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<br />0~2GC3 <br /> <br />is concluded that since approximately 1950 the surface supply available <br /> <br /> <br />to the ditches and the flow at the state 1 ine have been reduced materially. <br /> <br /> <br />Above John Martin Dam the average break in the mass diagrams occurred in <br /> <br /> <br />1951, and below John Martin, the average break occurred in 1958. The <br /> <br /> <br />average annual change since heavy pumping began for the various ditches <br /> <br />and the Arkansas River at Canon City and the state I ine is shown in <br /> <br />Table No.9. <br /> <br /> <br />The pumpage of ground water in the Arkansas River Basin has increased <br /> <br />considerably in the years since 1940 with the sharpest increa~ occurring <br /> <br /> <br />in the period 1951 through 1965. This period of increase in pump age <br /> <br /> <br />corresponds with the beginning of the loss of surface water between <br /> <br /> <br />Canon City and the state line. Based on figures obtained from the <br /> <br /> <br />Colorado Water Conservation Board, the average pump age for the period <br /> <br />1953 through 1965 was 128,700 acre-feet per year. Irrigation efficiency <br /> <br /> <br />for well water in the Arkansas Valley has been estimated by the U. S. <br /> <br /> <br />Geological Survey to be about 80 percent. Using this efficiency, <br /> <br />103,000 acre-feet of the total water pumped would be consumptively used. <br /> <br /> <br />If a 70 percent efficiency is used, the consumptive use of well water <br /> <br /> <br />would average 90,000 acre-feet per year. <br /> <br />As stated previously, canal diversions below Pueblo have been <br /> <br />reduced in recent years by an average of about 113,000 acre-feet per <br /> <br /> <br />year. Had this water been diverted, the average depletions to the <br /> <br /> <br />streamflow, at 60 percent efficiency, would approximate 68,000 acre-feet <br /> <br /> <br />per year. When this value is added to the previously mentioned state <br /> <br />line reduction in flow of 105,000 acre-feet per year, the total decrease <br /> <br /> <br />in consumptive use below Pueblo was about 173,000 acre-feet per year. <br /> <br />If the depletion by pumped well water of between 90,000 and 103,000 <br /> <br /> <br />acre-feet is reasonable, there remains approximately 83,000 to 96,000 acre- <br /> <br />feet of recent river losses which may be charged to more efficient use <br /> <br />I <br /> <br />of the irrigation water fr~ direct flow and storage, which includes use <br /> <br /> <br />of John Martin Reservoir water; greater consumptive use by phreatophytes; <br /> <br />possible reduction in tributary inflow and other minor causes. <br /> <br /> <br />Canal diversions by the various ditches in the upper reaches of <br /> <br /> <br />the Arkansas River Basin have not been tabulated and analyzed. To <br /> <br /> <br />do this on the main stream and on the tributaries above Canon City <br /> <br />- 20 - . <br />