Irrigation. Ancient Irrigation

Irrigation is the artificial application of water to crop and livestock production. Farmers, engineers, and government officials gather water from streams, aquifers, or rainfall and channel it to plants and animals. Irrigation is one of the most important agricultural techniques ever devised. In ancient times it helped generate food surpluses that supported the hallmarks of civilization: social hierarchy, bureaucracy, science and engineering, complex technology, organized religion, powerful militaries, alphabetic writing, cities, and empires.

By the early twenty-first century the Earth's 6 billion inhabitants derived 40 percent of their food from irrigation. However, irrigation also has generated profound environmental transformations and problems. It has made small inland seas and destroyed them, created and eliminated habitats, altered rivers beyond recognition, spread disease, and displaced communities of people.

Ancient Irrigation. Between about 4000 все and 1200 ce agricultural societies built irrigation systems in the Middle East, Asia, around the Mediterranean, and in tire Americas. Tire greatest of these early irrigation civilizations used centralized social organization and large-scale technology to divert rivers for crop and livestock production. In the process they created distinctive ecologies that supported a wealth of plants and. animals, produced agricultural surpluses, and fed large populations. Some suffered from severe environmental problems.

The German historian and social theorist Karl Wittfogel coined the term hydraulic civilizations to describe these distinctive early societies. Wittfogel believed that the diversion of rivers for large-scale irrigated agriculture inevitably required hierarchical, authoritarian government. Only a powerful centralized state could mobilize the resources necessary to build and maintain large dams and canals.

Irrigated fields in the desert in Egypt. In the foreground are the stone ruins of an ancient village, whose inhabitants once farmed the same valley

Bureaucrats and technical experts designed the hydraulic works, disciplined large numbers of forced laborers, kept records of the operations, repaired and maintained the systems, and collected the taxes necessary to pay for it all. Scholars have attacked Wittfogel's model for being simplistic, static, and deterministic. Among other criticisms, they point out that powerful regimes elsewhere in the world developed without irrigation.

But some scholars concede that Wittfogel's hydraulic civilizations thesis contains a degree of validity. Large-scale irrigation, along with political, economic, and agricultural conditions, probably contributed to the consolidation of governmental authority. Moreover, large-scale irrigation and state power at least evolved together.

In Mesopotamia a series of empires built and regulated extensive irrigation systems that tapped the Tigris and Euphrates Rivers for agricultural production, and their kings boasted of their hydraulic achievements. One Babylonian king, Hammurabi, in the period 1792-1750 все oversaw the construction of irrigation works and dictated a legal code that in part dealt with irrigation. In Egypt, elites with titles such as "chief of irrigation," "chief of the water office," and "chief of the canal workmen" occupied the top positions in an extensive bureaucracy that guided water from the Nile River through complex irrigation networks.

One potentate, the Scorpion King, in about 3100 все depicted himself opening an irrigation network. In Peru beginning about 1000 все, in Mexico about 320 все, and in what is now Arizona in 400 ce, powerful civilizations developed extensive irrigation networks to raise corn and other crops. Irrigation certainly did not evolve into despotism as neatly as Wittfogel suggested, but the control of water and the creation of powerful government certainly influenced one another.

Early irrigation supported an intensification of crop and livestock production. In Mesopotamia irrigators kept sheep, pigs, goats, and cattle; gathered fish from canals; and raised wheat and barley along with flax, dates, apples, plums, grapes, and many other types of fruits and vegetables. Along the Nile in Egypt farmers kept ducks, geese, and asses in addition to other hoofed livestock, which grazed in nearby marshes, swamps, unused lands, and on the stubble of fallow fields.

The Egyptians also grew lentils, onions, beans, and cotton along with the more standard staple crops, and they harvested papyrus from wetlands. Chinese farmers, who may have adopted irrigation from Babylon, raised millet and later rice in addition to other types of crops and livestock. Human and animal populations often lived in dense concentrations in the early irrigation civilizations. In about 3000 все in Ur, a Sumerian city in Mesopotamia, air estimated ten thousand animals lived in proximity to the settlement's human population of roughly six thousand.

Early irrigation on such a vast scale produced enormous quantities of food that supported growing populations, a division of labor, and social stratification. By 3000 все Sumeria encompassed eight cities, the most populous of which contained upward of twenty thousand people. Ancient Egyptian irrigated agriculture eventually fed as many as 2.5 million or perhaps even 3 million people.

Surpluses allowed some members of society to engage in activities other than agriculture, including writing, record keeping, mathematics, technological innovation (most notably the development of the wheel), craft work, and the priesthood. Social stratification appeared, with administrative, religious, and military officials occupying the highest ranks, and merchants, craftspeople, farmers, and slaves occupying the lower ranks.

