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002330 cHAPrER III PROJECT DEVELOP~:ENT (Hayden l,lesa unit) . some of the lands in the eastern part of the area have poor drainability and would become seeped with irrigation. Soils throughout the area are moderately calcareous and have good water-holding capacity. Despite the prevai~ing semiarid climate, they ~ntain sufficient organic material for successful crop production. A~kalinity is low. Some salinity occurs in valley bottoms and other ~ow-lying areas, Land use is influenced to a marked degree by climate, The averar;e frost-free period is 9~ days and the average irrigation season is 127 days, Precipitat:i.on averages ~6 inches annually, 5 to 6 inches of which usually occurs from early ~EY to mid-September, Nonirrigated lands in the unit area are devoted mainly to the produc- tion of dry land wheat while those with a partial irrigation supply produce alfalfa, small grains, and pasture. With adequate irrigation provided by the Hayden l<\esa unit, dairying is expected to be the main farm enterprise, In support of the dairy industry crop lands would, as at present, be devoted to alfalfa, small grains, and pasture, Some other types of farm- ing would probably be practiced in the area but these are expected to be of minor importance. . Water supply With development of the Hayden Mesa unit, irrigation supplies for the unit lands would be increased by an average of 65,905 acre-feet ~~ually at the heads of the main canals. to'nst of this increase, 65,650 acre-feet annually, would be supplied to the full service lands and the remaining 255 acre-feet annually would be supplied to the supplemental service lands. The total supply would average about 94.1 percent of ideal requirements. Stream depletions resulting from the unit would average about ~2,200 acre- feet annually. Repayment According to this preliminary appraisal, water users on the Hayden Mesa unit could pay only about $58,520 each year towards unit costs. At this rate they 'WOuld fal~ short of meeting annual operation, maintenance, and replacement costs by about $5,280 and could pay nothing towards con- struction costs. Benefit-cost analysis . Irrigation benefits of the Hayden Mesa unit would compare with the average annual equivalent costs in a ratio of about ~ to 1. The benefits are expected to amount to $460,900 annual~y, including direct benefits of $2~8,6oo, indirect benefits of $88,600, and public benefits of $1:;3,700. The average snnual equivalent costs would amount to $474,600 as shown in the tabulation on the following page. ~3