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Irrigation

Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been developed by many cultures around the world. Irrigation helps to grow crops, maintain landscapes, and revegetate disturbed soils in dry areas and during times of below-average rainfall. In addition to these uses, irrigation is also employed to protect crops from frost,[1] suppress weed growth in grain fields, and prevent soil consolidation. It is also used to cool livestock, reduce dust, dispose of sewage, and support mining operations. Drainage, which involves the removal of surface and sub-surface water from a given location, is often studied in conjunction with irrigation.

There are several methods of irrigation that differ in how water is supplied to plants. Surface irrigation, also known as gravity irrigation, is the oldest form of irrigation and has been in use for thousands of years. In sprinkler irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure water devices. Micro-irrigation is a system that distributes water under low pressure through a piped network and applies it as a small discharge to each plant. Micro-irrigation uses less pressure and water flow than sprinkler irrigation. Drip irrigation delivers water directly to the root zone of plants. Subirrigation has been used in field crops in areas with high water tables for many years. It involves artificially raising the water table to moisten the soil below the root zone of plants.

Irrigation water can come from groundwater (extracted from springs or by using wells), from surface water (withdrawn from rivers, lakes or reservoirs) or from non-conventional sources like treated wastewater, desalinated water, drainage water, or fog collection. Irrigation can be supplementary to rainfall, which is common in many parts of the world as rainfed agriculture, or it can be full irrigation, where crops rarely rely on any contribution from rainfall. Full irrigation is less common and only occurs in arid landscapes with very low rainfall or when crops are grown in semi-arid areas outside of rainy seasons.

The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme. The effects stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme. Amongst some of these problems is depletion of underground aquifers through overdrafting. Soil can be over-irrigated due to poor distribution uniformity or management wastes water, chemicals, and may lead to water pollution. Over-irrigation can cause deep drainage from rising water tables that can lead to problems of irrigation salinity requiring watertable control by some form of subsurface land drainage.

Extent

[

Share of agricultural land which is irrigated (2015)

In 2000, the total fertile land was 2,788,000 km2 (689 million acres) and it was equipped with irrigation infrastructure worldwide. About 68% of this area is in Asia, 17% in the Americas, 9% in Europe, 5% in Africa and 1% in Oceania. The largest contiguous areas of high irrigation density are found in Northern and Eastern India and Pakistan along the Ganges and Indus rivers; in the Hai He, Huang He and Yangtze basins in China; along the Nile river in Egypt and Sudan; and in the Mississippi-Missouri river basin, the Southern Great Plains, and in parts of California in the United States. Smaller irrigation areas are spread across almost all populated parts of the world.[2]

By 2012, the area of irrigated land had increased to an estimated total of 3,242,917 km2 (801 million acres), which is nearly the size of India.[3] The irrigation of 20% of farming land accounts for the production of 40% of food production.[4][5]

Global overview

The scale of irrigation increased dramatically over the 20th century. In 1800, 8 million hectares globally were irrigated, in 1950, 94 million hectares, and in 1990, 235 million hectares. By 1990, 30% of the global food production came from irrigated land.[6] Irrigation techniques across the globe includes canals redirecting surface water,[7][8] groundwater pumping, and diverting water from dams. National governments lead most irrigation schemes within their borders, but private investors[9] and other nations,[8] especially the United States,[10] China,[11] and European countries like the United Kingdom,[12] also fund and organize some schemes within other nations.

Irrigation enables the production of more crops, especially commodity crops in areas which otherwise could not support them. Countries frequently invested in irrigation to increase wheat, rice, or cotton production, often with the overarching goal of increasing self-sufficiency.[12]

Example values for crops

Approximate values of seasonal crop water needs[13]| Crop | Crop water needs mm / total growing period |

Sugarcane1500–2500
Banana1200–2200
Citrus900–1200
Potato500–700
Tomato400–800
Barley/oats/wheat450–650
Cabbage350–500
Onions350–550
Pea350–500

Water sources

Traditional irrigation channel in Switzerland, collecting water from the high Alps

(https://en.wikipedia.org/wiki/File:Pump-enabled_Riverside_Irrigation_in_Comilla,_Bangladesh,_25_April_2014.jpg)

Irrigation is underway by pump-enabled extraction directly from the Gumti, seen in the background, in Comilla, Bangladesh.

