Arid and semi-arid areas have significant problems with water supply due to high water demand and less water resources. The average annual precipitation in some arid and semi-arid countries in the north part of Africa and the Middle East is less than 50 mm per year. Current water supply methods like water supply from a dam are not applicable in arid area since there is a minimal amount of surface water. Very often, groundwater is the only available water resource in arid and semi-arid regions.
Groundwater constitutes about two thirds of the freshwater resources of the world and, if the polar ice caps and glaciers are not considered, groundwater accounts for nearly all usable freshwater. Even if consideration is limited to only the most active and accessible groundwater aquifers, then groundwater still makes up 95% of total freshwater, with lakes, swamps, reservoirs, and rivers accounting for 3.5% and soil moisture accounting for only 1.5%. Groundwater has been extracted for domestic use (drinking, cleaning) as well as for agriculture (water for livestock and irrigation) since the earliest times. In the United States, where groundwater is important in all regions, about 40% of the overall public water supplies rely on a groundwater source. In rural areas of the United States, 96% of domestic water is supplied from groundwater. Also, many of the major cities of Europe are dependent on groundwater .
Groundwater has a number of key advantages when compared to surface water. It is usually of higher quality, better protected from direct pollution, less subject to seasonal and perennial fluctuations, and is significantly more uniformly spread over large regions of the world than surface water. In arid and semi-arid countries, groundwater is widely used for irrigation. In some arid and semi-arid countries such as Libya or Tunisia, groundwater is the only traditional source of fresh water for all purposes .
Boring or drilling the ground as a water well to access the groundwater has been widely used by people in arid areas for water supply. Lately it has been found out that the wells are significantly harmful for aquifer and decrease the level of groundwater dramatically, besides the large amount of energy which is needed to extract water from the ground. More than 5,000 years ago, Persians invented a sustainable ground water system which is named Qanat.
Qanats are artificial underground water channels up to 305 m deep beneath the surface of the earth, which bring a continual stream of water to the earth’s surface for human agricultural and domestic use. The water emanating from Qanats is not lifted to the surface but flows down the channel away from the point of seepage, as if a normal well had been pushed over on its side until
the water flowed from its aperture. A Qanat then is a horizontal, rather than a vertical well, which functions in a non-mechanical manner, relying solely on gravity to move the water from its source to its point of use .
Qanats are usually excavated where there is no surface water. Digging Qanats involves a considerable amount of work and requires engineering skills originally developed in Iran. Digging a Qanat used to be a traditional family job in Iran and the person who digs the Qanat was called Muqanni. The techniques for digging Qanats date back some 5,000 years or more and spread rapidly throughout southwest Asian and North Africa during Achaemenid times. The general construction of a Qanat is shown as Fig. 1.
A Qanat system consists of:
1) Mother well: To build a Qanat, skilled Muqanni (specialized Qanat diggers) hand excavates a mother well, which penetrates deep into the water table. The diameter of the mother well is usually around 1 m.
2) Qanat channel: The Qanat channel is excavated by hand, and is only large enough to fit the person digging. The size depends on the depth of the water table and the slope of the ground surface; however, it can be several kilometers (Some Qanat channels in Iran are more than 100 km). The Qanat tunnel slopes gently down from the mother well to an outlet at a village or an agricultural area.
3) Vertical access shafts: The channel is connected to the surface by a series of vertical shafts which are used for removing excavated materials, and providing ventilation and access for repairing and maintenance activities.
4) Qanat outlet: The outlet or Mazhar is the point where people obtain water and it is generally located in the upstream end of a village or agricultural area. The water outlet point is very important; it is well kept and water use is monitored from the viewpoint of quality and quantity.
2. Review of Ancient Wisdom of Qanat
It is not easy to say exactly when Qanats came into existence, but the historical research and evidence prove that Qanats have existed on the mile-high plateau of Iran for at least two millennia . A comprehensive chronicle of Qanat history in Iran has been reported by the International Centre on Qanats & Historic Hydraulic Structures. Thanks to detailed descriptions by several early writers, a brief summary of the Qanat history has been presented here as follows:
The beginning of Qanat has been explored by Henry Goblot for the first time. In his book entitled “Qanat: A Technique for Obtaining Water” he mentioned that during the early first millennium BC, some small tribal groups gradually began immigrating to the Iranian plateau where less precipitation was enjoyed than the territories these groups came from. They originated from areas where there were many surface streams, so their agricultural techniques required an amount of water that was out of proportion to the amount of water available in the Iranian plateau. Therefore, their only hope was to rely on the rivers and springs that originated in the mountains. As farmers, these people faced two barriers: the first barrier was the seasonal rivers which were lacking of water during the dry and hot seasons. The second barrier was the springs that drained the shallow groundwater and became dry during the hot seasons. However, they noticed some permanent runoffs flowing through the tunnels excavated by the Acadian miners who were in search of copper. These farmers started a relationship with the miners and asked them to dig more tunnels in order to supply more water. The miners agreed to do this, because there was no technical difficulty for the miners in constructing more canals. In this manner, the ancient Iranians made use of the water that the miners did not need, and founded a basic system, named Qanat, to supply the required water to their farm lands. According to Goblot, this innovation developed in the northwest of the present day Iran and later was introduced to the neighboring area, then known as the Zagros Mountains .
