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Show 1362 consumptive use of water in irrigation Project Consumptive Use It is important to remember that farm and project consumptive trse in general are likely to be, respectively, equal to or greater than the consumptive use, and also that during the early years of irrigation the difference between these quantities is likely to be greater than after many years of farming under the canal. The following are examples of some approximations of project consumptive use. Steward's Idaho Work.-In the Boise Yalley, Idaho, in connection with drainage operations, Steward (20) found project consumptive use on the Pioneer District Drainage area (approximately 13 500 acres) by subtracting the drainage run-off from the sum of the rainfall plus the irrigation water applied, a difference of 2.13 acre-ft. in 1916 and 2.18 acre-ft in 1917. On the Twin Falls South Side Project, in 1915, Sloan (20) found, by working on a 12 000-acre tract, a project consumptive use of 2.95 acre-ft. Steward and Paul (21) made a careful study of sources and disposition of water on the Nampa Meridian Drainage Districts in 1917. These investigators found on the Mason and Indian Creek tracts, having an area of approximately 50 000 acres, a transpiration plus evaporation of 1.9 ft. from April to October, inclusive. The factors of supply, Ep, of Equation (5) were as follows : (a) The inflow consisted largely of irrigation water and was 4.16 acre-ft. per acre; (6) the draft on soil moisture was neglected, probably without greatly influencing the results; (c) the absorption from the ground-water was not estimated; and (d) the crop-season rainfall was 0.36 ft. The factors in project run-off of Equation (5) were measured as follows: (a) Run-off was measured at all drainage outlets, and amounted to 2.02 acre-ft. per acre; (6) the deep-soil percolation losses were measured by making direct observations on water-table fluctuations and amounted to 0.60 acre-ft. per acre; and (c) the deep-soil percolation losses which re-appeared at the boundaries of the project, were measured as waters commingled with those in Factor (a). Applying Equation (5), the approximate project consumptive use, Up = (4.16 + 0.36) - (2.02 + 0.60) = 1.90. A complete report of the work of Steward and Paul is beyond the scope of this report. CrandalVs Snake River Valley Work.-Crandall (1) measured consumptive use in the Lower Snake River Valley. He considered an irrigated area of nearly 90 000 acres in 1917 and of more than 100 000 acres in 1918. Using three different methods, he obtained close agreement. These methods were: 1.-Measurement of percolation losses from the irrigated land by finding the annual increase in discharge of springs below the tract. 2.-By making soil moisture determinations before and after irrigations. 3.-By computations from water-requirement studies under somewhat similar climatic and soil conditions. A brief review of each method and of the results obtained are given as follows. 1.-Crandall's Measurement of Percolation Losses The normal annual discharge of the springs as determined by measurements for a period of 5 years prior to irrigation was 3 885 sec.-ft. By allow- |