Groundwater and surface water

Grapes in Petrolina, Brazil only made possible in this semi arid area by drip irrigation

Irrigation water can come from groundwater (extracted from springs or by using wells), from surface water (withdrawn from rivers, lakes or reservoirs) or from non-conventional sources like treated wastewater, desalinated water, drainage water, or fog collection.

While floodwater harvesting belongs to the accepted irrigation methods, rainwater harvesting is usually not considered as a form of irrigation. Rainwater harvesting is the collection of runoff water from roofs or unused land and the concentration of this.

Treated or untreated wastewater

This section is an excerpt from Reclaimed water § Agricultural reuse.

....

Challenges

Environmental impacts

Main article: Environmental impact of irrigation

(https://en.wikipedia.org/wiki/File:1960-_Groundwater_loss_-depletion_-Central_Valley_of_California.svg)

Within a long period of groundwater depletion in California's Central Valley, short periods of recovery have been mostly driven by extreme weather events that typically caused flooding and had negative social, environmental and economic consequences.[32]

Negative impacts frequently accompany extensive irrigation.[33] Some projects which diverted surface water for irrigation dried up the water sources, which led to a more extreme regional climate.[34] Projects that relied on groundwater and pumped too much from underground aquifers created subsidence and salinization. Salinization of irrigation water in turn damaged the crops and seeped into drinking water.[34] Pests and pathogens also thrived in the irrigation canals or ponds full of still water, which created regional outbreaks of diseases like malaria and schistosomiasis.[35][36][37] Governments also used irrigation schemes to encourage migration, especially of more desirable populations into an area.[38][39][40] Additionally, some of these large nationwide schemes failed to pay off at all, costing more than any benefit gained from increased crop yields.[41][42]

Overdrafting (depletion) of underground aquifers: In the mid-20th century, the advent of diesel and electric motors led to systems that could pump groundwater out of major aquifers faster than drainage basins could refill them. This can lead to permanent loss of aquifer capacity, decreased water quality, ground subsidence, and other problems. The future of food production in such areas as the North China Plain, the Punjab region in India and Pakistan, and the Great Plains of the US is threatened by this phenomenon.[43][44]

This section is an excerpt from Environmental effects of irrigation.

The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme. The effects stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme.

Amongst some of these problems is depletion of underground aquifers through overdrafting. Soil can be over-irrigated due to poor distribution uniformity or management wastes water, chemicals, and may lead to water pollution. Over-irrigation can cause deep drainage from rising water tables that can lead to problems of irrigation salinity requiring watertable control by some form of subsurface land drainage. However, if the soil is under irrigated, it gives poor soil salinity control which leads to increased soil salinity with the consequent buildup of toxic salts on the soil surface in areas with high evaporation. This requires either leaching to remove these salts and a method of drainage to carry the salts away. Irrigation with saline or high-sodium water may damage soil structure owing to the formation of alkaline soil.

Technical challenges

(

Overirrigation because of poor distribution uniformity in the furrows. Potato plants were oppressed and turned yellow

Irrigation schemes involve solving numerous engineering and economic problems while minimizing negative environmental consequences.[33] Such problems include:

Social aspects

History

Ancient history

Animal-powered irrigation, Upper Egypt, ca. 1846

Archaeological investigation has found evidence of irrigation in areas lacking sufficient natural rainfall to support crops for rainfed agriculture. Some of the earliest known use of the technology dates to the 6th millennium BC in Khuzistan in the south-west of Iran.[53][54] The site of Choga Mami, in present-day Iraq on the border with Iran, is believed to be the earliest to show the first canal irrigation in operation at about 6000 BCE.[55]

Irrigation was used as a means of manipulation of water in the alluvial plains of the Indus valley civilization, the application of which is estimated to have begun around 4500 BC and drastically increased the size and prosperity of their agricultural settlements.[56] The Indus Valley Civilization developed sophisticated irrigation and water-storage systems, including artificial reservoirs at Girnar dated to 3000 BCE, and an early canal irrigation system from c. 2600 BCE. Large-scale agriculture was practiced, with an extensive network of canals used for the purpose of irrigation.[56][57]

