Environmental impact of irrigation
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Environmental impacts of irrigation are the changes in quantity and quality of soil and water as a result of irrigation and the ensuing effects on natural and social conditions at the tail-end area of the river basin and downstream of an irrigation scheme.
The impacts stem from the changed hydrological conditions owing to the installation and operation of the scheme.
An irrigation scheme often draws water from the river and distributes it over the irrigated area. As a hydrological result it is found that:
- the downstream river discharge is reduced
- the evaporation in the scheme is increased
- the groundwater recharge in the scheme is increased
- the level of the water table rises
- the drainage flow is increased
These may be called direct effects.
The effects thereof on soil and water quality are indirect and complex, waterlogging and soil salination are part of these, whereas the subsequent impacts on natural, ecological and socio-enonomic conditions are very intricate.
Irrigation can also be done extracting groundwater by (tube)wells. As a hydrological result it is found that the level of the water descends. The effects may be water mining, land/soil subsidence, and, along the coast, saltwater intrusion.
Irrigation projects can have large benefits. The irrigated area occupies world wide about 16% of the total agricultural area, yet the crop yield is roughly 40% of the total yield. However, the negative side effects are often overlooked
- 1 Reduced downstream river discharge
- 2 Increased groundwater recharge, waterlogging, soil salinity
- 3 Reduced downstream drainage and groundwater quality
- 4 Reduced downstream river water quality
- 5 Affected downstream water users
- 6 Lost land use opportunities
- 7 Groundwater mining with wells, land subsidence
- 8 Simulation and prediction
- 9 See also
- 10 Further reading
- 11 External links
- 12 References
Reduced downstream river discharge
The reduced downstream river discharge may cause:
- reduced downstream flooding
- disappearance of ecologically and economically important wetlands or flood forests
- reduced availability of industrial, municipal, household, and drinking water
- reduced shipping routes. Water withdrawal poses a serious threat to the Ganges. 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 River in Pakistan faces scarcity due to 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, one of the world’s rarest mammals. Fish populations, the main source of protein 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 (e.g. in Ghana) and salt water intrusion in delta's and estuaries (e.g. in Egypt, see Aswan dam). Current water withdrawal from the river Nile for irrigation is so high that, despite its size, in dry periods the river does not reach the sea. The Aral Sea has suffered an "environmental catastrophe" due to the interception of river water for irrigation purposes.
Increased groundwater recharge, waterlogging, soil salinity
The increased groundwater recharge stems from the unavoidable deep percolation 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 be obtained with sophisticated techniques like sprinkler irrigation and drip irrigation, or by precision land levelling for surface irrigation, in practice the losses are commonly in the order of 40 to 60%. This may cause:
- rising water tables,
- increased storage of groundwater that may be used for irrigation, municipal, household and drinking water by pumping from wells,
- 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 are 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 soil salinity problems develop,
- stagnant water tables at the soil surface are known to increase the incidence of water borne diseases like malaria, filariasis, yellow fever, dengue, and schistosomiasis (Bilharzia) in many areas. Health costs, appraisals of health impacts and mitigation measures are rarely part of irrigation projects, if at all.
- to mitigate the adverse effects of shallow water tables and soil salinization, some form of watertable control, soil salinity control, drainage 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 built up of those nutrients in the ground water aquifer. High nitrate levels in drinking water can be harmful to humans particularly for infants under 6 months where it is linked to 'blue-baby syndrome' (see Methemoglobinemia).
- In India 2.189.400 ha have been reported to suffer from waterlogging in irrigation canal commands. Also 3.469.100 ha were reported to be seriously salt affected here,
- In the Indus Plains in Pakistan, more than 2 million hectares of land is waterlogged. The soil of 13.6 million hectares within the Gross Command Area was surveyed, which revealed that 3.1 million hectares (23%) was saline. 23% of this was in Sindh and 13% in the Punjab. 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 (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 of Egypt, 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
- In Mexico, 15% of the 3.000.000 ha if irrigable land is salinized and 10% is waterlogged
- In Peru some 300.000 ha of the 1.050.000 ha of irrigable land suffers from this problem (see Irrigation in Peru).
- 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 50%, Egypt 30%. Irrigation-induced salinity occurs in large and small irrigation systems alike
- FAO has estimated that by 1990 about 52 x 106 ha of irrigated land will need to have improved drainage systems installed, much of it subsurface drainage to control salinity
Reduced downstream drainage and groundwater quality
- The downstream drainage water quality may deteriorate owing to leaching of salts, nutrients, herbicides and pesticides with high salinity and alkalinity. There is threat of soils converting into saline or alkali soils. 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 Aral Sea, for example, is seriously polluted by drainage water.
- The downstream quality of the groundwater may deteriorate in a similar way as the downstream drainage water and have similar consequences
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 and fertilizers, 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 sea shore (see Aswan dam).
Affected downstream water users
Downstream water users often have no legal water rights and may fall victim of the development of irrigation.
Flood-recession cropping may be seriously affected by the upstream interception of river water for irrigation purposes.
- In Baluchistan, Pakistan, the development of new small-scale irrigation projects depleted the water resources of nomadic tribes traveling annually between Baluchistan and Gujarat or Rajastan, India
- After the closure of the Kainji dam, Nigeria, 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 pressure on the remaining lands may increase considerably, because the ousted traditional pastoralist tribes will have to find their subsistence and existence elsewhere, overgrazing may increase, followed by serious soil erosion and the loss of natural resources.
The Manatali reservoir formed by the Manantali dam in Mali intersects the migration routes of nomadic pastoralists and destroyed 43000 ha of savannah, probably leading to overgrazing and erosion elsewhere. Further, the reservoir destroyed 120 km² of forest. 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 is being mined. Irrigation from groundwater is no longer sustainable then. The result can be abandoning of irrigated agriculture.
