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Iran (Islamic Republic of)
In 2004, the total agricultural, municipal and industrial water withdrawal was estimated at about 93.3 km3, of which 40.0 km3 from surface water, 53.1 km3 from groundwater (qanats and wells) and 0.2 km3 desalinated water (Table 4, Table 5 and Figure 2). Groundwater depletion is estimated at 3.8 km3/year. Most of the overexploitation happens in the central basins where less surface water is available. Total surface water and groundwater withdrawal represents almost 68 percent of the total actual renewable water resources. Use of non-conventional sources of water is minimal. The treated wastewater is said to be indirectly used in agriculture. In some towns, albeit in a limited form, raw wastewater is used directly for irrigation, resulting in some health-related problems (Mahmoodian, 2001). Agriculture is the main water withdrawal sector, with 86 km3 in 2004 (Figure 3). Its part of the total water withdrawn remains identical compared to 1993 (around 92 percent). Municipal and industrial water withdrawal amount to 6.2 and 1.1 km3 respectively. About 16 km3 of water was used for electrical power generation in 1999.
Groundwater discharge (through wells, qanats and springs) varied from less than 20 km3/year in the early 1970s to over 74 km3/year at the beginning of the present millennium (Table 4). The number of wells during that period increased fivefold, from just over 9 000 to almost 45 000.
The qanat is a traditional system in the Islamic Republic of Iran for using groundwater. It is a subterranean water collection and conduction device for bringing water from one place to another. It consists of three parts (Figure 4): (i) the mother well dug at the beginning of the qanat where water is available; (ii) access shafts built along the tunnel to provide ventilation and for the removal of debris, at a distance of 20ľ50 meters and with the depth depending on the depth of the underground tunnel; (iii) the tunnel per se dug from downstream to upstream with a slope gradient of 1/500 to 1/2 500 in order to prevent erosion and siltation, and with a length varying from about 100 metres to 120 km in a qanat in the Yazd region. Its diameter is just enough for a maintenance worker to crawl through.