[permaculture] Qanats, ancient water system.

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Thu Mar 1 23:31:29 EST 2012


Qanats: ancient system providing household and irrigation water and 
cooling - is this amazing technology ever used in any permaculture 
systems anywhere these days? It would seem that with modern excavating, 
trenching and tunneling equipment boreholes could be made that could be 
connected by tunnels and trenches with reinforced concrete pipe set in 
each to form a permanent water collection and conduit system. Of course 
you could just find a water source along a slope, dig a well and pump 
the water out but there are still plenty of reasons why a traditional 
qanat is a better system: less evaporation and ground seepage, no energy 
required to move the water and possibly purer water at the destination.

Qanat
Qanat: type of underground irrigation canal between an aquifer on the 
piedmont to a garden on an arid plain. The word is Arabic, but the 
system is best known from Iran.
http://www.livius.org/q/qanat/qanat.html
To make a qanat, one needs a source of water, which may be a real well, 
but can also be an underground reservoir (e.g., a cave with a lake) or a 
water-bearing geological layer, which can be recognized as a damp area 
in an otherwise arid region. When one has identified this source, a 
tunnel is cut to the farm or village that needs the water.
A qanat near Anšan, seen from the air (Google Earth)
Shafts are added for three reasons: as air supply, to remove sand and 
dirt, and to prevent the tunnels from becoming dangerously long. The 
shafts are not very far apart, and as a result, a qanat 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.
Typically, the qanat becomes a ditch near its destination; in other 
words, the water is brought to the surface by leading it out of the 
slope. In fact, one creates an artificial artesian well and an oasis.
The exit of a qanat
As the ceramics of the farms at the exit of a qanat offer an indication 
of its age, it is possible to date the first qanats to the late second 
millennium B.C.E.; they were constructed in the country that was once 
known as Maka and is now called Oman.
Today, qanats can be found as far west as Morocco and Andalusia, and 
even the Sicilian capital Palermo boasts a medieval qanat.
Being about 1½ meter high and ¾ meter wide, qanats are rather narrow, 
but they can reach depths of 30 meters (the record seems to be 60) and 
can cover distances of many kilometers (the longest Iranian qanat is 
said to be 70 kilometers long.) The trick is to make the angle of the 
qanat not too steep, because in that case, the water will grind itself 
down into the bottom and create pools that will make the qanat collapse; 
on the other hand, if the angle is not steep enough, the water will be 
tainted. Everything depends, therefore, on the correct angle. The 
diggers or muqannis were brilliant surveyors.
A qanat, once built, can exist for a long time, but agriculture with 
qanats is extremely labor-intensive. Not only is it difficult to dig an 
underground canal, but it also needs a visit every spring to clean it 
out. Usually, this work is left to boys, whose fathers are standing near 
the shaft and pull up buckets and can come to their children's rescue 
when the gallery collapses.
....at least 20,000 qanats are still in use....

Qanat
 From Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Qanat

A qanāt (from Arabic: قناة‎, in Persian: کاریز‎ kariz) is a water 
management system used to provide a reliable supply of water for human 
settlements and irrigation in hot, arid and semi-arid climates.

The qanat technology is known to have developed on the Iranian plateau 
and possibly also in the Arabian peninsula sometime in the early 1st 
millennium BC spread from there slowly west- and eastward.[2]
The value of a qanat is directly related to the quality, volume and 
regularity of the water flow. Much of the population of Iran and other 
arid countries in Asia and North Africa 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.[3]
Technical features

Cross-section of a Qanat.

Qanats are constructed as a series of well-like vertical shafts, 
connected by gently sloping tunnels. Qanats tap 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. Qanats allow water to be transported over long distances in hot 
dry climates without losing a large proportion of the 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 
aquifer, qanats must often extend for long distances.[3]

Qanats are sometimes split into an underground distribution network of 
smaller canals called kariz. Like qanats, these smaller canals were 
below ground to avoid contamination. In some cases water from a qanat is 
stored in a reservoir, typically storing night flow for daytime use. An 
Ab Anbar is an example of a traditional qanat fed reservoir for drinking 
water in Persian antiquity.
The qanat 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 the levels of 
precipitation, delivering a flow with only gradual variations from wet 
to dry years.

[edit]Features common to regions which use qanat technology

The qanat technology is used most extensively in areas with the 
following characteristics:[citation needed]
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.
Irrigation and drinking water supply
The primary applications of qanats are for irrigation, providing cattle 
with water and drinking water supply. Other applications include cooling 
and ice storage.