The hundreds of tubewells installed in the state of Uttar Pradesh, 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 Baluchistan, Pakistan, the development of tubewell irrigation projects was at the expense of the traditional qanat or karez users
Groundwater-related subsidence of the land due to mining of groundwater occurred in the USA at a rate of 1m for each 13m that the watertable was lowered
Homes at Greens Bayou near Houston, Texas, where 5 to 7 feet of subsidence has occurred, were flooded during a storm in June 1989 as shown in the picture
Simulation and prediction
The effects of irrigation on watertable, 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 and SahysMod
- Environmental issues with agriculture
- Environmental impacts of reservoirs
- Alkali soils
- Irrigation in viticulture
- T.C. Dougherty and A.W. Hall, 1995. Environmental impact assessment of irrigation and drainage projects. FAO Irrigation and Drainage Paper 53. ISBN 92-5-103731-0. On line: http://www.fao.org/docrep/v8350e/v8350e00.htm
- R.E.Tillman, 1981. Environmental guidelines for irrigation. New York Botanical Garden Cary Arboretum.
- A comparative survey of dam-induced resettlement in 50 cases by Thayer Scudder and John Gray
- Download of simulation and prediction model SaltMod from: 
- Download of simulation and prediction model SahysMod from: 
- "SaltMod: A tool for interweaving of irrigation and drainage for salinity control": 
- "Modern interferences with traditional irrigation in Baluchistan": 
- Bruce Sundquist, 2007. Chapter 1- Irrigation overview. In: The earth's carrying capacity, Some related reviews and analysis. On line : 
- Effectiveness and Social/Environmental Impacts of Irrigation Projects: a Review. In: Annual Report 1988, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands, pp. 18 - 34 . Download from  , under nr. 6, or directly as PDF : 
- Himanshu Thakkar. Assessment of Irrigation in India. World Commission on Dams. On line : http://www.dams.org/docs/kbase/contrib/opt161.pdf
- World Wildlife Fund, WWF Names World's Top 10 Rivers at Greatest Risk, on line: http://www.ens-newswire.com/ens/mar2007/2007-03-21-01.asp
- Timberlake, L. 1985. Africa in Crisis - The Causes, Cures of Environmental Bankruptcy. Earthscan Paperback, IIED, London
- World health organization (WHO), 1983. Environmental health impact assessment of irrigated Agriculture. Geneva, Switzerland.
- N.K.Tyagi, 1996. Salinity management: the CSSRI experience and future research agenda. In: W.B.Snellen (Ed.), Towards integration of irrigation and drainage management. ILRI, Wageningen, The Netherlands, 1997, pp. 17-27.
- N.T.Singh, 2005. Irrigation and soil salinity in the Indian subcontinent: past and present. Lehigh University Press. ISBN 0-934223-78-5, ISBN 978-0-934223-78-2, 404 p.
- Green Living Association Pakistan, Environmental Issues.
- A.K.Bhatti, 1987. A review of planning strategies of salinity control and reclamation projects in Pakistan. In: J.Vos (Ed.) Proceedings, Symposium 25th International Course on Land Drainage. ILRI publ. 42. International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands
- Asian Development Bank (ADB), Water in the 21st Century : Imperatives for Wise Water Management, From Public Good to Priced Commodity.
- M.S.Abdel-Dayem, 1987. Development of land drainage in Egypt. In: J.Vos (Ed.) Proceedings, Symposium 25th International Course on Land Drainage. ILRI publ. 42. International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands.
- L. Pulido Madrigal, 1994. (in Spanish) Anexo Tecnico: Estudio general de salinidad analizada. CNA-IMTA, Cuernavaca, Mexico. The data can be seen on line in the article: "Land drainage and soil salinity: some Mexican experiences". In: Annual Report 1995, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands, pp. 44 - 52, : 
- Claudio O. Stockle. Environmental impact of irrigation: a review. State of Washington Water Research Center, Washington State University. On line: http://www.swwrc.wsu.edu/newsletter/fall2001/irrimpact2.pdf
- United Nations, 1977. Water for Agriculture. In: Water Development and Management, Proceedings of the United Nations Water Conference, Part 3. Mar del Plata,Argentina.
- 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 : 
- C.A.Drijver and M.Marchand, 1985. Taming the floods. Environmental aspects of the floodplain developments of Africa. Centre of Environmental Studies, University of Leiden, The Netherlands.
- Ecosystems Ltd., 1983. Tana delta ecological impact study. Nairobi, Kenya.
- A. deGeorges and B.K. Reilly, 2006. Dams and large scale irrigation on the Senegal river: impacts on man and the environment. UNDP Human Development Report. On line: http://hdr.undp.org/en/reports/global/hdr2006/papers/DeGeorges%20Andre.pdf
- Peter Bosshard. A Case Study on the Manantali Dam Project (Mali, Mauritania, Senegal), Berne Declaration/internationalrivers. March 1, 1999
- Center for development studies (CDS), 1988. A study of water distribution and management in new design public tubewells in eastern Uttar Pradesh. Lucknow, UP, India
- Anthropogenic subsidence
- D.K.Todd, 1980. Groundwater hydrology. 2nd edition. John Wiley and sons, New York
- US Geological Survey, Land Subsidence in the United States. on line: http://water.usgs.gov/ogw/pubs/fs00165/
- SaltMod: A tool for interweaving of irrigation and drainage for salinity control. In: W.B.Snellen (ed.), Towards integration of irrigation, and drainage management. ILRI Special report, pp. 41-43. Free download from :  , under nr. 8: Saltmod application, or directly as PDF :