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Irrigation

IRRIGATION

IRRIGATION, the delivery of water to grow crops, has been a factor in North American society and agriculture since long before the existence of the United States. Mostly practiced in the arid western regions of the country, its expansion in the twentieth century dramatically altered the national landscape and food production.

Possibly as early as a.d. 300, the Hohokam erected the first large-scale irrigation systems in the area that later became the southwestern United States. Although their rawhide and basket tools were simple and their dams small by modern standards, these indigenous societies maintained thousands of acres under irrigation for centuries. The Papago and Pueblo nations later practiced similar techniques, though they generally irrigated only smaller fields near arroyo mouths and seasonal stream-beds. The coordinated efforts to construct and maintain this sophisticated infrastructure required these early irrigators


to develop political institutions and tribal affiliations larger than those of their hunter-gatherer neighbors.

Spanish and Mexican settlers in New Mexico created similar irrigation systems to support their own agriculture. Many of their villages and fields were actually built around an acequia madre or "mother ditch," and they boasted well-articulated lines of command and labor expectations to maintain the ditch. This social and physical system still existed in some of these villages at the end of the twentieth century.

The Mormon settlers arriving in the Salt Lake area in the 1840s drew on these precedents in the erection of their own irrigation networks. Using the cooperative religious institutions that characterized their society, by 1850 they grew such diverse crops as potatoes, wheat, hay, and oats on more than sixteen thousand irrigated acres.

The westward expansion of the United States in the nineteenth century brought the regions where irrigation was needed to practice extensive agriculture under American control. At first, however, migrating Americans were slow to recognize the challenge that aridity posed to their traditional agricultural practices. At less than twenty inches a year, the average rainfall west of the one-hundredth meridian—roughly the line that runs north and south through the middle of the states of Texas, Oklahoma, Kansas, Nebraska, and the Dakotas—is just below the amount needed to grow wheat, and ten inches less than that needed by corn.

The enormous challenge of the arid West was initially difficult to recognize. During the 1880s, when thousands of farmers settled on the Great Plains, rainfall was significantly above average, in some cases twice as heavy as the long-term pattern. Farmers and policymakers were thus lulled into a false sense of security. One theory even held that the plowing of so much virgin territory had in fact fundamentally changed the natural patterns of rainfall, increasing precipitation to facilitate the conquest of the continent.

Private efforts to irrigate the arid regions of the West met with very limited success. Irrigation was generally outside the reach of individual farmers for the simple reason that it required the control of large stretches of rivers and streams and the erection of sizable dams for storage. In the 1870s and 1880s, private land companies entered the irrigation business, constructing dams, building extensive canal systems, and then selling nearby lands to farmers who would remain dependent on the companies for their water. High capital costs, however, constrained these efforts. Only the most opportune sites were irrigated, the total acres under irrigation soon stagnated, and by 1900 nearly nine out of ten of these irrigation companies were in financial jeopardy.

The Federal Role

The failure of private efforts created an opening for those who thought that the federal government should build massive irrigation works. John Wesley Powell, a pioneering scientist and ethnographer who headed the United States Geological Survey, had made the most radical proposals in this regard. Surveying the lands of the arid West in the 1870s, Powell came to the conclusion that the country's model for the settlement of newly acquired territory was deeply flawed. Extinguishing the public domain by giving settlers 160-acre tracts (under the provisions of the Homestead Act) might work where enough rain fell to grow crops, but the development of the West hinged on water rather than land. Since very little of the West could be farmed in the traditional way, the government, Powell believed, should divide the region by watershed. Much like the Mormons—whose communal irrigation made quite an impression on Powell—settlers should govern themselves by watershed, forming a cooperative to raise the capital for the necessary irrigation network. Irrigated farms, more productive and labor intensive, would be smaller than farms back east, probably about 80 acres. Unirrigated lands, which he thought would always comprise the vast majority of the West, would be reserved for ranching in large tracts of 2,500 or more acres.

