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<br />104,'i <br /> <br />HEADGATE DIVERSIONS <br /> <br />Reasonably accurate records of headgate diversions by the Oxford <br />Farmers Ditch are available for many years. However, records for years prior <br />to 1949 are not strictly comparable to those obtained since because of changes <br />in methods of water administration brought about by the Arkansas River Compact. <br />Therefore, this study has been based on the 22-year period 1949-1970. Table I <br />is a tabulation of headgate diversion records for this period. Data are tabu- <br />lated on the basis of the "compact year" which begins November 1 and ends the <br />following October 31, thus including the entire irrigation season. Subtotals <br />are shown for the November to March winter storage period and for the April to <br />October irrigation season. <br /> <br />It may be noted from Table 1 that average compact year diversions <br />for the 22-year period total 23,700 ac-ft (acre-feet), of which 4,130 ac-ft are <br />diverted for winter irrigation and stock water during the period November <br />through March. Historic diversions during the April through October irrigation <br />season have ranged from a low of 8,890 ac-ft in 1954 to 27,110 ac-ft in 1951, <br />and the average is 19,570 ac-ft. <br /> <br />Figure 1 is a plot of the 5-year moving average of irrigation season <br />diversions for the years 1949-70. It should be noted that the trend is slightly <br />downward. The reason for this is not apparent. Figures I-A and I-B are plots <br />of the 5-year progressive average of monthly headgate diversions. The downward <br />trend noted in Figure 1 is evident for the months of June and July, but is less <br />pronounced in May. However, the trend for September diversions is very defi- <br />nitely upward. This suggests that September streamflow at the Company's head- <br />gate has not been reduced because of pumping from wells. <br /> <br />Records of monthly diversions are not sufficient to determine the <br />adequacy of a water supply for irrigated land, so records of daily diversions <br />were analyzed on a frequency basis and Figure 2 was prepared. This figure shows <br />the percent of time during an average irrigation season that varying amounts of <br />water have been available. The important point to note is that for 60% of the <br />time between April 1 and October 31 the surface water supply available to the <br />Company has been less than 20 cfs. This amount of water is quite obviously an <br />inadequate supply for irrigating 6,000 acres of land as it would provide a <br />seasonal headgate supply of only 1.43 ac-ft per acre. The second decree is a- <br />vailable in full only about 10% of the time. About 30% of the time the diversion <br />rate is somewhere between 14 and 130 cfs. Although Figure 2 shows that the <br />Company diverts no water 7% of the time, this is largely due to sluicing opera- <br />tions or headgate and ditch repairs rather than to non-availability of the first <br />decree. <br /> <br />In July 1968, a gaging station was established by the Colorado Water <br />Conservation Board at the outlet end of the Oxford Farmers Ditch to measure and <br />record the hitherto unknown spill to the Apishapa. Significant spillage usually <br />occurs when the ditch is diverting at rates in excess of 75 cfs, but substantial <br />spills at lower flows are not uncommon, particularly during the non-irrigating <br />season. When the ditch is diverting both decrees amounting to 129.4 cfs, spills <br />have been as high as 42 cfs. During the 1969 irrigation season, spill to the <br />Apishapa totaled 4,350 ac-ft or about 22% of the total headgate diversion. Dur- <br />ing the 1970 irrigation season the spill amounted to 5,920 ac-ft or 24% of the <br /> <br />- 4 - <br />