The Persian Qanat

A qanat or kariz is a system for transporting water from an aquifer or water well to the surface through an underground aqueduct. Constructed in Iran, Iraq, and numerous other societies, this is an ancient water supply system that allows water to be transported over long distances in hot, dry climates without loss of much of the water to evaporation. The 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 precipitation levels, delivering a flow with only gradual variations from wet to dry years.

Karez is constructed as a series of well-like vertical shafts connected by a gently sloping tunnel. This taps into underground water and delivers it to the surface by gravity without pumping. The vertical shafts along the underground channel are purely for maintenance purposes, and water is typically used only once it emerges from the daylight point.

The qanats still create a reliable water supply for human settlements and irrigation in hot, arid, and semi-arid climates. Still, this system's value is directly related to the quality, volume, and regularity of the groundwater. Much of the population of Iran and other arid countries in Asia and North Africa depended upon the water from qanats, with many population areas corresponding closely to the areas where qanats are possible.

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