Irrigation is the artificial exploitation and distribution of water at project level aiming at application of water at field level to agricultural crops in dry areas or in periods of scarce rainfall to assure or improve crop production.
This article is about organizational forms and means of management of irrigation water at project level.
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The most important physical elements of an irrigation project are land and water. In accordance with the propriety relations of these elements there may be different types of water management [1] :
Until the end of the 19th century the development of irrigation projects occurred at a mild pace,[2] reaching a total area of some 50 million ha worldwide, which is about 1/5 of the present area (see Irrigation statistics). The land was often private property or assigned by the village authorities to male or female farmers, but the water resources were in the hands of clans or communities who managed the water resources cooperatively.
The enterprise type of water management occurred under large landowners or agricultural corporations, but also in centrally controlled societies. Both the land and water resources are in one hand.
Large plantations were found in colonised countries in Asia, Africa, and Latin America, but also in countries employing slave labor. It concerned mostly the large scale cultivation of commercial crops such as bananas, sugarcane and cotton.
As a result of land reforms, in many countries the estates were reformed into a cooperatives in which the previous employers became members and exercised a cooperative form of land and water management.
The utility type of water management occurs in areas where the land is owned by many, but the exploitation and distribution of the water resources are managed by (government) organizations.
After 1900 governments assumed more influence over irrigation because [1] :
The water management signified a large subsidy on irrigation schemes. From 1980 the operation and maintenance of many irrigation projects was gradually handed over to water user organizations (WUA's) who were to assume these tasks and a large part of the costs, whereby the water rights of the members had to be respected.
The exploitation of water resources via large storage dams - that often provided electric power as well - and diversion weirs normally remained the responsibility of the government, mainly because environmental protection and safety issues were at stake.
In the past, the utility type of water management witnessed more conflicts and disturbances then the other types (see water delivery practices below).
Irrigation water has a price by which the management costs must be covered. The following tariff (water charge) systems exist [3] :
The use of groundwater for irrigation is often licensed by government and the well owner may be permitted to withdraw only a maximum volume of water per year at a certain price.
The recovery of water charges may be below target, because [3] :
The cost recovery is often insufficient for full cost coverage, for example:
| Country | Cost recovery (%) | Cost coverage (%) | Remarks |
|---|---|---|---|
| Argentine [4] | 67 | 12 | low tariff: $70/ha/year |
| Bangladesh [5] | 3-10 | <1 | tariffs not enforced |
| Brazil, Jaiba project [6] | 66 | 52 | |
| Colombia [4] | 76 | 52 | |
| Turkey [7] | 76 | 30-40 | |
| Sri Lanka [8] | 8 | <1 | tariffs not enforced |
From 1980 programs were developed to transfer the operation and maintenance tasks from the government to water user associations (WUA's) that show some resemblance to water boards in the Netherlands, with the difference that it concerns irrigation rather than drainage and flood control.
An effective development occurred in Mexico,[9] where in 1990 a program of WUA's was initiated with tradable water rights. By 1998 some 400 WUA's were in operation commanding on average 7600 ha per WUA. They were able to recover more than 90% of the tariffs, mainly because they had to be paid in advance. Government subsidies to the water distribution and maintenance reduced to only 6% See also Irrigation in Mexico#Legal and institutional framework. Similar efforts were made in Peru, see Irrigation in Peru#Legal and institutional framework, but the progress is not yet at the level of that in Mexico.
In large irrigation schemes, the distribution of irrigation water and the delivery at the farm gate is often arranged by rotational turns (e.g. every fortnight). The quantity of water to be received is often proportional to the farm size. As the canals usually transport constant flows, the water is being received during a period of time proportional to the farm size (e.g. every fortnight during 2 hours).
The method of rotational turns is typical for the utility form of irrigation management.
In smaller irrigation schemes the water delivery may be arranged "on demand" with water charges are on a volumetric basis. This requires a precise bookkeeping system. As the demand may be fluctuating over time, the distribution system and infrastructure is relatively expensive because it must be able to cope with periods of peak demand. During periods of water scarcity, negotiations are due to regulate the supply or restriction agreements must have been made.
From point of view of efficient irrigation water-use this is the most effective system.
In projects with an uncertain supply of water due to annual variations in river discharge, water users at the top (the head users) of the irrigation system (i.e. near the system's take-off point) often have preference, to a certain extent, over users at the tail-end. Hence, the number of farmers that are able to grow an irrigated crop may vary from year to year according to the riparian water rights.
The preferential method of irrigation can be found in spate irrigation systems. It is likely that the irrigators near the headworks, or their ancestors, did contribute more to the construction and maintenance of the works than the others, and therefore acquired the preferential rights.[11]
In regions with a structural water scarcity, the principle of water duty is often applied, whereby the duty per ha per season is only a fraction of the full irrigation need per ha (i.e. the irrigation intensity is less than 100%). Thus, farmers can irrigate only part of their land or irrigate their crops with a limited amount of water, whereby they may choose between crops with a high consumptive use (e.g. rice, sugarcane, most orchards) or a low consumptive use (e.g. cereals - notably barley, millet, and sorghum - or cotton). In India, such practice is called protective irrigation,[12] which aims at equal distribution of scarce means and prevention of acute famine.
The method of protective irrigation is typical for the utility form of irrigation management.
Owing to competition for water, the water delivery practices may deviate from the principles.
In practice the distribution of irrigation water is subject to competition. Influential farmers may be able to acquire more water than they are entitled to. Water users at the upstream part of the irrigation system can more easily intercept extra water than the tail-ender. The degree of farmers' influence is often correlated to the relative position of their land in the topography of the scheme.
R.Chambers [13] cites authors who have reported tail-end problems. Examples are:
Also in Egypt, in 1984, considerable differences in the water distribution over the canal systems have been reported [14] :
| Lateral canal | Water supply in m³/feddan *) |
|---|---|
| Kafret Nasser | 4700 |
| Beni Magdul | 3500 |
| El Mansuria | 3300 |
| El Hammami (upstream) | 2800 |
| El Hammami (downstream) | 1800 |
| El Shimi | 1200 |
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