One of the 3.4-km-long twin tunnels, the key engineering feature along the central route of the massive South-to-North Water Diversion (SNWD) project, was completed more than 35 meters beneath the Yellow River on Tuesday.

Construction of the tunnels, the first to be excavated so deep, began in July 2007. They are at Mangshan, some 40-km from Zhengzhou, capital of Henan Province.

The other tunnel is expected to be drilled through by September. The twin tunnels have a designed water flow capacity of 265 cubic meters per second each, or a maximum flow capacity of 320 cu m per second each. They cost about 3.14 billion yuan (US$459 million).

Upon completion, they will take water from Danjiangkou Reservoir on the Hanjian River, the largest tributary of the Yellow River, and carry it to the parched cities in the country's arid north, especially Beijing and Tianjin.

The tunnels can prevent the fresh water from being polluted by the Yellow River, the world's muddiest one due to its high content of sediments, by channeling the water deeply beneath the riverbed.

If needed, the water can also be used to replenish the Yellow River during its extremely dry season.

The SNWD project, an effort that will take at least 40 years to complete, consists of three canals each stretching more than 1,000 km. The diversion will ultimately connect the country's Yangtze, Huaihe, Yellow and Haihe rivers via three water-diversion channels.

The western route, meant to replenish the Yellow River with water diverted from the upper reaches of the Yangtze River, is still on the drawing board.

According to SNWD's office, the first phase of the eastern route will begin to provide water in 2013, and the central canal is expected to begin providing water in 2014.

After years of delay, construction on SNWD is proceeding at full capacity thanks to an unprecedented investment boom started by the central government late last year.

(chinadaily.com.cn June 23, 2010)