Abstract: On the basis of Schumm’s theory of river subsections and the method of river segmentation with a maximum of five reaches proposed by the author earlier, we present an optimized method of river segmentation with five subzones. Subzoning of watershed is regarded as essence and segmentation of main channel as objective. Watershed is partitioned into five subzones in line with river source, upstream, middle stream, downstream and estuary. Subsequently, the main channel is segmented according to selected knickpoints of river regime and/or tributary confluence, hence the proper number of river segments can be determined. The present method is verified through comparison with the segmentation practices of ten large rivers worldwide, among which the methods for the Changjiang River segmentation can be classified as watershed-and-channel dominated, watershed-feature dominated, and channel-feature dominated. Furthermore, by using the present method, we recommend to divide the Changjiang River into five segments as river source-Zhimenda/Batang river estuary-Yichang-Hukou-Xuliujing-Changjiang River estuary; or three segments as river source-Yichang-Hukou-Changjiang River estuary; or two segments as river source-Yichang-Changjiang River estuary. We also summarized other methods for the segmentation of mainstream Changjiang River, which are based on conventional river names for reaches, confluences of sub-basins divisions, administration zones, river index and professional management etc.

Key words: river segmentation, watershed subzoning, method of river segmentation with five subzones, Schumm’s theory on river subsections, method of river segmentation with a maximum of five reaches, mainstream Changjiang River