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PART VI FUTURE DEVELOPMENT e f. Navajo Indian Irrigation Project Various estimates for projected agricultural use deple- tions have been prepared, including the studies for the all-sprinkler lrrigation system for the Navajo Indian Irrigation Project prepared by the Southwest Region of the Bureau of Reclamation. This study estimated agricultural consumptive use of 226,000 acre-feet. Several other esti- mates have been made, and a 5-year field study to determine actual con- sumptive use on the project was begun in 1978 and recently concluded. Recent technical estimates reported by the Secretary of the Department of the Interior Report, Economic Study, May 1980, are 254,000 acre-feet for agricultural depletions. In November 1981 it was concluded and agreed by the Assistant Secretary, Department of the Interior, Land and Water Resources, and Assistant Secretary, Department of the Interior, Indian Affairs, that the productive acreage of the project should be 110,630 acres, rather than the lOS, 000 acres which had been assumed in the past. Correspondingly, the annual depletion estimate has been re- vised from 254,000 acre-feet to 267,000 acre-feet. e The first block of land (about 9,300 acres) was irri- gated in 1976. In 1983, Blocks I through 5 were in production. Histori- cal net diversion from Navajo Reservoir in 1983 was 128,523 acre-feet, rounded to 129,000 acre-feet for the report. To date only small amounts of return flow from the project have been observed. It has, therefore, been assumed that the depletion of river flow is, as yet, very nearly equal to the water diverted from Navajo Reservoir. Return flow to the river will increase as deep percolation from irrigation charges the aquifer. It was originally expected that water deliveries could be made to Blocks 1 through 9 by 1990 and to the remaining blocks by 2000. Recent funding constraints have delayed development of the project, but if funding were restored, it is assumed that up to one additional block could be developed each year. Based on this assumption, Table A shows a 208,000-acre-foot depletion in 1990 and the full 267,000-acre-foot depletion in 2000. g. Hammond Project The New Mexico Interstate Stream Commission estimates that depletions on the nearly fully developed Hammond Project currently average 8,000 acre-feet a year and that fully developed depletions of 10,000 acre-feet a year will be occurring by 1985. h. Hogback Expansion e Minor increases in depletions are expected to occur be- tween now and 1990. Studies are underway by the Bureau of Indian Affairs and the Navajo Tribe to determine additional water requirements in this area. Present uses are estimated to be 5,000 acre-feet a year, with a projected ultimate level of 10,000 acre-feet a year by 1990. 37