The Three Gorges Dam on Yangtze River, the country's largest, is offering a buffer for the worst flood in decades as it blocks more than 40 percent of upstream water.

The world's largest hydropower station was holding up against its first major flood-control test Tuesday, said officials of the China Three Gorges Corporation.

The flow on the river's upper reaches topped 70,000 cubic meters a second Tuesday -- 20,000 cubic meters more than the flow during the 1998 floods that killed 4,150 people and the highest level since the dam was completed last year.

The flood peak at the Three Gorges Dam at 8:00 AM was slightly below the record high of 70,800 cubic meters per second in 1981, a spokesman with the corporation said.

"Compared to 1998, the biggest difference is the Three Gorges Dam. Without it, thousands of soldiers and rescuers would have been needed to fight the floods," said Yuan Jie, director of the Three Gorges Cascade Dispatching Center of China Three Gorges Cooperation.

"There are three reasons why the dam is withstanding the enormous water pressure, which are the precise monitoring systems, the huge reservoir and the good decisions made by the corporation," said Chen Fei, general manager of the Three Gorges Corporation.

The upper reaches of Yangtze River covers an area of one million square kilometers, 60 percent of which was covered by the Three Gorges monitoring system and another 20 percent was covered by systems of the Dadu and Yalong rivers.

"The peak flow is high, but it has not exceeded the designed capacity of 100,000 cubic meters of water per second," said Cao Guangjing, the corporation's chairman.

The peak flow was greater than in 1998 but the peak period was shorter so far, Cao said.

The discharged amount had been kept under 40,000 cubic meters per second, which means the dam blocked 43 percent of upstream water and prevented severe flooding in the lower reaches, Cao said.

The Three Gorges Corporation had reduced the reservoir's water level to below 146 meters before the raining season. The reservoir has a capacity of more than 20 billion cubic meters as water level can rise to as high as 175 meters.

The current flood control will store about 7.6 billion cubic meters of water, said Cai Qihua, chief of Yangtze River Water Resources Commission. It is estimated to reduce the water level in Jingjiang, a 360-km section of Yangtze in the plain region of Hubei and Hunan provinces that is most vulnerable to flooding, by 2.5 meters, Cai said.

Breaches of dikes on the above-ground Jingjiang section could threaten 15 million residents and 1.5 million hectares of crops.

Water level in the lower Jiujiang section in eastern province of Jiangxi is expected to be reduced by 0.5 meters when the flood crest reaches Jiujiang on July 25.

The will make a severe flood into a common flood, said Tan Guoliang, head of the Jiangxi maritime bureau.

The current situation was stable in the lower reaches, said an official of the Bureau of Hydrographic, Yangtze River Water Resources Commission.

The water level has begun to fall in the Hankou area of Wuhan City, capital of central China's Hubei Province, the official said.

As of 2:00 PM Tuesday, the water flow there dropped to 66,000 cubic meters per second, the official said.

According to the monitoring systems at the dam, power generation continued as normal during the high flow, the official said.

All ferry services were halted at the Three Gorges Dam on Monday and the 30-km road along the river had been opened to vehicles carrying shipping cargoes, said an official of the Three Gorges Navigation Administration.

Services would be resumed after the flow decreased from 70,000 to 45,000 cubic meters per second, the official said.

Ferries near the Gezhouba Dam, on the lower reaches of the Three Gorges, were still operating as the flow there was 40,000 cubic meters a second, below its designed capacity of 60,000 cubic meters per second, the official said.

Days of torrential rains has raised water levels in many tribunaries of Yangtze to record levels and inundated seven county seats in Sichuan, Chongqing and Shaanxi.

A total of 630,000 people in provinces along Yangtze, including Hubei, Anhui and Hunan, were battling the flood. Landslides and floods had affected 9.2 million residents and left 44 people dead and further 95 missing in mainly mountainous areas of the three regions by Monday.

Historically, the Yangtze River floods caused huge losses for China in 1931, 1945 and 1998. The floods in 1998 killed 4,150 people, and forced more than 18 million people out of their homes and caused economic losses of 255 billion yuan (about US$38 billion).

(Xinhua News Agency July 21, 2010)