The Yellow River, China's second longest one, has been deepened
by at least 30 centimeters as artificial waves have flushed away 10
million tons of sand since a third round of silt washing operation
started last week.
The operation, which started on June 19 to create artificial
tides in Xiaolangdi Reservoir and stir its sediments, has lowered
the riverbed by an average 30 to 40 centimeters, according to data
provided by the Lijin hydrological station, which is the last one
before river water enter 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 loss of sand had increased water flow,
hydrological workers said.
Water flow was 2,500 cubic meters per second and the watercourse
was 340 meters wide, as 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 the hydrological report.
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, washing 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 watercourse 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 in terms of workload, has prevented some900
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, as 400 million tons silt up on the
riverbed every year, raising the water level by 10 centimeters.
The 5,464-meter-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.
(Xinhua News Agency June 26, 2004)