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.