Historical, structural, Economical, Cultural, Social and Tourism Aspects of Qanat

in general there have been four methodes of in irrigation in iran. These four methodes are listed as cisterns or water reservoris, channels, canals, weirrs and dams. Qanats are a relic from of underground irrigation important for dryland agriculture. A qanat is horizontal underground gallery that conveys water from an aquifer in remountainous alluvial fans to lower- elevation irrigated fields, In practice , a qanat consist of series of vertical shafts in sloping graound, interconnected at the bottom by a tunnel with a gradient flatter than that of the ground. Written records leave little doubt that ancient Iran (Paesia) was the birthplace of the qanat. As More than three thousand years ago the inhabitants of the dry, mountainous regions of western Iran perfected a system for directing snowmelt through underground channels, called qanatas. During the period 550-331 BC , when Persian rule extended from the Indus to the Nile, qanat technology spread throughout the empire. Qanats are constructed by specialists and have the advantage of using less slope than surface canals, of preventing loss by evaporation and of avoiding the construction of lifting devices. there are three significant benefits of a qanat water delivery system:(1) putting the majority of the channel underground reduce water loss from seepage and evaporation (2) dince the system is fed entirely by garvity , the need for pumps is eliminated and (3) it exploits groundwater as renewable resource. Qanat has several economical utility. For example all the Iranian qanats have fish in them. Traditional heavenly gardens or paradise (derived from old Persian pairi daeza) in Iran were watered by entirely natural and sustainable means, fed by qanats , springs, or a combination of both. In the Sahara desert, to this very day, innocent tourisits are probably hearing exotic tales of the foggaras and yet these foggaras are qanats, just like those in Iran. Qanats can be used for cooling as well as water supply. the qanat antedate the use of aqueducts and was associated with their development. Roman aqueducts in Tunisia and Lyons (France) survive as examples. Nowdays, qanats can be found in Japan, China, Central Asia in the Arab world, from Iraq until Morocco and from Syria until Oman, Pakistan ranging until North Africa, Spain and finally South America. In general qanata are only found in dry areas and it has a profound influence on the lives of the water users. It allows those living in a desert enviroment adjacent to a mountain watershed to create a large oasis in an otherwise stark enviromemnt. The United Nations and other organazations are encouraging the revitalization of traditionalwater harvesting and supply technologies in aride areas because they feel it is important for sustainable water utilization. Qanats provide ecosystem goods and services such as water, ataples, fruits and vegtable and promote social cohesion through participation and cultural ritunals.