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WEEKLY NEWSLETTER
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Iran
Index
Siphon irrigation being used in a sugar-beet field near Qazvin
Courtesy United Nations
Iran's land surface covers 165 million hectares, more than half
of which is uncultivable. A total of 11.5 million hectares is under
cultivation at any time, of which 3.5 million hectares were
irrigated in 1987, and the rest watered by rain. Only 10 percent of
the country receives adequate rainfall for agriculture; most of
this area is in western Iran. The water shortage is intensified by
seasonal rainfalls. The rainy season occurs between October and
March, leaving the land parched for the remainder of the year.
Immense seasonal variations in flow characterize Iran's rivers. The
Karun River and other rivers passing through Khuzestan (in the
southwest at the head of the Gulf) carry water during periods of
maximum flow that is ten times the amount borne in dry periods.
Several of the government's dam projects are on these rivers. In
numerous localities, there may be no precipitation until sudden
storms, accompanied by heavy rains, dump almost the entire year's
rainfall in a few days. Often causing floods and local damage, the
runoffs are so rapid that they cannot be used for agricultural
purposes.
Water shortages are compounded by the unequal distribution of
water. Near the Caspian Sea, rainfall averages about 128
centimeters per year, but in the Central Plateau and in the
lowlands to the south it seldom exceeds 10 to 12 centimeters, far
below the 26 to 31 centimeters usually required for dry farming
(see Climate
, ch. 2).
Scarcity of water and of the means for making use of it have
constrained agriculture since ancient times. To make use of the
limited amounts of water, the Iranians centuries ago developed
man-made underground water channels called qanats that were
still in use in 1987. They usually are located at the foot of a
mountain and are limited to land with a slope. A qanat taps
water that has seeped into the ground and channels it via straight
tunnels to the land surface. The qanats are designed to
surface in proximity to village crops.
The chief advantage of the qanat is that its underground
location prevents most of the evaporation to which water carried in
surface channels is subject. In addition, the qanat is
preferable to the modern power-operated deep well because it draws
upon underground water located far from the villages. The chief
disadvantages of the qanat's are the costs of construction
and maintenance and a lack of flexibility; the flow cannot be
controlled, and water is lost when it is not being used to irrigate
crops.
In the late 1980s, an estimated 60,000 qanats were in
use, and new units were still being dug (although not in western
Iran, where rainfall is adequate). To assist villagers, the
government undertook a program to clean many qanats after
the Revolution in 1979. Qanat water is distributed in
various ways: by turn, over specified periods; by division into
shares; by damming; and by the opening of outlets through which the
water flows to each plot of land. So important is the qanat
system to the agricultural economy and so complex is the procedure
for allocating water rights (which are inherited), that a large
number of court cases regularly deal with adjudication of
conflicting claims.
Construction of large reservoir dams since World War II has
made a major contribution to water management for both irrigation
and industrial purposes. Dam construction has centered in the
province of Khuzestan in the southwest as a result of the
configuration of its rivers flowing from the Zagros Mountains. The
upper courses flow in parallel stretches before cutting through the
surrounding mountains in extremely narrow gorges called
tangs. The terrain in Khuzestan provides good dam sites. The
government set up the Khuzestan Water and Power Authority in 1959
to manage natural resources in that province. All economic
development plans emphasized the need to improve water supplies and
reservoirs so as to improve crop production. Large reservoirs were
built throughout the country, beginning with the Second Development
Plan. The first dams were built on the Karaj, Safid, and Dez
rivers.
The first of the major dams had a significant impact on the
Iranian economy. Completed in 1962, the Mohammad Reza Shah Dam on
the Dez River was designed to irrigate the Khuzestan plain and to
supply electricity to the province. After several years of
operation, the dam had achieved only a small part of its goals, and
the government decided that the lands below the dam and other dams
nearing completion required special administration. As a
consequence, a law was passed in 1969 nationalizing irrigable lands
downstream from dams. The lands below the Mohammad Reza Shah Dam
were later leased to newly established domestic and foreign
companies that became known as agribusinesses.
Data as of December 1987
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