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The tail river channel serves as a critical zone for the interaction between rivers and oceans, holding significant ecological and environmental implications. This study employs a physical experimental approach to simulate the evolution processes of common trumpet-shaped and meander-shaped (left- bending and right- bending at the estuary) tail river channels. The research investigates the morphological evolution patterns under varying water and sediment conditions. Evaluation of different river types′ stability is based on coefficient of fluvial facies and relative roughness. The experiments reveal that the planar morphology of the river undergoes stages of “ stabilitymicro- change- strong change. ” The average elevation and slope of the riverbed increase over time, with the most significant changes occurring in the upstream and estuary sections and the least in the midstream. Sediment addition results in upstream riverbank erosion and riverbed sedimentation. Following cessation, downstream and estuary sections experience more pronounced riverbank erosion than riverbed erosion, leading to estuarine bifurcation, oscillation, and shifting. The unstable areas in planar morphology are the downstream section for meander- shaped channels and the estuary section for trumpet-shaped channels, with significant differences in river phase coefficients. For cross-sectional morphology, the downstream section is unstable for left-bending meander-shaped channels (with a more than 3-fold difference in relative roughness), the upstream section for right- bending meander-shaped channels (more than a 2. 03-fold difference in relative roughness), and the downstream section for trumpet-shaped channels (more than a 4. 09-fold difference in relative roughness). [ABSTRACT FROM AUTHOR]

Low-slope bedrock meandering rivers widely exist in areas controlled by geological structures (the bed slope is less than 5‰). Flood has a great influence on riverbed sedimentation and erosion in bedrock meandering rivers, however, we have a poor understanding of dynamic structure of flood for bedrock meandering rivers. By geometrically generalizing bedrock meandering reaches, considering the Froude similarity and side wall roughness, a generalized model of a bedrock meandering channel is established in order to analyze the water surface profile distribution, time average flow fields and turbulence structure characteristics for bends under flood. The results show that under the flood flow, the minimum water surface transverse gradient, separation of flow on the convex bank, development of double circulation on the concave bank, velocity-dip-phenomenon and maximum secondary circulation intensity are caused at the upstream of the bend apex, and the maximum water surface transverse gradient and circulation splitting are caused at the downstream of the bend apex; the bed shear stress is distributed in the flow separation area at the convex bank as well as the center of the upstream of the bend apex, and the transverse momentum transport is concentrated at the upstream of the bend apex. The experiment results show an explanation in view of hydrodynamics in respect to bed erosion and sedimentation in bedrock meandering rivers. [ABSTRACT FROM AUTHOR]