The environmental effects of irrigation relate to the changes in quantity and quality of

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

as a result of

irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...

and the subsequent effects on natural and social conditions in

river basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, the ...

s and downstream of an

irrigation scheme 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 develo ...

. 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 An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

through

overdrafting Overdrafting is the process of extracting groundwater beyond the equilibrium yield of an aquifer. Groundwater is one of the largest sources of fresh water and is found underground. Groundwater depletion is comparable to a bank account in which mor ...

. Soil can be over-irrigated due to poor

distribution uniformity Distribution uniformity or DU in irrigation is a measure of how uniformly water is applied to the area being watered, normally expressed as percentage, and not to be confused with efficiency. The distribution uniformity is often calculated when pe ...

management Management (or managing) is the administration of an organization, whether it is a business, a nonprofit organization, or a government body. It is the art and science of managing resources of the business. Management includes the activities o ...

wastes water, chemicals, and may lead to

water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...

. Over-irrigation can cause deep drainage from rising water tables that can lead to problems of irrigation

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

requiring

watertable control Watertable control is the practice of controlling the height of the water table by drainage. Its main applications are in agricultural land (to improve the crop yield using agricultural drainage systems) and in cities to manage the extensive under ...

by some form of subsurface land drainage. However, if the soil is under irrigated, it gives poor

soil salinity control Soil salinity control relates to controlling the problem of soil salinity and reclaiming salinized agricultural land. The aim of soil salinity control is to prevent soil degradation by salination and reclamation of already salty (saline) soil ...

which leads to increased

soil salinity Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...

with the consequent buildup of toxic

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...

on the soil surface in areas with high

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

. This requires either

leaching Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to: * Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...

to remove these salts and a method of

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic conditio ...

to carry the salts away. Irrigation with saline or high-sodium water may damage soil structure owing to the formation of

alkaline soil Alkali, or Alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico- ...

Direct effects

draws water from groundwater,

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s or

overland flow Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the s ...

, and distributes it over a certain area.

Hydrological Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...

, or direct, effects of doing this include reduction in downstream river flow, increased

in the irrigated area, increased level in the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in ...

in the area is increased and flow increased in the irrigated area. Likewise, irrigation has immediate effects on the provision of moisture to the atmosphere, inducing atmospheric instabilities and increasing downwind rainfall, or in other cases modifies the atmospheric circulation, delivering rain to different downwind areas. Increases or decreases in irrigation are a key area of concern in

precipitationshed A precipitationshed is the upwind ocean and land surface that contributes evaporation to a given, downwind location's precipitation. The concept has been described as an "atmospheric watershed". The concept itself rests on a broad foundation of sc ...

studies, that examine how significant modifications to the delivery of evaporation to the atmosphere can alter downwind rainfall.

Indirect Effects

Indirect effects are those that have consequences that take longer to develop and may also be longer-lasting. The indirect effects of irrigation include the following: * Waterlogging *

Soil salination Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...

* Ecological damage *

Socioeconomic Socioeconomics (also known as social economics) is the social science that studies how economic activity affects and is shaped by social processes. In general it analyzes how modern societies progress, stagnate, or regress because of their local ...

impacts The indirect effects of waterlogging and

soil salination Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...

occur directly on the land being irrigated. The

ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

and

socioeconomic Socioeconomics (also known as social economics) is the social science that studies how economic activity affects and is shaped by social processes. In general it analyzes how modern societies progress, stagnate, or regress because of their local ...

consequences take longer to happen but can be more far-reaching. Some

s use

water wells A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

for irrigation. As a result, the overall water level decreases. This may cause water mining, land/soil

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...

, and, along the coast,

saltwater intrusion Saltwater intrusion is the movement of saline water into freshwater aquifers, which can lead to groundwater quality degradation, including drinking water sources, and other consequences. Saltwater intrusion can naturally occur in coastal aquifers ...

