A traditional water source

Published : Apr 14, 2001 00:00 IST

THE kareze system of irrigation originated about 3,000 years ago in northwestern Iran, and spread with the expansion of the Persian Achaemenian empire. The kareze, or qanat, was devised to tap groundwater through gravity flow. It is a gently sloping tunnel that conveys water from below the ground to the surface.

Specialists known as muqannis construct karezes. The traditional method is to sink a well (the head or the mother well) to the level of the water table, which is generally less than 50 metres in depth. This is usually done at the apex of an alluvial fan. The point where the gently sloping tunnel will reach the surface of the ground is then calculated and the tunnel is dug to the mother well. In Iran these tunnels can be as long as 50 km, but they are generally about 0.5-5 km in length, depending on the slope of the ground. Vertical shafts are dug along the length of the tunnel to provide ventilation and to enable the removal of soil. The average kareze can irrigate 10-20 hectares of land. The kareze is dependent on the water table and therefore the flow of water varies from season to season.

The kareze represents an enormous capital cost. It takes many years to construct, but the operating costs are minimal. The kareze is normally used in conjunction with other systems of irrigation; only in the most arid regions are they the sole source of water.

In Balochistan, karezes are usually constructed on a communal basis. A kareze is owned in shares, each share representing the amount of time that water is available for irrigation purposes. Typically they yield upto 200 litres a second and serve a maximum of 200 share-holding families. The shares may in turn be rented out and are often fragmented into very small units. The nature of the kareze system has even helped create certain patterns of particular societal relationships and socio-economic conditions in the villages they serve.

The utility of the kareze system cannot be overstated. Unfortunately, however, internationally sponsored irri- gation surveys in the 1970s viewed the kareze as traditional and outmoded and not amenable to updating. The transition to tubewells and dug wells was encouraged.

Source: ''Balochistan Conservation Strategy'', 2000, IUCN

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