An irrigation ditch is a man-made stream used to carry water from a source to land for agriculture or landscaping. Reliable water flow can be a challenge, but methods such as reservoirs and dams can be used. Efficient use of water is important, and modern irrigation canals are managed with conservation in mind.
An irrigation ditch is a stream, often man-made or enhanced, constructed for the purpose of carrying water from a source such as a lake, river or stream, to land used for agriculture or landscaping . An essential element of agriculture found in archaeological excavations dating back to 4,000 BC, irrigation canals have often made the difference between livelihoods and starvation. An irrigation ditch, in its most basic form, is a ditch filled with water. It can be dug into the ground and then filled with water, or an existing stream can be widened in a process called ‘canalisation’ and diverted as appropriate to provide maximum efficiency. Another way to create a canal is to build the walls first, using dry soil as a bed, and only connect it to a water source when fully built.
One of the challenges with irrigation ditches is providing reliable water flow. When the canal is connected directly to a water source such as a lake or river, the water supply is fairly reliable, but care must be taken to avoid using so much water that other areas are affected. When an irrigation ditch traverses a great distance or has to traverse elevation changes, other strategies must be employed. It is common, for example, to build a reservoir to store water for irrigation and to fill irrigation channels with dam and sluice systems. Another method is to dig channels next to water supply sources and build dams or locks separating the two, opening them when water is needed in the irrigation channel and closing them later.
Irrigation channels do not always carry water directly to the land to be irrigated; in many cases the water must be conveyed from the canal to the crops in other ways. A common way to do this is to divert water from the canal into irrigation channels, or “laterals”, dug near the rows. When crops are planted on slopes, complex systems are sometimes built to supply water upstream from an irrigation ditch.
Efficient and economical use of water in irrigation is a major concern. While 40% of all food produced in the world comes from irrigated land, irrigation itself consumes 80% of the freshwater supply, which is a very inefficient use of water. In some cases, too much water is simply absorbed into the soil; in others, it comes out of the ground to be irrigated. Modern irrigation canals are built and managed according to increasingly sophisticated models of water management and conservation. Care should also be taken to protect irrigation water and runoff from contamination by pesticides and fertilizers.
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