Powell's vision was at once too radical and too modest to gain the political support it needed to be implemented. Western boosters were enraged by his assumption that little of the region's land was fit for agriculture, and even fewer were willing to accept the drastic revision in territorial laws for which his watershed proposal called. After the failure of private irrigation in the West, the form that federal intervention took was much more modest. The 1902 Newlands Reclamation Act created the Bureau of Reclamation, a federal agency charged with building dams, reservoirs, and irrigation canals for the benefit of private farmers. The West, in other words, was meant to resemble the East, with a little more help from the federal government.

The Newlands Act married conservation's technical expertise with its emphasis on antimonopoly. Farmers were to repay the construction costs through annual charges for their water. Individuals could buy water for a maximum of only 160 acres. The Newlands Act thus extended the provisions of the Homestead Act, seeking to create egalitarian farming communities with dispersed land ownership.

The Bureau of Reclamation was remarkably successful in its goal of irrigating the West. Whereas in 1906, fewer than thirty thousand acres west of the one-hundredth meridian were under irrigation, by 1992 that number had skyrocketed to more than 45 million. The Bureau of Reclamation, the Army Corps of Engineers, and other federal agencies erected more than one thousand dams in the West. These massive structures not only provided water for crops, but also generated much of the electricity that lit the region's cities and towns. For decades, the politics of irrigation proved irresistible. The construction of dams,


aqueducts, and canals created numerous jobs, and the lands that they opened up for agriculture benefited real estate speculators and the local tax rolls alike. While the New Deal saw a significant expansion in the scope of these projects, the fact that their ultimate goal was to support private agriculture kept them attractive to more antistate politicians.

In the 1930s, affordable pumps and low-cost electricity opened up a new dimension in irrigation: ground-water pumping. By 1970, such pumping watered more than 40 percent of the nation's irrigated acreage, most of it on the Great Plains. This irrigation differed from federal projects in that it drew upon generally unrenewable aquifers and was easily affordable by individual farmers.

Social and Environmental Issues

Such intensive irrigation, however, generated its own social and environmental effects. From its inception, the Bureau of Reclamation operated much differently than its founders had envisioned. Very few irrigation projects were actually paid for by their beneficiaries, and so these public works quickly became subsidies. The proliferation of modest homesteads that had been so important to justify giving the federal government primary responsibility for irrigation never came to be. Land speculators bought much of the land where they anticipated dams might be built, and the bureau showed little interest in enforcing its 160-acre limit on what came to be some of the most powerful political interests in the West. In most areas served by the bureau's projects, it was actually impossible to purchase small tracts of land. The high productivity and costs of irrigated lands meant that such agriculture tended to be more market-oriented, more mechanized, and to employ more migrant labor than elsewhere. In practice, then, irrigation helped to solidify the dominance of large-scale agribusiness in the West.

Environmental problems have increasingly limited the effectiveness of irrigation and reduced its public support. The damming of most of the West's major rivers has decimated their salmon runs. Natural river flows have been dramatically altered. The Colorado River, for example, once mighty enough to carve the Grand Canyon, was so heavily drawn on for irrigation that it did not reach the Pacific from 1964 to 1983. Proposals to build further dams on the Colorado sparked an environmental backlash as early as the 1950s. The buildup of silt behind reservoir walls quickly became a problem; by 2000, most reservoirs built before 1945 had lost from 7 to 15 percent of their capacity. Salinization, the accretion of salt in perpetually water-logged soil, puts thousands of acres out of production each year. Groundwater pumping on the Great Plains seemed headed for extinction, with the aquifer predicted to dry up within a few decades.

No large federal irrigation projects were approved from the late 1970s to the turn of the century. In part this was because so many of the most feasible dam sites had been taken, but the loss of support for federal irrigation also reflected the growing political power of more environmental-minded urbanites. Nevertheless, irrigation continues to be a decisive force in American agriculture and the landscape of the West.

BIBLIOGRAPHY

Hundley, Norris, Jr. The Great Thirst: Californians and Water—A History. Rev. ed. Berkeley: University of California Press, 2001.

Pisani, Donald J. To Reclaim a Divided West: Water, Law, and Public Policy, 1848–1902. Albuquerque: University of New Mexico Press, 1992.

