Modelling from single river bifurcations to complex deltas and comparison with field observations

Rivers, ranging from small mountain streams to expansive lowland deltas, play a fundamental role in shaping the landscapes we inhabit. Their natural evolution gives rise to diverse patterns, including small-scale bedforms, sinuous meandering paths, and the multi-threaded configurations characteristic of braided rivers. At their termini, rivers form deltas, whose shapes vary widely depending on local conditions. In their dynamic evolution, rivers frequently split into multiple channels that eventually rejoin downstream. Understanding the mechanisms governing these patterns and predicting their future evolution is crucial for mitigating potential risks to both natural ecosystems and built environments. This thesis focuses on examining the patterns of multiple-channel systems through the lens of their fundamental functional unit: river bifurcations. Building on established models to analyze the evolution of downstream channels in bifurcations, this study incorporates additional factors to better represent the complexities of real-world bifurcations. These concepts are further applied to meandering river loops with cutoff channels, a setting of growing interest in re-naturalization projects. Key findings from this analysis reveal potential unintended consequences that could emerge during the evolution of such systems. Moreover, the study extends to bifurcations within river networks, enabling the characterization of equilibrium states in river-dominated deltas. This analysis uncovers intriguing internal feedback mechanisms. By applying the developed model to real-world deltas, as the Po River Delta (Italy), current equilibrium states and potential alternative configurations are identified, offering insights into possible catastrophic outcomes under changing conditions. Particular emphasis is placed on the Wax Lake Delta in the United States, a system often cited as a benchmark for coastal restoration efforts in degraded environments. Using the insights gained from this thesis, combined with depth-averaged numerical simulations, this research provides new perspectives on hidden effects that may influence the delta’s future development.