Farmers in the Mesopotamian plain used irrigation from at least the third millennium BCE.[58] They developed perennial irrigation, regularly watering crops throughout the growing season by coaxing water through a matrix of small channels formed in the field.[59] Ancient Egyptians practiced basin irrigation using the flooding of the Nile to inundate land plots which had been surrounded by dikes. The flood water remained until the fertile sediment had settled before the engineers returned the surplus to the watercourse.[60] There is evidence of the ancient Egyptian pharaoh Amenemhet III in the twelfth dynasty (about 1800 BCE) using the natural lake of the Faiyum Oasis as a reservoir to store surpluses of water for use during dry seasons. The lake swelled annually from the flooding of the Nile.[61]

(

Young engineers restoring and developing the old Mughal irrigation system in 1847 during the reign of the Mughal Emperor Bahadur Shah II in Indian subcontinent.

The Ancient Nubians developed a form of irrigation by using a waterwheel-like device called a sakia. Irrigation began in Nubia some time between the third and second millennia BCE.[62] It largely depended upon the flood waters that would flow through the Nile River and other rivers in what is now the Sudan.[63]

In sub-Saharan Africa irrigation reached the Niger River region cultures and civilizations by the first or second millennium BCE and was based on wet-season flooding and water harvesting.[64][65]

Evidence of terrace irrigation occurs in pre-Columbian America, early Syria, India, and China.[60] In the Zana Valley of the Andes Mountains in Peru, archaeologists have found remains of three irrigation canals radiocarbon-dated from the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE. These canals provide the earliest record of irrigation in the New World. Traces of a canal possibly dating from the 5th millennium BCE were found under the 4th-millennium canal.[66]

Ancient Persia (modern day Iran) used irrigation as far back as the 6th millennium BCE to grow barley in areas with insufficient natural rainfall.[67][53] The Qanats, developed in ancient Persia about 800 BCE, are among the oldest known irrigation methods still in use today. They are now found in Asia, the Middle East and North Africa. The system comprises a network of vertical wells and gently sloping tunnels driven into the sides of cliffs and of steep hills to tap groundwater.[68] The noria, a water wheel with clay pots around the rim powered by the flow of the stream (or by animals where the water source was still), first came into use at about this time among Roman settlers in North Africa. By 150 BCE the pots were fitted with valves to allow smoother filling as they were forced into the water.[69]

Sri Lanka

Main article: Sri Lankan irrigation network

The irrigation works of ancient Sri Lanka, the earliest dating from about 300 BCE in the reign of King Pandukabhaya, and under continuous development for the next thousand years, were one of the most complex irrigation systems of the ancient world. In addition to underground canals, the Sinhalese were the first to build completely artificial reservoirs to store water.[citation needed] These reservoirs and canal systems were used primarily to irrigate paddy fields, which require a lot of water to cultivate. Most of these irrigation systems still exist undamaged up to now, in Anuradhapura and Polonnaruwa, because of the advanced and precise engineering. The system was extensively restored and further extended[by whom?] during the reign of King Parakrama Bahu (1153–1186 CE).[70]

China

Inside a karez tunnel at Turpan, Xinjiang, China.

The oldest known hydraulic engineers of China were Sunshu Ao (6th century BCE) of the Spring and Autumn period and Ximen Bao (5th century BCE) of the Warring States period, both of whom worked on large irrigation projects. In the Sichuan region belonging to the state of Qin of ancient China, the Dujiangyan Irrigation System devised by the Qin Chinese hydrologist and irrigation engineer Li Bing was built in 256 BCE to irrigate a vast area of farmland that today still supplies water.[71]

By the 2nd century AD, during the Han Dynasty, the Chinese also used chain pumps which lifted water from a lower elevation to a higher one.[72] These were powered by manual foot-pedal, hydraulic waterwheels, or rotating mechanical wheels pulled by oxen.[73] The water was used for public works, providing water for urban residential quarters and palace gardens, but mostly for irrigation of farmland canals and channels in the fields.[74]

