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<br />Monthly runoff records of the stream gaging station, "Chinle Creek <br /> <br />near Mexican Water, Arizona," are shown in Table 4. This station measures <br /> <br />~ <br /> <br />runoff from 3,300 square miles (contributing area), which is about half of <br /> <br />N <br />~ <br />= <br /> <br />the study area total. Runoff during 1973 was 34,670 acre-feet, which is 260 <br /> <br />percent of the 9-year average and the highest annual runoff on record. <br /> <br />Irrigation Consumptive Use <br /> <br />In the Arizona portion of the Upper Colorado River Basin there are <br /> <br />26 Navajo Indian irrigation projects, 22 of which have been developed. <br /> <br /> <br />(In addition, there is a 40-acre non-Indian development at Lees Ferry.) <br /> <br />About 16,000 acres of land associated with the irrigation projects have <br /> <br />been classed as irrigable, with nearly 11,000 acres being presently under <br /> <br />ditch. There are large year-to-year variations in the irrigated acreage and <br /> <br />cropping patterns due mainly to the variability of the. water supply. <br /> <br />The Bureau of Indian Affairs issues an annual land. use inventory and <br /> <br />production record report. The irri~ated acreages and cropping patterns <br /> <br />reported for 1973 are presented in Table 5. Total irrigated acreage was <br /> <br />estimated to be about 3,400 acres. This represents only about one-quarter <br /> <br />of the lands under ditch. <br /> <br />There are no records of reservoir storage, diversions, or return flow <br /> <br />that could be used to compute consumptive use on an inflow-outflow basis. <br /> <br />Consequently, it was necessary to estimate the. historical irrigation <br /> <br />consumptive use by first computing the theoretical potential irrigation <br /> <br />consumptive use, then.adjusting these values to compensate for a less than <br /> <br />adequate water supply. The potential irrigation consumptive use was <br /> <br />computed using the Blaney-Criddle formula. Computed values are shown in <br /> <br />Table 5. <br /> <br />~ <br />