|
Iran
Water
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
|
