|
The Yellow River is the second longest river in China. The Yellow River valley was the birthplace of ancient Chinese civilization and the cradle of the Chinese nation. It has over 300 million mu of cultivated land (one-fifth of the country?s total), a dense population, well-developed agriculture and abundant mineral deposits. Major cities along the river are Lanzhou, Baotou, Zhengzhou and Jinan.
Rising at the northern foothills of the Bayanhar Mountains, the Yellow River flows past Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shanxi, Shaanxi, Henan and Shandong for 5,464 kilometers until it empties into the Bohai Sea, draining an area of 750,000 square kilometers. It has a total descent of more than 4,400 meters from the headwaters to the river mouth, an average annual flow of 48,000 million cubic meters, and a total power potential of more than 40 million kilowatts.
The Yellow River system is largely sandwiched between the Yinshan and Kunlun-Qinling ranges. The upriver covers the section from it source in the grasslands in Qinghai to Hekou Town in Togtoh County, Inner Mongolia. The headstream is crystal-clear and flows sluggishly to the Qinghai-Gansu border, where it turns from the top of the country?s topographical staircase to its second step and enters a section of gorges. Here a dozen or so famous gorges are ideal sites for hydroelectric power stations, including the Longyangxia, Liujiaxia, Yanguoxia and Qingtongxia gorges. Out of the Qingtongxia Gorge, it winds its way into the Ningxia and Hetao plains, where the current is gentle and good for irrigation.
The Yellow River is joined by the Fenhe from Shanxi, the Weihe from Shaanxi, and scores of other rivers in its middle section, which start from Hekou to Mengjin in Henan. From there it abruptly veers south and twists and turns among the canyons of Shanxi and Shaanxi where the famed Hukou Waterfall is located. South of Longmen, the river widens out. At Tongguan in Shaanxi, it swerves east and meanders again among gorges, the best-known being the Sanmenxia Gorge. In its middle section the Yellow River flows past the Loess Plateau. Here, unprotected by vegetation, large quantities of yellow soil are washed away by torrential summer rains and carried into the Yellow River by its tributaries, making the river one of the world?s largest silt-carriers. With about 20 kilogrammes of silt per cubic meter of flow, it carries more than 1,000 million tons of sediment (90 percent of which from the middle reaches) each year to its lower reaches. The Loess Plateau today is planted with grass and trees to help prevent soil erosion.
In its lower section, which starts from Mengjin down to the estuary, the Yellow River flows slowly through the broad and flat North China Plain, where annually 400 million tons of silt from the middle reaches is deposited on its widening riverbed. With an annual increase of 10 cm., the riverbed has risen 3-4 meters-in some places even over 10 meter-above the two banks, making it virtually an ?above-ground river?.
Flooding has been a major problem. In the old days, little was done to bring this notorious scourge, the Yellow River, under control. History records more than 1,500 dyke breaches and 26 major changes of course, including 9 violent changes, in 2,000 years. Preliminary efforts to make over the river since 1949 have ended the days when ?dykes were breached two years out of three?. Water conservancy projects have been built along its upper and middle reaches, including the Sanmenxia, Qingtongxia and Liujiaxia key irrigation projects and hydroelectric power stations. Work on the Longyangxia power station, which has a planned installation capacity of 1.28 million kilowatts, was started in 1976. Dykes totalling1,800 kilometers along the lower reaches have been repaired or reinforced. The irrigated area in the drainage basin has increased steadily. The Yellow River has threatened nine floods in the past three decades or more, but nor once have they occurred.
(china.org.cn)
|
