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<br />" <br /> <br />for purposes of this study, estimates of streamflow on Bear Creek <br /> <br /> <br />at the Evergreen Water System intake were assumed to be 88% of t~e <br /> <br /> <br />recorded Bear Creek flow at Morrison for base flow periods. This <br /> <br /> <br />assumption was confirmed in studies by W. W. Wheeler & Associates, <br /> <br /> <br />Inc., utilizing actual measured discharges at Evergreen in 1968 and <br /> <br /> <br />1969. The drainage area of Bear Creek above Evergreen is 101 square <br /> <br /> <br />miles as compared to 164 square miles above Morrison, however, even <br /> <br /> <br />though only 61% of the watershed above Morrison lies above Evergreen, <br /> <br /> <br />it is the most water productive portion as evidenced by the average <br /> <br /> <br />basin elevation of 9.540 feet above Evergreen as compared to 7,600 <br /> <br /> <br />feet between Evergreen and Morrison. Hydrologically speaking, water <br /> <br /> <br />production from Rocky Mountain Watersheds increases as the average <br /> <br /> <br />basin elevation increases. <br /> <br />., <br /> <br /> <br />Historic records of the Bear Creek flows at Morrison were studied, <br /> <br /> <br />In addition, a statistical analysis of the daily gage flow records <br /> <br /> <br />waS obtained from the U.S. Geological Survey. Annual low-flow statistics <br /> <br /> <br />for two different seasons were obtained. These were the entire water <br /> <br />7' <br /> <br />2 <br /> <br />year and the May through September period. Because of the nature <br />of the water rights and the high rate of use during May through SeptembeF, <br />it ~Jas concluded that this restricted pe r i ad should be analyzed separately. <br /> <br />A low-flow period of 30 days was selected for detailed analysis. <br /> <br /> <br />Figure 1 shows the frequency of occurreoce of the annual recorded <br /> <br /> <br />lowest average consecutive 3D-day periods for Bear Creek at Morrison. <br /> <br /> <br />Lowest average flows for other durations ranging from I to 183 days <br /> <br /> <br />were also obtained. Both the entire water year and May through September <br /> <br /> <br />frequencies are shOl.m. The actual data points vlere plotted and fitted <br /> <br /> <br />with a Log-Pearson Type I I I frequency distributioo. The five lowest <br /> <br /> <br />years of occurrence as picked from the curves are shown in Table 5. <br /> <br /> <br />It should be understood that these curves are based on daily gage <br /> <br /> <br />data, reflecting losses through upstream diversions. Because of this, <br /> <br /> <br />it is probable that the lower data points are more biased by the <br /> <br /> <br />diversions than the others. Consequently, caution should be exercised <br /> <br /> <br />in using the curves for return periods greated than 20 years. Ideally, <br /> <br />. <br /> <br />-14- <br /> <br />! I <br /> <br />! <br />