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Show 105 at best a prediction-an estimate based on the past. The reliability of the estimate is, of course, conditioned upon the accuracy of the historical data and upon the probability that the past will to a substantial degree repeat itself. With regard to the historical data, there is the difficulty of measuring stream flow,29 which always involves a degree of inaccuracy.29 The reason for the inaccuracy becomes apparent when one considers the measurement process. Stream flow at any particular gauging point is determined by a series of measurements and calculations which involve engineering judgment. It is necessary to determine the cross-sectional area of the stream at the gauging point and to obtain the velocity of the flow for a given stage (i.e., surface level of water) at that point. Some gauging stations have a continuous stage recorder, which gives a continuous measurement of the fluctuating stream level, but others do not. When stages are measured infrequently, some error is necessarily introduced. The calculation of the cross-sectional area depends on the width, depth and contour of the stream bed. Securing of these data involves some uncertainty, partly because of the fact that the cross-sectional area is unstable, since it changes with sedimentation and scouring. Even the determination of flow velocity by current meters is inexact, because of variations in readings depending upon the depth of the meter below the water surface. The United States 28For example, Ariz. Ex. 64 (House Document 419, 80th Cong.) at p. 283 states: "Throughout the Gila River Basin the securing of stream-flow records is made difficult by violent floods, shifting channels, and sand and silt. Except in the Phoenix area, where extensive irrigation development has been made, there are no reliable long-time records of the Gila River and its tributaries." 29Tr. 4285 (Tipton). The witness also said that even delivery of water through a pipe to municipal water users cannot be measured with complete accuracy. |
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Original Report: State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Imperial Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California |