According to an inscription written by Sargon II, the king of Assyria, in 714 BC 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. During the period 331？550 BC, when Persian rule extended from the Indus to the Nile, Qanat technology spread throughout the empire. The Achaemenid rulers provided a major incentive for Qanat builders and their heirs by allowing them to retain profits from newlyconstructed Qanats for five generations. As a result, thousands of new settlements were established and others expanded. To the west, Qanats were constructed from Mesopotamia to the shores of the Mediterranean, as well as southward into parts of Egypt. To the east of Persia, Qanats were constructed in Afghanistan, the Silk Route oases settlements of central Asia, and Chinese Turkistan (i.e., Turpan). During the Roman-Byzantine era (64 BC to 660), many Qanats were constructed in Syria and Jordan. From here, the technology appears to have diffused north and west into Europe. There is evidence of Roman Qanats as far away as the Luxembourg area (http://www.waterhistory.org/histories/qanats/).
Certainly by 209 BC Qanats were an important feature of the Persian landscape and were described by Polybius (Greek historian, ca. 203？120 BC) during the campaign of Antiochus (III, the Great, sixth ruler of the Seleucid Empire, ca. 241？187 BC) against Arsaces (I, King of Parthia, ca. 250？211 BC). In his description, Polybius records how Arsaces tried to destroy the Qanats and so cut off the water supply in order to halt the advance of Antiochus towards the lost Parthian capital of Hecatompylos. Although the methods of Qanat construction were carried westwards into the Mediterranean and subsequently into Latin America, Qanat and Qanat systems attained their maximum development in Iran .
The expansion of Islam initiated another major diffusion of Qanat technology. The early Arab invasions spread Qanats westward across North Africa and into Cyprus, Sicily, Spain, and the Canary Islands. In Spain, the Arabs constructed a system at Crevillente, most likely for agricultural use, and others at Madrid and Cordoba for urban water supply. Evidence of New World Qanats can be found in Western Mexico, in the Atacama regions of Peru, and in Chile at Nazca and Pica. The Qanat systems of Mexico came into use after the Spanish conquest. While the above diffusion model appears to be orderly and logical (Fig. 2), human activities are rarely so orderly. Qanat technology may have been introduced into the central Sahara and later into the Western Sahara by Judaized Berbers fleeing Cyrenaica during Trajan’s persecution in the year 118. Since the systems in South America may predate the Spanish entry into the New World, their development may have occurred independently from any Persian influence. The Chinese, while acknowledging a possible Persian connection, found an antecedent to the Qanats of Turpan in the Longshouqu Canal (constructed approximately 100 BC). The Romans used Qanats in conjunction with aqueducts to serve urban water supply systems (a Qanat-aqueduct system was built in Roman Lyons). A Roman Qanat system was also constructed near Murcia in southeastern Spain. The Catalan Qanat systems (also in Spain) do not seem to have been related to Islamic activity and are more likely later constructions, based on the knowledge of Roman systems in southern France (http://www.waterhistory.org/histories/qanats/).
2.2. Current Situation of Qanat
Qanats are known as
The 22,000 Qanats in Iran, with their 273,600 km of underground conduits all built by manual labor, deliver a total of 552,200 m3 of water per second―an amount equivalent to 75% of the discharge of the Euphrates River into the Mesopotamian plain. This volume of water production would be sufficient to irrigate 3,000,000 acres of arid land if it were used entirely for agriculture. It has made a garden of what would otherwise have been an uninhabitable desert .
