Karez: Afghanistan’s Traditional Irrigation System

Created on 26 Nov 2007 by Jamalladin Tamuri

Karez are a type of underground irrigation canal running between an aquifer on the piedmont to a garden on an arid plain. They are common in Afghanistan. The karez technology is used most extensively in areas with an absence of larger rivers with year-round flows sufficient to support irrigation. They are common when potentially fertile areas are close to precipitation-rich mountains or mountain ranges, and when the climate is arid and has a high surface evaporation rates. They are also found where there is an aquifer at a potentially fertile area which is too deep for convenient use of simple wells. In the middle of the 20th century it is estimated that approximately 20,000 karezes were in use in Afghanistan, each commissioned and maintained by local users. Although most are shorter than 5km, the length of the karez can run up to 16 km and it is said that the longest Afghanistani karez is 70 kilometers long. One of the oldest known karez in the Afghanistan is in Jalrez distict of Wardak province, which after 300 years still provides drinking and agricultural water to nearly 3000 people. Its main well depth is more than 60 meters and its length is 8 kilometers.

The karez system has the advantage of being relatively immune to natural disasters (such as earthquakes and floods) and human destruction in war. Further it is relatively insensitive to the levels of precipitation; a karez typically delivers a relatively constant flow with only gradual variations from wet to dry years.

To make a karez, one needs a source of water, such as a well, an underground reservoir or a water-bearing geological layer, a tunnel is cut to the farm or village that needs the water. The trick is to make the angle of the karez not too steep, because in that case, the water will grind itself down into the bottom and create pools that will make the karez collapse; on the other hand, if the angle is not steep enough, the water will be tainted. In some Karez where the gradient was high, the water flow has been slowed down by building weirs inside the channel or even by constructing underground mill. The builders of the Karez (‘muqannis’) therefore had to be brilliant surveyors and engineers.

The length of a Karez is punctuated with access shafts, which are added for three reasons: as an air supply, to allow the removal of sand and dirt, and to prevent the tunnels from becoming dangerously long. The shafts are not very far apart, and as a result, a karez 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 (see photo, left). The shafts can be between 30 meter to 1 km apart, although in some rare cases they can be up to 3km apart. The shafts usually range from 20 to 100 meters in depth.

Typically, the karez becomes a ditch near its destination; in other words, the water is brought to the surface by leading it out of the slope. The Karez therefore creates an artificial artesian well and oasis at the point at which it emerges. Fields and gardens are located both over the karezes a short distance before they emerge from the ground and after the surface outlet. Water from the karezes defines both the social regions in the city and the layout of the city. The water is freshest, cleanest, and coolest in the upper reaches and more prosperous people live at the outlet or immediately upstream of the outlet. Downstream of the outlet, the water runs through surface canals called jubs (jūbs) which run downhill, with lateral branches to carry w