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During the winter dry season the Huang He is slow-moving and silt-laden, and occupies only part of its huge bed; with the summer rains, it can become a raging torrent. Since the 2d cent. B.C., the lower Huang He has inundated the surrounding region some 1,500 times and has made nine major changes in its course. In an attempt to halt the Japanese invasion of China in 1938, the Chinese diverted the Huang He south, flooding more than 20,000 sq mi (51,800 sq km) and killing some 900,000 people; it was returned to its present course in 1947.
The Chinese have long sought to control the Huang He by building dikes and overflow channels. Silt deposition, the principal cause of flooding, has elevated the riverbed; in places the river flows 60 to 70 ft (18–21 m) above the surrounding plains. During the summer high-water period, water pressure against the dikes can break through the retaining walls to cause devastating floods, which have led the Huang He to be called "China's Sorrow." In 1955 the Chinese initiated a 50-year construction plan for control of the river. Dikes have been repaired and reinforced, and a series of silt-retaining dams are being constructed to control the upper river, produce electricity, and provide water for irrigation. The People's Victory Canal, a 40-mi-long (64-km) diversion and irrigation channel, connects the Huang He with the Wei River.
In recent years, however, extensive use of the river's waters has severely reduced the flow of the Huang He in its lower reaches. In 2000 the Chinese government embarked on program to replenish the oversubscribed waters of the Huang He with those of the Chang (Yangtze); three sets of canals would divert water from the upper, middle, and lower Chang. Although the work on the upper (western) diversion routes could take as much as 50 years, much of the work on the other routes was expected to be completed in a decade.
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