. Irrigated land area worldwide occupies about 16% of the total agricultural area and the crop yield of irrigated land is roughly 40% of the total yield.Bruce Sundquist, 2007. Chapter 1- ''Irrigation overview''. In: The earth's carrying capacity, Some related reviews, and analysis. On line: In other words, irrigated land produces 2.5 times more product than non-irrigated land.

Adverse impacts

Reduced river flow

The reduced downstream river flow may cause: *reduced downstream flooding *disappearance of ecologically and economically important wetlands or flood forestsWorld Wildlife Fund, ''WWF Names World's Top 10 Rivers at Greatest Risk'', online: http://www.ens-newswire.com/ens/mar2007/2007-03-21-01.asp *reduced availability of industrial, municipal, household, and drinking water *reduced shipping routes. Water withdrawal poses a serious threat to the

Ganges The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...

. In India, barrages control all of the tributaries to the Ganges and divert roughly 60 percent of river flow to irrigation *reduced fishing opportunities. The

Indus The Indus ( ) is a transboundary river of Asia and a trans-Himalayan river of South and Central Asia. The river rises in mountain springs northeast of Mount Kailash in Western Tibet, flows northwest through the disputed region of Kashmir, ...

River in

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...

faces scarcity due to the over-extraction of water for agriculture. The Indus is inhabited by 25 amphibian species and 147 fish species of which 22 are found nowhere else in the world. It harbors the endangered

Indus river dolphin The Indus river dolphin (''Platanista minor''), also known as the ''bhulan'' in Urdu and Sindhi, is a species of toothed whale in the family Platanistidae. It is endemic to the Indus River Basin of Pakistan and northwestern India. This dolphin ...

, one of the world's rarest mammals. Fish populations, the main source of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

and overall life support systems for many communities, are also being threatened *reduced discharge into the sea, which may have various consequences like

coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...

(e.g. in

Ghana Ghana (; tw, Gaana, ee, Gana), officially the Republic of Ghana, is a country in West Africa. It abuts the Gulf of Guinea and the Atlantic Ocean to the south, sharing borders with Ivory Coast in the west, Burkina Faso in the north, and To ...

) and saltwater intrusion in delta's and estuaries (e.g. in

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...

, see

Aswan dam The Aswan Dam, or more specifically since the 1960s, the Aswan High Dam, is one of the world's largest embankment dams, which was built across the Nile in Aswan, Egypt, between 1960 and 1970. Its significance largely eclipsed the previous Aswan L ...

). Current water withdrawal from the river

Nile The Nile, , Bohairic , lg, Kiira , Nobiin language, Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered ...

for irrigation is so high that, despite its size, in dry periods the river does not reach the sea. The

Aral Sea The Aral Sea ( ; kk, Арал теңізі, Aral teñızı; uz, Орол денгизи, Orol dengizi; kaa, Арал теңизи, Aral teńizi; russian: Аральское море, Aral'skoye more) was an endorheic basin, endorheic lake lyi ...

has suffered an "environmental catastrophe" due to the interception of river water for irrigation purposes.

Increased groundwater recharge, waterlogging, soil salinity

Increased groundwater recharge stems from the unavoidable

deep percolation Groundwater recharge or deep drainage or deep percolation is a Hydrology, hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually ...

losses occurring in the irrigation scheme. The lower the irrigation efficiency, the higher the losses. Although fairly high irrigation efficiencies of 70% or more (i.e. losses of 30% or less) can occur with sophisticated techniques like sprinkler irrigation and

drip irrigation Drip irrigation or trickle irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. ...

, or by well managed

surface irrigation Surface irrigation is where water is applied and distributed over the soil surface by gravity. It is by far the most common form of irrigation throughout the world and has been practiced in many areas virtually unchanged for thousands of years. S ...

