1.1.3 Water and Sediment

The Yellow River is well-known sediment laden river throughout the world. The annual averaged delivery of sediment through Sanmenxia calculates approximately 1.6 billion t with averaged sediment content 35 kg /m³, however, the total volume of annual runoff is merely 58 billion m³ within the whole basin. The sediment of the Yellow River mainly originates from the Loess Plateau of the Middle Yellow River, mostly concentrates over the areas between Hekouzhen to Longmen and that between Longmen-Tongguan, which constitutes 90% of the total volume of the Yellow River sediment and the silt in grain size more than 0.05 mm in diameter is also mainly from these two areas.

The water and sediment of the Yellow River is mainly characterized by (1) less water and more sediment and, high sediment content. The water volume of the Yellow River is no more than one-twentieth of that of the Yangtze River, but the sediment is three times more than that of the Yangtze River, which is very seldom seen among the rivers throughout the world. (2) Unevenly Distribution of different sources of water and sediment. The water of the Yellow River mainly yields from the Upper Yellow River and the sediment mainly from the Middle Yellow River and, the upper river water mostly comes from the reach above Guide. The sediment yield on the Middle River is also extremely concentrated, the regions where sediment transport modulus more than 10,000 t/km.a are only the three segment areas, the tributaries between Hekouzhen to Shuiguan of Yan¡¯an, the river sources in Baiyushan and the river sources in Liupanshan mountain; (3) Great changes between water and sediment and unevenly distribution in a year. For example of 11 years of continuously dry from 1922-1932, the observed maximum flow at Sanmenxia is 65.9 billion m³ (1937), and the minimum is 20.2 billion m³ (1928), which differs 3.2 times in that, however, the annual maximum delivery of sediment is 3.91 billion t (1933) and the minimum is 488 million t (1928), which differs 8 times in that; Moreover, the water and sediment annual distribution is unevenly as well, mostly concentrates in the flood season or even in a few floods events.

1.1.4 Natural hazards.

The drought frequently happens to within the Yellow River basin in the history, therefore, it has been called as the ¡°Sorrow of China¡±. Most of the basin belongs to the arid and semi-arid area with less precipitation, greatly variation and frequent droughts. According to statistics, for a period of 3,711 years from BC 1766 to AB 1945, there are recorded 1,070 times or more of big droughts that have brought about great sufferings, just 201 times out of which occurred in Qing Dynasty, about one time out of one more year on average. From 1877 to 1879, there occurred continuous three years droughts, which killed about 13 million people in Shanxi, Hebei, Shandong and Henan four provinces; and the drought in 1929, about 34 million people of the provinces in the Yellow River basin struggled for existence on the verge of death. Many historical documents and current data convince that the drought happens to within the Yellow River basin with great frequency, large area and more affected people. For 42 years from founding the People¡¯s Republic of China to 1990, there always occurred droughts in the farming area of the Yellow River basin, especially the cropped land without any yields reached to 70,000 hm² due to the drought in 1982 and grain output reduced by 3.32 million t due to the drought in 1980.

The flood on the Lower Yellow River has been the focus of the world attention in the history. For 2,540 years, from the fifth year of Zhouding King (BC 602) to 1938 as the manually opening the main dyke, there are recorded dyke-breaches 543 times years that causing flooding and dyke-breaches 1,590 times, five significant channel changes and shifts with inundated area North up to Tianjin, South to Yangtze and Huai River basins, including the Huanghuaihai Plain of Hebei, Shandong, Henan and Jiangsu five province with total affected area of 250,000 km² and great disasters.

1.2 Social and economic background

1.2.1.Population

People had started inhabitation in the Yellow River basin 1 million years ago and Stone Age cultural ruins widely scattered over the basin and a plenty of systematical cultural relics of the mankind in different periods are preserved there. The inscriptions on bones or tortoise shells recorded the human history are also excavated on the bank of the Yellow River. Therefore, the Yellow River basin is praised as the cradle of the Chinese nationality.

According to the statistics of 1990, a population of 97.81 million people is settled in the Yellow River basin, constituting 8.6% of the total nation number. Among the over all 56 nationalities in China, there are 9 nationalities in the Yellow River basin, among which, the Han nationality is the major one, occupying 92.5% of the total inhabitants in the basin, Huis 1.67% and the next others are the Mongolians, Dongxiangs, Tus, Slas, Baoans as well as the Mans.

1.2.2 Land and mineral resources

The Yellow River basin is rich in land and mineral resources with total land area 79.33 million hm², constituting 8.3% of the total country land area, among which, 11.93 million hm² is the cultivated land, 10.20 million hm² is forest and forage land 27.93 million hm². Additionally, about 2 million hm² of wasteland is available for reclaim.

In 1990, among the proven 45 major mineral deposits in China, 37 of those kinds are deposited in the Yellow River basin. The deposited volume more than 32 % of that in China are the rare-earth metal, gypsum and coal and so on 8 kinds. And that about 16%-32% are oil and mirabilite and 10-16% are natural gas, alkaline, copper and gold six kinds. The water energy on the Upper Yellow River, the coal on the Middle and the oil and natural gas on the Lower are all quite rich in deposits, therefore, the Yellow River basin is also called as the ¡°Energy Basin¡± playing a considerable position in China.