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1 <br />'• Water Budget <br />The consumptive irrigation requirement is an ideal requirement. Many times the <br />irrigation system does not deliver sufficient water to meet the crop needs. It is necessary to <br />simulate the irrigation practices using a water budget procedure and determine if all or only <br />' apart of the consumptive irrigation requirement was provided. The water budget uses the <br />consumptive irrigation requirements, the diversion records, irrigation system efficiency, and <br />water holding capacity of the soil. The water delivered monthly to the crop root zone that is <br />' surplus to the consumptive irrigation requirement is stored in the root zone for use at times <br />when the delivery is insufficient to meet the consumptive irrigation requirement. Water <br />delivered to the root zone in any month that is surplus to the consumptive irrigation <br />' requirement and the storage capacity, percolates through the root zone to the ground water <br />or runs off the field. The water budget operates for the entire growing season, accounting <br />for all water delivered to the crop root zone. <br />' Tailwater which is not reused will flow to Dry Creek within a few days of the diversion. <br />Water which percolates through the root zone to the ground water flows through the alluvium <br />' to the stream over many months. The timing and amount of this flow were estimated from <br />monthly factors developed from "Glover techniques" (Schroeder, 1987. <br />' The Dry Creek Ditch will continue to operate in the future so two water budgets were <br />performed. The first water budget simulated the combined operation of the Sage Creek and <br />the Dry Creek systems. As shown in Table 1 1, the combined diversions averaged 362.1 acre- <br />feet annually and the historical consumptive use averaged 224.7 acre-feet annually for 1965 <br />through 1993. <br />' The second water budget simulated the operation of the Dry Creek Ditch which is <br />summarized in Table 12. The diversions averaged 129.9 acre-feet annually and the historical <br />consumptive use averaged 71.9 acre-feet annually. <br />' The historical consumptive use associated with the Sage Creek Reservoir and Outlet <br />Ditch is the difference between the results of the two above-described simulations and is <br />shown in Table 13. The diversions averaged 232.2 acre-feet annually and the historical <br />' consumptive use averaged 152.8 acre-feet annually. The Sage Creek Reservoir Outlet Ditch <br />did not divert any water from 1985 through 1990 which significantly reduced the long term <br />averages. The historical consumptive use was prorated into direct flow and storage <br />' components by the ratio of historical diversions from each source. The historical consumptive <br />use associated with the direct flow component averaged 12.3 acre-feet annually and the <br />historical consumptive use associated with the storage component averaged 140.5 acre-feet <br />' annually. <br />' Sage Creek Reservoir Evaporation <br />An additional component of historical consumptive use is the volume of evaporation <br />' which occurred at Sage Creek Reservoir. The net evaporation was estimated by subtracting <br />monthly effective precipitation for 1965 through 1993 from the gross lake evaporation values <br />shown in Table 2 and multiplying the result by the estimated water surface area of the <br />reservoir. The water surface area was estimated from storage content records and the <br />elevation-area-capacity table shown in the original map and filing statement for the reservoir. <br />' 7 <br />