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<br />O~2002 <br /> <br />junior water rights, the Fort Lyon Canal, had an e~perienced variation <br /> <br /> <br />of 19,400 and 7,400 acre-feet for 50 percent and 90 percent of the time <br /> <br /> <br />in August. <br /> <br /> <br />The investigations of canal diversions up to this point were for <br /> <br /> <br />long period conditions. Because of the major man-made changes in the <br /> <br /> <br />Arkansas River Basin, which were the construction of John Hartin Dam <br /> <br /> <br />and Reservoir, the utilization of water stored therein, and the use of <br /> <br /> <br />ground water by pumping from wells, it is necessary to analyze the avail- <br /> <br /> <br />able water supply and the historic diversions for shorter periods of <br /> <br /> <br />time. This was done to determine the magnitude of changes in use of <br /> <br /> <br />the water resources in the basin. The use of short periods of record <br /> <br /> <br />covering these changes together with the overlapping of the use of John <br /> <br /> <br />Martin Reservoir water and the use of ground water by pumping must be <br /> <br /> <br />used as long term records are not available. <br /> <br /> <br />One method of making the short term analysis was by use of a <br /> <br /> <br />double mass diagram: the summation of streamflow records of one station <br /> <br /> <br />plotted against the summation of streamflow or canal records at another <br /> <br /> <br />station. These diagrams will plot as a straight line if no significant <br /> <br /> <br />changes in the streamflow or diversions have occurred. To isolate the <br /> <br /> <br />station records which have changes (shown by a break in the straight <br /> <br /> <br />line plot), the inde~ station records should plot as a straight line <br /> <br /> <br />when plotted against time. In the analysis, the reconstructed Arkansas <br /> <br /> <br />River flow at Canon City was found to meet this criterion and is indica- <br /> <br /> <br />tive of the inflow into the reach of the river under investigation. <br /> <br />With the adoption of the Arkansas River flow at Canon City as an <br /> <br /> <br />index, double mass diagrams were plotted by computer for the major <br /> <br />ditch diversions below Pueblo and the Arkansas River at the state <br /> <br /> <br />line. The plots were on both an annual and a monthly basis. These <br /> <br /> <br />mass diagrams indicate that, since the early fifties, the river flow <br /> <br /> <br />at the state I ine has been losing with respect to the historical <br /> <br /> <br />trends established prior to 1950. At the state line, the loss shown <br /> <br /> <br />by the double mass diagram amounted to an average of 105,000 acre-feet <br /> <br />a year. During this same time, the total diversions by the ditches <br /> <br /> <br />decreased by an average of 113,000 acre-feet per year. As the inflow, <br /> <br /> <br />as indicated by the Canon City data, has not decreased appreciably, it <br /> <br />- 19 - <br />