A qanat or kariz is a gently sloping underground channel to transport water from an aquifer or water well to surface for irrigation and drinking, acting as an underground aqueduct. This is an old system of water supply from a deep well with a series of vertical access shafts. The qanats still create a reliable supply of water for human settlements and irrigation in hot, arid, and semi-arid climates, but the value of this system is directly related to the quality, volume, and regularity of the water flow.

Qanat of the Moon is located in Ardestan. Ardestan is a town within Esfahan province, the centre of Iran. This town is the centre of Ardestan county. Based on the 2012 census it has a population of 15,701. Ardestan is located between Natanz and Naein at the borders of the desert and is divided into two parts: semi-tropical and cold. The semi-tropical part covers the northern low areas called Rigestan, it enjoys a sand and desert landscape. The cold area covers the southern hills and mountains called Kuhestan.

Ardestan town is on the high foothills, on the edge of Rigestan area. It has a slight slope stretched from south to north and as a result, the area is where all underground water, especially water from higher areas pass. Ardestan town is 1250 m above sea level and has 11 qanats. Qanat of the Moon is a valuable sample of these qanats. This qanat is the most famous water resource of Ardestan because it has two levels. Moon is one of the eight neighbourhoods of Ardestan, its qanat is called upon the area’s name which it provides water for (Safi Nejad, 2000).

There are two galleries in Qanat of the Moon instead of one; a gallery above, the other with a distance below; they are separated from mother well up to Mazhar. Creatively, water flows in each gallery separately. The reason behind this two-level qanat and its discharge system reflects high intelligence of hydrologists of the time and their deep understanding of nature. This is one of the great values of this traditional and local technology in the central desert plateau of Iran. Two levels of this qanat are called Zir (Below) and Roo (Above). The two levels do not enjoy common aqueous branches before mother well, but from this well to Mazhar-e qanat both levels share the same wells.

This Qanat has two main tunnels located above each other with 3m difference in elevation. There is no leakage between the two tunnels due to the impermeable layer between the two tunnels. This Qanat has two mother-wells, one for each of the tunnels. The top tunnel goes through a half-circle path when it reaches the vertical shafts. This Qanat is 2 km long, has 30 shafts that are spaced 42.4m apart and Its average outward flow rate is 50 litres per second.

The qanat is older. Dredging the upper qanat, the hydro gist distinguished that there existed a forger aquifer below it, so started to dig the second qanat. This is the oldest operation system of groundwater which highlights the expertise of the ancient Iranian hydrologists.

Water Heritage

The strangest qanat in Iran is the two-storey qanat of Moon-e Ardestan that was built approximately 800 years ago; it has ordinary wells together with different mother-wells and side-wells. The only two-level qanat ever known is Qanat of the Moon, constructed by the knowledge and creativity of Moqannis (Qanat digger) created a complex unique qanat. It is considered a masterpiece in the sense that, it is located in an area which ensures permanent underground water, enough for two qanats, with two upper and downsides, an exact special calculation had done for finding the suitable slope for both qanats and innovation in putting aqueous layers higher than Mazhar in a way that the water flows incessantly within qanat. Also paying attention to the soil of the area so that the distance between two qanats has been considered in a very exact way, this way soil of both qanats is neither hard nor soft. The soil of qanat is a special kind of sticky clay which has a sweet taste and good smell. It has some pebbles in its mixture and is a durable and of high quality. Well sinkers realized that the soil would not solve in water and the water of the upper qanat would not penetrate to the lower one. Traditional knowledge used at the time of its construction is among unique aspects that show the advanced traditional knowledge applied in the digging of qanats in this area.

Experts who have visited this two-level qanat consider it as one of the masterpieces of ancient engineering because of its age and digging technique. Historical documents show a water-sharing transcript for the region that is said to be written by Sheikh Baha'i.

Qanat of the Moon in Ardestan with a double gallery- that are running parallel but not at the same level - hence it is called a two-stage qanat. The water flow in each gallery is independent of the other gallery's water. The upper gallery is about 3m higher than the lower one, but because of the geological structure, its water does not leak into the lower gallery. The qanat's mother well is a twin well: in which there are two mother wells near each other.

