right or privilege is usually acquired either by priority of use or by purchase. In an arid region, where so much depends upon the supply of water, a water right is a very valuable property. See Hydrography; Water-Supply.
Fig. 15. DIVISION BOX.
Quality of Irrigation Water. The character of the water available for irrigation purposes is a matter of great importance. All natural waters carry more or less organic and mineral matter in suspension or solution, and thus furnish, in addition to the water so necessary for the growth of plants, a certain amount of fertilizing matter. Waters carrying a large amount of soluble matter should, however, be used with caution, since they may cause the accumulation of alkali in the soil in injurious amounts. Of the waters available for irrigation, sewage is most valuable on account of the fertilizing matter carried to the land. Sewage irrigation is practiced with success in Great Britain and on the Continent of Europe, notably on the Craigenlinny meadows, near Edinburgh; at Gennevilliers, near Paris; in the vicinity of Berlin; at Milan, Italy; and also at a number of places in the United States.
Laws and Institutions. The development of irrigation in the Western United States has given rise to many complex legal, economic, and social problems. This has resulted from lack of uniform laws regarding ownership, control, and distribution of the water-supply and uncertainty as to State and Federal jurisdiction. These complications become acute, for example, when, under State laws, all the water of a stream is absorbed for irrigation purposes, and the Federal courts assert the paramount importance of riparian rights and the protection of navigation, regardless of the use of the water in irrigation. Again serious complications arise when a stream crosses the boundaries of two or more States and each claims all the water flowing on its soil, as well as when the sum of the individual claims largely exceeds the amount of water available.
There is a strong popular demand in the West for public aid in the construction of irrigation works too large for private capital and enterprise to undertake, especially for the building of reservoirs for the storage of water, as is done, for example, by England in Egypt and India, where the largest irrigation works in the world are being built by the British Government. Another matter of vital importance in connection with irrigation is the protection of the forest growth of the watersheds of the streams, with a view to mitigating floods and securing a more uniform flow of the streams. The importance of this matter is beginning to be realized, and steps are being taken to protect the forests of these watersheds from the wanton destruction to which they have been subjected in the past. The practice of irrigation has given rise to many interesting economic and social conditions. Among other things it has been productive of small proprietors and diversified and intensive farming; it furnishes admirable training in self-government and encourages coöperation; and has removed the evils of isolation in farm life by making possible the building of homes in village centres, thus realizing a happy combination of town and country life.
Irrigation in Humid Climates. Supplemental irrigation to carry crops through periods of drought has been found profitable in many cases in humid regions, especially on light, well-drained soils and with crops of high value. To what extent the practice may be extended with advantage has not been definitely determined. The rainfall of such regions is a disturbing factor. If a heavy rain occurs soon after a thorough irrigation, more serious damage may be done by excess of water than would have resulted from drought, especially if the soil be compact and poorly drained. Irrigation should therefore be attempted in such regions only on soils provided with thorough natural or artificial drainage.
Bibliography. The more important literature relating to irrigation includes publications of the United States Department of Agriculture on irrigation; water-supply and irrigation papers and other publications of the United States Geological Survey, Division of Hydrography; Report of a Senate Committee for Irrigation and Proclamation of Arid Lands (Washington, 1890); Special Reports to Congress on Irrigation in the United States (Washington, 1891); Hinton and others, Artesian and Underflow Investigations (Washington, 1892); Chittenden, Report to Congress on Reservoir Sites in Wyoming and Colorado (Washington, 1898); Newell, “Irrigation,” in the Eleventh and Twelfth United States Census Reports (Washington, 1890 and 1900); reports and bulletins on irrigation of the agricultural experiment stations in California, Colorado, Utah, and Wyoming, and the reports of the State engineers of these and other States in the arid regions; American Society of Irrigation, Engineers' Annuals; Mead, Irrigation Institutes (New York, 1903); Dennis, Reports on Irrigation and Canadian Irrigation Surveys (Ottawa, 1894-96); Deakin, Irrigation in Western America (Melbourne, 1885); Hall, Irrigation Development and Irrigation in California (Southern) (Sacramento, 1886-88); Brough, Irrigation in Utah (Baltimore, 1898); Flynn, Irrigation Canals and Other Irrigation Works (San Francisco, 1892); Buckley, Irrigation Works in India and Egypt (London, 1893); Willcocks, Egyptian Irrigation (London, 1899); Newell, Irrigation in the United States (New York, 1902); Schuyler, Reservoirs for Irrigation (New York, 1902); Ross, Notes on Distribution of Water of Upper Egypt (Cairo, 1882); Brunhes, L'irrigation dans la péninsule ibrique et dans l'Afrique du nord (Paris, 1902); Baird-Smith, Italian Irrigation (London, 1855); Moses, L'irrigation en Asie centrale (Paris, 1894); Parral, Les irrigations dans les bouches du Rhône (ib., 1876); id., Les irrigations de Vaucluse en 1877 (ib., 1878); Wilson, Manual of Irrigation Engineering (New York, 1895); Stephens, Practical Irrigator and Drainer (Edinburgh, 1884); Stewart, Irrigation for the Farm, Garden, and Orchard (New York, 1877); Scott, Irrigation and Water Supply (London, 1895); Ronna, Les irrigations (Paris, 1889-90); Salvador, Hydraulique agricole (ib., 1900); Llaurado, Tratado de aguas y riegos (Madrid,
