Preliminary Research on Watershed Division and Stream Order Classification of the Yangtze River

According to the recommended watershed division and by means of the Horton method,we preliminarily researched the stream order classification of the Yangtze River(exclusive of the Taihu Lake watershed sub-basin) by properly choosing the minimum stream.Tree diagrams and tables were obtained.Results show that:(1) The Yangtze River is recommended to be divided into main channel watershed basin and 8 tributary watershed sub-basins inclusive of Yalong River,Minjiang River,Jialing River,Wujiang River,Dongting Lake,Hanjiang River,Poyang Lake and Taihu Lake.(2) Statistic and regressive analysis of 581 streams of the Yangtze River shows that stream length is about 0.5 power related to watershed area.Streams with watershed area no less than 2 000km2or stream length no shorter than 100km are selected as the minimum stream.Thereupon based on the minimum stream,the total number of streams of the Yangtze River is determined to be 374.(3) With Minjiang River watershed sub-basin as an example,tree diagrams and tables of streams for all watershed sub-basins of the Yangtze River are elaborately fabricated.The diagrams and tables illustrate the basic information such as river kinship and affiliation,stream order,basin area,and river length.(4) The highest stream order of the Yangtze River is the 6thorder.In regard to streams,there are 1 or 0.3% 6th-order stream,3 or 0.8% 5th-order streams,6 or 1.6% 4th-order streams,14 or 3.7% 3rd-order streams and 71 or 19.0% 2nd-order streams and 279 or 74.6% 1st-order streams;while in terms of watershed division,sub-basins of Minjiang River,Jialing River and Poyang Lake belong to 5th-order stream,sub-basins of main channel,Yalong River,Dongting Lake and Hanjiang River belong to 4th-order stream,and Wujiang River sub-basin belongs to 3rd-order stream.