Xinjiang Uygur Autonomous Region in northwest China plans a US$182 million renovation of its centuries-old karez irrigation system, a program that is intended to improve irrigation and ease the impact of drought.

The karez (subterranean canals) are considered along with the Great Wall and Grand Canal as the largest, most impressive man-made structures surviving from Chinese antiquity.

The program, in the arid northwestern Xinjiang, will run from 2008 to 2010, a spokesman with the Xinjiang Regional Development and Reform Commission said on Wednesday.

"The program will help protect the karez wells still in use in the region's Turpan and Hami prefectures, boost the construction of irrigation infrastructure, and ease long-term water shortages in the eastern areas of Xinjiang," the spokesman said.

Of the total cost, US$100 million will be provided in a grant from the World Bank. The rest will come from the governments of Turpan and Hami prefectures, he said.

The techniques behind the karez date back some 2,000 years. The wells convey water from deep below ground to the surface. They can also be used as household wells.

The wells are comprised of vertical shafts and subterranean canals that surface in the form of ditches and small ponds. A vertical shaft can be as deep as 230 feet and a subterranean canal can be about 6.2 miles long.

The canals, which are built to adapt to varying amounts of water, are supplied from the melted ice and snow of the Tianshan Mountains.

Karez wells are also found in nearby countries, such as Afghanistan, Iran and Pakistan. Domestically, they can also be seen in Gansu, Shaanxi and Shanxi provinces.

Xinjiang's karez wells are mainly found in Turpan and Hami prefectures. There are about 600 karez running an aggregate 5,000 km. Because of their broad distribution, they are also called "the underground Great Wall."

Xinjiang had more than 1,700 karez half a century ago, which irrigated more than 500,000 mu (33,333 hectares) of cropland. But their number has decreased by more than 20 annually in the past few years as underground water tables have fallen.

"There is a dire need to save and conserve the karez wells," the spokesman with the Xinjiang commission said.

(Xinhua News Agency November 29, 2007)