, in practice the losses are commonly in the order of 40% to 60%. This may cause the following issues: * rising water tables * increased storage of groundwater that may be used for irrigation, municipal, household, and drinking water by pumping from

well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

s * waterlogging and drainage problems in villages, agricultural lands, and along roads - with mostly negative consequences. The increased level of the water table can lead to reduced agricultural production. * shallow water tables - a sign that the aquifer is unable to cope with the groundwater recharge stemming from the deep percolation losses * where water tables are shallow, the irrigation applications are reduced. As a result, the soil is no longer leached and

problems develop * stagnant water tables at the soil surface are known to increase the incidence of water-borne diseases like

malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...

filariasis Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding insects such as black flies and mosquitoes. They belong to the group of diseases called helminthiases. These ...

yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains – particularly in the back – and headaches. Symptoms typically improve within five days. In ...

dengue Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. Symptoms typically begin three to fourteen days after infection. These may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic ...

, and

schistosomiasis Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a disease caused by parasitic flatworms called schistosomes. The urinary tract or the intestines may be infected. Symptoms include abdominal pain, diarrhea, bloody s ...

(Bilharzia) in many areas. Health costs, appraisals of health impacts and mitigation measures are rarely part of irrigation projects, if at all.Himanshu Thakkar. ''Assessment of Irrigation in India''. World Commission on Dams. On line: http://www.dams.org/docs/kbase/contrib/opt161.pdf * to mitigate the adverse effects of shallow water tables and soil salinization, some form of

and drainage system is needed * as drainage water moves through the soil profile it may dissolve nutrients (either fertilizer-based or naturally occurring) such as nitrates, leading to a buildup of those nutrients in the ground-water aquifer. High nitrate levels in drinking water can be harmful to humans, particularly infants under 6 months, where it is linked to "blue-baby syndrome" (see Methemoglobinemia).

Reduced downstream river water quality

Owing to drainage of surface and groundwater in the project area, which waters may be salinized and polluted by agricultural chemicals like

biocides A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a sli ...

and

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

s, the quality of the river water below the project area can deteriorate, which makes it less fit for industrial, municipal and household use. It may lead to reduced public health.
Polluted river water entering the sea may adversely affect the ecology along the seashore (see

). The natural contribution of sediments can be eliminated by the detention of sediments behind the dams critical to surface water irrigation diversions. Sedimentation is an essential part of the ecosystem that requires the natural flux of the river flow. This natural cycle of sediment dispersion replenishes the nutrients in the soil, which will, in turn, determine the livelihood of the plants and animals that rely on the sediments carried downstream. The benefits of heavy deposits of sedimentation can be seen in large rivers like the Nile River. The sediment from the delta has built up to form a giant aquifer during flood season and retains water in the wetlands. The wetlands that are created and sustained due to built-up sediment at the basin of the river are a habitat for numerous species of birds. However, heavy sedimentation can reduce downstream river water quality and can exacerbate floods upstream. This has been known to happen in the Sanmenxia reservoir in China. The Sanmenxia reservoir is part of a larger man-made project of hydroelectric dams called the Three Gorge Project In 1998, uncertain calculations and heavy sediment greatly affected the reservoir’s ability to properly fulfill its flood-control function This also reduces the downstream river water quality. Shifting more towards mass irrigation installments in order to meet more socioeconomic demands is going against the natural balance of nature, and use water pragmatically- use it where it is found

Affected downstream water users

Downstream water users often have no legal water rights and may fall victim to the development of irrigation.

Pastoralists Pastoralism is a form of animal husbandry where domesticated animals (known as "livestock") are released onto large vegetated outdoor lands (pastures) for grazing, historically by nomadic people who moved around with their herds. The animal s ...

and

nomadic tribes A nomad is a member of a community without fixed habitation who regularly moves to and from the same areas. Such groups include hunter-gatherers, pastoral nomads (owning livestock), tinkers and trader nomads. In the twentieth century, the popu ...

may find their land and water resources blocked by new irrigation developments without having legal recourse. Flood-recession cropping may be seriously affected by the upstream interception of river water for irrigation purposes. * In

Baluchistan Balochistan ( ; bal, بلۏچستان; also romanised as Baluchistan and Baluchestan) is a historical region in Western and South Asia, located in the Iranian plateau's far southeast and bordering the Indian Plate and the Arabian Sea coastline. ...

