Irrigation Systems, Ancient

Humans are newcomers to Earth, even though their achievements have been enormous. It was only during the Holocene epoch (10,000 years ago) that the development of agriculture occurred, keeping in mind that the Earth and solar system are 4.6 billion years old. Humans have spent most of their history as hunting and food-gathering beings. Only in the past 9,000 to 10,000 years have humans discovered how to raise crops and tame animals. Such changes probably first took place in the hills to the north of present-day Iraq and Syria.

Irrigation in Egypt and Mesopotamia

The first successful efforts to control the flow of water were made in Mesopotamia and Egypt, where the remains of the prehistoric irrigation works still exist. In ancient Egypt, the construction of canals was a major endeavor of the pharaohs and their servants, beginning in Scorpio's time. One of the first duties of provincial governors was the digging and repair of canals, which were used to flood large tracts of land while the Nile was flowing high. The land was checkerboarded with small basins, defined by a system of dikes . Problems regarding the uncertainty of the flow of the Nile were recognized. During very high flows, the dikes were washed away and villages flooded, drowning thousands. During low flows, the land did not receive water, and no crops could grow. In many places where fields were too high to receive water from the canals, water was drawn from the canals or the Nile directly by a swape or a shaduf. These consisted of a bucket on the end of a cord that hung from the long end of a pivoted boom, counterweighted at the short end. The building of canals continued in Egypt throughout the centuries.

The Sumerians in southern Mesopotamia built city walls and temples and dug canals that were the world's first engineering works. It is also of interest that these people, from the beginning of recorded history, fought over water rights. Irrigation was extremely vital to Mesopotamia, Greek for "the land between the rivers." Flooding problems were more serious in Mesopotamia than in Egypt because the Tigris and Euphrates carried several times more silt per unit volume of water than the Nile. This resulted in rivers rising faster and changing their courses more often in Mesopotamia.

Both the Mesopotamian irrigation system and that in the Egyptian delta were of the basin type, which were opened by digging a gap in the embankment and closed by placing mud back into the gap. Water was hoisted using the swape, as in Egypt. Laws in Mesopotamia not only required farmers to keep their basins and feeder canals in repair but also required everyone to help with hoes and shovels in times of flood or when new canals were to be dug or old ones repaired. Some canals may have been used for 1,000 years before they were abandoned and others were built. Even today, 4,000 to 5,000 years later, the embankments of the abandoned canals are still present. These canal systems, in fact, supported a denser population than lives there today. Over the centuries, the agriculture of Mesopotamia began to decay because of the salt in the alluvial soil. Then, in 1258, the Mongols conquered Mesopotamia and destroyed the irrigation systems.

The Assyrians also developed extensive public works. Sargon II, invading Armenia in 714 b.c.e., discovered the qanat (Arabic name) or kariz (Persian name), which is a tunnel used to bring water from an underground source in the hills down to the foothills. Sargon destroyed the area in Armenia but brought the concept back to Assyria. This method of irrigation spread over the Near East into North Africa over the centuries and is still used. Sargon's son Sennacherib also developed waterworks by damming the Tebitu River and using a canal to bring water to Nineveh, where the water could be used for irrigation without hoisting devices. During high water in the spring, overflows were handled by a municipal canebrake that was built to develop marshes used as game preserves for deer and wild boar, and birch-breeding areas. When this system was outgrown, a new canal, nearly 19 kilometers (30 miles) long, was built, with an aqueduct that had a layer of concrete or mortar under the upper layer of stone to prevent leakage.

Irrigation (Prehistoric Mexico)

During the earliest years of canal irrigation in Mexico, the technology changed little, as there are very few remains of these systems. The technological achievements were not very great prior to around 600 to 500 b.c.e. Storage dams were constructed of blocks mortared together as opposed to the earlier ones constructed of loosely piled rocks. Some of the spillways were improved, and floodgates were used in some spillways. Some of the dams could even be classified as arch dams. The canals were modified somewhat during this time. Different cross-sectional areas were used, and some were lined with stone slabs. During this time, crops were irrigated with more carefully controlled water as opposed to the earlier methods of somewhat haphazard flooding.

Between 550 and 200 b.c.e., there were significant improvements in both the irrigation-related features and the entire canal systems. The channelization of streambeds, along with the excavation of canals and the construction of dams, was probably the most significant. In a brief period, the technology of canal irrigation improved significantly; however, the technology stopped developing after 200 b.c.e., and no significant developments occurred for approximately 500 years. Around 300 C.E., minimal new developments started, and the technology remained essentially the same through the classic period (200–800/1000 C.E.) and early postclassic period (800/1000–1300 C.E.).

Canal Irrigation (North America: Chaco and Hohokam Systems)

The Hohokam and the Chaco regional systems stand out as two of the major prehistoric developments in the American Southwest. These two systems expanded over broad geographic areas of similar size (the Hohokam in Arizona and the Chacoans in New Mexico). These systems were of the similar time period but seemed to have developed and functioned independently, with little interaction. The Chaco and the Hohokam systems evolved in quite different environments, having considerably different irrigation infrastructure.

The Hohokam people inhabited the lower Salt and Gila River valleys in the Phoenix area in Arizona. These Hohokam Indian canal builders were given the name later by the Pima Indians. Even though the Indians of Arizona began limited farming nearly 3,000 years ago, the construction of the Hohokam irrigation systems probably did not begin until a few centuries C.E. It is unknown who originated the idea of irrigation in Arizona, whether it was local technology or introduced to them from cultures in Mexico.

Around 1450 C.E., the Hohokam culture declined, possibly because of a combination of factors: flooding in the 1080s, hydrologic degradation in the early 1100s, and the recruitment of labor by the surrounding population. A major flood in 1358 ultimately destroyed the canal networks, resulting in movement of the people. Canal use was either quite limited or entirely absent among the Pima Indians, who were the successors to the Hohokams Indians. The prehistoric people who lived outside the Hohokam culture area also constructed irrigation systems, but none was of near the grand scale as the Hohokam irrigation systems.

Around 900 C.E., the Anasazi of northwestern New Mexico developed a cultural phenomena that now has more than 2,400 archaeological sites with nine towns each with hundreds of rooms along a 5.6-kilometer (9-mile) stretch. The Chacoan system is located in the San Juan basin in northwestern New Mexico. This basin has limited surface water , with most surface discharge from ephemeral washes and arroyos. The water collected from the side canyon that drained from the upper mesa top was diverted by either an earth or a masonry dam near the month of the side canyon into a canal. These canals averaged 4.5 meters (about 15 feet) wide and 1.4 meters (more than 4 feet) deep and were lined in some areas with stone slabs and bordered in other areas by masonry walls. These canals ended at a masonry headgate. Water was then diverted to the fields in small ditches or into overflow ponds and small reservoirs.

see also Irrigation Management; Water Works, Ancient.

Larry W. Mays

Bibliography

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