1. Basic information of the basin

1.1 Basin natural features

1.1.1 Geography

The Yellow River, originating from the Yueguzonglie basin on the northern part of the Bayankela Mountain in Tibet highlands at el. 4,500 m

is flowing through Qinghai, Sichuan, Gansu, Ningxia, Inner-Mongolia, Shanxi, Shaanxi, Henan and Shandong nine provinces and autonomous regions, with a total length of 5,464 km, waterdrops 4,480 m, basin area

795,000 km² and, finally empties itself into the Bohai sea. (Including

isolated inflow area 42,000km²). It is the second largest river in China.

(See 1.1.1 Sketch Map of the Yellow River Basin).

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1.1.1 Sketch Map of the Yellow River Basin

The Yellow River basin has three stages from west to east in terrain and drops stage by stage. The top stage is the Qinghai Highlands on the northern part of the Qinghai highlands at elevation of 4,000 m or more, where distributes a number of north-west to south-east mountains and the Yellow River is flowing back and forth cross and through gullies and mountains in big ¡°S¡± bend. The second stage is up to the Taihang Mountain as its eastern boundary, partially belongs to Inner-Mongolia Highlands and mostly belongs to the Loess Plateau at elevation of 1,000-2,000 m in differentials. The Loess Plateau starts from the Great Wall in the north, bordering Qinling mountain in the south, western up to Riyue mountain and eastern to Taihang mountain with area of 630,000 km and loess layer from several 10 m to 200 or 300 m in thickness, where

soil losses and erodes heavily due to soil structure soft, less grass coverage rate and gullies criss-cross. From the east of Taihang mountain to the sea beach, is the third stage, where mostly is the alluvial plain area of the Lower Yellow River 100 m below the sea level, the rolling area of Shandong province at elevation of 400-1,000 m and the delta area of the Yellow River mouth at elevation 10 m in terrain.

The main stream of the Yellow River is divided into three river reaches, the upper, middle and lower, according to its basin characteristics. (See Table 1.1.1 Characteristics Value of Each Reach of the Main Stream) The Upper Yellow River is rich in water resources where is the major water-originating place. The Middle Yellow River, flowing through the Loess Plateau with high intensity of heavy rain, where soil losses and erodes severely and, floodwater and sediment both are two most crucial problems in flood-control and sediment disposal over the Lower Yellow River. The Lower Yellow River is the ¡°suspended ¡± river and flood-control is really challenging task.

Table 1.1.1 Characteristics Value of Each Reach of the Main Stream

1.1.2 Climate

The Yellow River basin locates in between of the dry area of north-west China and wet area of south-east China, where mostly belongs to the arid and semi-area of continental monsoon climate and be controlled by the cold air ball from the polar torrid zone with more north-west winds and in scarcity of precipitation and snow. In summer, the high pressure of sub-tropical zone with rich water air and more precipitation mainly affects it. The annual averaged temperature within the Yellow River basin is between ¨C 4 - 14 C with averaged precipitation 478 mm for years and total precipitation volume 370 billion m³. The annual precipitation distribution trends to be more in south, less in north, more in east and less in west and, reduces from 600 mm downward to 200 mm more or less progressively from south-east to north-west in great differentials.

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