Underground Irrigation Tunnels 2008-5-29 14:55:00
In the Hami and Turpan areas of Xinjiang, there is an unusual kind of irrigation system formed by underground tunnels and wells. A system worked out by the people in the light of local climate and topography, it has a history of over 2,000 years.
These areas are extremely arid. The Turpan area, for instance, has an annual precipitation of 16 mm only but a rate of evaporation of 3,000 mm. Given such conditions, surface irrigation is evidently out of the question. Fortunately Turpan is a basin surrounded by snow-covered mountains, which prove to be sources of abundant underground water. Making use of the land inclination, the local people succeeded in building such kan'erjing systems. Though simple in construction, the tunnels and wells represent gigantic engineering work. First many perpendicular wells are sunk at inervals of one or several dozen metres. Then underground tunnels are dug, linking up the bottoms of the wells. The sand and gravel thus excavated are usually piled around the mouths of the wells, making them look like miniature volcano crater.
The depths of the wells vary from those on high ground, which are as deep as 60-70 metres, to those close to the outlet of the water, which are only a few metres.
The underground water, following the sloping tunnels, flows in a steady stream to the oases, where it is guided into open channels and finally farmlands, making an ideal system of irrigation by gravity flow.
The tunnels are generally about three kilometres long, but can be more than ten kilometres in some exceptional cases.
According to a recent count, there are in the Turpan area alone 300 underground irrigation channels. In the whole of Xinjiang, the total length of all kan'er jing is estimated at 3,000 kilometres, forming a great underground canal system. The Xinjiang kan'erjing, also known as "karez", is thought to have been introduced from ancient Persia. Historical sources suggest, however, it may have been developed in China proper. According to the Book on Rivers and Channels of Sima Qian's Historical Record (completed in about 90B.C.), Emperor Wu of the Han Dynasty (140-87 B.C.) ordered 10,000 troops to build a canal in what was today's Shaanxi Province. But the earth in these parts was loose, landslides were frequent, so wells were sunk, some as much as 40 zhang*", deep, and they were linked up from below to allow the water to flow..." It was thus obvious that a karez was built in China as early as 2,000 years ago. Wang Guowei (1877-1927), a scholar on the history of Xinjiang, in his Channel-Building in the Northwest, offered the theory that it was people from the Han Empire who came to Xinjiang after relations were established and taught the local people how to construct underground tunnels through the soft, sandy and collapsible ground.
Visitors to Turpan as a rule wish to try the local grapes and inspect a kan 'erjing irrigation system. They are fight in menttioning these two things in the same breath, for without underground irrigation how could the "Land of Flames" produce grapes so sweet and tasty?
