ECO-IEST President, Alternative Member to the IPBES Bureau

Water
Technology
Polybius in the second century B.C. described a Ghanat
that had been built in a Persian desert "during the
Persian ascendancy." It had been constructed underground,
he remarked, "At infinite toil and expense ...
through a large tract of country" and brought water to
the desert from sources that were mysterious to "the
people who use the water now."
During the periods of Roman and then the Muslim
Rule, the technology was so simple and effective that it
was adopted in North Africa, Spain and Sicily. In the
Sahara region a number of oasis settlements are irrigated
by the Ghanat method. The value of a Ghanat is
directly related to the quality, volume and regularity of
the water flow. Although a Ghanat was expensive to
construct, its long-term value to the community, and
therefore to the group who invested in building and
maintaining it, was substantial.
Technical Features
Ghanats are constructed as a
series of well-like vertical shafts,
connected by gently sloping tunnels
which tap into the subterranean
water in a manner that
efficiently delivers large quantities
of water to the surface without
need for pumping.
Being about 1½ meter high and
¾ meter wide, Ghanats are rather
narrow, but they can reach depths
of 30 meters (the record seems to
be 60) and can cover distances of
many kilometers (the longest
Iranian Ghanat is said to be 70 kilometers long.)
Shafts are built for three reasons: to supply air, remove
sand and dirt and prevent the tunnels from becoming
dangerously long. The shafts are not very far apart, and
as a result, a Ghanat seen from the air gives the impression
of a long, straight line of holes in the ground - as if
the land has been subjected to a bombing run.
Ghanats are sometimes split into an underground distribution
network of smaller canals called Kariz. Like
Ghanats, these smaller canals were below ground to
avoid contamination. In some cases water from a
Ghanat is stored in a reservoir, typically storing night
flow for daytime use. An Ab Anbar is an example of a
traditional Ghanat fed reservoir for drinking water in
Persian antiquity. Ghanats allow water to be transported
over long distances in hot dry climates without losing a
large proportion of the water to seepage and evaporation.The
Ghanat system has the advantage of being
resistant to natural disasters such as earthquakes and
floods, and to deliberate destruction in war.
Construction Process
A Ghanat system is usually dug in the slope of a
mountain or hillside where material washed down the
slope has been deposited in alluvial fans. The surveyor
examines these fans closely, generally during the fall,
looking for traces of seepage to
the surface or slight variations in
the vegetation that may suggest
the presence of water sources
buried in the hillside. On locating
a promising spot, lie arranges for
the digging of a trial well.
Two diggers, called muqanni,
take up this task. They set up a
pulley at the surface to haul up
the excavated material in leather
buckets and proceed to dig a vertical
shaft about three feet in
diameter, one man working with a
mattock and the other with a
short-handled shovel. As they load
the spoil in the buckets, two workers at the surface pull
it up with the pulley and pile it around the mouth of
the shaft.
If luck is with them, the diggers may strike an aquifer
at a depth of 50 feet or less. Sometimes, however, they
dig down 200 to 300 feet to reach water, and this
necessitates installing a relay of pulleys at stages 100 feet
apart on the way down.
When they arrive at a moist layer - a potential aquifer
- the diggers scoop out a cavity to its impermeable clay
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