关键词: 长江, 水系划分, 河流分级, Horton法, 最小河流(流域)单元, 河流树状图表

Abstract: 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 000km² or 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 6^th order. In regard to streams, there are 1 or 0.3% 6^th-order stream, 3 or 0.8% 5^th-order streams, 6 or 1.6% 4^th-order streams, 14 or 3.7% 3^rd-order streams and 71 or 19.0% 2^nd-order streams and 279 or 74.6% 1^st-order streams; while in terms of watershed division, sub-basins of Minjiang River, Jialing River and Poyang Lake belong to 5^th-order stream, sub-basins of main channel, Yalong River, Dongting Lake and Hanjiang River belong to 4^th-order stream, and Wujiang River sub-basin belongs to 3^rd-order stream.

Key words: Yangtze River, watershed division, stream order classification, Horton method, minimum stream, tree diagram and table of stream