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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />surface width in the ditch system under normal operations was about 3.5 to 4.0 <br />feet, with the main ditch a little wider (about 5.0 feet) and some of the <br />field laterals less. <br /> <br />Utilizing Mr. Broyles' description of ditch operations, the ditch system <br />was subdivided into individual components, including the main ditch, the three <br />main laterals and individual field laterals. Distance measurements of these <br />components were made from aerial photographs and weighted according to the <br />irrigated area served. This analysis resulted in a weighted mean ditch <br />distance to a single field of about 15,000 feet (2.8 miles), of which 6600 <br />feet (1.2 miles) was along the main ditch and the remainder in laterals. <br />Utilizing this mean single field distance, lengths of ditch system in use and <br />corresponding surface areas were estimated for various rates of diversion <br />using the following assumptions: <br /> <br />- One field irrigated for each 3 to 4 cfs of diversions. <br /> <br />For three or less fields, ditch distance corresponds to the <br />average single field distance x number of fields. <br /> <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 />- For higher diversion rates and more than three fields irrigated, <br />there is increasing overlap in ditch usage and the average single <br />field distance relationship becomes less applicable. <br /> <br />For the normal <br />assumed to average <br />all laterals. <br /> <br />range of diversions water surface <br />5.0 feet for the main ditch and 4.0 <br /> <br />width <br />feet <br /> <br />was <br />for <br /> <br />For higher diversion rates, the average surface width was <br />increased. <br /> <br />For example, at a typical diversion rate of 13.5 cfs, three or four <br />fields would be under irrigation. Assuming that the total length of the main <br />ditch were in use (6600 feet) with an average width of 5.0 feet, the <br />calculated surface area for this component would be about 33,000 square feet. <br />With four fields being irrigated, and overlap in the use one of the main <br />laterals, a reasonable estimate of the length of laterals in use could be <br />obtained by multiplying the average lateral distance by three, for a total of <br />about 25,000 feet. Using an average width of 4.0 feet, the lateral surface <br />area would be about 100,000 square feet, or a total of 133,000 square feet <br />including the main ditch. <br /> <br />Determination of Ditch Seepa~e <br /> <br />Combining the unit seepage rate of 0.685 ft/day with the estimated ditch <br />water surface area of 133,000 square feet for the example diversion rate of <br />13.5 cfs, the calculated seepage would be 1.05 cfs. This corresponds to a <br />seepage loss of 7.8 percent, or a delivery efficiency of 92.2 percent. This <br />methodology was applied for different rates of diversion and the resulting <br />seepage estimates in terms of actual seepage in cfs and as a percent of <br />diversions are graphed on Figure B-1. <br /> <br />As a method of addressing the question of seasonal variations in <br />efficiency, monthly ditch seepage and delivery efficiency estimates were <br /> <br />ditch <br />made <br /> <br />3 <br />