Reisner, Marc. Cadillac Desert: The American West and Its Disappearing Water. Rev. ed. New York: Penguin, 1993.

Walton, John. Western Times and Water Wars: State, Culture, and Rebellion in California. Berkeley: University of California Press, 1992.

Worster, Donald. Rivers of Empire: Water, Aridity, and the Growth of the American West. New York: Pantheon, 1985.

Benjamin H.Johnson

See alsoAgriculture ; Agriculture, American Indian ; Reclamation ; Water Supply and Conservation .

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Irrigation

Irrigation

IRRIGATION TECHNIQUES

SUCCESSES AND FAILURES

BIBLIOGRAPHY

Irrigation refers to techniques for augmenting the moisture content of soil to grow crops. These techniques have played an important role in intensifying agriculture, increasing production, and improving the productivity of land and labor. Early civilizations in China, Egypt, Mesopotamia, Peru, and India relied on them to support large and complex populations. One of the earliest and most successful large-scale hydraulic works was the Dujiangyan irrigation project built in the third century BCE in southwest Chinas Sichuan Province. The project was designed to simultaneously solve the problem of the incessant flooding of the Minjiang River, a tributary of the Yangtze River, in the summer, and provide water during the winter when it was beset with drought. Working without a dam, the river was divided by a long bank in the middle, with the inner river serving as a channel for delivering water for irrigation and the outer river used as a floodway. This enabled the delivery of water during the dry season and the return of excess water during the winter to the mainstream of the Minjiang River. A weir made of bamboo cages filled with stones balanced the channels inflow. The project fed a grid of irrigation canals watering 160,000 hectares of arable land in the Chengdu Plain.

Many ancient large-scale irrigation systems were accompanied by elaborate, complex, social organization. Descriptions of these systems in the nineteenth century intrigued the social theorists Karl Marx (18181883) and Max Weber (18641920). Marxs idea of the Asiatic mode of production, based largely on irrigation-based societies in China, included state control and collection of rents, a despotic political system, and societal organization obtained through religion, rather than economics and exchange. Village life, rather than cities, circumscribed the social spheres of people. Weber, in contrast, drew attention to the peculiar hydraulic-bureaucratic official-state in China and India. Although flawed due to limits in the data then available, these constructs were quite influential in the subsequent development of social theory.

Karl Wittfogel, inspired by the writings of Weber, revisited the materials and proposed in Oriental Despotism (1957) that large-scale waterworks required centralized direction, bureaucratic organization, and disciplined armies. He distinguished such hydraulic societies from smaller-scale hydroagricultural societies relying on less provident water sources in regions where geographical features hydraulically compartmentalized the countryside. Wittfogels hydraulic society thesis generated various criticisms, of which the most telling were examples of locally controlled and managed irrigation in societies where irrigation authority was formally centralized. More recently, Donald Worster in Rivers of Empire (1985) reinvigorated the discussion of large-scale irrigation, arguing that Wittfogels hydraulic societies take a somewhat different form in the modern world. In his analysis of river-based irrigation in the western United States he finds parallels between the archaic centralized regimes of ancient hydraulic societies and the centralized state agencies of the Bureau of Reclamation and the Army Corps of Engineers.

IRRIGATION TECHNIQUES

The motivation for irrigation stems from the difficulties of farming in arid and semiarid areas of the world beset with insufficient or unreliable precipitation. Where precipitation is insufficient, irrigation may be the only way farmers can supply moisture for growing crops. In areas with sufficient, but otherwise unreliable, precipitation, it can provide insurance against crop failure. And in lands with adequate moisture, irrigation can be used to grow water-intensive subsistence crops such as rice, or highvalue market crops such as sugar beets or beans.

Irrigators commonly draw on gravity to move surface water from a source through canals and furrows to fields and to store water in reservoirs and cisterns. Techniques to move surface water run the gamut from simple and unsophisticated counterbalanced poles mounted with buckets to complex, labor-intensive feats of engineering such as large-scale dams and canal systems. Surface-water irrigation often works in concert with the control and manipulation of floodwater. In one frequent form, as soon as the flood in a perennial river reaches a sufficient level, inundation canals start to flow and water is led over fields. In another, recession irrigation, a rising perennial river overflows its banks and inundates the plains alongside the river. Crops are grown on the rising or receding flow or on the residual moisture.

