Abstract: Braided rivers widely develop in the Yangtze River source, forming a huge cluster of braided rivers. Yet, the spatial-temporal variation of the braided channel morphology remains unclear owing to the shortage of flow, sediment, and riverbed topography data. In the present paper, braided channel morphology and branching intensity in the local braided channel of Tongtian River were studied using the Landsat remote sensing images in 1987-2016 to extract water area. The ratio of water area to riverbed area above water changed periodically associated with the hydrological cycle in a year, i.e., the ratio in flood season (April-September) gradually increased, while in non-flood season (October to next March) decreased and eventually remained unchanged. In the past three decades, the ratio of water area to riverbed area displayed a trend of increasing, which implies the increasing trend of runoff in the source region of the Yangtze River. Of the 36 cross sections of braided river reach, the index of branch number and index of branching length ranged in 4-10, and 5-12, respectively; but the mean values of the two indexes in 1994, 2005, and 2015 almost remained unchanged, indicating that the braided river reach is of holistic self-similarity and invariant river pattern.

Key words: braided river, morphological change, water area, branching intensity, remote sensing image, Yangtze River source, Tongtian River