Underground Irrigation Tunnels
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 16mm only but a rate of evaporation of 3,000mm. 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.