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<br />.. O~ 1877 <br />'. <br /> <br />Much of the irrigation water supply comes from spring snowmelt <br />or frOll\ brief summer rains in such magnitudes that for short periods the <br />supply exceeds the irrigation requirement. At other times only the most <br />senior water rights receive water. Usually only a small portion of the <br />water needed late in the growing season is available. The Trinidad <br />Project through storage of water will, to a great extend, regulate this <br />very erratic water supply. When water is available in Trinidad <br />Reservoir for use later in the season irrigation in excess of the crop <br />requirement will be uneconomical and unnecessary. <br /> <br />The Bureau of Reclamation has determined the average annual crop <br />requirement as shown below: <br /> <br />Item <br /> <br />Consumptive use requirement of crops a/ <br />Less effective precipitation - <br />Crop irrigation requirement <br />Add farm losses (30~) <br />Farm deli very requirement <br />Add canal and lateral losses (3~) <br />Diversion requirement at main canal <br />headgates <br /> <br />Acre-feet <br />per acre <br /> <br />Project total <br />(19,717 acres) <br /> <br />2.30 <br />0.78 <br />1.52 <br />0.65 <br />2.17 <br />0.93 <br />3.10 <br /> <br />61,200 <br /> <br />!I Computed by Lawry-Johnson method <br /> <br />This average requirelOOnt of 3.1 acre-feet per acre will, of course, vary <br />from year to year. The project operating principles provide that the <br />conservancy district board determine the crop requirement for each <br />year and for variations within the irrigation season. Historically, <br />the project has diverted 53,200 acre-feet per year. In the past the <br />effectiveness of these diversions has been limited. No storage facilities <br />have been available except to the Model system. Consequently, users with <br />direct flow rights have diverted water when it was available in the stream <br />regardless of whether or not it could be efficiently used. With the <br />project, such water can be stored for later use. Severe depletion of <br />storage space in the Model Reservoir by sedimentation has increased the <br />uncertainty of water supply to the Model lands. The historic operation <br />study showed that of the 53,200 acre-feet diverted annually, only 71 <br />percent ~r 37,300 acre-feet have been diverted to coincide with actual <br />crop requirements. Of the 15,900 acre-feet inefficiently used, 9,300 <br />acre-feet were diverted in the winter time and 6,600 acre-feet during <br />the irrigation season in excess of crop requirements. Although part <br />of this water did some good in building up the soil moisture content, <br /> <br />4 <br />