Qanats are still found throughout the regions that came under the cultural sphere of the Persians, Romans, and Arabs (Fig. 3). The Qanat system in Turpan, China, is still very much in use. In the Sahara region a number of oasis settlements are irrigated by Qanats, and some still call the underground conduits “Persian works”. The Palestinians and their neighbors had for some 2,000 years irrigated terraces of olive groves, vineyards, and orchards with water tapped from some 250 Qanat-like tunnels beneath the hills on the eastern shores of the Mediterranean. However, today the terraces and tunnels are largely unused and abandoned since the day in 1948 when Palestinians vacated following the creation of the state of Israel. The demise of these irrigation systems is, according to Zvi Ron, an Israeli geographer from the University of Tel Aviv who has mapped the tunnels, a human, ecological and cultural tragedy. Qanats are to this day the major source of irrigation water for the fields and towering hillside terraces that occupy parts of Oman and Yemen. They have for some 2,000 years allowed the villages of the desert fringes of the Arabian Peninsula to grow their own wheat as well as alfalfa to feed their livestock. In these villages, there are complex ownerships of water rights and distribution canals. In Oman, their importance was underlined in the 1980s with a government-funded repair and upgrade program (http://www.waterhistory.org/histories/qanats/).
2.3. Advantages of the Qanat System
There are several significant advantages to a Qanat water delivery system when compared to the simple well or other water supplying technologies available today: Qanat exploits groundwater as a renewable resource, in contrast to the simple well. The rate of flow of water in a Qanat is always 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 (Fig. 4).
Evaporation returns large quantities of water to the atmosphere from wet surfaces such as ponds and lakes of dams . By placing the majority of the channel underground, the Qanat reduces water loss from seepage and evaporation.
Since the system is fed entirely by gravity, the Qanat delivers large quantities of water to the surface without the need for using a pump and an energy supply. Instead by using a special instrument such as a water mill (Fig. 5) we can obtain energy from a Qanat system.
The Qanat system has the advantage of being relatively immune
to human destruction during wars and in natural disasters . On the other hand, by absorbing runoff from the surface through the vertical shafts, the Qanat system can reduce the risk of floods (Fig. 6). Therefore, the Qanat system can also be used in wet areas with high annual rainfall for control of flash floods and groundwater level.
The Qanat is relatively insensitive to the level of seasonal and annual precipitation so a Qanat typically delivers a relatively constant flow with only gradual variation from wet to dry years. In some cases, water from Qanats is stored in a reservoir which typically stores 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’s water is filtrated naturally through the earth so a Qanat can deliver cold fresh water with low pollution in a hot dry climate. Generally, a Qanat’s water is sweet so it can wash the downstream salt soil.
A Qanat can be used for cooling as well as water supply . In the system shown in Fig. 7, a shaft connects the Qanat to the basement of the building to be cooled. Hot dry air enters the Qanat through one of its vertical shafts and is cooled as it flows along the cold water. Since the underground water is usually cold, the rate of cooling is quite high.
2.4. Why Will Qanats Be Abandoned?
Notwithstanding the above mentioned advantages and long term value of the qanat to the community, this artificial groundwater system will be abandoned for the following reasons:
1) It is difficult to continually maintain and repair old Qanat systems. Flooding can destroy, or deposit sediment into, the vertical shaft and main channel. Therefore, the channels of Qanats must be periodically inspected for erosion or caveins, and cleaned of sand and mud and other constrictions.
2) Traditional Qanats are built by a group of skilled laborers (muqannis) by hand. The profession was typically handed
[Fig. 9.] Multi-purpose rainwater infiltration management in the Qanat system (RWIQ). Blue line and red line are the critical RWIQ model for wet and dry cities, respectively.
down from father to son, but today the young generation does not show any interest in this traditional knowledge. Therefore, Qanat specialists are usually too old or have passed away.
3) Qanats were frequently used for domestic purposes, as well as irrigation. As a result, they can transport disease vectors . A chemical analysis of water, conducted in 1924, from 6 Qanats found water of potable quality in only 2 cases. In 3 other cases, water purity was questionable and in the remaining 1 case the water was definitely unfit for drinking. These results were especially extraordinary since the samples were taken from closed Qanats before they were open to contamination. It has been hypothesized that Qanats were a major contributor to the cholera epidemics of the 19th century.
4) It is not possible to establish a Qanat system in any type of ground such as flat areas since a minimum slope and water head is required for building the Qanat system. However, in the flat planes of Iran such as Yazd, numerous Qanat systems have been constructed, while they are exceptionally long due to the very gentle slope of the area, and in some cases they reach 40 km.
3. Suggestion for Future Water Management
The Qanat system is a traditional way to supply agricultural water in arid areas that suffer from the absence of permanently flowing rivers, and where aquifers are too deep for convenient simple wells. The Qanat system can be used as a sustainable urban water management either in dry cities for water supply or wet cities for flood control. Here, a new multi-purpose water management model has been introduced based on rainwater infiltration management over the Qanat system (RWIQ).
