Irrigation

Irrigation is when water is applied to the soil usually for growing crops during times of little or no rain. While irrigation is mainly used to replace missing rainfall during periods of drought, it also used to protect plants against frost. Irrigation also helps keep weeds from growing in rice fields.

Many archaeological digs in Mesopotamia and Egypt, has identified evidence of irrigation as far back as the 6th millennium BCE, where barley was grown in areas where the natural rainfall could not support such a crop.

In the Zana Valley of the Andes Mountains in Peru, archaeologists found the remains of three irrigation canals. These irrigation canals were radiocarbon dated and showed that these irrigation canals went back to the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE. So far, these canals are a few of the earliest signs of irrigation being used anywhere in the world. There are possible traces of another irrigation canal that may date from the 5th millennium BCE found under the 4th millennium canal.

The Indus Valley Civilization in Pakistan and North India, dating from around 2600 BCE, also had an irrigation system. Large-scale agriculture was practiced and a huge network of canals was used to irrigate the crops. Very sophisticated irrigation and storage systems were developed by the peoples of this area and time period, including the reservoirs built at Girnar in 3000 BCE.

There is evidence of the ancient Egyptian pharaoh Amenemhet III of the twelfth dynasty, around 1800 BCE, using the natural lake of Fayûm as a reservoir to store surpluses of water for use during the dry seasons. The lake would swell every year due to the annual flooding of the Nile.

The Qanats, which were developed in ancient Persia around 800 BCE, are some of the oldest known irrigation methods still being used even today. These ancient irrigation systems are found in Asia, the Middle East and North Africa. This irrigation system is made up of a network of vertical wells and sloping tunnels that are hollowed out into the sides of cliffs and steep hills to tap into the groundwater. A water wheel with clay pots around the rim powered by the flow of the stream, or sometimes powered by animals where the water source was not flowing, was brought into use around this time, by Roman settlers who had come to North Africa. Around 150 BCE the pots were fitted with valves to allow easier filling as they were pushed into the water.

Many other parts of the world still use irrigation methods to produce many of their food crops.