In spate irrigation, found throughout semiarid environments of the Middle East, North Africa, East Africa, West Asia, and parts of Latin America, seasonal water is used as a source. Seasonal floods are contained in mountain catchments or diverted from riverbeds and spread over large areas. Seasonal floodwater may last only a few hours or a few days, and sophisticated local knowledge is required to organize and manage the accumulation and distribution of the floodwater. Spate irrigation is associated with low returns to labor, great variability in productivity between good and bad years, and a high degree of social organization. Its uncertainty restricts its appeal to only the very poorest.

In areas with high water tables or surface depressions, human or animal energy has been used to raise groundwater for irrigation. Gravity usually has only limited potential in this regard. One exception is the complex horizontal wells that tapped subterranean aquifers through filtration galleries in the ancient Middle East (qanats ), and the Andes (puquios ). In the nineteenth century pumps driven initially by steam, and later by electricity and gasoline or diesel, were adopted to irrigate with groundwater from shallow aquifers and deep groundwater basins. The availability of small, portable, inexpensive, submersible pumps in the late twentieth century expanded groundwater irrigation dramatically. In groundwater-rich spate-irrigated areas, hydraulic infrastructure has been neglected and land use intensified through perennial cropping.

The adoption of industrial irrigation altered significantly the scale, impact, and productivity of agriculture, and its reliance on inanimate mechanical converters of energy, especially fossil fuels. Irrigation played a key role in the Green Revolution of the 1960s, helping to ensure the high yields of miracle seeds. It remains instrumental in realizing the potential of genetic engineering and precision agriculture, the application of space-age technologies to tailor soil and crop management to local conditions. Two techniques now in widespread use include drip irrigation, relying on emitters to release carefully calibrated amounts of water, and sprinkler irrigation, with relatively permanent or portable sprinkler systems.

Despite new and more efficient irrigation technologies, todays demands for water produced by the Green Revolution, population growth, urbanization, and industrialization outstrip supply. Scarcity of water provokes conflicts in many areas of the world; they are endemic in the Middle East over access to the water of the Euphrates, Jordan, and Nile Rivers. At the heart of the Arab-Israeli conflict is the allocation to Israel, Jordan, the Palestinian Territories, and Syria of the water of the Jordan River, its tributaries, coastal rivers, and two aquifer systems.

SUCCESSES AND FAILURES

Although many regions in China, Egypt, Mesopotamia, and India have enjoyed continuous and sustainable irrigation for centuries, it has not always been an unmitigated success. Archaeological and historical research has uncovered significant evidence of cases of agrarian collapse due to environmental degradation and mismanagement. Poorly managed surface-water irrigation can lead to the excessive buildup of salts, exacerbated by shallow soils, water with relatively high salt content, aridity, and high water tables. For example, the Aral Sea, located in inland Central Asia, has been shrinking since the 1960s as the U.S.S.R. diverted the rivers that feed it for irrigation.

Often, inadequate drainage is at the root of the irrigation failures. Drainage does not always have to be a problem, however. Some societies have devised techniques for draining heavily waterlogged soils to levels sufficient to support intensive agriculture. Raised-bed agriculture in Lake Titicaca of southern Peru and Bolivia achieved levels of productivity comparable to irrigated land.

In the industrial era, irrigation has increased the risks of ground and surface-water pollution from the intensive use of pesticides and nitrate fertilizers. Groundwater extraction poses an additional problem; it is much more difficult to regulate than surface-water irrigation and in many regions of the world, overpumping has contributed to the drying up of aquifers and groundwater basins.

SEE ALSO Development, Rural

BIBLIOGRAPHY

Glick, Thomas. 1970. Irrigation and Society in Medieval Valencia. Cambridge, MA: Harvard University Press.

Mabry, Jonathan B., ed. 1996. Canals and Communities. Tucson: University of Arizona Press.

