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Monday, 08 April 2013 12:21

Kariz: Ancient Water System

Kariz (also known as qanat) is an ancient water supply system that can be described as one of the biggest contributions made by Iranians to hydraulics. This system must have been started at least 5,000 years ago in Iran.

The system is usually found in central Iran toward the east and southeast of Iran. Some of the existing examples in Iran include the Old Zavareh Kariz dating back to 5,000 years and the 350-meter deep well of Gonabad Qanat dating back to 2,500 years, DestinationIran reported.

Since antiquity, the supply of water for drinking, irrigating and other household uses has been essential for survival.

To meet these needs, kariz, water reservoirs, icehouses, water mills, water dams, bridges and diversion dams have been built.

Kariz is a mining installation using galleries or canals to extract water from the depths of the earth to the ground. In fact, water is brought by gravity flow from the upper end, where it seeps into the gallery to a ground surface outlet and irrigation canal at its lower end. This is done by means of a gently sloping tunnel.

 

Kariz Mining Technique

The first step in making a kariz is to sink a Gamaneh (trial shaft) to estimate the presence of water and determine its depth.

When the trial shaft is sunk and water is reached, it must be determined whether the well has struck a constant flow of water in an impermeable stratum. If so, the alignment and slope of the kariz from the shaft have to be established. This shaft becomes the mother well.

The gradient of the gallery must not be too steep, because the water will then flow too fast and erode the walls and the tunnel will fall in. Work on kariz usually begins at the lower end where its water is to come to the surface.

Using spike and shovel, workers dig the tunnel toward the mother well. At times, it begins simultaneously at both ends.

Vertical shafts are sunk from the surface to the tunnel approximately every 20 meters, or are sunk first and then connected by a tunnel. Mud or stone linings at the upper parts strengthen these shafts.

The soil excavated is moved to the surface in a bucket by a windlass. If the shaft is too deep, a second windlass may be set halfway down in a niche.

Usually, there accumulates a ring of soil around the shaft on the surface. So, looking from the air, sets of wells look like a line of small craters.

The gradient of a kariz is established by the use of a spirit level suspended between two pieces of cord, each about nine meters long. In a short kariz, the gradient varies from 1:1000 to 1: 1500, but in a long one, it is nearly horizontal.

In some cases, when the kariz slope should be steeper, they usually break the route line at one point and allow water to flow lower than the original level.

Therefore, an underground waterfall was created. Iranians also built water mills to make use of water energy for other purposes like grinding cereals.

Discharge of water from kariz varies according to ground water characteristics, type of soil and season.

Those that tap a permanent aquifer usually have a constant flow throughout the year. If a kariz does not tap a stable groundwater source or is in porous soil, its flow may be reduced to a trickle in summer, or in a dry year.

 

Maintenance of Qanats

Kariz routes need to be regularly cleaned and maintained: They are subject to damage and destruction by flash floods. To prevent shafts from being filled with sand, they are covered by stone slabs or other objects.

The people involved in digging and maintaining kariz systems or qanat are called Moqannies. They suffer great inconvenience in performing their laborious jobs.

They carry castor-oil lamps to test the ventilation underground. If the air does not keep the flame alight, another shaft is sunk.

They clear the deposited sediments formed by minerals at the bottom of the aqueducts. In case of damages, nothing can be done, which means water would not be accessible in the kariz water-supplied areas.

Damages could include the falling in of the ceiling of aqueducts or walls of shafts, the accumulation of sediments, sands or mud in the underground galleries, or the blockage of subterranean waterways.

It is worth knowing that moqannies of Yazd in central Iran are well known for their skills to work professionally on qanat projects.

 

Vitality of Kariz Systems

Without kariz, many human settlements could not emerge. Also, there would be no oases to turn later into large cities like Hamedan, Qazvin, Neyshabour, Kerman, Yazd and a lot more smaller cities and towns.

In these regions, no piece of land could have been cultivated either.

Since ancient times, there have been laws as to how to distribute water fairly among various small and large villages on the kariz routes to prevent any disagreements resulting in consequent disorder, clashes or disturbances.

However, kariz still remains to be the principal, and in some cases, the only source of irrigation and domestic water supply in many parts of Iran. But in areas with more densely-populated districts, kariz has lost its importance as the main source of water supply.

Finally, as an integral part of society in ancient Iran, kariz has had a key impact on many aspects of local communities.

(Source: Iran Daily)

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