A simple but applicable analytical model is presented to predict the lateral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation,and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.
The present paper studies the physics of the breach erosion process, particularly, the breach initiation process in overtopped landslide dams. Due to great complexities involved, only homogeneous landslide dams are considered. The flume experiments of dam overtopping are conducted to study the breach growth process. And in order to reveal the effects of the seepage during the breach development, the permeability characteristics of the dam materials are also taken into consideration. With the experimental observation, the details of the breach growth are examined, and the whole breach process could be distinguished into five stages, i.e., Stage Ⅰ, the seepage erosion, Stage Ⅱ, the formation of the initial breach, Stage Ⅲ, the erosion toward the head, Stage Ⅳ, the expansion and incision of the breach, and Stage Ⅴ, the re-equilibration of the river channel through the breach. It is shown that once triggered the entire breach process goes continually without stop, which highlights the significant impact of the early stages on the later deformation of the dam. Evidence shows that the initial breach of the dam is most likely to take place in the downstream slope of the dam, near the upper edge of the seepage face. The experimental results show a "headcut" mechanism of the breach initiation.
