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<br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />I ___ <br /> <br />the St. Vrain Basin Reconnaissance Study published by the Colorado Water <br />Resources and Power Development Authority. According to this study over a 30 <br />year period, a combined cropping pattern of alfalfa, corn and grain consump- <br />tively uses an average of 18.41 inches of irrigation water (taking effective <br />precipitation into consideration). Assuming a 50% irrigation efficiency, the <br />total water requirements would be approximately 37 inches, or about 3 acre-feet <br />per acre. This cropping pattern is representative of the crops grown by Ish <br />Reservoir stockholders. Projecting these irrigation requirements onto the <br />acreage under Ish Reservoir indicates that approximately 46,500 acre-feet of <br />water are required annually to meet theoretical irrigation needs of 15,500 <br />acres. With respect to conveyance losses, the ditch rider estimates 3.5%. This <br />estimate is based on measurements of water taken at the flume as the water <br />leaves the reservoir compared with measurements taken at the lower end of Mr. <br />Robinett's jurisdiction. The gauging station at the lower end is located east <br />of Thomas Reservoir and west of the confluence of Mead Lateral with New Ish <br />Ditch (see map on p. 11,). The station has a measuring flume and a recording <br />device that graphs the flow throughout the irrigation season. <br />Obviously, the irrigation requirements plus conveyance losses are many <br />times more than the c~pacity of the Ish Reservoir. Ish Reservoir water is used <br />in combination with other sources to meet the irrigation needs of the crops. <br /> <br />B. Surface Water Supply <br />1) Diversion Records <br />Ish Reservoir fills through the Ish Inlet Ditch (capacity approximately <br />220 cfs) which diverts water from the Little Thompson River in Section 1, <br />T3N, R70W. Colorado Big Thompson project water also comes through the Ish <br />inlet and can go into the reservoir or bypass the reservoir through a <br />headgate constructed for that specific purpose. There ar~! two more outlet <br /> <br />-16- <br /> <br />, <br />I <br />I <br />.jt <br /> <br />L. <br /> <br />I <br />j L . <br />