant 100 year probable return the associated streamflow discharge rate. Streamflow The Gore Creek streamflows have an annual cycle. The high discharges in the cycle, which are caused by the annual snowmelt, occur from late May to late June. Flows then decrease to 'less than ten percent of the yearly peak by August and further decrease to the period snowpacks and water contents are as follows: Station Snowpack Water Content I (in.) (in.) , Shrine Pass 77 29.0 I Vail Pass 90 36.2 A revised analysis using data through 1975 would Show moderate yearly low in Oecember or January. On the average, Gore Creek pro- duces an annual runoff of 24,000 acre~feet of water, of which 85% Maximum recorded snowpacks at Shrine Pass and Vail PijSS are 26.7 inches . . 1s drawn off during this snowmelt portion of the annual cycle. Ouring the snowmelt season, the ground is partially saturated and still frozen. Consequently, the majoritv of the melted snow enters the stream as runoff without significant infiltration losses. The snowmelt runoff is characterized by a diurnal fluctuation. The annual peak discharge is caused by warm temperatures which pro. duce a higher diurnal fluctuation for the peak discharge day. This peak is seldom much higher than those on preceeding or succeeding days, as can be seen in Figures 11I-3, 111-4 and III.5, which show the record discharges of June 1952. Flows usually remain very high for one to three weeks, depending on mean daily temperature fluctuations. differences because of the longer recording period. In June 1952, the highest stream discharges on record were at the ~ Upper Gore, Lower Gore and 8lack Gore Creek stations; the snowpack a~ Shrine Pass was 22.0 inches on May 1 and 23.7 inches at Vail Pass. , on April I, 1965 and 27.9 inches on May 1, 1970, respectively.