The Ucayali is one of the largest freely meandering rivers in the world and its planform migration produces complex meander shapes dominated by not only fluvial erosion but mainly geotechnical processes since changes on water stage are appreciable compared to medium- and small-meander rivers. The Amazon is the one of the largest anabranching rivers in the world and it is formed by the confluence of the anabranching Marañon River together with the meandering Ucayali River. The seasonal increase and decrease in water and sediment discharges from the Amazonian lowland rivers produce changes in the river’s planform configuration, river flooding, and streambank erosion affecting nearby towns and navigation and shoaling issues. Even though, extensive work has been dedicated to understand both river systems, there is still no absolute understanding of their physically-based formation processes and dynamics, especially at large scales as these lowland Amazonian rivers.
The Ucayali Meandering River migrates at greater rates than the Amazon Anabranching River mainly due to their single channel condition; however localized secondary channels of the latter could behave as meandering channels dominating and modifying the planform dynamics of the entire anabranching system. Insights on how a large meandering river (Ucayali) is similar and at the same time different from an anabranching river (Amazon) will be described herein.
A team composed of the Earth Processes & Environmental Flows Group (EPEF) at the University of Pittsburgh and the Directorate of Hydrology and Navigation (DHN) from the Peruvian Navy is working towards gathering information and field measurements concerning the dynamics of the Amazonian rivers. Therefore, based on three-dimensional velocity and bed morphodynamic measurements (performed in both river systems using acoustic profilers and echo sounders respectively) combined with mathematical hydrodynamic models, some insights on the flow structure, bed morphology and planform dynamics of large meandering and anabranching systems are presented.