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Excerpted from Wikipedia, the free encyclopedia

A qanat (Arabic) or kareez (Persian) or karez (Turpan) is a water management system used to provide a reliable supply of water to human settlements or for irrigation in hot, arid and semi-arid climates.
The widespread distribution of qanat known in different places in their local names has confounded the question of its origin, but the earliest evidence of this technology dates back to ancient Persia, and spread west during the Arab Muslim conquests, to the Iberian peninsula, southern Italy and North Africa.

Qanats are constructed as a series of well-like vertical shafts, connected by gently sloping tunnels.
This technique taps into subterranean water in a manner that efficiently delivers large quantities of water to the surface without need for pumping.
The water drains relying on gravity, with the destination lower than the source, which is typically an upland aquifer.
This allows water to be transported long distances in hot dry climates without losing a large proportion of the source water to seepage and evaporation.
It is very common in the construction of a qanat for the water source to be found below ground at the foot of a range of foothills of mountains, where the water table is closest to the surface.
From this point, the slope of the qanat is maintained closer to level than the surface above, until the water finally flows out of the qanat above ground.
To reach an underground aquifer qanats must often be of extreme length.

The qanat technology was used most extensively in areas with the an absence of larger rivers with year-round flows sufficient to support irrigation. Proximity of potentially fertile areas to precipitation-rich mountains or mountain ranges.
Arid climate with its high surface evaporation rates so that surface reservoirs and canals would result in high losses.
An aquifer at the potentially fertile area which is too deep for convenient use of simple wells.
The investment and organization required by the construction and the maintenance of a qanat is typically provided by local merchants or landowners in small groups.
In the middle of the twentieth century, it is estimated that approximately 50,000 qanats were in use in Iran, each commissioned and maintained by local users.
The qanat system has the advantage of being relatively immune to natural disasters (earthquakes, floods.) and human destruction in war.
Further it is relatively insensitive to the levels of precipitation; a qanat typically delivers a relatively constant flow with only gradual variations from wet to dry years.

A typical town or city in Iran and elsewhere where the qanat is used has more than one qanat.
Fields and gardens are located both over the qanats a short distance before they emerge from the ground and after the surface outlet.
Water from the qanats 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.

A kariz (a small qanat) surfacing in Tehran.

When the qanat is still below grade, the water is drawn to the surface via Ater-wells or animal driven Persian wells.
Private subterranean reservoirs could supply houses and buildings for domestic use and garden irrigation as well.

Air flow from the qanat is used to cool an underground summer room (shabestan) found in many older houses and buildings.

Qanat or karez construction

Downstream of the outlet, the water runs through surface canals called jubs (jubs) which run downhill, with lateral branches to carry water to the neighborhood, gardens and fields.
The streets normally parallel the jubs and their lateral branches.
As a result, the cities and towns are oriented consistent with the gradient of the land; what is sometimes viewed as chaotic to the western eye is a practical response to efficient water distribution over varying terrain.

The lower reaches of the canals are less desirable for both residences and agriculture.
The water grows progressively more polluted as it passes downstream.
In dry years the lower reaches are the most likely to see substantial reductions in flow.

Traditionally qanats are built by a group of skilled laborers, muqannis, with hand labor.
The profession historically paid well and was typically handed down from father to son.

The critical, initial step in qanat construction is identification of an appropriate water source.
The search begins at the point where the alluvial fan meets the mountains or foothills; water is more abundant in the mountains because of orographic lifting and excavation in the alluvial fan is relatively easy.
The muqannis follow the track of the main water courses coming from the mountains or foothills to identify evidence of subsurface water such as deep-rooted vegetation or seasonal seeps.
A trial well is then dug to determine the location of the water table and determine whether a sufficient flow is available to justify construction.
If these prerequisites are met, then the route is laid out aboveground.

Equipment must be assembled.
The equipment is straightforward: containers (usually leather bags), ropes, reels to raise the container to the surface at the shaft head, hatchets and shovels for excavation, lights, spirit levels or plumb bobs and string.
Depending upon the soil type, qanat liners (usually fired clay hoops) may also be required.

Although the construction methods are simple, the construction of a qanat requires a detailed understanding of subterranean geology and a degree of engineering sophistication.
The gradient of the qanat must be carefully controlled-too shallow a gradient yields no flow - too steep a gradient will result in excessive erosion, collapsing the qanat.
And misreading the soil conditions leads to collapses which at best require extensive rework and, at worst, can be fatal for the crew.

Construction of a qanat is usually performed by a crew of 3-4 muqannis.
For a shallow qanat, one worker typically digs the horizontal shaft, one raises the excavated earth from the shaft and one distributes the excavated earth at the top.

The crew typically begins from the destination to which the water will be delivered into the soil and works toward the source (the test well).
Vertical shafts are excavated along the route, separated at a distance of 20-35 m.
The separation of the shafts is a balance between the amount of work required to excavate them and the amount of effort required to excavate the space between them, as well as the ultimate maintenance effort.
In general, the shallower the qanat, the closer the vertical shafts.
If the qanat is long, excavation may begin from both ends at once.
Tributary channels are sometimes also constructed to supplement the water flow.

