Published as Chapter 21 of The Social and Environmental Effects of Large Dams: Volume 1. Overview. Wadebridge Ecological Centre, Worthyvale Manor Camelford, Cornwall PL32 9TT, UK, 1984. By Edward Goldsmith and Nicholas Hildyard.
Perhaps one of the most sophisticated systems of traditional irrigation known to us is that associated with the qanats of Iran. The qanats are underground conduits which collect the water from an aquifer on the slope of a hill and exploit the natural gradient of the land to transport the water underground to the agricultural areas below. The conduits – which are usually 50-80 cm. wide and 90 cm to 1.5 metres high – vary between 1 km and 70 kms in length. Their rate of discharge is between a litre per second and 500 litres per second. 
Qanats were first developed in Iran but their use spread to India, Arabia, Egypt, North Africa, Spain and even to the New World. They are referred to by different names in different areas: in Afghanistan and Pakistan, they are known as karezes; in North Africa, as foggaras; and in the United Arab Emirates, as falaj. 
What is astonishing is the number and length of these qanats. There are some 22,000 of them in Iran, comprising more than 170,000 miles of underground channels.  Equally astonishing, much of that network is still functioning, sometimes thousands of years after the channels were originally built. Indeed, until recently, qanats still supplied 75 percent of the water used in Iran, for both irrigation and household purposes.
Most of the area that qanats serve to irrigate is arid and rainless. Without an effective and sustainable form of irrigation, such as is provided by the qanats, agriculture in those regions would have been impossible. For that reason, one cannot over-estimate the important role the qanats have played in Iran. To quote H. E. Wulff,
“They have made a garden of what otherwise would have become an uninhabitable desert.” 
It must also be stressed that this incredible network of underground conduits was built entirely by hand. Moreover, the method of construction used today is still much the same as that used 2,000 years ago. Thus, a series of manholes is sunk along the proposed route of the qanat, which is then dug to connect them.
The great advantages of transporting water underground in this way are obvious. As the qanats are often dug into hard subsoil and, when necessary, lined with relatively impermeable clay hoops, there is little seepage, no raising of the water-table, no waterlogging, no evaporation during transit – and hence no salinisation or alkalisation in the area surrounding the conduits. Nor do they provide a niche for the vectors that transmit the water-borne diseases that so seriously affect the population of areas irrigated by modern technological means.
What is particularly important, as Pazwash points out in Civil Engineering, is that the discharge from qanats “is fixed by nature”.  They can only provide water produced naturally by a spring in a mountain area and then transport it by the force of gravity. As a result, the aquifer is not depleted and the quality of its water is maintained. By contrast, the amount of water extracted in a modern irrigation system by pumps and other technological means
“is determined by man, who, in a modern economy, will be under pressure to extract the maximum amount possible, thereby depleting the aquifer and reducing the quality of the water.” 
Gunter Garbrecht, Chairman of the Working Party on History of the International Commission for Irrigation and Drainage, makes the same point. Qanats
“tap the groundwater potential only up to, and never beyond, the limits of natural replenishment and, as a consequence, do not unbalance the hydrological and ecological equilibrium of the region. ” 
Qanats, like the irrigation system of ancient Egypt, were successful because they were self-regulating and “functioned within the limits set by nature”. In a sense, modern irrigation technology is thus a confidence trick. It provides far more water but only at the cost of depleting supplies in the long-term. To achieve a short-term supply of water is, of course, very easy, notes Garbrecht:
“If water can be withdrawn at will, regardless of the limits of natural recharge, a water supply can certainly be increased for a period of time. But sooner or later, the water potential will become exhausted and agriculture and economy will have to fall back to its original level, a process that inevitably carries serious socio-economic consequences for the society.” 
Until recently, the majority of qanats were under the control of local feudal landlords. Each landlord would appoint a bailiff to supervise the allocation of water to tenants, in accordance with the size of the tenant’s farm and the nature of the crop he was growing.  Where the peasants owned the qanats, they themselves elected a trustworthy water bailiff who made sure that each family had an equitable share of the water at the time it needed it. The water bailiff received a free share for his services. Wulff knows of
“three hamlets in the region of Sehdeh in western Iran that still receive the shares that were allocated to them in the 17th century . . . in the reign of Shah Abbas the Great. 
In addition to the qanats, the peasants also developed ‘Jar’ irrigation – a system which reduced water wastage to a minimum. Thus, a slim-necked jar was filled with water and buried close to a plant’s roots whenever required, on average once every two weeks. The seepage through the permeable wall of the clay jar was sufficient to keep the soil at a constant moisture – one that was a little less than the ‘field capacity’, that is to say the amount of water the soil could retain against the force of gravity.
