Many models have been proposed to simulate and understand the long-term evolution of meandering rivers. Nevertheless, some modeling problem still needs to be solved, e.g., the stability of long-term simulations when width variations are accounted for. The present thesis proposes a physics-statistical based approach to simulate the river bank evolution, such that erosion and deposition processes act independently, with a specific shear stress threshold for each of them. In addition, the width evolution is linked with a river-specific parametric probability distribution. The analysis of a representative sample of meandering configurations, extracted from Lidar images, indicate that Generalized Extreme Values (GEV) probability density function nicely describe the along channel cross-section width distribution. For a given river, the parameters of the distribution keep almost constant in time, with significant variations observed only as after cutoff events that significantly sharpen the length of the river. The constraint of the river width based on the assumption of a GEV probability distribution ensures as the river moves throughout the floodplain adapting its width, the stability of long-term simulations. The application of the model to a reach of the Ucayali river appears to satisfactorily reproduce the planform evolution of the river and yields realistic values of the cross-section widths.
The second topic considered in the thesis is the formation of chute cutoffs, which produce substantial and non-local changes in the river planform, thereby affecting the morphological evolution. The occurrence of this type of cutoffs is one of the less predictable events in the evolution of rivers, as a multiplicity of control factors are involved in their formation and maintenance. Significant contributions have appeared in the literature in the recent years, which shed light on the complex mechanisms that first lead to the incision of chutes through the floodplain, and that eventually determines the fate of both the cutoff bend and the new channel. However, the subject is not yet settled, and a systematic physic-based framework is still missing. In this thesis, two different forcing factors leading to chute cutoffs are highlighted, the channelized flow inertia and the topographic and sedimentary heterogeneity of the floodplain. Using two hydrodynamic models, the general features of the processes leading to chute cutoffs are investigated by assessing a few representative case studies