[edit]Cooling

Wind tower and qanat used for cooling.
Qanats used in conjunction with a wind tower can provide cooling as well 
as a water supply. A wind tower is a chimney-like structure positioned 
above the house; of its four openings, the one opposite the wind 
direction is opened to move air out of the house. Incoming air is pulled 
from a qanat below the house. The air flow across the vertical shaft 
opening creates a lower pressure (see Bernoulli effect) and draws cool 
air up from the qanat tunnel, mixing with it. The air from the qanat was 
drawn into the tunnel at some distance away and is cooled both by 
contact with the cool tunnel walls/water and by the giving up latent 
heat of evaporation as water evaporates into the air stream. In dry 
desert climates this can result in a greater than 15°C reduction in the 
air temperature coming from the qanat; the mixed air still feels dry, so 
the basement is cool and only comfortably moist (not damp). Wind tower 
and qanat cooling have been used in desert climates for over 1000 years.[7]

[edit]Ice storage

Yakhchal in Yazd Province
In 400 BC Persian engineers had already mastered the technique of 
storing ice in the middle of summer in the desert.[8]

The ice could be brought in during the winters from nearby mountains. 
But in a more usual and sophisticated method they had a wall made along 
east-west direction close to the yakhchal (ice pit). In winter the qanat 
water was being canalized to north side of the wall. The shadow of the 
wall makes water freeze more quickly so they could have more ice per 
each winter day. Then ice was stored in yakhchals, specially designed, 
naturally cooled refrigerators. A large underground space with thick 
insulated walls was connected to a qanat, and a system of windcatchers 
or Wind Towers was used to draw cool subterranean air up from the qanat 
to maintain temperatures inside the space at low levels, even during hot 
summer days. As a result, the ice melted slowly and ice was available 
year-round.[8]

[edit]Qanats by country

<>This Qanat surfacing in Fin is from a spring thought to be several 
thousand years in running, called The Spring of Solomon ("Cheshmeh-ye 
Soleiman"). It is thought to have been feeding the Sialk area since 
antiquity.<>

Qanats
Background
In the early part of the first millennium B.C., Persians started 
constructing elaborate tunnel systems called qanats for extracting 
groundwater in the dry mountain basins of present-day Iran (see figure 
1). Qanat tunnels were hand-dug, just large enough to fit the person 
doing the digging. Along the length of a qanat, which can be several 
kilometers, vertical shafts were sunk at intervals of 20 to 30 meters to 
remove excavated material and to provide ventilation and access for 
repairs. The main qanat tunnel sloped gently down from pre-mountainous 
alluvial fans to an outlet at a village. From there, canals would 
distribute water to fields for irrigation. These amazing structures 
allowed Persian farmers to succeed despite long dry periods when there 
was no surface water to be had. Many qanats are still in use stretching 
from China on the east to Morocco on the west, and even to the Americas.

http://www.waterhistory.org/histories/qanats/

There are significant advantages to a qanat water delivery system 
including: (1) putting the majority of the channel underground reduces 
water loss from seepage and evaporation; (2) since the system is fed 
entirely by gravity, the need for pumps is eliminated; and (3) it 
exploits groundwater as a renewable resource. The third benefit warrants 
additional discussion.

The rate of flow of water in a qanat is controlled by the level of the 
underground water table. Thus a qanat cannot cause significant drawdown 
in an aquifer because its flow varies directly with the subsurface water 
supply. When properly maintained, a qanat is a sustainable system that 
provides water indefinitely. The self-limiting feature of a qanat, 
however, is also its biggest drawback when compared to the range of 
technologies available today.

Water flows continuously in a qanat, and although some winter water is 
used for domestic use, much larger amounts of irrigation water are 
needed during the daylight hours of the spring and summer growing 
seasons. Although this continuous flow is frequently viewed as wasteful, 
it can, in fact, be controlled. During periods of low water use in fall 
and winter, water-tight gates can seal off the qanat opening damming up 
and conserving groundwater for periods of high demand. In spring and 
summer, night flow may be stored in small reservoirs at the mouth of the 
qanat and held there for daytime use.

In countries like Syria, qanats are rapidly drying up. In a recent 
exercise, three sites were chosen for renovation; each still had 
significant quantities of flowing water. The selection of these sites 
was based on a national survey conducted in 2001. The renovation of one 
the three (Drasiah qanat of Dmeir) was concluded in the spring of 2002.

Lessons learned from pilot projects like the one in Syria led to the 
development of renovation criteria which included: (i) a stable 
groundwater level, (ii) a consistent underground tunnel construction; 
(iii) social cohesion in the community using the qanat; (iv) existing 
system of water rights and regulation; and (vi) willingness of the water 
users to contribute. Cleaning of an ancient qanat is not an easy 
exercise. Not only is the work technically difficult, but also the 
social organization associated with a qanat has major implications on 
its future viability (Wessels, 2000).

History

The precise dating of qanats is difficult, unless their construction was 
accompanied by documentation or, occasionally, by inscriptions. Most of 
the evidence we have for the age of qanats is circumstantial; a result 
of their association with the ceramics or ruins of ancient sites whose 
chronologies have been established through archeological investigation, 
or the qanat technology being introduced long ago by people whose 
temporal pattern of diffusion is known.

Written records leave little doubt that ancient Iran (Persia) was the 
birthplace of the qanat. As early as the 7th century BC, the Assyrian 
king Sargon II reported that during a campaign in Persia he had found an 
underground system for tapping water. His son, King Sennacherib, applied 
the "secret" of using underground conduits in building an irrigation 
system around Nineveh.


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