Korea

Korea, Jang Yeong-sil, a Korean engineer of the Joseon Dynasty, under the active direction of the king, Sejong the Great, invented the world's first rain-gauge, uryanggye (Korean:우량계) in 1441. It was installed in irrigation tanks[by whom?] as part of a nationwide system to measure and collect rainfall for agricultural applications. With this instrument, planners and farmers could make better use of the information gathered in the[which?] survey.[75]

North America

Main article: Hohokam

The earliest agricultural irrigation canal system known in the area of the present-day United States dates to between 1200 B.C. and 800 B.C. and was discovered by Desert Archaeology, Inc. in Marana, Arizona (adjacent to Tucson) in 2009.[76] The irrigation-canal system predates the Hohokam culture by two thousand years and belongs to an unidentified culture. In North America, the Hohokam were the only culture known to rely on irrigation canals to water their crops, and their irrigation systems supported the largest population in the Southwest by AD 1300. The Hohokam constructed an assortment of simple canals combined with weirs in their various agricultural pursuits.

Between the 7th and 14th centuries they built and maintained extensive irrigation networks along the lower Salt and middle Gila Rivers that rivaled the complexity of those used in the ancient Near East, Egypt, and China. These were constructed using relatively simple excavation tools, without the benefit of advanced engineering technologies, and achieved drops of a few feet per mile, balancing erosion and siltation. The Hohokam cultivated varieties of cotton, tobacco, maize, beans and squash, as well as harvesting an assortment of wild plants. Late in the Hohokam Chronological Sequence, they also used extensive dry-farming systems, primarily to grow agave for food and fiber. Their reliance on agricultural strategies based on canal irrigation, vital in their less-than-hospitable desert environment and arid climate, provided the basis for the aggregation of rural populations into stable urban centers.[77][need ^quotation ^to verify]

South America

See also: Zaña Valley

The oldest known irrigation canals in the Americas are in the desert of northern Peru in the Zaña valley near the hamlet of Nanchoc. The canals have been radiocarbon dated to at least 3400 B.C. and possibly as old as 4700 B.C. The canals at that time irrigated crops such as peanuts, squash, manioc, chenopods, a relative of Quinoa, and later maize.[66]

Modern history

The scale of irrigation increased dramatically over the 20th century. In 1800, 8 million hectares globally were irrigated, in 1950, 94 million hectares, and in 1990, 235 million hectares. By 1990, 30% of the global food production came from irrigated land.[78] Irrigation techniques across the globe included canals redirecting surface water,[79] [80] groundwater pumping, and diverting water from dams. National governments led most irrigation schemes within their borders, but private investors[81] and other nations,[82] especially the United States,[83] China,[84] and European countries like the United Kingdom,[85] funded and organized some schemes within other nations.

Irrigation enabled the production of more crops, especially commodity crops in areas which otherwise could not support them. Countries frequently invested in irrigation to increase wheat, rice, or cotton production, often with the overarching goal of increasing self-sufficiency.[86] In the 20th century, global anxiety specifically about the American cotton monopoly fueled many empirical irrigation projects: Britain began developing irrigation in India, the Ottomans in Egypt, the French in Algeria, the Portuguese in Angola, the Germans in Togo, and Soviets in Central Asia.[87]

Negative impacts frequently accompanied extensive irrigation. Some projects which diverted surface water for irrigation dried up the water sources, which led to a more extreme regional climate.[88] Projects that relied on groundwater and pumped too much from underground aquifers created subsidence and salinization. Salinization of irrigation water in turn damaged the crops and seeped into drinking water.[89] Pests and pathogens also thrived in the irrigation canals or ponds full of still water, which created regional outbreaks of diseases like malaria and schistosomiasis.[90][91][92] Governments also used irrigation schemes to encourage migration, especially of more desirable populations into an area.[93][94][95] Additionally, some of these large nationwide schemes failed to pay off at all, costing more than any benefit gained from increased crop yields.[96][97]

