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<br />22. The more important considerations in determining the <br />reliability of the results reached by a given expert depend more <br />upon the assumptions utilized by the expert and in this regard the <br />Court makes the following comparisons regarding various assump- <br />tions: <br /> <br />a. study Period: Arapahoe I s consultants used a period of <br />record from 1950 through 1988 as the basis for their modelling <br />effort for the reason that a period of record should be long <br />enough to include several dry, as well as several wet, <br />periods. In the belief that the modelling needed to recognize <br />more current situations on the river system, Mr.. Spronk, <br />expert for Crystal Creek, utilized a period of analysis from <br />1975, after the Blue Mesa Reservoir of the Aspinall Unit was. <br />completed, through 1988, but Mr. Helton, expert for the River <br />District, studied a period from 1950 to 1989. Experts for the <br />opposers did give somewhat greater emphasis to the more recent <br />years, because they believed (and the evidence supported their <br />conclusion) that there was some increase in diversions through <br />the Gunnison Tunnel in more recent years. The Court concludes <br />that this approach utilized by the opposers is more reliable <br />than that used by the Applicant. <br /> <br />b. Regression Analysis: Because stream gauges did not <br />exist at each point of diversion contemplated by the Appli- <br />cant's collection system, all of the experts found it neces- <br />sary to utilize regression analyses in an attempt to predict <br />(on the basis of known stream gauge records) the amount of <br />water available at a given point of diversion in a given <br />month. In its regression analysis, wac carefully considered <br />the effect of altitude and prec:,)itation upon runoff, conclud- <br />ing that higher sub-basins proG:lce more runoff'per unit area <br />than lower sub-basins due to greater winter precipitation. <br />Then WRC allocated the actual gauged stream flows at long term <br />stream gauge stations to Sub-basins, based upon the equation <br />it had developed which considers average sub-basin precipita- <br />tion as well as area. In certain instances, such as Willow <br />Creek, where Arapahoe'S method gave lower basin runoff than <br />short term gauging stations, the calculated results were used. <br />Experts for the Opposers also estimated stream flow at <br />Arapahoe'S points of diversion, but allocated actual stream <br />gauge records solely on the basis of sub-basin area, without <br />taking the increase of precipitation with altitude into <br />effect. WRC's analysis demonstrated that the virgin average <br />annual flow of water (before any constraints were imposed) at <br />the Applicant's proposed points of diversion totalled 295,000 <br />acre feet per year, while Opposers' experts estimated said <br />total to be 278,000 acre feet per year. While it is diffi- <br />cult to say which of these alternatives is more reliable, it <br />would seem reasonable that there would be an increase in <br />precipitation as elevation increases because of greater snow <br />fall and snow pack. However, Arapahoe's experts testified <br />that estimates of physical water availability can normally be <br />expected to vary between 10% and 20% (Andrews, 6/12/91) or at <br />least between 5% and 15% (Leak, 7/2/91). Further, Opposers <br /> <br />13 <br />