Tehran, YJC. Ancient water supply in Khorasan dates 2,700 back.
Gonabad’s Qasabeh qanat is a world masterpiece not only in
water supply systems, but in all that has been created by the ancient hand.
Stretched 2,700 years ago, the qanat consists of two main
streams and 6 substreams.
The qanat is more than 33 kilometers long. The main
wellspring is 300 meters deep.
Iran registered the qanat as a national heritage in 2000 and
is now trying to register it internationally.
The qanat is frequently visited by tourists, making the
small town of Gonabad a tourist attraction.
Qanats are constructed as a series of well-like vertical
shafts, connected by gently sloping tunnels. Qanats tap into subterranean water
in a manner that efficiently delivers large quantities of water to the surface
without need for pumping. The water drains by gravity, with the destination
lower than the source, which is typically an upland aquifer. Qanats allow water
to be transported over long distances in hot dry climates without loss of much
of the water to evaporation.
It is very common in the construction of a qanat for the
water source to be found below ground at the foot of a range of foothills of
mountains, where the water table is closest to the surface. From this point,
the slope of the qanat is maintained closer to level than the surface above,
until the water finally flows out of the qanat above ground. To reach an
aquifer, qanats must often extend for long distances.
Qanats are sometimes split into an underground distribution
network of smaller canals called kariz. Like qanats, these smaller canals are
below ground to avoid contamination. In some cases water from a qanat is stored
in a reservoir, typically with night flow stored for daytime use. An Ab Anbar
is an example of a traditional qanat-fed reservoir for drinking water in
Persian antiquity.
The qanat system has the advantage of being resistant to
natural disasters such as earthquakes and floods, and to deliberate destruction
in war. Furthermore, it is almost insensitive to the levels of precipitation, delivering
a flow with only gradual variations from wet to dry years.