Li Junzhu, a senior engineer in charge of the dam's maintenance, said Saturday it will no longer be necessary to block the inner canal to dredge and remove silt on an annual basis due to the marked reduction in silt accumulation.

The Dujiangyan irrigation system traditionally underwent dredging and maintenance on an annual basis, a rule set by its builder Li Bing, an official of the Qin Kingdom during the Warring States period (475 BC-221 BC).

Between 1974 and 1992, according to Liu Zhenghui, an engineer from the Dujiangyan Administrative Bureau, the system's inner canal was dammed for dredging every four to five years on average. The system's last maintenance took place ten years ago.

"This is largely due to fewer floods on the Minjiang River, better water quality and less silt in the water control project area," he said.

Water and soil conservation efforts in the Minjiang source area over the past decade have contributed to reducing the amount of silt in the river.

With regard to soil conservation, deforestation was prohibited in mid-1990s, and some farm land was converted into woodlands.

Another major factor behind the silt reduction is the scientific and management of the irrigation system, said Peng Shuming, director of the Dujiangyan Administrative Bureau.

Currently, a large water conservancy project is being built upstream from the Dujiangyan irrigation system, which will help protect the ancient irrigation system from the threat of floods.

The 2,250-year-old irrigation system, on the upper reaches of the Minjiang River, a major tributary of the Yangtze River, is considered the oldest functioning irrigation system in the world. Restoration of the system to its original form got underway Wednesday and is expected to be completed in 42 days.

(Xinhua News Agency November 16, 2002)