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I I I I I I I I I I I I I I I I I I I MAXIMUM IRRIGATION EFFICIENCY By co~bining the two components of irrigation efficiency discussed above, monthly estimates of the maximum irrigation efficiency were made for the Keesee Ditch system and are included in Table B-2. These estimates reflect a seasonal variation in irrigation efficiency, with a peak in efficiency in mid-summer and a significantly reduced efficiency in the winter months. As previously discussed, the maximum irrigation efficiency determines the maximum potential water availability and is reached only under water-short conditions. The actuai efficiency and resulting consumptive use of irrigation water are also a function of other factors such as diversions, irrigation water requirements, and soil moisture conditions. OTHER DITCHES As a,comparison to the calculated irrigation efficiency for the Keesee Ditch, measured and calculated efficiencies for two other Arkansas River ditch systems, the Colorado Canal and the Ft. Lyon Canal, were examined. Information primarily on delivery efficiencies were available from engineering reports performed in connection with Change of Water Rights Case Nos. 84CW62, 63 & 64 for the Colorado Canal and Case No. 79CW178 for the Fort Lyon Canal. Colorado fill!.!!.! The Colorado Canal engineering report Colorado Ganal, Lake Meridith and Lake Henry Wheeler & Associates, dated October, 1985. Colorado Canal seepage losses under varying seepage losses for canal laterals. was entitled "Final Report Change of Water Rights" by W.W. This report included measured diversion rates and estimated Seepage measurements made for various diversion rates and lengths of the approximate 53-mile main canal ranged between 10 and 27 percent of the headgate diversions. Focusing on the canal segments adjacent to the Arkansas Ri vel' as 'being most similar to Keesee Ditch conditions, the seepage loss averaged about 0.6 percent per mile, with a range between 0.4 percent and 0.9 percent per mile. As a comparison, the calculated seepage loss for the Keesee Ditch at the example diversion rate of 13.5 cfs and 6.0 miles of system in use would be about 1.5 percent per mile. The Cplorado Canal report also included estimates of the seepage losses for laterals within the Colorado Canal System. These seepage loss estimates are illustTated on the attached Figure 2 (from W.W. Wheeler, 1985). Seepage loss is given in percent as a function of percent lateral capacity and represents an upper limit of potential seepage for use as a method of seepage accounting under future administration of the ditch system for non- agricultural uses. Given the size of the Colorado Canal system (47,000 irrigated acres) relative to the Keesee Ditch, the seepage estimates made for the Colorado Canal laterals probably provide a better comparison to Keesee Ditch conditions than the se~page measurements for the main canal. The Colorado Canal report includes an: example seepage calculation for a lateral diversion at 80 percent 5