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MAY 1982 at the deeper natural drainages that ultimately convey return flows back to the river system. Flow in these drains occurs near the groundwater level, so essentially no seepage losses occur. Volume of seepage and deep percolation, determined for each of six drainage areas, was used to calculate the salt load. Although average deep percolation is about 0.3 acre-feet per acre per year, the salt load froD these areas ranges from 1.8 to 3.8 tons per acre per year. This range in salt loads suggests examining the potential salt load reduction from each drainage area to determine priorities for treatment. WATER SUPPLY MANAGEMENT Total crop irrigation requirement is estimated to be 54,OUO acre-feet per year or about 1.8 acre-feet per acre. Present seasonal net irrigation is estimated to be 47,000 acre-feet, about 87 percent of the total requirement. Present farm delivery, estimated to be about 107,000 acre-feet, averages 3.7 acre-feet per acre and is 1.9 acre-feet per acre more than is required. Much of the excess water delivered to the farm contributes to salt loading from the irrigated land. WATER HUDGET ANALYSIS Irrigation water diverted from the Dolores River is transported through a network of canals and laterals to the farms. Evaluation of transmission losses occurring through seepage, evaporation, transpiration and spillage from the Hontezuma Valley Irrigation Canal System have been evaluated by the Bureau of Reclamation. Analysis indicates that of the water diverted for irrigation, about 107,000 acre-feet ultimately reaches the farms and present estimated onfarm irrigation efficiency averages about 45 percent (See Table IV-2). Irrigation water, classified by components related to the irrigation process, is defined as follows: (1) Seepage - Water losses from the off-farm and the onfarm supply field head ditches and tailwater return flows. an9 1 87 :. r: (~. J, IV-6 .. H" ..... ,- '.0'" '-b~., ".~;;:",.~:.