, the development of new small-scale irrigation projects depleted the water resources of

traveling annually between Baluchistan and

Gujarat Gujarat (, ) is a state along the western coast of India. Its coastline of about is the longest in the country, most of which lies on the Kathiawar peninsula. Gujarat is the fifth-largest Indian state by area, covering some ; and the ninth ...

Rajasthan Rajasthan (; lit. 'Land of Kings') is a state in northern India. It covers or 10.4 per cent of India's total geographical area. It is the largest Indian state by area and the seventh largest by population. It is on India's northwestern si ...

, India''Modern interferences in traditional water resources in Baluchistan''. In: Annual Report 1982, pp. 23-34. ILRI, Wageningen, The Netherlands. Reprinted in Water International 9 (1984), pp. 106- 111. Elsevier Sequoia, Amsterdam. Also reprinted in Water Research Journal (1983) 139, pp. 53-60. Download from

under nr. 10, or directly as PDF

/ref> *After the closure of the Kainji Dam, Kainji dam,

Nigeria Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...

, 50 to 70 per cent of the downstream area of flood-recession cropping was lost

Lost land use opportunities

Irrigation projects may reduce the fishing opportunities of the original population and the grazing opportunities for cattle. The

livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animals ...

pressure on the remaining lands may increase considerably, because the ousted traditional pastoralist tribes will have to find their

subsistence A subsistence economy is an economy directed to basic subsistence (the provision of food, clothing, shelter) rather than to the market. Henceforth, "subsistence" is understood as supporting oneself at a minimum level. Often, the subsistence econo ...

and existence elsewhere,

overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...

may increase, followed by serious

soil erosion Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and ...

and the loss of

natural resources Natural resources are resources that are drawn from nature and used with few modifications. This includes the sources of valued characteristics such as commercial and industrial use, aesthetic value, scientific interest and cultural value. O ...

.
The Manatali reservoir formed by the Manantali dam in

Mali Mali (; ), officially the Republic of Mali,, , ff, 𞤈𞤫𞤲𞥆𞤣𞤢𞥄𞤲𞤣𞤭 𞤃𞤢𞥄𞤤𞤭, Renndaandi Maali, italics=no, ar, جمهورية مالي, Jumhūriyyāt Mālī is a landlocked country in West Africa. Mali ...

intersects the migration routes of nomadic pastoralists and destroyed 43000 ha of

savannah A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the Canopy (forest), canopy does not close. The open canopy allows sufficient light to rea ...

, probably leading to overgrazing and erosion elsewhere. Further, the reservoir destroyed 120 km² of

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

. The depletion of groundwater aquifers, which is caused by the suppression of the seasonal flood cycle, is damaging the forests downstream of the dam.

Groundwater mining with wells, land subsidence

When more groundwater is pumped from wells than replenished, storage of water in the

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

is being mined and the use of that water is no longer sustainable. As levels fail, it becomes more difficult to extract water and pumps will struggle to maintain the design flow rate and may consume more energy per unit of water. Eventually, it may become so difficult to extract groundwater that farmers may be forced to abandon irrigated agriculture.
Some notable examples include: * The hundreds of tubewells installed in the state of

Uttar Pradesh Uttar Pradesh (; , 'Northern Province') is a state in northern India. With over 200 million inhabitants, it is the most populated state in India as well as the most populous country subdivision in the world. It was established in 1950 ...

, India, with World Bank funding have operating periods of 1.4 to 4.7 hours/day, whereas they were designed to operate 16 hours/day * In

, the development of tubewell irrigation projects was at the expense of the traditional

qanat A qanat or kārīz is a system for transporting water from an aquifer or water well to the surface, through an underground aqueduct; the system originated approximately 3,000 BC in what is now Iran. The function is essentially the same across ...

karez A qanat or kārīz is a system for transporting water from an aquifer or water well to the surface, through an underground aqueduct; the system originated approximately 3,000 BC in what is now Iran. The function is essentially the same across ...

users *

groundwater-related subsidence Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation an ...

of the land due to mining of groundwater occurred in the United States at a rate of 1m for every 13m that the water table was lowered * Homes at Greens Bayou near

Houston Houston (; ) is the most populous city in Texas, the most populous city in the Southern United States, the fourth-most populous city in the United States, and the sixth-most populous city in North America, with a population of 2,304,580 in ...

