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I I I I I I I I I I I I I I I I I I I 0672 Water from these supplemental sourceS has amounted to an annual average of 1,210 acre-feet during compact years 1949-73, as shown on Table 3. Estimates of the acreages of crops grown under the Catlin Canal were made using data published for otero County in "Agricul- tural Statistics, 1971." The percentage that each irrigated acreage was to the total in the county was applied to 18,660 acres to obtain the following values for crops under the Catlin Canal: Corn 32.79 percent 6,120 acres Grain sorghums 12.62 percent 2,350 acres Alfalfa 43.62 percent 8,140 acres Sugar beets 6.58 percent 1,230 acres Winter wheat 4.39 percent 820 acres As part of its investigation for the Fryingpan-Arkansas project, the USBR inspected the major irrigation systems in the Arkansas Valley and estimated irrigation efficiencies. For the catlin system, the estimates were as follows: Canal losses Lateral losses On-the-farm losses 20 percent 10 percent 25 percent These figures would combine (0.80 x 0.90 x 0.75) to form an overall system efficiency of 54 percent. This efficiency corre- sponds to average conditions, and it would actually increase during dry years and decrease during wet years. consultation with representatives of the U.S. Soil Conservation Service (SCS) indicated that these figures are reasonable. The USGS has developed a digital-computer model technique that provides an estimate of return flow under the Catlin system. It computes the percentage of applied irrigation water and pre- cipitation that recharges the groundwater aquifer. The Arkansas River Valley from Pueblo to the state line was modeled by divid- ing the river into seven reaches and by calibrating with his- toric data during 1964-68 including streamflow, irrigation diversions, groundwater withdrawals by wells, and precipitation. Recharge for the reach encompassing the catlin system was 23 percent. This figure is not strictly identical to return flow -12-