Qanat

Qanat – Sloping Underground Channel

A qanat is considered to be a gently sloping underground channel with various vertical access shafts which is used to send water from an aquifer under a hill. Qanats tends in creating a reliable supply of water for human settlements as well as irrigation in hot, arid and semi-aridatmospheres. Qanat, an ancient type of water supply system have been developed and still in use in arid regions of the world.

 A qanat tends to tap underground mountain water source which could be trapped in and under the upper reaches of alluvial fans and channels the water resource downhill through various sloping tunnels. These often tend to be several kilometres long, to the places of irrigation as well as domestic use. Development of qanats began around 2,500 or 3,000 years back in Iran and this technology has been spreading eastward towards Afghanistan and westward to Egypt.

Several old qanatas are still in use in Afghanistan and Iran for the purpose of irrigation and new qanats are rarely built currently. The qanat technology is considered to have been established by the Persian people during the early first millennium BC and through the fourth millennium BC spreading from there slowly westward as well as eastward.

Value Related to Volume/Quality/Regularity of Flow of Water

Value of the qanat is related directly to the volume, quality as well as the regularity of the flow of the water. Most of Iran’s population and the other arid countries of Asia and North Africa depend on the water from qanats and the areas of population tend to correspond closely to those areas where qanats exist.

Though qanat were expensive to build, it had a long term value to the community and hence to the group that contributed in building and maintaining it, was said to be substantial. The qanats were created as series of vertical shafts similar to wells and connected by gently sloping tunnels and taps into subterranean water in such a way as to efficiently deliver huge quantities of water to the surface without the need for pumping it.

The water then tends to drain by gravity to the destination lower than the source that is an upland aquifer thus enabling water to be transported over long distance in hot arid climates without loss of water due to evaporation.

Water Source Below Ground at Foothill of Mountains

In the construction of a qanat, it is very common for the water source to be below ground at the foot of a range of foothills of mountains where the water table seems to be nearest to the surface. From this junction, the slope of the ganat is conserved closer to the level than the surface above till the water tends to finally flow out of the qanat above the ground. Qanats often tends to extends for long distances, to reach an aquifer. It is also at times split into an underground distribution network of small canals known as kariz.

These smaller canals, like the qanats are beneath the ground in order to avoid contamination. In some cases, water from a qanat is stored in a reservoir, naturally with night flow stored for daytime usage. An example of a traditional qanat fed reservoir for drinking water in Persian antiquity is an Ab Anbar.Moreover, the qanat system also has the advantage of being unaffected by natural disasters like earthquakes and floods and deliberate destruction in war.