American West

Irrigated land in the United States increased from 300,000 acres in 1880 to 4.1 million in 1890, then to 7.3 million in 1900.[42] Two thirds of this irrigation sources from groundwater or small ponds and reservoirs, while the other one third comes from large dams.[98] One of the main attractions of irrigation in the West was its increased dependability compared to rainfall-watered agriculture in the East. Proponents argued that farmers with a dependable water supply could more easily get loans from bankers interested in this more predictable farming model.[99] Most irrigation in the Great Plains region derived from underground aquifers. Euro-American farmers who colonized the region in the 19th century tried to grow the commodity crops that they were used to, like wheat, corn, and alfalfa, but rainfall stifled their growing capacity.

Between the late 1800s and the 1930s, farmers used wind-powered pumps to draw groundwater. These windpumps had limited power, but the development of gas-powered pumps in the mid-1930s pushed wells deep into the Ogallala Aquifer. Farmers irrigated fields by laying pipes across the field with sprinklers at intervals, a labor-intensive process, until the advent of the center-pivot sprinkler after WWII, which made irrigation significantly easier.[100] By the 1970s farmers drained the aquifer ten times faster than it could recharge, and by 1993 they had removed half of the accessible water.[101]

Large-scale federal funding and intervention pushed through the majority of irrigation projects in the West, especially in California, Colorado, Arizona, and Nevada. At first, plans to increase irrigated farmland, largely by giving land to farmers and asking them to find water, failed across the board. Congress passed the Desert Land Act in 1877 and the Carey Act in 1894, which only marginally increased irrigation.[102] Only in 1902 Congress passed the National Reclamation Act, which channeled money from the sale of western public lands, in parcels up to 160 acres large, into irrigation projects on public or private land in the arid West.[103] The Congressmen who passed the law, as well as their wealthy supporters, supported Western irrigation because it would increase American exports, ‘reclaim’ the West, and push the Eastern poor out West in search of a better life.[104]

While the National Reclamation Act was the most successful piece of federal irrigation legislation, the implementation of the act did not go as planned. Originally, the Reclamation Service planned to construct a small number of projects that would allow engineers to learn from the process, but President Roosevelt chose instead push as many irrigation projects through as fast as possible. The Reclamation Service also chose to push most of the Act’s money toward construction rather than settlement, so the Service overwhelmingly prioritized building large dams like the Hoover Dam.[105]

Over the 20th century Congress and state governments grew more frustrated with the Reclamation Service and the irrigation schemes in general. Frederick Newell, head of the Reclamation Service, proving uncompromising and difficult to work with, falling crop prices, resistance to delay debt payments, and refusal to begin new projects until the completion of old ones all contributed.[106] The Reclamation Extension Act of 1914, transferring a significant amount of irrigation decision-making power regarding irrigation projects from the Reclamation Service to Congress, was in many ways a result of an increasing political unpopularity of the Reclamation Service.[107]

In the lower Colorado Basin of Arizona, Colorado, and Nevada, the states derive irrigation water largely from rivers, especially the Colorado River, which irrigates more than 4.5 million acres of land, with a less significant amount coming from groundwater.[108] In the 1952 case Arizona v. California, Arizona sued California for increased access to the Colorado, under the grounds that their groundwater supply could not sustain their almost entirely irrigation-based agricultural economy, which they won.[109] California, which began irrigating in earnest in the 1870s in San Joaquin Valley,[110] had passed the Wright Act of 1887 permitting agricultural communities to construct and operate needed irrigation works.[111] The Colorado also irrigates large fields in California’s Imperial Valley, fed by the National Reclamation Act-built All-American Canal.[112][113]

Soviet Central Asia

When the Bolsheviks conquered Central Asia in 1917, the native Kazakhs, Uzbeks, and Turkmens used minimal irrigation. The Slavic immigrants pushed into the area by the Tsarist government[114] brought their own irrigation methods, including waterwheels, the use of rice paddies to restore salted land, and underground irrigation channels. Russians dismissed these techniques as crude and inefficient. Despite this, in absence of other solutions, tsarist officials maintained these systems through the late 19th century.[115]

