Three-Dimensional probabilistic analysis of flow around island in a braided river model

The channel patterns of an alluvial river reach reflects the flow dynamic within the channel and related channel process of energy expenditure and sediment transport. Modifications of equilibrium channel pattern may occur over a period of time depending on the channel forming sediments mobility and may reflects the consequences of any intervention by human for controlling sediment water discharges that determine the fluvial process. Channel pattern form a continuum in response to varying energy conditions, ranging from straight to meandering channels to multi thread braided forms. A braiding generally occurs in high energy environments of large and variable discharges, steeper gradient with erodible banks, and heavy sediment load. Braided channels are characterized by shallow and wide cross sections with haphazard bar formations creating divisions of flow. Three-dimensional octagonal bursting process was proposed by Ali Reza Keshavarzi, it enables to take the effect of secondary flow. In natural streams flow is mostly three dimensional, thus the 3D analysis of laboratory experiment will provide greater details regarding the sediment transport mechanism. It will provide greater insight of the flow structure near the braided island. In the three-dimensional octagonal bursting event, lateral velocity is also considered in addition to the longitudinal and vertical velocity. Occurrence probability of octagonal bursting events were computed at 12 points near the island. From the analysis, it was found that the class I-A and class III-A events are closely related with the scouring characteristics around the island. In addition, it was found that the Class II-A and Class IV-A bursting events are related with the depositional characteristics around the island in braided river model. The transition probability of bursting events was also computed in this study, from their analysis it was found that the p₂→₂ and p₄→₄ movements are closely related with the Scouring/Deposition pattern around the island in the braided river model.