Abstract: Rivers in the southwest plateau of China are affected by the geological and fluvial dynamic processes, and present alternating wide and narrow valleys shaped like lotus root joints. The wide valleys are featured with braided fluvial landscapes－irregular shapes of incessant sand bars interspersed in reticular channels. In this study, field observations have been carried out on sediment particle sizes and river landscapes in a typical reach of wide valleys, and the morphological features of its braided streams are interpreted through analysis of remote sensing data, including river geometric parameters and bar geometric parameters. Comparison between column and surface sediment samples shows that in this reach, the sediment diameter increases first and then decreases as the channel width changes, and its riverbed is covered with a surface layer featuring mostly medium and fine sands while the vertical profile of grain sizes is relatively uniform. Remote sensing images show that significant geomorphic differences exist between flood and dry seasons and this can be demonstrated using certain geomorphic parameters. The results lay a basis for further studies of the river morphology and sediment movement in plateau rivers.

Key words: braided river, plateau river, sediment particle diameter, sand bar, river bifurcation