Irrigation systems can be divided into four main categories:
* Kareze systems. A kareze (qanat) is an unlined tunnel in the hillside, bringing water by free flow from underground aquifers to be used for surface irrigation. Dug by local craftsmen from shafts at close intervals, they are small in size but may be many kilometres in length. It is estimated that 6 470 kareze still supply water to 167 750 ha, as in 1967, the date of the last inventory. It should be noted that kareze are often used for domestic water supply.
* Small-scale informal surface water systems. These are the traditional irrigation systems, many of which have been established for centuries. In the past, maintenance and reconstruction were generally arranged on a traditional informal or communal village basis, and water rights were determined and recognized in a similar manner. Technical knowledge and operational systems were thus dependent on traditional community structures, and were largely retained in the memory of individuals.
* Large-scale informal surface water systems. These are located mainly in the plains and along the main valleys. Although they are called informal, their operation and maintenance was highly structured. Repair and maintenance works can mobilize very large quantities of labour for a long period and farmers in the command area have to contribute in labour, cash or kind. Large parts of these schemes have been abandoned because of the sterilization of the land (waterlogging and salinization), particularly in the Hari Rud, Farah Rud and Helmand valleys.
* Formal irrigation schemes. Formally organized large-scale irrigation systems are a relatively recent innovation. However, by the late 1970s three large-scale modern irrigation systems had been built and were in operation: the Helmand-Arghandab system in the south-west, the Ghaziabad farms near Jalalabad in the east, and the Kunduz-Khanabad system in the northern part of the country. By 1993, only a very small part of these schemes was still operational. Land tenure was different from most traditional systems in that ownership of land was registered. Some schemes were operated under private land ownership agreements, while others were operated as state farms where land ownership was deeded to the State.
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