The number of the wells of a 2,000-year-old irrigation system in Xinjiang Uygur Autonomous Region has reduced from 1,784 to 614 during the past half-century, according to local water resources department.

The karez system, a network that uses underground channels to tap and distribute water using only gravity, is still in use.

"Declining groundwater levels mainly caused by the sharp rise of motor-pumped wells should be blamed for the ongoing disappearance of the ancient irrigation wells," said Wupur, general secretary of the Xinjiang Karez Research Association.

Since the 1950s, 1,170 karez have dried up and the amount of water they provide annually has decreased by 381.4 million cubic meters. As a result around 190.5 thousand mu (12.7 thousand hectares) have been cut off from the irrigation system, according to Wupur.

With 23 karez disappearing each year, the system established by local people so long ago will die out in 20 to 25 years without effective protection from local government, said Wupur.

The history of the karez, which have mainly been used in the Hami and Turpan areas of Xinjiang, where it is hot and dry, dates back to the Han Dynasty (206 B.C. - 220 A.D.). It is considered one of the three great projects of ancient China, along with the Great Wall and the Beijing-Hangzhou Grand Canal.

The karez system consists of four parts: a hole as deep as 50 to 60 meters, an underground canal, an aboveground canal and a small reservoir. It has many advantages, such as little evaporation from season to season and little percolation, and can provide a stable water supply that does not consume energy or cause pollution.

Wandering underground over 5,000 kilometers, the system has also been called "the underground Great Wall."
 
(Xinhua News Agency December 20, 2004)