“In this way no excess water is lost to percolation. Also the conveyance loss which is inevitable with channel and furrow irrigation is altogether eliminated. ” 
Because of the introduction of machinery and the increasing price of labour, the cost of building qanats has risen sharply. In 1983, Pazwash estimated that it would cost about $1 million to build an 8-kilometre long qanat with an average tunnel depth of 15 metres. That high capital cost, however, is amply compensated by the low cost of the water delivered – about 75 cents per 100 cubic metres. At that price, the qanat would be paid for in some 30 years – and would, of course, be operative for centuries.
Since water is conveyed through qanats making use of the force of gravity only, they are obviously economical to operate. Pump wells, on the other hand, need a continuous energy supply and also require very much more maintenance. Pazwash estimates that if Iran’s water were only provided by qanats, there would be an energy saving of 100 Kwh per capita per year. If one takes into account the costs of energy and maintenance, pumped well-water would cost $1-2 per 100 cubic metres, which makes it on average twice as expensive as that provided by qanats. 
As part of the developmental process, qanats have inevitably been replaced by a more modern system for providing water to the cities. The 36 qanats in Tehran – some of them built more than 250 years ago – were quite capable of satisfying the domestic needs of a city with a population of 1.5 million – in addition to irrigating neighbouring gardens and farmlands. Unfortunately, in 1955, piped water was introduced, supplied from Amir Kabir reservoir in Karaj, situated 40 miles away. When this was done, Tehran’s existing qanat system was completely ignored by the builders. 
Qanats have also fallen into disuse following the 1962 Land Reform Act, which broke up the large estates and re-distributed land to the peasants. On the face of it, such land reform might sound like a step forward, but it caused problems on a number of counts. To begin with, the traditional system of land-tenure was well adapted to the optimum use of the qanat system.
For instance, traditional landowners not only provided credits to peasants to help them maintain the qanats and irrigation channels, but they also co-ordinated the maintenance work. Once the landlords were ousted, there was no longer a mechanism for assuring the maintenance of the qanats.
Moreover, the land holdings given to the peasants were too small – less than 10 acres (2.5 hectares) per family. On such an acreage, it was impossible to finance the maintenance of the qanats and the irrigation channels. Since the 1962 Act, there has been a rapid substitution of wells for qanats, with the consequent depletion of groundwater, many of the wells having already dried up.
Also many of the peasants, who found they could not survive on their small acreage moved to the cities in search of work leading at once to the depopulation of the countryside and the creation of a vast, depressed urban proletariat – a process Fritz Schumacher referred to as “mutual poisoning”.
Modern irrigation systems, totally unsuited to local conditions and built regardless of their impact on society, are now replacing the qanats. Many of those irrigation projects are supplied by large dams – of which Sefid Rud and Dez are the most notorious. The former, designed to last 100 years, was finished in 1962. But 21 years later, it is already half silted up – the sedimentation rate having proved to be three times higher than expected.
Meanwhile the Dez dam is known to have had an extremely unfavourable impact on traditional farming. It has led to the setting up of three types of experimental schemes – agro-industrial companies, agri-business enterprises and farm corporations.. Those schemes cover 96,000 hectares. Throughout the area, peasants have been forced off their land. Pazwash blames the authorities who planned the dam, who were, he says, “concerned only with the technical aspects of the plan”.
So too, the Khuzestan Water and Power Authority was, apparently, only concerned with “economic criteria without regard to the living conditions of the peasants whom they regarded as instruments in this experiment”. 
|1.||Gunther Garbrecht, “Ancient Water Works – Lessons from history”. Impact of Science on Society, UNESCO 1983 No.1; p.10.|
|2.||Anil Agarwal, Water and Sanitation for All?. Earthscan Press Briefing Document No.22. Earthscan, London 1980; p.53.|
|3.||H. E. Wulff, “The Qanats of Iran”. Scientific American Vol. 218 No. 4, April 1968, p.94.|
|5.||H. Pazwash “Iran’s Modes of Modernisation: Greening the Desert, Deserting the Greenery?”. Civil Engineering, March; p.50.|
|7.||Gunter Garbrecht, op.cit. 1983; p.10.|
|8.||H. E. Wulff, op.cit. 1968; p.100.|
|10.||H. Pazwash, op.cit. 1983; p.50.|