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<br />r..c"/ <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />CfJ020R <br /> <br />must be compared with a suggested average of 41 percent for the study <br /> <br /> <br />area, when water is not limiting and nonimproved management is used. <br /> <br />Whittelsey (1977) gives a value of 44 percent for the South Platte River <br /> <br /> <br />Valley. <br /> <br />(2) Existing system, improved management, additional labor <br /> <br />This scenario requires irrigation labor, in addition to improved <br /> <br /> <br />management, and allows the farmer to increase surface irrigation effi- <br /> <br /> <br />ciencies through cutback flows on row crops, However, the estimated <br /> <br /> <br />increase in efficiency brought it only to 68 percent. This does not meet <br /> <br /> <br />the level indicated in the Series III-B model runs, i.e., 75 percent. <br /> <br /> <br />Additional improvement is needed, <br /> <br />(3) Improved system, improved management, additional labor <br /> <br />No calculated attainable efficiencies are given by the Bureau (USDI, <br /> <br /> <br />1970) for this level of improvement, However, it is expected to include a <br /> <br /> <br />complete tailwater reuse system with a concrete-lined pond, a pipe convey- <br /> <br /> <br />ance system, and gated pipe for delivery to furrows, or a totally enclosed <br /> <br /> <br />automatic surface irrigation system with an underground conveyance system <br /> <br />and vertical risers to gated pipe, in conjunction with a reuse system and <br /> <br /> <br />soil-moisture sensing devices, or a mechanized sprinkler system. <br /> <br />The writer's experience indicates that in reality most farms in <br /> <br /> <br />the study area obtain improved performance by going to a reuse system or <br /> <br /> <br />center-pivot irrigation. The reuse system usually consists of an unlined <br /> <br />pond, plus a pump and pipeline to the upper end of the field. As the <br /> <br /> <br />result of conversations with the experts mentioned in an earlier portion <br /> <br /> <br />of this report it was concluded that center pivots operated with the <br /> <br /> <br />benefit of a modern management system would average about 63 percent field <br /> <br /> <br />irrigation efficiency, Those operated under an irrigation scheduling <br /> <br /> <br />program--one that determines the time and amount of water to apply based <br /> <br /> <br />upon monitoring crop use--would have a field irrigation efficiency of <br /> <br />about 83 percent. <br /> <br />I <br />I <br /> <br />For the purposes of the cost estimate it is assumed that the 75 percent <br /> <br /> <br />farm irrigation system efficiency could be met in the study area if half <br /> <br />-51- <br />