Most qanats in Iran run less than 5 km.
The overall length of the qanat often runs up to 16 km, while some have been measured at ~70 km in length near Kerman.
The vertical shafts usually range from 20 to 200 meters in depth, although in Iran qanats in the province of Khorasan have been recorded with vertical shafts of up to 275 m.
The vertical shafts support construction and maintenance of the underground channel as well as air interchange.
Deep shafts require intermediate platforms to simplify the process of removing spoils.

The qanat's water-carrying channel is 50-100 cm wide and 90-150 cm high.
The channel must have a sufficient downward slope that water flows easily.
However the downward gradient must not be so great as to create conditions under which the water transitions between supercritical and subcritical flow; if this occurs, the waves which are established result in severe erosion and can damage or destroy the qanat.
In shorter qanats the downward gradient varies between 1:1000 and 1:1500, while in longer qanats it may be almost horizontal.
Such precision is routinely obtained with a spirit level and string.

In cases where the gradient is steeper, underground waterfalls may be constructed with appropriate design features (usually linings) to absorb the energy with minimal erosion.
In some cases the water power has been harnessed to drive underground mills.
If it is not possible to bring the outlet of the qanat out near the settlement, it is necessary to run a jub or canal overgound.
This is avoided when possible to limit pollution, warming and water loss due to evaporation.

The construction speed depends on the depth.
At 20 meters depth, a crew of 4 people can excavate a horizontal length of 40 meters per day.
When the vertical shaft reaches 40 meters, they can only excavate 20 meters horizontally per day and at 60 meters in depth this drops below 5 horizontal meters per day.
Deep, long qanats (which many are) require years and even decades to construct.

The excavated material is usually transported by means of leather bags up the vertical shafts.
It is mounded around the vertical shaft exit, providing a barrier that prevents windblown or rain driven debris from entering the shafts.
From the air, these shafts look like a string of bomb craters.

The vertical shafts may be covered to minimize in-blown sand.
The channels of qanats must be periodically inspected for erosion or cave-ins, cleaned of sand and mud and otherwise repaired.
Air flow must be assured before entry for human safety.

The value of a qanat is directly related to the quality, volume and regularity of the water flow.
Much of the population of Iran historically depended upon the water from qanats; the areas of population corresponded closely to the areas where qanats are possible.
Although a qanat was expensive to construct, its long-term value to the community, and therefore to the group who invested in building and maintaining it, was substantial.

Qanats were frequently split into an underground distribution network of smaller canals called kariz when reaching a major city.
Like Qanats, these smaller canals were below ground to avoid contamination.

Qanats in practical application

Karez gallery near Turpan

Model of karez well system (Turfan Water Museum)

An oasis at Turpan in the deserts of northwestern China uses water provided by qanat (locally called karez).
Turfan has long been the center of a fertile oasis and an important trade center along the Silk Road's northern route, at which time it was adjacent to the kingdoms of Korla and Karashahr to the southwest.
The historical record of the karez system extends back to the Han Dynasty.
The Turfan Water Museum is a Protected Area because of the importance of the local karez system to the history of the area.
The number of karez systems in the area is slightly below 1,000 and the total length of the canals is about 5,000 kilometers in length.

For a more information about Qanat see Wikipedia, the free encyclopedia

This page was retrieved and condensed from (http://en.wikipedia.org/wiki/Qanat) see Wikipedia, the free encyclopedia, November 2007.
All text is available under the terms of the GNU Free Documentation License (see Copyrights for details).
About Wikipedia

This information was correct in November 2007. E. & O.E.

Hui Chin and I joined a conducted bus tour from Urumchi to visit Turpan.

It was a very interesting trip and full of drama, as there was many interesting places to visit and there was also a number of arguments on the bus about the tickets and sights to be visited, the sitting arrangements on the bus and also about the food and the quality and hygene standard of the restaurants we have visited.

To cap it all of, my camera's battery ran flat, half way through, our spare battery and another camera sitting safely back at the hotel in Urumchi (laughing at our misfortune), but a few weeks later I had even worst news, when, after returning home, I found out that two of my new 2Gigabyte SD memory cards, although seemed to work perfectly at the time, have invisible pictures on them.
The pictures seem to exist alright, with all around the 200 plus kilobyte properties and showing as jpeg pictures, but can't be viewed.
I have lost some very interesting, unusual and irreplacable pictures of Turpan, Urumchi, Bishkek in Kyrgizstan and pictures of the countrysides of Kyrgizstan and Kazakstan.


Now altough we were there and had our visual and phisical experiences, I have to take advantage of using Wikipedia, the free encyclopedia's resources with our greatful thanks.


I would like to mention a few things, that was mentioned to us during our visit to Turpan, but I do not find any mention on the pages and articles I read before putting this page together.
Turpan is sited in a basin (Turfan Depression), at the second deepest hole after the Dead Sea - under sea level. (328ft. below sea level).
Turpan is one of the hottest place on earth, due to its desert location and relative altitude.
Turpan also one of the driest place on earth again due to it's location and altitude. (This last two points make it ideal place to grow grapes and other fruit with the Karez (water) System's help.
Some of Turpan's listed attractions may be 40+ kilometres away, normally they still will be listed as Turpan's attraction.
On the way to Turpan from Urumchi our bus stopped at a fortress, as I lost the many photos I have taken of this place - as I have explained above, now I can't find any reference or mention of the place - can somebody help me, please?

The Karez System as operated in Turpan

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