Abstract: A generalized flume experiment was conducted based on typical morphological parameters of alternative bars in midstream Yangtze River to investigate the longitudinal, transverse, and horizontal changes in scouring and silting of the bars under varying conditions. The aim was to comprehensively understand the evolution of alternate bars in straight channel under clear water scouring. The findings indicate that the bed experiences extensive erosion over a long distance in the longitudinal direction, with a greater discharge resulting in increased scouring depth. To be specific, the average thalweg scouring depth at a flow rate of 215 L/s is approximately 2.1 times that at a flow rate of 46.71 L/s. Additionally, the longitudinal gradient of the thalweg attenuates under larger discharge. In the transverse direction, the alternative bars primarily undergo scouring, with maximum scouring typically occurring at the edge. Other sections demonstrate fluctuating patterns of scouring, silting, and then scouring (e.g., at a discharge of 215 L/s, the average scouring depth outside section 2^# ranges around 3.5 cm in (0,2] hours, followed by an average silting height of approximately 0.5 cm in (2,12] hours, and finally an average scouring depth of about 0.7 cm in (12,21] hours). Regarding the planar movement, the bar shifts downstream as a unified entity and becomes elongated, with deposition mainly concentrated within 1 m downstream of the bar. Furthermore, the presence of an upstream bar initially promotes sedimentation of the downstream bar, subsequently intensifying scouring of the downstream bar, particularly affecting the toe of the bar.

Key words: clear water scouring, alternate bar, deposition and erosion variation, flume experiment, straight channel