Watson, Andrew M. 1983. Agricultural Innovations in the Early Islamic World. Cambridge, U.K.: Cambridge University Press.

Wittfogel, Karl. 1957. Oriental Despotism. New Haven, CT: Yale University Press.

Worster, Donald. 1985. Rivers of Empire: Water, Aridity, and the Growth of the American West. New York: Pantheon Books.

David W. Guillet

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irrigation

irrigation, in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. Estimates of total irrigated land in the world range from 543 to 618 million acres (220 to 250 million hectares), almost half of them in India, Pakistan, and China. The United States had almost 60 million acres (23.8 million hectares) of irrigated farmland in 1991.

Methods of applying water include free-flooding of entire areas from canals and ditches; check-flooding, in which water flows over strips or checks of land between levees, or ridges; the furrow method, in which water runs between crop or tree rows, penetrating laterally to the roots; the surface-pipe method, in which water flows in movable slip-joint pipes; sprinklers, including large-scale center-pivot and other self-propelled systems; and a variety of water-conserving drip and trickle systems. In many cases irrigation is correlated with drainage to avoid soil salinity, leaching, and waterlogging. Irrigation may also involve preliminary clearing, smoothing, and grading of land. Especially in areas of high evaporation rates, intensive irrigation can result in excessive quantities of salts accumulating in the upper layers of the soil as water evaporates from the surface, rendering the soil unfit for crop production.

Since prehistoric times water has been diverted from waterways to fields by ditching. Early improvements for raising water included counterbalanced poles with attached water vessels, and adaptations of the wheel and of a pump called the Archimedes' screw. The use of canals, dams, weirs, and reservoirs for the distribution, control, and storage of water was probably initiated in ancient Egypt. In modern times pumps have facilitated the use of underground as well as surface water, but overuse of water in aquifers can exhaust their usable water. Large-scale 20th-century irrigation projects commonly also include water supply, hydroelectric power, and flood control.

Many regions, notably in China, Egypt, Mesopotamia, and India, have been under continuous irrigation from ancient times. Today China, India, the United States, and Pakistan rank highest in irrigated land. In North America, where most of the arid and semiarid land lies west of the 100th meridian, irrigation was first practiced in the Southwest by Native Americans and later by the Spanish, especially in California. As agriculture expanded, early irrigation initiatives by individual farmers or local groups were soon supplemented by commercial projects, until more ambitious water conservation and development schemes involved state and federal governments in vast projects.

See J. Keller and R. D. Bliesner, Sprinkle and Trickle Irrigation (1990); B. A. Stewart and D. R. Nelson, Irrigation of Agricultural Crops (1990); W. F. Ritter, ed., Irrigation and Drainage (1991).

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Irrigation

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 (18611865), 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

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irrigation

irrigation The provision of water for crops by artificial methods; for example by constructing ditches, pipe systems, and canals. Irrigation can lead to problems when the water leaches trace elements from the soil; selenium, for example, can be toxic to both local fauna and flora. Irrigation can also increase the salinity of the soil, if diverted rivers are used to provide the water. Evaporation of surface water leaves a crust of salt, which can drain down to deeper layers of the soil.

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irrigation

irrigation Artificial watering of land for growing crops. Irrigation enables crops to grow in regions with inadequate precipitation. The first irrigation systems date from before 3000 bc in Egypt, Asia and the Middle East. Today, most water for irrigation is surface water (from streams, rivers and lakes) or ground water (obtained from wells). In some regions, freshwater for irrigation is obtained by desalination. Canals, ditches, pumps and pipes are used to convey water to fields.

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irrigation

irrigation (i-ri-gay-shŏn) n. the process of washing out a wound or hollow organ with a continuous flow of water or medicated solution. whole-gut i. washing out the entire intestinal tract as a prelude to surgery on the lower intestine.

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irrigation

irrigation The process of artificially augmenting the amount of water available to crops. The water may be sprayed directly on to the plants or made available to their root systems through a series of surface channels or ditches.

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irrigation

irrigation The artificial augmentation of the amount of water available to crops, either by spraying water directly on to the plants or making it available to their root systems through a series of surface channels or ditches.

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