IRRIGATION

Irrigation is an artificial watering of the land to produce crops. Irrigation compensates for the lack of regular rainfall in the more arid regions of the world and requires large supplies of water. The two water sources are surface water in lakes, streams, and rivers, and groundwater stored beneath earth's surface in aquifers. Aquifers are natural underground reservoirs where water accumulates.

The two main types of irrigation making use of surface water are the basin system and the perennial system. Basin irrigation relies on annual flooding to fill canals dug adjacent to the overflowing river. The canals traverse through farmland, flooding the area with nutrient-rich water. The modern and widely used perennial system, utilizing reservoirs generally created by dams and extensive canal networks, allows water to be supplied at suitable intervals throughout the year. The other source of irrigation water, groundwater, is pumped to the surface from wells dug into aquifers. The well is placed as near to the land to be irrigated as possible and a system of canals or pipes carries water to the crops.

Recognizing the value of irrigation as an aid to permanently settling the arid American West, Mormon settlers in the Salt Lake Valley in present-day Utah built the first large scale irrigation canal system in 1847. Demand for food by the gold rush miners in California and Colorado in the 1840s and 1850s spurred development of ditch systems to irrigate bottomlands along streams. After the American Civil War (1861–1865), the great agricultural settlement boom, lasting from the 1870s to the 1940s, promoted more efficient irrigation institutions as a means of stimulating economic development of the West. Mutual irrigation companies, first formed in Utah, were followed by irrigation districts in California formulated through the Wright Act of 1887. The districts could levy taxes and issue bonds for irrigation development. With the Carey Act of 1894 and the Reclamation Act of 1902, the federal government began major dam construction efforts. The Reclamation Act established the Reclamation Service, later known as the U.S. Bureau of Reclamation. The agency planned the two largest irrigation systems in the United States, the Colorado River Project with Hoover Dam completed in 1936 and the Columbia River Basin Project with the Grand Coulee Dam completed in 1942. The projects transformed immense expanses of arid lands into productive farmland.

The development of deep-well turbine pumps in the 1930s and 1940s lead to a rapid increase in acreage irrigated by wells, particularly in the Great Plains and Texas.

See also: Westward Expansion