Qanat

A Qanat (Arabic قناة, DMG Qanah, also Kanat ) is a traditional form of promotion usually fresh water in desert areas. It is water tunnel that relate drinking and industrial water from higher mountain regions.

Designations

Qanats can be seen in almost all countries of the Persian Gulf, Afghanistan, Pakistan, Syria, Libya, situated on the edge of the Taklamakan and the whole Maghreb, the Canary Islands or in the resin. Therefore, there are many different labels for them. In Persian they are called Kariz or Karez ( كاريز, DMG Kariz ). In Oman, they are called Faladsch, in North Africa, the Maghreb, is the name Foggara, which means " underground tunnels ". In Morocco, the names Rhetara, khettara, Hattaras or Käris are common.

History

The origin of the qanat water production is probably about 2000 BC in the area of ​​today's Iran, which first written notes in a report on a campaign of Sargon II ( 722-705 BC). Especially on the edge of deserts Lut and Kavir is still obtained in this type of water. As one of the earliest qanats that may apply from Zavareh, which is over 5000 years old. Another example is the Qanat of Gonabad, with a mother wells of 350 m depth and an age of about 2500 years.

From Iran, the technique used mainly via the Silk Road in the ancient world and reached after the first Persian conquest in 525 BC Egypt. Qanatsysteme are detected, for example in the oasis of Kharga. Later on, this technique also spread in the Roman Empire, where, however, the technique of aqueducts was authoritative. In the opposite direction, the technique spread to northern India, as Megasthenes about 300 BC reported. But even in China they are found, for example, in the irrigation system of Turfan. With the Arabs the qanats experienced a spread to Algeria, Morocco, Sicily (eg, the qanats of Palermo), after Spain and from here to South America.

Planning and construction

Cause of the Qanatbau and origin of the water

The reasons why the Qanattechnik developed, especially in the highland cultures and extended is in the first place, the absence of larger rivers and in the second place, the proximity of the settlements to a relatively high rainfall mountain or mountain range. However, the arid climate with extremely high evaporation rates is partly responsible for this, as sources dry out quickly and a superficial line of water would require over long distances to high losses. Especially the orographic rainfall on the mountain slopes are for groundwater wealth responsible for their water seeps and collects in depth over a groundwater dielectric. These aquifers are often too deep for simple fountain in the distance to the seepage zones. In the mountains, however, the water table is higher, there is the possibility to intercept the water before it disappears into greater depths. However, The aquifers have their own flow dynamics, so that this groundwater is present everywhere or not is reached.

Preparations

For this reason, first put on trial wells and determined the water volume by pumping tests. To which as a uniform and adequate water flow should be noted. If this is the case, above ground, the future directions of the Qanats is fixed, and only then begin with the creation of reaching to the groundwater mother well ( gamaneh ) the actual work on.

Performed these are usually of work crews from 3 to 4 people - in the Maghreb took you this black slaves. These are equipped because of the narrow shafts and tunnels with only the simplest device. These include ropes, short spades or hoes, mostly simple light sources and the necessary utensils to determine the direction of propulsion (water balance, Lot ). Regional also own, specially adapted tools have been developed. Another tool, the builders used a hose - in bubble level, they hung between 2 each 9 m long cords.

Design and construction of qanats require detailed knowledge of the subsoil and thereby related behavior of the water, especially for the safety of the workers to ensure. Nevertheless, the work is very dangerous to a Qanat. Only their small size protects shafts and tunnels against the forces acting in the underground, the risk of collapse or flooding is omnipresent. In addition to these safety aspects especially surveying skills are essential as you have to guarantee a constant slope, the Qanatverlauf should be as straight as possible and the work can only be successful if the base of the shafts is targeted correctly. With comparatively primitive tools, a weak lighting and generally adverse conditions however, this is extremely difficult and requires a lot of experience.

Construction

Starting from the mother well and the specified route through it, you start from the destination of the water, so the human settlements, to dig about every 20 to 35 meters fountain -like shafts. However, there are also some cases where it was dug from both sides simultaneously. The shafts are in a row and have the targeted parent fountain. Sometimes they are supplemented in the area of the aquifer to increase the amount of water through branches, the Qanat switched in Unterqanate (sort of underground tributaries ). The distance between the shafts the workload, which is why he is often extended as part of the subsequent maintenance Verantwortbaren, especially when you need to dig very deep conditioned. However, this is difficult to always necessary redefinition of the excavation direction. Even more important is likely to be the fact that the excavation in the later horizontal excavations can be delivered to remote bays very cumbersome which has thus limiting effect on their maximum distance. To keep the distance between the shafts is low, the lower is the excavation depth here, the cheaper (sometimes barely 20 meters). The overall length of such slot chains can be up to 16 km in the normal case, however, there are records of up to 80 km. In these cases, one can assume that one of the mountains toward began construction in the settlement without knowing when ( and in what amount) met the aquifer. Due to desertification (and thus the falling aquifer ) is also assumed that these long qanats were used and extended in the course of centuries. The shafts are 20 to 200 feet deep usually said to have been achieved with 450 m in Iran in an individual case of a qanats in the province of Khorasan. They are used to manufacture, and maintenance of the tunnel as well as for air exchange.

The soles of the shafts are connected together so that occurs towards the valley of water for irrigation from the mountain. Also, the condensation of the air collects, dripping down from the rock walls in the tunnel channel. The water-carrying tunnel itself is 50 to 80 cm wide and 90 to 150 cm high. The lugs must have a small slope downwardly directed slope in order to ensure a flow of water. This gap must not be too large, otherwise the water reaches too high a speed and erodes the dirt tunnel walls. This would destabilize the tunnels and eventually lead to collapse, minimizing at the same time strongly influenced by the water load and the water quality. With a slope> 1 ° also the aquifer may not be achieved. In shorter Qanaten the gap between 1:1000 and 1:1500 varies; in longer it is almost horizontal. If the height difference is too large, steps can be installed and thus underground waterfalls are created. This is followed mills were connected to exploit the hydroelectric power in some cases.

The driving speed is very different and depends mainly on the depth, the number of workers and the quality of soils. At 20 meters depth, a working party of 4 people reached about 4 m / day, at a depth of 40 m, this value is halved. The Qanatbau therefore usually takes several decades.

The excavated material is usually transported by means of leather bags out of the shafts and clustered around the shaft output. From the air, the shafts look like a long succession unusually large Maulwürfshügel.

Maintenance

For the generation of clean drinking water, the constant cleaning the gutters of mud and sand is necessary. This follows precise rules. In order to shield the shafts before material entry from the outside, they were covered, especially in the direct settlement area.

Number and role

Historically, the Persian Empire 40000-50000 qanats were simultaneously active alone in Iran at the time. Many ancient Qanatsysteme but were abandoned and fell into disrepair. They were rediscovered in the recent past in the context of aerial surveys. Today in Iran about 20,000 to 25,000 qanats are entertained. They have a transport capacity of an average of about 2,000 to a maximum of 35,000 cubic meters per day. At the time of the Persian Empire was a flow of 1,000 m³ / sec (31 bcm / year), which is about three times the Elbe in Dresden. Had they not reached a permanent aquifer, the flow could vary greatly depending on the season. The water was used for drinking, but the vast majority was as process water in the oasis agriculture use and made this so that in the otherwise arid areas only possible; for alternatives to the Qanaten there were in the respective areas hardly.