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The turbulent upper Huang He meanders east through a series of gorges to the fertile Lanzhou valley. Hydroelectric dams in the Liujia gorge and at Lanzhou, the largest city on the river, generate electricity and impound irrigation water. Past Lanzhou, the Huang He becomes a wide, slow-moving stream as it begins its bend around the Ordos and separates the northern uplands from the desert and loess lands of the south and west. It is navigable in places for small vessels. The west end of the “great northern bend” passes through the heavily populated Ningxia agricultural region, a heavily irrigated oasis c.60 mi (100 km) long, where cereals and fruits are raised. At the northwest corner of the “great northern bend,” the Huang He divides into numerous branches, watering a fertile area where ancient irrigation canals have been repaired and are now in use. At the northeast corner lies the most fertile land outside the Great Wall; it was farmed without irrigation until 1929.
Turning south, the Huang He passes through the Great Wall and enters the fertile loess region (where rich coal deposits are also found on both sides of the river). Cutting deep into the loess, the river receives most of the yellow silt from which its name is derived. After receiving the Wei and Fen rivers, its chief tributaries, the Huang He turns east and flows through Sanmen gorge, site of the Sanmenxia dam, which is used for power production, flood control, and navigation. Below the Sanmenxia dam is the multipurpose Xiaolangdi dam, located in the river's last valley before the North China Plain, a great delta created from silt dropped at the Huang He's mouth over the millennia. The North China Plain extends over much of Henan, Hebei, and Shandong provs. and merges with the Chang (Yangtze) delta in N Jiangsu and N Anhui provs. The Huang He meanders over the fertile, densely populated plain to reach the Bohai. The plain is one of China's most important agricultural regions, producing corn, sorghum, winter wheat, vegetables, and cotton.
Ancient Floods and Recent Water Scarcity
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 repaired04/00 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, and its flow often fails to reach the sea. In 2000 the Chinese government embarked on the South-to-North Water Diversion Project 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. The eastern route brings water from the lower Chang to the Huang He utilizing in part sections of the Grand Canal, and a central route connects the Han (a tributary of the Chang) to the Huang He. A third, western route, linking the headwaters of the Chang to those of the Huang He, is planned.