Irrigation ecology contributed to the spread of pests and diseases adapted to agriculture and dense settlement. Weeds grew in fields. Rats invaded granaries. Cockroaches, flies, and mice moved in to households. ' Humans and animals shared parasites and diseases. As early as 1200 все Egyptians suffered from schistosomiasis, a debilitating malady caused by bloodworms that pass from mollusks to human hosts through irrigation water.

Humans and animals exchanged viruses that evolved into cowpox, smallpox, distemper, rinderpest, measles, and influenza. Viruses were a double- edged sword: Afflicted humans suffered, but eventually their societies developed a degree of immunity that gave them an enormous demographic advantage when they came into contact with virally inexperienced and immunologically defenseless peoples.

Some ancient irrigation civilizations experienced environmental problems that may have weakened them. Although such problems probably occurred in Mesoamerica and along the Indus River, some scholars assert that Mesopotamia best illustrates what can happen when irrigation goes wrong. Several civilizations from about 4000 все to about 1200 ce diverted water from the Tigris and Euphrates Rivers into extensive canal networks that ran for miles.

Irrigators used the shaduf, a simple but efficient device consisting of a lever, a bucket, and a counterweight, to lift water from canals into smaller conduits that ran to the crops. These vibrant civilizations were highly successful, and they established cultural forms, notably alphabetic writing, still practiced by modem people. But erosion, drought, the clogging of canals with silt, and the buildup of poisonous salts in the soil probably contributed to, if not outright caused, their disappearance. Deforestation and overgrazing at the headwaters eroded the soil, which in combination with drought and reduced river flows caused silt to deposit in the canals.

Clearing the canals required intensive labor and resources from societies already under stress from food shortages and other problems. Salt posed an even greater problem. Irrigation water seeped into the ground and dissolved naturally occurring salts. The rising groundwater eventually reached the surface, and as it evaporated it precipitated a toxic white crust harmful to most plants. Laborers scraped away the salt to reach the fresh soil below.

Farmers produced more barley, a relatively salt-tolerant grain. But eventually salinization led to land abandonment, a shift in agriculture toward higher ground, usually to the north, and the rise of new civilizations. The process occurred several times: between roughly 2400 and 1700 все, in the seventh century ce, and from about 1200 to 1500 ce.

Irrigation was more stable and endured longer in Egypt. For millennia irrigators waited each autumn for the "Night of the Drop," when, in their belief, a celestial tear fell and caused the Nile River to bring forth a flood of nourishing water and silt from the Ethiopian highlands. Although at first the Egyptians relied only on the floodwaters to wet their fields and deposit the fertilizing silt, they eventually built systems of canals, dikes, and basins to capture, move, and impound the flood, helping it to saturate and replenish the soil before they planted.

To lift water and increase the area of irrigated land they adopted the shaduf around 1500 все and the animal-powered waterwheel, the saijiya, around 325 все. They installed sophisticated measuring devices, Milometers, that recorded the river's level. Some scholars believe that Egypt's many canals and basins were less tied to centralized authority than those in Mesopotamia. Also, Egyptian irrigators never experienced the problems of siltation and salinity that bedeviled their Mesopotamian counterparts.

Most important, when the Nile's volume dropped after the annual flood, the water table fell and carried with it most of the harmful salts. Egyptian irrigation works did require much maintenance, especially after floods. Droughts and a weak flood at times meant not enough water, and famines occurred. But through these trials the Egyptian system, attuned to the Nile's annual rise and fall, persisted.

A range of smaller, less-centralized systems existed apart from the great hydraulic civilizations. Some systems involved run-off farming in which irrigators channeled water from slopes or washes and spread it across fields. Nabateans, who inhabited the Negev Desert of what is now Israel from the fourth century все through the first century ce, practiced this technique, as did the Anasazi people who lived in the U.S. Southwest from about 100 ch to 1200 ce, as did the Chagga of Africa's Mount Kilimanjaro, who as early as 1000 cr channeled snowmelt to banana groves.

In tire Andes in South America and in the Philippines and other Asian regions, farmers created mountainside terraces that collected rainfall for various crops. In China and other parts of Asia, farmers grew rice in paddies, using human and animal excrement as fertilizer. Other peoples around the Mediterranean world adopted the ancient Persian practice of excavating a qaiwt, an underground aqueduct that tapped aquifers and carried water to oasis villages.

Still other irrigators built stone cisterns and tanks or tapped small springs or rivers and channeled water to their fields. Arab Muslims were instrumental in adopting, synthesizing, improving, and spreading irrigation techniques as far as Spain. The Spanish then transplanted the techniques to the New World, where colonists carried them to the far comers of the empire. By the nineteenth century CE, in what are now New Mexico and Colorado, small communal acequias (canals) showed a faint but nonetheless recognizable Arab influence.