3.1. Multi-Purpose Rainwater Infiltration Management in Qanat System
A rainwater infiltration system can be applied with the Qanat system for making maximum infiltration in times of intensive rain in desert and protect Qanats from collapsing (Fig. 8). Rainwater management (RWM) by infiltration in the whole watershed can be combined with the Qanat system to develop a multi-purpose water management model (Fig. 9).
[Fig. 10.] (a) Thames Water Ring Main: existing tunnels and tunnels under construction and (b) the 21 shafts connecting the ring main to the surface.
As previously mentioned the RWIQ paradigm can be applied for either arid or wet areas. For example as it can be seen in Fig. 9 that the blue line shows the RWIQ model application for a wet area in which controlling groundwater or making a cool space or evaporation are not main targets of water management but on the other hand flood control, saving money and energy and supplying water sustainably as well are significantly important. The red line represents the application of the RWIQ model for an arid area where a flood may occur is not the biggest problem while a sustainable water supply, groundwater level or temperatures are extremity important.
The RWIQ model also can increase the water self-sufficiency ratio (WSSR) by increasing self-supply. The water self-sufficiency index is an index for evaluating the integrity of the artificial urban water cycle. It is expressed as the ratio of the amount of selfsupplied water to total water use, which represents both reliance on an external water resource and regional water self-sufficiency [11,12]. Total water use is therefore the sum of the external water supply and the internal water supply. The external water supply includes the multiregional water supply (A) and the city’s own water supply, which includes groundwater (B), rainwater (C), treated sewage reuse water (D), and a regional water supply service (E) having its own water resource.
However, as mentioned previously, there are a number of problems with a Qanat system. Here, some new methods are suggested in order to solve these problems.
By using Geotextile pipes and Geomembrane materials in a Qanat system, the Qanat’s tunnel can be protected from erosion and will be easier to maintain and repair. Also, in this case, the Qanat’s water can be filtered from sediments and pollution. The inlet of the vertical shaft can be covered with permeable materials (Fig. 8).
Although a local specialist’s knowledge plays an important role in following the track of the main water sources and the direction of digging, modern geophysics and georadar techniques, geographical information systems and remote sensing instruments can be used for finding the water table, the direction of a Qanat’s main channel and the location of the vertical shaft .
Since the Qanat’s water is frequently used for domestic purposes, it can also transport diseases. By building a reservoir tank or room in a location among the main channel we can separate the domestic used water from the main water. However, the water quality of a Qanat should be monitored and controlled.
3.3. London Water Ring Main, a Good Example of Applying Qanat Technology in Modern Water Supply Management
The London Water Ring Main is a good example of acquiring old wisdom from the Qanat idea into new modern water supply management. The system uses no pump energy, just gravity and saves energy and money.
The London or Thames Water Ring Main is a 2.5 m internal diameter tunnel that forms a closed loop around London conveying potable water from water treatment works in the Thames Valley (Fig. 10), in the southwest of London, to pump out 21 shafts all around London where the water is transferred to surface mains. The Stoke Newington to New River Head Thames Water Ring Main (TWRM) extension tunnel (from here on referred to as the TWRM tunnel) is a 4.5 km long tunnel constructed at depths of between 40 and 60 m. The tunnel was constructed entirely under urban areas and also passed under 13 third party tunnels along its route .
Flow through the main is not pumped but rather flows by gravity under the driving head of the service reservoirs at the source water treatment works. By virtue of its depth the pipeline is under some pressure, however, the hydraulic grade line rarely exceeds ground level, and to enter the supply, water must be pumped up into the distribution zones at the various pump-out shafts. In some respects, therefore, the ring main can be considered as a reservoir (albeit with negligible capacity), from which supply is drawn as required. For gravity to keep the water going the tunnel must be full . The initial ring was constructed between 1988 and 1993. As of 2006, two extensions are under construction. There are plans for further extensions through 2025.
The Qanat is an ancient water management system used to provide a reliable supply of water to human settlements and for irrigation in arid and semi-arid climates. The Qanat system is an Asian masterpiece of climate change adaptation. However, it is a traditional water supply system that needs to be protected and refined. As technology progressed, simple wells came to be used instead of Qanats, and they thus stopped functioning. We do not need to build new Qanats, we merely need to maintain and refine them.
This study analyses the history of the Qanat and identifies the advantages of this groundwater water delivery system as well as the reasons why Qanats will be abandoned. The study also provides suggestions for technical methods to refine the Qanat by using new materials and modern geological techniques. The methods suggested in this study are expected to contribute to the restoration and reconstruction of the Qanat system.
Enabling people to incorporate modern scientific approaches in their traditional knowledge networks requires preparatory research, training and appropriate support. Qanats can be used as educational resources for students, technicians, professionals and researchers as well as the general public.