The Yellow River, China's second longest, has been deepened by at least 30 centimeters with the help of artificial waves that have flushed away 10 million tons of sand since a third round of silt-washing operations started last week. 

The work, which started on June 19, created artificial tides in the Xiaolangdi Reservoir and stirred its sediments to the lower riverbed by an average 30 to 40 centimeters, according to data provided by the Lijin hydrological station.

The Lijin hydrological station is the last such station the river water has to pass before entering the Bohai Sea.

The peak of the artificial floods arrived at the Lijin hydrological station at 10:24 am Thursday, nearly 48 hours ahead of schedule because the loss of sand had increased waterflow, hydrological workers said.

Waterflow was 2,500 cubic meters per second and the water course was 340 meters wide, as the peak of the flood - which contained 18 kilograms of sand in every cubic meter of water - reached the Lijin hydrological station.

The silt-washing operation also raised the water level by 1.2 meters to 13.03 meters, according to hydrological reports.

The peak then flowed into the Bohai Sea at 6:30 pm Thursday. By then, the silt-washing operation had poured 700 million cubic meters of muddy water into the sea.

The operation will be a landmark for China to shift from traditional to modern means in harnessing and exploring the Yellow River, according to Li Guoying, director of the Yellow River Water Resources Committee.

The committee carried out two sand-washing operations in July 2002 and September 2003 by discharging currents from the Xiaolangdi Reservoir on the lower reaches of the river. The two operations washed a total of 187.1 million tons of sand into the sea.

According to Li, the ongoing third round will rush off silt stored at Wanjiazhai, Sanmen Gorge and Xiaolangdi reservoirs to clear up the whole water course and expand in particular the runoff of its lower reaches.

Silt-stirring vessels are in place to churn the densely silted river sections and sediments of the Xiaolangdi Reservoir, the largest water conservation project on the Yellow River.

The Xiaolangdi project, which is second only to the Three Gorges Dam on the Yangtze River in terms of workload, has already prevented some 900 million tons of silt from flowing into the lower reaches since it started storing water in October 1999.

But experts say the build-up of silt in the lower reaches of the Yellow River is still worrying, since 400 million tons silt up on the riverbed every year, raising the water level by 10 centimeters.

The 5,464-kilometre-long Yellow River originates on the Qinghai-Tibet Plateau, winds its way through eight provinces and autonomous regions, and empties into the Bohai Sea in north China.

Once a notorious troublemaker in the Chinese history, the Yellow River used to breach its embankment twice every three years and change its course every 100 years over the past 2,000 years.

Now the river carries some 1.6 billion tons of silt into the sea annually.

(China Daily June 28, 2004)