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<br />..j ,j.'> " <br /> <br />IJU021.4 <br /> <br />. <br /> <br />SUMMARY AND CONCLUSIONS <br /> <br />The following items are based only upon study results prior to <br /> <br /> <br />completion of computer model runs. Full SUMMARY AND CONCLUSIONS will <br /> <br /> <br />accompany the supplemental report on the model studies. <br /> <br /> <br />1. Irrigation water-use efficiency can be viewed from a number of <br /> <br /> <br />different standpoints. The individual farmer is primarily concerned about <br /> <br /> <br />how efficiently he can use water on his farm. Officials of canal and <br /> <br /> <br />reservoir companies are principally concerned about delivering a high <br /> <br />percentage of the amount of water diverted from the river to the farm <br /> <br /> <br />turnouts. On a larger scale, the efficiency of water use within a river <br /> <br /> <br />reach or river basin is often important. This study is principally directed <br /> <br /> <br />at evaluating the effects of changing farm and canal system efficiencies <br /> <br /> <br />upon river reach and basin water-use efficiencies~ These effects are to <br /> <br /> <br />be evaluated using a computer model of a study reach (the lower 90 miles) <br /> <br /> <br />on the South Platte River. <br /> <br />. <br /> <br />2. The existing farm irrigation system efficiencies in the study <br /> <br /> <br />reach were evaluated using available soil and slope information, Further <br /> <br />adjustments were made by considering historical water deliveries and crop <br /> <br /> <br />requirements under each canal and reservoir system, The estimated average <br /> <br /> <br />farm irrigation efficiency before these adjustments is41 percent, ranging <br /> <br />from 31 to 50 percent at individual grid points used in the computer model. <br /> <br /> <br />3. Estimates of existing canal and reservoir system efficiencies <br /> <br /> <br />were obtained from canal and reservoir company personnel and other indi- <br /> <br /> <br />viduals knowledgeable in the study area. The delivery efficiencies of the <br /> <br /> <br />systems vary considerably, but most are in the 60-80 percent range. One <br /> <br /> <br />system delivers less than 30 percent of the water it diverts from the river, <br /> <br /> <br />but most of the losses from the system are recovered by downstream ditches <br /> <br />and wells. <br /> <br />4. Costs of improving farm and canal system efficiencies were esti- <br /> <br /> <br />mated. The cost of raising the average farm irrigation water-use efficiency <br /> <br /> <br />from 41 percent may be only a few dollars per acre per year if done by <br /> <br /> <br />improving management techniques. The cost of further increasing the average <br /> <br />. <br /> <br />-56- <br />