The important characteristic of qanat of Moon is related to its two storeys which the layer between the tunnels is impermeable, so water does not leak between them. Maintaining the environmental sustainability and being the most ancient way of supplying potable water and agricultural water of northern areas of Ardestan, the two-storey qanat has considerably enhanced the economy of the region.

Traditional management and distribution of Moon qanat's water

Water from these two qanats is used to irrigate 250 Jeribs of farms. Qanat-e Roo has three Farazeh of water for 100 Jaribs of farms, one Farazeh for Telk Abad town and two Farazeh for Moon neighbourhood. Qanat-e Zir has three Farazeh water for 150 Jaribs of farms, one Farazeh for Telk Abad and two Farazeh for Moon. Out of 250 Jaribs irrigated by this qanat, about 165- 170 Jaribs of both qanats are the share of Moon neighbourhood which is distributed in 10 days cycle for1320 shares. The ownerships of farms and water in this area are separated.

When this qanat was built, the water of Telk Abad qanat was cut. After some long conflicts,700 years ago the water of the two qanats was distributed as one third for Telk Abad town and two-third for Moon neighbourhood, locals declared. This distribution of shares has been valid until now.

Distribution unit and the water cycle

Until 1961 water distribution of Moon neighbourhood was done by a bowl called Hendu or measurement (paymaneh) or water clock (sa'at-e abi). In Ardestan it takes 11 minutes for Hendu to sink and it is called one Saraqah or Sarajah or Sahm (water share). Inside of Sarajah was divided into six parts each one called a dang of time usually about two minutes of water. Every five and a half Hendu was one hour of water.

In Moon neighbourhood 24 hours equals two Taqs4, each equal to 12 hours of water flow or 66Sarajah or Sahm, the total amount of which is 1320:

(Each hour based on minutes 24×60)/(Two Taqs equal to 132 shares)= 10/9 a 24 hour

Sarajah or the total share of Moon neighbourhood 1320= duration of water cycle period is 10× 24 hours in 2 Taq× 66 each Taq of Moon neighbourhood water share.

The water cycle of Moon neighbours is 10 days and there is a name for each, of which the first day is Sari. The irrigation intervals based on water share in the districts calls Mar (cycle period), of which, after a night irrigation cycle of a farm, on the next cycle the farmer benefits of a day irrigation share and that is because of the time requires to irrigate all the farms and gardens of the district

There are different aspects considering the calculations regarding water cycle of irrigations (Mar) such as water discharge of two qanats, the area of farms, quality of water (sweet or saltwater), soil type (clays or sandy), crop types of which the last three are among the most important. After 1961 Hendues were replaced by hours. By converting Hendues to hours, the same shares are reserved up to the present time.

People who share a Taq of water are called Ham-Ab group. They decide about the expenses, maintenance, and decision makings regarding their own Taq of water. If the shareholders need more water in a cycle, the 10-day cycle extends to an 11-day cycle, this extension is called Saboo. This extra day distributes among all shareholders, the next cycle, however, goes back to its 10 days procedure.

Present State of Conservation

Restoration and conservation of this historical hydraulic structure is carried out via the budget allocated by the Jihad-e Agriculture and the Cultural Heritage organizations. The budget is spent on opening the water routes (passes) and rehabilitation of qanats channels as well as repairing its vertical access shafts every year.

The qanat is in good working condition and is regularly monitored by experienced well-sinkers. Maintenance works are mostly concentrated on the prevention of cave-ins. So, by periodic inspection, those sections of qanat which are likely to fall are reinforced by Kaval, ring or stone support walls.

Qanat of the Moon is being cleaned out every year. They put a windlass on a well shaft and first clean the Roo gallery and then dredge the Zir gallery, afterwards they go to another well shaft. In every shaft, there is an entryway about a meter higher than the water level through which qanat practitioners go to the gallery and dredge qanat's tunnels.

Dredging is the most important protective measures for the revival of the qanat for both layers as required. Dredging of the two-storey qanat is carried out naturally and synthetically. Vertical access shafts are still all right; however, they shall be repaired and renewed as required.