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In this paper we analyze the dynamics of meandering rivers that flow in geologically confined floodplains. We use a state of art meander morphodynamic model in which the floodplain erodibility can be spatially variable, and can thus be highly reduced where nearly unerodible lateral walls are simulated. We propose a hybrid empirical and model-based indicator to estimate the degree of confinement relative to the potential, unconfined meander belt. Together with commonly used meander morphometric indicators, we propose two novel planform metrics to represent the observed tendency of confined meanders (i) to develop long reaches attached to the geological boundaries, and (ii) to develop more frequent crossing of the floodplain central axis. Results reproduce realistic planforms of confined meanders, quantitatively support previously suggested qualitative classifications of confined meandering rivers, and provide a rational framework to compare meandering rivers having different degree of confinement (strong, moderate, unconfined), as well as different hydro-morphological conditions. Good agreement between model predictions and the few existing field observations support the proposed approach. • Hybrid, model and observation based indicator for the degree of meander confinement • Existing and new metrics for characterizing confined meanders • Model-based classification of meanders with different confinement degrees • Insights into the morphodynamics of confined meandering rivers • Qualitative agreement between model predictions and field data [ABSTRACT FROM AUTHOR]

Meander migration results from the interaction between inner bank accretion and outer bank erosion/collapse. This interaction has been usually treated as a long‐term average of a sequence of erosion events determined by flow hydrographs. Little attention has been paid to the role that individual bank collapse events play on meander evolution. To fill this gap, we developed a numerical model of river meandering that describes explicitly bank collapse. Results show that as bend curvature increases due to meander migration and elongation, the initially scattered locations of bank collapse events converge toward the channel section where bed shear stress attains a maximum. Simulations illustrate the observed catch‐up behavior between inner and outer banks, driven by intermittent bank collapse events. Moreover, bank collapse is found to speed up short‐term meander migration and, consistent with field observations, meanders turn out to evolve toward a state characterized by constant channel width. Plain Language Summary: Meanders are one of the most ubiquitous morphological features observed in natural rivers. They consist of a series of alternating bends that, seen from above, display one of the most striking morphological patterns in nature. The migration of meandering rivers is attributed to outer bank retreat, due to erosion, and inner bank accretion, due to deposition. In this work, we propose a morphodynamic model to investigate the effects that repeated bank collapse events have on meander evolution. Our results show that the migration of meander bends can be described through a catch‐up behavior, driven by outer bank collapse and subsequent inner bank accretion, that on average ensures a nearly constant channel width. Key Points: Meander bend migration is described through a catch‐up behavior, driven by intermittent bank collapse eventsAs the river bend evolves increasing its apex curvature, bank collapse tends to occur at the location of maximum shear stressIndividual bank collapse events speed up the short‐term migration rate of meandering rivers [ABSTRACT FROM AUTHOR]

Many models have been so far proposed to simulate and understand the long‐term evolution of meandering rivers. Nevertheless, some modeling problems still need to be solved, for example, the physical soundness of long‐term simulations when width variations are accounted for. The present work proposes the use of statistical tools to capture the spatiotemporal variations of channel width and to embed their effect into a physics‐statistics‐based model that simulates the river bank evolution. Erosion and deposition processes are assumed to act independently, with a specific shear stress threshold for each of them. In addition, the width evolution is linked with a river‐specific probability density function. The analysis of a representative sample of meandering configurations, extracted from Landsat images, indicates that in many cases a generalized extreme value distribution nicely describes the along‐channel distribution of cross‐section width. For a given river, the parameters of this distribution keep almost constant in time. Significant variations are observed only after cutoff events that shorten the length of the river. The constraint of the river width based on the assumption of a generalized extreme value distribution ensures physically plausible configurations as the river moves throughout the floodplain, adapting continuously its local width. The application of the model to a reach of the Ucayali River appears to reasonably reproduce the planform river morphodynamics and yields realistic values of the cross‐section widths. Key Points: Statistics of channel width variations in alluvial rivers can be described trough a Generalized Extreme Value (GEV) probability density functionModeling of channel width evolution constrained by statistics provides a river-specific characterization of width fluctuations that can be coupled with planform evolution modelsLong‐term simulations of planform channel evolution accounting for width variations reveal the presence of looping cycles that resemble closely the observed river behavior [ABSTRACT FROM AUTHOR]

The fate and transport of soluble contaminants released in natural streams are strongly dependent on the spatial variations of the flow field and of the bed topography. These variations are essentially related to the presence of the channel banks and to the planform configuration of the channel. Large velocity gradients arise near to the channel banks, where the flow depth decreases to zero. Moreover, single thread alluvial rivers are seldom straight, and usually exhibit meandering planforms and a bed topography that deviates from the plane configuration. Channel axis curvature and movable bed deformations drive secondary helical currents which enhance both cross sectional velocity gradients and transverse mixing, thus crucially influencing longitudinal dispersion. The present contribution sets up a rational framework which, assuming mild sloping banks and taking advantage of the weakly meandering character often exhibited by natural streams, leads to an analytical estimate of the contribution to longitudinal dispersion associated with spatial non-uniformities of the flow field. The resulting relationship stems from a physics-based modeling of the flow in natural rivers, and expresses the bend averaged longitudinal dispersion coefficient as a function of the relevant hydraulic and morphologic parameters. The treatment of the problem is river specific, since it relies on an explicit spatial description, although linearized, of the flow field that establishes in the investigated river. Comparison with field data available from tracer tests supports the robustness of the proposed framework, given also the complexity of the processes that affect dispersion dynamics in real streams. [ABSTRACT FROM AUTHOR]

The majority of tidal channels display marked meandering features. Despite their importance in oil-reservoir formation and tidal landscape morphology, questions remain on whether tidalmeander dynamics could be understood in terms of fluvial processes and theory. Key differences suggest otherwise, like the periodic reversal of landscape-forming tidal flows and the widely accepted empirical notion that tidal meanders are stable landscape features, in stark contrast with their migrating fluvial counterparts. On the contrary, here we show that, once properly normalized, observed migration rates of tidal and fluvial meanders are remarkably similar. Key to normalization is the role of tidal channel width that responds to the strong spatial gradients of landscape-forming flow rates and tidal prisms. We find that migration dynamics of tidal meanders agree with nonlinear theories for river meander evolution. Our results challenge the conventional view of tidal channels as stable landscape features and suggest that meandering tidal channels recapitulate many fluvial counterparts owing to large gradients of tidal prisms across meander wavelengths. [ABSTRACT FROM AUTHOR]

The article presents a study on the chaotic behaviour and dynamics of meandering rivers considering the analysis of local curvatures and channel sinuosity. It states that the study was carried out through mathematical models for planimetric evolution and nonlinear series analysis. Results of the analysis reveal the lack of a scaling range which will determine the dimensions for meandering dynamics. Moreover, it asserts that determining the existence of the chaotic behaviour remains unresolved.