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

, where 5 to 7 feet of subsidence has occurred, was flooded during a storm in June 1989 as shown in the picture

Simulation and prediction

The effects of irrigation on the water table, soil salinity and salinity of drainage and groundwater, and the effects of mitigative measures can be simulated and predicted using agro-hydro-salinity models like

SaltMod SaltMod is computer program for the prediction of the salinity of soil moisture, groundwater and drainage water, the depth of the watertable, and the drain discharge (hydrology) in irrigated agricultural lands, using different (geo)hydrologic cond ...

and

SahysMod SahysMod is a computer program for the prediction of the salinity of soil moisture, groundwater and drainage water, the depth of the watertable, and the drain discharge in irrigated agricultural lands, using different hydrogeologic and aquifer con ...

Case studies

#In India 2.19 million ha of land has been reported to suffer from waterlogging in irrigation canal commands. Also, 3.47 million ha were reported to be seriously salt-affected, # In the

Plains in

, more than 2 million hectares of land are waterlogged.Green Living Association Pakistan, ''Environmental Issues''. The soil of 13.6 million hectares within the Gross Command Area was surveyed, which revealed that 3.1 million hectares (23%) were saline. 23% of this was in

Sindh Sindh (; ; ur, , ; historically romanized as Sind) is one of the four provinces of Pakistan. Located in the southeastern region of the country, Sindh is the third-largest province of Pakistan by land area and the second-largest province ...

and 13% in the

Punjab Punjab (; Punjabi: پنجاب ; ਪੰਜਾਬ ; ; also romanised as ''Panjāb'' or ''Panj-Āb'') is a geopolitical, cultural, and historical region in South Asia, specifically in the northern part of the Indian subcontinent, comprising ...

. More than 3 million ha of water-logged lands have been provided with tube-wells and drains at the cost of billions of rupees, but the reclamation objectives were only partially achieved. The

Asian Development Bank The Asian Development Bank (ADB) is a regional development bank established on 19 December 1966, which is headquartered in the Ortigas Center located in the city of Mandaluyong, Metro Manila, Philippines. The bank also maintains 31 field office ...

(ADB) states that 38% of the irrigated area is now waterlogged and 14% of the surface is too saline for use #In the

Nile delta The Nile Delta ( ar, دلتا النيل, or simply , is the delta formed in Lower Egypt where the Nile River spreads out and drains into the Mediterranean Sea. It is one of the world's largest river deltas—from Alexandria in the west to Po ...

, drainage is being installed in millions of hectares to combat the water-logging resulting from the introduction of massive perennial irrigation after completion of the High Dam at

Assuan Aswan (, also ; ar, أسوان, ʾAswān ; cop, Ⲥⲟⲩⲁⲛ ) is a city in Southern Egypt, and is the capital of the Aswan Governorate. Aswan is a busy market and tourist centre located just north of the Aswan Dam on the east bank of the ...

#In Mexico, 15% of the 3 million ha of irrigable land is salinized and 10% is waterlogged #In

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

some 0.3 million ha of the 1.05 million ha of irrigable land suffers from degradation (see

Irrigation in Peru Water resources and irrigation infrastructure in Peru vary throughout the country. The coastal region, an arid but fertile land, has about two-thirds of Peru’s irrigation infrastructure due to private and public investment aimed at increasing ...

). #Estimates indicate that roughly one-third of the irrigated land in the major irrigation countries is already badly affected by salinity or is expected to become so in the near future. Present estimates for Israel are 13% of the irrigated land, Australia 20%, China 15%,

Iraq Iraq,; ku, عێراق, translit=Êraq officially the Republic of Iraq, '; ku, کۆماری عێراق, translit=Komarî Êraq is a country in Western Asia. It is bordered by Turkey to Iraq–Turkey border, the north, Iran to Iran–Iraq ...

