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Show 1374 CONSUMMIVE USE OF WATER IN IRRIGATION Meeker's Valley Consumptive Use Studies in Colorado.-Meeker has conducted investigations concerning consumptive use in several typical valleys in Colorado and has also assembled and compiled data for other valleys. His analyses were made with the viewpoint of determining the net depletion of river water by irrigated lands either naturally or artificially drained. Wasteful evaporation from seeped areas, therefore, was excluded as a form of consumption. Re-use of seepage or return waters and water recovered by drainage systems within an area were automatically included and served to decrease the burden on the original river flow. Large irrigated areas were used and records of stream flow were considered of from 5 to 10 years to eliminate minor irregularities of climatic and variations in crops in irrigated lands. The crop-year draft on soil moisture and the water drawn from ground-water sources, being, respectively, Factors (&) and (d) of Hv in Equation (7), were not evaluated in Meeker's studies. The values of the valley consumptive use reported herewith, therefore, may be slightly smaller than the actual magnitudes of consumptive use in the respective valleys. Unpublished records supplied the Committee by Meeker contain interesting data concerning gross and net duty of water in 18 river systems, and on 9 of these consumptive-use data are available. The observations on these 9 systems are reported in Table 7. It will be noted in Column (9) of Table 7 that the consumptive use, defined as dimunition in stream flow, varied from 0.9 acre-ft. per acre per year in the Little Laramie River Basin to 1.3 acre-ft. per acre per year in the Sevier River Basin and on the Boise Project. Column (9a) which has been added to Table 7 by the Committee, gives the valley consumptive use as here defined, with the exception noted that there are no measurements of draft on soil moisture or ground-water. Assuming the seasonal draft on soil moisture and ground-water to be 0.3 acre-ft. per acre, as was assumed for the Sevier River Basin, then valley consumptive use varies fnom 1.5 to 2.2 acre-ft. per acre for the river basins reported in Table 7. Investigations of the return flow on the Cache la Poudre and South Platte River by Meeker (13) and on the Lower South Platte by Parshall (15) give further evidence concerning consumptive use. In a resume of factors affecting return flow, Meeker places the consumptive use (not including crop-season rainfall or draft on soil moisture) at 1.25 ft. and reports that from 35 to 65% of waters diverted for irrigation appear as return flow in the Colorado streams mentioned. Meeker's conclusion, based on rather extensive investigations, is as follows: "The conclusion from these studies and from comparisons with the natural return flow from large older irrigated areas is that the amount of water actually consumed by crops is relatively small compared with the amount diverted, and further that with efficient drainage on an irrigated project, the actual plant consumption has decidedly low limits regardless of the water applied." Discussion It has been pointed out that many independent factors influence the valley consumptive use. However, there is urgent need for arriving at some relatively simple method of estimating its magnitude. Therefore, in order further |