Thursday, July 21, 2016

Let’s not muddy the water! Maybe, down the river a dove is drinking water - Sohrab Sepehri, Iranian Poet and Artist

Ancient Engineering I
Introducing Kariz/Qanats


Iran is a country surrounded in its entirety by mountains with Mt. Damavand reaching an elevation of 5610 meters (18,406 feet). In the center of the land lie two major deserts, Lout Desert and Namak Desert. To the north sits the Caspian Sea while in the south are the Persian Gulf and the Sea of Oman.

Geography of Iran.

Due to the arid climate in the country, only one-third of the surface is suited for farmland (see the post Nuts and More Nuts). Yet this one-third can produce an abundance of products. The key: Kariz/Qanats for water transportation.
* Note: From this point, I will use the more common, Arabic term qanat, although the Persian terms is kariz.

A qanat in Iran feeding the crop the much needed water.
A qanat in Kerman.

Qanat technology was developed in Iran around 1000 BC and gradually spread east through the Silk Road to Parthia, Aria, Bactria, and Sogdia (present day Afghanistan, Pakistan, Turkmenistan and parts of India), and into Xinjiang in Northwestern China. The technology spread west with the Arabs to North Africa and Spain and then to Mexico and South America via the Spanish. 

The spread of qanat engineering.
Diffusion of qanat technology to the rest of the world.

The way a qanat works is quite ingenious. Qanats tap into the subterranean water and efficiently deliver water to the surface without pumping. The source of the water is always above the destination, with gravity draining the water through downhill, underground tunnels. Because the water is transported through underground tunnels, it can travel long distances in hot, dry climates without contamination and loss of water through evaporation. 

The skilled laborers who specialize in building and maintaining qanats are called Moqanis.
 
Diagram of the qanat.

In order to start building a qanat, an aquifer has to be found near a slope or hill from which water can be extracted using a water well. An aquifer is an underground layer of water-bearing porous rock such as gravel, or loose materials such as sand or silt, through which water can flow. 


An aquifer.

The mountains surrounding the land provide ample aquifers and once one has been located near a hill or a slope, an initial water well is built. This water well is called Madareh Chah, or Mother Well. From there, vertical shafts are dug 20 to 35 meters apart (65.6 to 114.8 feet) and the shallower the qanat, the closer the vertical shafts are to each other. Each shaft supports the underground construction of the qanat, and later on, the maintenance of it. The shafts also allow for air to interchange through the qanat. The laborers transport the excavated material up the vertical shafts using leather bags.

Two different views of the construction of the qanat.
A qanat delivering water to farms in Iran.
Aerial view of the Qanat. The Circles are the openings 
to each vertical shaft going into the ground 
and reaching the water.
The underground tunnel of a qanat.
The average length of a qanat is 5 km (3.1 ml) with the longest qanat measuring at 70 km (43.5 ml) in Kerman. The depth of the shafts range from 20 to 200 meters (65.6 to 656 feet) with the deepest shaft measuring 275 meters (902 feet) in Khorasan.

Chesheme Ali Qanat in Rey, Iran.
Baghe Shazdeh Qanat in Kerman, Iran.
Niavaran Qanat in Tehran.
Shahrood Qanat near Semnan, Iran.

By the middle of the twentieth century, 50,000 qanats were in use in Iran.

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