Morphodynamics of the anabranching structures on the upper Amazon river basin

Recent research in numerical modeling of large rivers has focused in reproducing typical morphodynamic planform shapes. One of the typical planform shapes of large river systems is the anabranching structure, which is characterized by a main channel and several secondary channels. Although current models reproduce planform shapes very realistically, there is still a lack of data to validate such models and therefore any outcome from these predictions are questionable. To overcome this issue, an analysis of the morphodynamics on large river systems at different scales is carried out. This research will provide a better understanding of the processes involved in anabranching planforms that could be used to improve prediction of morphodynamic features by using high-resolution mathematical models. First, the effect of the main channel sinuosity in an anabranching planforms at two selected locations in the Amazon River at Peru is assessed with field measurements, numerical modeling and satellite imagery characterization. Next, a three dimensional hydrodynamic model for a bend of the Wabash River (at the Stateline between Indiana and Illinois) is carried out to study the modulation of the bank shear stresses due to the presence of bed forms. Lastly, a three dimensional model to study the turbulence of the bed amalgamation process is performed. From the analysis of the two locations along the Amazon River, it was confirmed that in a medium to high sinuosity stage, the secondary channels behave as non-developed meanders. Also, it was concluded that in all sinuosity stages, the planforms of the secondary channels are controlled by the main channel migration. On the other hand, the model of the Wabash River confirmed that the bank shear stress is greater when bed forms are present. Finally, the modeling of the amalgamation processes showed that there was a region of high shear stresses associated to turbulence production, in which the streamwise velocity uctuations were associated to the modification of the bed morphology. Also, the Turbulence Horseshoes Vortices (THV) were more frequent at the beginning of the amalgamation process while the frequency of bursting events was highest when the amalgamation process is at the middle stage.