50%,

30%. Irrigation-induced salinity occurs in large and small irrigation systems alike #FAO has estimated that by 1990 about 52 million ha of irrigated land will need to have improved drainage systems installed, much of it

subsurface drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic condition ...

to control salinity

Reduced downstream drainage and groundwater quality

*The downstream drainage water quality may deteriorate owing to

of salts,

nutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

herbicides Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...

and

pesticides Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampric ...

with high salinity and alkalinity. There is the threat of soils converting into saline or

alkali soils Alkali, or Alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico ...

. This may negatively affect the health of the population at the tail-end of the river basin and downstream of the irrigation scheme, as well as the ecological balance. The

, for example, is seriously

polluted Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

by drainage water. *The downstream quality of the groundwater may deteriorate in a similar way as the downstream drainage water and have similar consequences

Mitigation of adverse effects

Irrigation can have a variety of negative impacts on

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

and

socioeconomy Socioeconomics (also known as social economics) is the social science that studies how economic activity affects and is shaped by social processes. In general it analyzes how modern society, societies social progress, progress, economic stagnation ...

, which may be mitigated in a number of ways. These include siting the irrigation project in a location that minimizes negative impacts. The efficiency of existing projects can be improved and existing degraded

croplands A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used f ...

can be improved rather than establishing a new irrigation project Developing small-scale, individually owned irrigation systems as an alternative to large-scale, publicly owned and managed schemes. The use of sprinkler irrigation and

micro-irrigation Micro-irrigation, also called Micro-spray,localized, low-volume, low-flow, or trickle irrigation, is an irrigation method with lower water pressure and flow than a traditional sprinkler system. Low-volume irrigation is used in agriculture for r ...

systems decreases the risk of waterlogging and

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

. Where practicable, using treated

wastewater Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...

makes more water available to other users Maintaining flood flows downstream of the dams can ensure that an adequate area is flooded each year, supporting, amongst other objectives,

fishery Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...

activities.

Delayed environmental impacts

It often takes time to accurately predict the impact that new irrigation schemes will have on the

and

of a region. By the time these predictions are available, a considerable amount of time and resources may have already been expended in the implementation of that

project A project is any undertaking, carried out individually or collaboratively and possibly involving research or design, that is carefully planned to achieve a particular goal. An alternative view sees a project managerially as a sequence of even ...

. When that is the case, the project managers will often only change the project if the impact would be considerably more than they had originally expected.

Case study in Malawi

Frequently irrigation schemes are seen as extremely necessary for

well-being especially in

developing countries A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...

. One example of this can be demonstrated from a proposal for an

Malawi Malawi (; or aláwi Tumbuka: ''Malaŵi''), officially the Republic of Malawi, is a landlocked country in Southeastern Africa that was formerly known as Nyasaland. It is bordered by Zambia to the west, Tanzania to the north and northeast ...

. Here it was shown that the potential positive effects of the

project that was being proposed "outweighed the potential negative impacts". It was stated that the impacts would mostly "be localized, minimal, a short term occurring during the construction and operation phases of the Project". In order to help alleviate and prevent major environmental impacts, they would use techniques that minimize the potential negative impacts. As far as the region's socioeconomic well-being, there would be no "displacement and/or resettlement envisioned during the implementation of the project activities". The original primary purposes of the irrigation project were to reduce poverty, improve food security, create local employment, increase household income and enhance the sustainability of land use. Due to this careful planning, this project was successful both in improving the socioeconomic conditions in the region and ensuring that land and water are sustainable into the future.

External links

* Download of simulation and prediction model SaltMod from

* Download of simulation and prediction model SahysMod from

* "SaltMod: A tool for the interweaving of irrigation and drainage for salinity control"

* "Modern interferences with traditional irrigation in Baluchistan"

References

{{Agricultural water management Irrigation Environmental issues with water Environmental issues with soil Environmental impact of agriculture