After reading this article you will learn about the impact of irrigation on environment.
The introduction of irrigation to any site should result in the soil moisture micro-climate conditions being modified in controlled manner. Through these environmental changes, mankind achieves such benefits as increased food production, income generation and employment.
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Unfortunately these beneficial effects are often accompanied by unplanned and adverse effects, the significance of which may vary over the full range from minor, local and short term to major, global and long-term.
During the planning phase of any new irrigation project, responsibilities all generally split between those engineers who undertake the preparation of the individual project designs (Local responsibility), and those who consider the wider implications of the intended project (regional or national responsibility).
These two planning levels provide a useful basis for categorizing different types of environmental changes since uncertainty over responsibility is one of the most significant factors hindering the introduction of practical measures to prevent or control adverse effects.
To these levels of responsibilities (Local and regional) can be added a third level of global responsibility where such issues are the conservation of threatened species.
The three categories of change may be summarized as follows:
(i) Local responsibility:
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Factors which affect the operation of the project itself within its assumed economic life.
(ii) Regional responsibility:
Environmental effects which reach beyond the project boundaries or operate over larger time scales than those commonly used in project planning.
(iii) Global responsibility:
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Changes to the environment brought about by the project which destroys unique habitats or threaten endangered species. By identifying and recognizing the effects associated with each of these 3 categories, it is hoped that engineers and planners may see more clearly the areas of which they are responsible and the ways in which they can make a positive contribution to environmental matters.
These categories are considered in detail below:
(A) Drainage:
Excess water (Water logging) in the fields of an irrigation scheme is a common cause of lost production and results from a failure to provide an adequate drainage system or poor control over water application to the fields.
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For land to be called as “Water logged” the soil need only to be saturated, there does not necessarily have to be standing water on the surface. However, the drainage water need not be considered to be cost from the scheme since, by returning it to the distributary channels, it may be re-applied to fields at the tail end.
(B) Soil-Salination:
All naturally occurring water carries a range of dissolved salts and chemicals and their impact on the environment will usually be minimal. However, if irrigation scheme is poorly managed and the ground is allowed to become waterlogged, evaporation will take place from the ground surface, leaving the dissolved salts behind. In many irrigated areas this has resulted in reduced crop yields and has even caused some land to go out of production.
(C) Pests and Weeds:
The performance of many irrigated schemes is impaired by a proliferation of crop pests and weeds which was not anticipated by the designers. Due to extensive cultivation of crops under the conventional method of irrigation (flood irrigation under canal/well), the inefficiency in use of water has been increasing.
The negative externalities of over-use of water are enormous – water logging, soil salinity, soil erosion and formation of salt layer on the top of the soil. This has also affected the total availability of water.
The gap between availability and requirement of water arises mainly out of inefficient use. Keeping in view the growing needs of irrigation water, different measures have been introduced to improve the efficiency in water use.
The measures (Technological as well as economic alternatives) introduced so far could not bring any appreciable change in existing pattern of water use. However, the new water conservation technologies, namely, drip and sprinkler methods of irrigation introduced recently are proved to be efficient in terms of water use and increasing the productivity of water use and increasing the productivity of crops.
Drip method of irrigation has a wider acceptance and the area cultivated under this method has been increasing. Experiences from countries like Israel indicate that drip method of irrigation is not only economically feasible, socially acceptable but also has significant contribution towards sustainability in resource use.
Aquatic vegetation can have considerable detrimental impacts on the running of irrigation and drainage systems. The ability of channels to convey the design discharge is reduced by increases in channel roughness and resistance. Canals are restricted in size by marginal weed growth, and storage dams and flood protection ponds can be severely reduced in capacity.
A note in the assessment of environmental impact Tungabhadra project by Ranga Reddy:
In order to assess the environmental impact, irrigation wastes of Tungabhadra project (TBP) has been chosen to study its implications. The TBP was completed in 1955 and released irrigated water to the volume of 256.5 TMC, to cover 12, 11,400 acres of land under both right and left canals.
During the last four and a half decades, the impact of irrigation has brought significant changes in cropping pattern, income and employment among downtrodden classes, besides checking recurring floods and famines.
It is found that the unauthorized and unscientific cultivation has been observed under more un-congenial conditions, which carried water-logging and salinity around 20% in the irrigated fields. Due to two crops of wet irrigation, health hazards like water-borne diseases like Malaria, Jaundice and Typhoid are becoming rampant.
The downstream level of canal water was found to be surcharged with chlorides. Suppose, calcium concentration in reservoir water attains its peak as much as 27.20 mg per litre and in monsoon season it reaches to 9.20 mg per litre.
Poor drainage conditions and unlimited distributors have been contributed for water – logging and salinity. For checking the monster of wilt both in dam and canals, the authorities have to encourage forest cover both in catchment and command areas.
Industrialization on the adjacent places of main canals have been mushroomed up, which paved way for solid wastes, polluted water and poisonous gases, targeted the sensitive floura and fauna. Owing to continuous chemicalisation of agriculture the soil profile has lost its incessant colours, minerals and nutrients, which harms not only the prospects of farmers but also food security of the nation.