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-6- <br />• study conducted within the Trout Creek Basin within the Yampa <br />River Basin, southwest of North Park. Table 2 summarizes the <br />consumptive use computations using average precipitation and <br />temperature data. <br />The annual consumptive use of 1.73 feet, shown in Table 2 <br />represents the quantity of water that must be available to <br />the crops to support adequate growth during the full growing <br />season. Examination of the monthly irrigation consumptive use <br />in Table 2 shows that water must be provided through <br />September, and since the majority of the runoff for surface <br />flow is available in May, the need for carry-over storage is <br />apparent. <br />To determine the quantity of water that must be diverted to <br />the crop to satisfy the consumptive use demand, it is <br />necessary to establish an irrigation efficiency, which is the <br />• ratio for the consumptive use to the amount diverted and <br />which reflects the losses incurred in delivery and to deep <br />percolation. Irrigation efficiencies can range from 10 to 60 <br />percent. In a study of recorded diversions and consumptive <br />use data for a number of ditches located in the Trout and <br />Middle Creek watersheds in Routt County, a wide range of <br />irrigation efficiencies was indicated. The overall average <br />irrigation efficiency was 38 percent and reflected the fact <br />that the ditches were all operated under direct flow <br />irrigation rights with no supplemental storage. <br />For a system of direct flow diversions, supplemented by <br />storage as envisioned for this study, an irrigation <br />efficiency of 50 percent is considered realistic and was <br />adopted to determine the irrigation water requirements. <br />• <br />)C ~ Leonard Rice Consulting Water Engineers, Inc. <br />