Ancient Peruvian society used irrigation canals

The discovery of canals in the Peruvian Andes shows early civilization there had irrigation technology for intensive agriculture, anthropologists say.

Using irrigation to grow crops rather than harvesting plants in naturally moist areas is one of the signs of a civilized and complex society.

Huts (left arrow) were discovered near ancient canals (right arrow) in Peru's Zana Valley (Courtesy: Tom Dillehay)

Anthropologists had thought early Andean civilizations built canals but the evidence was missing.

Tom Dillehay, an anthropology professor at Vanderbilt University in Nashville, Tenn., and his colleagues found canals dating back over 5,400 years in Peru's upper middle Zana Valley, about 60 kilometres east of the Pacific coast.

"The evidence also points to communal organization of labour to construct and maintain the canals and to the scheduling of daily activities beyond individual households," the researchers wrote in the Nov. 22 issue of Proceedings of the National Academy of Sciences.

"The development of early organized irrigation farming was combined with a hunting and gathering economy to support an increase in the local population size."

Since the canals were initially discovered in 1989, anthropologists have learned more about the structures and the civilizations they supported.

Previously, researchers expected the early canals would be in elevated, coastal valleys. Dillehay's team excavated deeply further up the river valley to find the structures.

The simple, stone-lined hydraulic canals were built on a slope, where gravity carried the water downhill to crops.

The four canals range from one to four kilometres in length. All are narrow, symmetric, shallow and U-shaped. Tools, structures and remains of food have been found within 2.5 kilometres of the canals, which suggests mmon society in the area.

Preliminary results show one canal is over 6,700 years old, and another has been confirmed to be over 5,400 years old, the researchers reported.