Before conquering the area, the Russian government accepted a 1911 American proposal to send hydraulic experts to Central Asia to investigate the potential for large-scale irrigation. A 1918 decree by Lenin then encouraged irrigation development in the region, and development began in the 1930s. When it did, Stalin and other Soviet leaders prioritized large-scale, ambitious hydraulic projects, especially along the Volga River. The Soviet irrigation push stemmed largely from their late 19th century fears of the American cotton monopoly and subsequent desire to achieve cotton self-sufficiency.[116] They had built up their textile manufacturing industry in the 19th century, requiring increased cotton and irrigation, as the region did not receive enough rainfall to support cotton farming.[115]

The Russians built dams on the Don and Kuban Rivers for irrigation, removing freshwater flow from the Sea of Azov and making it much saltier. Depletion and salinization scourged other areas of the Russian irrigation project. In the 1950s Soviet officials began also diverting the Syr Darya and the Amu Darya, which fed the Aral Sea. Before diversion, the rivers delivered 55km3 of water to the Aral Sea per year, but after they only delivered 6km3 to the Sea. Because of its reduced inflow, the Aral Sea covered less than half of its original seabed, which made the regional climate more extreme and created airborne salinization, lowering nearby crop yields.[117]

By 1975, the USSR used eight times as much water as they had in 1913, mostly for irrigation. Russia’s expansion of irrigation began to decrease in the late 1980s, and irrigated hectares in Central Asia capped out at 7 million. Mikhail Gorbachev killed a proposed plan to reverse the Ob and Yenisei for irrigation in 1986, and the breakup of the USSR in 1991 ended Russian investment in Central Asian cotton irrigation.[118]

Africa

Different irrigation schemes with a variety of goals and success rates have been implemented across Africa in the 20th century, but have all been influenced by colonial forces. The Tana River Irrigation Scheme in eastern Kenya, completed between 1948 and 1963, opened up new lands for agriculture, and the Kenyan government attempted to resettle the area with detainees from the Mau Mau uprising.[119] Libya’s underground water resources were discovered by Italian oil drillers during the Italian colonization of Libya. This water lay dormant until 1969, when Muammar al-Gaddafi and American Armand Hammer built the Great Man-Made River to deliver the Saharan water to the coast. The water largely contributed to irrigation but cost four to ten times more than the crops it produced were worth.[120]

In 1912, the Union of South Africa created an irrigation department and began investing in water storage infrastructure and irrigation. The government used irrigation and dam-building to further social goals like poverty relief, both by creating construction jobs for poor whites and by creating irrigation schemes to increase white farming. One of their first major irrigation projects was the Hartbeespoort Dam, begun in 1916 as a mechanism to elevate the living conditions of the ‘poor whites’ in the region and eventually completed as a ‘whites only’ employment opportunity.[121] The Pretoria irrigation scheme, Kammanassie project, and Buchuberg irrigation scheme on the Orange River all followed in the same vein in the 1920s and 30s.[39]

In Egypt, modern irrigation began with Muhammad Ali Pasha in the mid-1800s, who sought to achieve Egyptian independence from the Ottomans through increased trade with Europe—specifically cotton exportation.[122] His administration proposed replacing the traditional Nile basin irrigation, which took advantage of the annual ebb and flow of the Nile, with irrigation barrages in the lower Nile which better suited cotton production. Egypt devoted 105,000 ha to cotton in 1861, which increased fivefold by 1865.

The majority of their exports were shipped to England, and the United-States-Civil-War-induced cotton scarcity in the 1860s cemented Egypt as England’s cotton producer.[123] As the Egyptian economy became more dependent on cotton in the 20th century, it became more important to control even small Nile floods. Cotton production was more at risk of destruction than more common crops like barley or wheat.[124] After the British occupation of Egypt in 1882, the British intensified the conversion to perennial irrigation with the construction of the Delta Barrage, the Assiut Barrage, and the first Aswan Dam. Perennial irrigation decreased local control over water and made traditional subsistence farming or the farming of other crops incredibly difficult, eventually contributing to widespread peasant bankruptcy and the 1879-1882 ‘Urabi revolt.[125]

Examples by country

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Irrigation - Wikipedia