Research On The Development Trend Of Upper Reaches Of Yangtze River And Preliminary Study On The Influencing Factors

Yangtze River originates from Tibetan Plateau , traverse east west,and flows into the East China Sea. It is 6300 kilometers long and its basin area is 1.8 million square kilometers. The research region of this paper locates in the upper reaches of Yangtze River, its basin area is 1.006 million square, accounts for 55.8% of the whole basin area. This section is 45ll kilometers long, accounts for 71.6% of the whole. It flows through Qinghai, Tibet, Yunnan, Guizhou, Sichuan, Chongqing, Gansu, Shanxi and Hubei 9 provinces and cities. The basin area in Sichuan is the maximum,account for 47.4%。The upper reach of Yangtze River is vast and the natural conditions are superior. The prospect of development and utilization is great, account for an important strategic position in our national economy and social development. For a long time, because of the natural factors and human factors, geological environment problem in upper reaches of Yangtze River is getting more, such as glacier retreat in source, groundwater level decrease, geological hazard (landslide and debris flow included) frequent occurrence and soil and water loss.Depending on China Geological Survey Bureau's Synthetic Research on Environmental Geology Survey in Upper Reaches of Yangtze River,this paper starts with the research on current situation and mainly studies on soil and water loss. It analyzes influencing factors of soil and water loss and gets some results as follows by studying typical areas:1. Features of soil and water loss in upper reaches of Yangtze River: According to geographic location, intensity in east is higher than that in west, intensity in north and south is higher than that in centre. According to soil erosion types, there is mainly surface erosion and other types grow. For example, gravity erosion in parts of Jinsha River and Jaling River exists; freeze-thaw erosion exists in source of Yangtze River and upper segment of Jinsha River. According to topography-geomorphology, intensity in high mountains is lower than hilly region. According to types of soil, intensity in purple soil region is highest. According to land use type intensity of cultivated land is higher than that of wasteland and intensity of grassland is higher than that of woodland. According to area of intensity of erosion, medium intensity area is the biggest, deep erosion area is the smallest. According to population density intensity of concentrated regions is higher than sparse regions.2. Intensity of lower segment of Jisha River is the most serious in the main stream of Yangtze River. Sources of sand are influenced by climates,terrains,geologies,vegetation and human activities. Sediment production and discharge of Upper reaches of Jinsha River divided by Yalong River are less; lower reaches of Jinsha River including Anning River, Niulan River, Xiao River, Longchuan River etc. are concentrated area of sediment sources, with result in sediment deposition of main stream. According to data of hydrologic station observation,sediment concentration and sediment deposition are also increase year by year.3.According to basin of upper reaches of Yangtze ,intensity of Sichuan province is the most outstanding; then that is Yun-Gui Plateau, the minimal area is from source to Panzhihua.4. Soil and water loss is the result of multi-factor. There may be one, two, even more factors in different soil and water loss regions. There are different expression forms in different regions and the factors in different sections of the same river are of very great different.5. Soil and water loss in upper reaches of Yangtze River declines year by year and parts of branches are significantly improvement. But some of river reaches and branches are not improving, even are getting worse. We should pay more intention to these areas.This paper studies soil and water loss in typical regions and analyses the factors of soil erosion. The result has great significance of soil and water conservation, soil and water loss treatment in the upper reaches and that of flood control project, economic development in the lower reaches.