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Show 580 OTHER WATERS AT THE SURFACE bottom. Obviously, it is seldom directly measurable. For a given stream section, the nearest quantitative approximation that can be made of invisible return flow is a calculation of invisible net gain (or net loss) within the section, made by deducting the sum of all measured inflows from the sum of all measured outflows. However, all accretions to a stream within an irrigated region, even where no surface importations are evident, may not be return water from irrigation. The problem of measuring the quantity of return is often complicated by additions to the ground water supply caused by seepage into the basin from surrounding elevations and by rainfall within the basin. Likewise, excessive return flow shown by measurements taken during the falling stages of streams has been attributed partly to the release of water stored in adjacent sands during the rising stages. Return Flow Within the Watershed Western streams commonly lose water by seepage and evaporation after leaving the mountains in which they arise. Return flow from irrigation partly offsets this loss in certain localities and may completely overcome it with resulting net gains in others. The phenomenon of return flow from irrigation had early recognition in the West, chiefly in Colorado and later in other States and territories. The downstream flow of many Western streams has been augmented by seepage from irrigation of upstream lands. This is a common phenomenon in irrigated valleys, and much development has been predicated wholly or partly upon the existence of return flow. The increase in flow does not consist of new water (unless brought in from another watershed, problems of which are noted below), but is the reappearance of water previously diverted from the stream. The water may reenter the stream by natural percolation through the soil and through natural channels, or it may be gathered into and discharged through artificial drainage ditches. In any event, if there is no intent on the part of the irrigator to recapture this water, it becomes a part of the watercourse and inures to the benefit of downstream claimants in accordance with their rights to the natural flow. A number of court decisions have been rendered to this effect.83 "Fortier, S., assisted by Stover, A. P., and Baker, J. S., "Irrigation in Montana," U.S. Dept. Agric, Off. Expt. Sta. Bull. 172, pp. 96-98 (1906); Parshall, R. L., "Return of Seepage Water to the Lower South Platte River in Colorado," Colo. Agric. Expt. Sta. Bull. 279, p. 48(1922). "See, e.g., Woolman v. Garringer, 1 Mont. 535, 545 (1872); Hagerman In. Co. v. East Grand Plains Drainage Dist, 25 N. Mex. 649, 653-658, 187 Pac. 555 (1920); Marks v. Hilger, 262 Fed. 302, 304 (9th Cir. 1920); Brosnan v. Boggs, 101 Oreg. 472, 476, 198 Pac. 890 (1921); Popham v. Holloron, 84 Mont. 442, 451, 275 Pac. 1099 (1929); Las Animus Consol. Canal Co. v. Hinderlider, 100 Colo. 508, 511, 68 Pac. (2d) 564 (1937); Jones v. Warmsprings Irr. Dist., 162 Oreg. 186, 198-199, 91 Pac. (2d) 542 (1939). |
