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<br />IRRIGATIO~ DELIVERY <br /> <br />The irrigation del ivery figures are based on the diversion records for the <br /> <br /> <br />Keesee Ditch for the period from 1950 to 1980. These diversion figures are <br /> <br /> <br />tabulated on Table I, and average 4,454 acre-feet per year. These are the <br /> <br /> <br />amounts of water that were actually delivered at the headgate of the Keesee <br /> <br />Ditch under the Keesee Ditch priorities. <br /> <br />In order to determine if the amount of water being diverted had changed <br /> <br /> <br />appreciably at any time during the period from 1950 to 1980, we constructed a <br /> <br /> <br />mass diagram of the actual amounts diverted from 1930 to 1980. This is depicted <br /> <br /> <br />in Figure 3. A mass diagram is simply a continuous summation of the annual <br /> <br /> <br />diversions in all previous years. Such a diagram masks the fluctuations in <br /> <br /> <br />individual years, and makes it possible to determine any trends in the diversion <br /> <br /> <br />amounts. As can be seen from Figure 3, the diversions have remained constant. <br /> <br />Not all of the water that is diverted from the river is available for use <br /> <br /> <br />by the crop, A certain portion is lost to seepage from the ditch, seepage in <br /> <br /> <br />the field, and evaporation. The ratio of the amount of water available for use <br /> <br /> <br />by the plant, to the amount diverted at the ditch headgate is referred to as the <br /> <br /> <br />irrigation efficiency. Because the Keesee Ditch begins delivering water to the <br /> <br /> <br />cropland immediately below where it is diverted from the river, it has a high <br /> <br />irrigation efficiency. An efficiency of 70% was determined in an investigation <br /> <br /> <br />conducted in 1968 ("Water Legislation Investigations for the Arkansas River Basin <br /> <br /> <br />in Colorado" by W. W. Wheeler & Associates and Woodward-Clyde & Associates). <br /> <br /> <br />This figure is consistent with our experience in this regard and was therefore <br /> <br /> <br />used in our analysis. <br /> <br />Applying the 70% efficiency figure to the total average diversions for the <br /> <br /> <br />period 1950 to 1980 results in a figure of 3,118 acre-feet for the average irri- <br /> <br /> <br />gation delivery or amount of water available for use by crops under the Keesee <br /> <br /> <br />Oitch. The moisture retention capacity of the soil on the land irrigated by the <br /> <br /> <br />Keesee Ditch is quite high. Therefore, the irrigated crops can draw on that soil <br /> <br /> <br />moisture at times when there is not water being del ivered by the ditch. Likewise, <br /> <br /> <br />when there is excess water del ivered by the ditch, that water is stored in the <br /> <br /> <br />soil for use by the crop some time later. Consequently, it is not necessary for <br /> <br /> <br />the ditch del iveries to be timed exactly with the crop requirements. <br /> <br /> <br />- 2 - <br /> <br />'. <br />