A costly project to enable a key dam on central China's Hanjiang River to control "100-year floods" is near completion,officials said Tuesday, days after heavy rains raised the river to its highest level in three decades.

Workers have finished raising the Danjiangkou Dam to allow the maximum water level to rise from 162 meters to 176.6 meters, adding 11.6 billion cubic meters to the reservoir's current capacity of 17.45 billion cubic meters.

Liu Song, an official with Danjiangkou Water Control Project Administration, said the five-year project, estimated to cost 2.4 billion yuan, was "almost finished."

The dam could operate at full capacity once it passed evaluation and residents in the area were properly resettled, he said.

The dam played a pivotal role when flood peaks came down from the upper reaches of the Hanjiang River on July 19 and 25, said He Ping, head of the administration.

About 7 billion cubic meters of water was held by the dam, relieving the pressure on downstream cities, he said.

One of the cities to benefit will be Wuhan, which has 9.1 million people and lies at the confluence of the Hanjiang River and the mainstream of the Yangtze.

Officials said the water level of the dam rose to 154.95 meters, the highest this year, on July 28.

"The dam can play an even more important role when it runs at full capacity. By then, it is expected to withstand floods that come every 100 years," Liu said.

The Hanjiang River is the largest tributary of the Yangtze River in the northwest part of Hubei Province.

Floods ravaged many parts of China this summer, raising the water levels of a number of the country's key rivers to dangerous highs.

The Three Gorges Dam, also in Hubei, withstood flood peaks on the swollen Yangtze River in July.

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

Floods and rain-triggered disasters had left 991 people dead and 558 others missing this year by the end of July, and affected the lives of 137 million people.