Qasabeh Qanat is one of the world's largest and oldest Qanats which dates back to 500 BC. Qasabeh Qanat is located at Gonabad in Razavi Khorasan which resistered on Iran UNESCO World Heritage Sites under the name of The Persian Qanats. Qasabeh Qanat consists of 427 water wells and has a total length of 33113 meters. Siah Kuh mountains, the main source of water of Qasabeh qanat, are in the western parts of this area whereas low lands are in north and northeast segments. Qasabeh Qanat catchment covers an area of 317.67 k.m. that is part of the central desert basin of Iran. The maximum and minimum height from the sea level in the western part of the aquifer are 2785 and 1104m respectively.
The average temperature in Siah koh is 127◦c degrees centigrade, thus it can be regarded as a semi-arid zone. However, Siah koh western parts receive higher rainfall compared to the northeast and north parts.
Qasabeh Qanat special features such as its construction method, antiquity, structural techniques and management system make it one of the most outstanding water structures of Iran. It is one of the important and historic Qanats of Plateau in Iran and has a basic role in the development of civilization based on Qanat not only in Iran but also in the world.
Digging technique in Qasabeh Qanat is unique. There is some interesting information based on interviews with local elders and some records which indicates that at least 75 m of a mother well of Doolab branch depth and other train wells have been surprisingly dug utilizing Sar Kuli Method. In this method digging is a different task and starts from bottom to up. It requires exact navigational calculation in a very difficult condition which has been carefully and artfully done by Iranian ancestors. Qasabeh Qanat is the main source of Saffron Farm in Gonabad.