The Birthplace of the Amazon River, the Confluence of the Maranon and Ucayali Rivers

Abstract:

The Amazon River starts at the confluence between the Maranon and Ucayali Rivers near Nauta City. The Maranon River is an anabranching channel while the Ucayali River near the confluence is transitioning from purely meandering to anabranching channel. The interaction of water and sediment between these two large rivers is important for the Pacaya-Samiria Peruvian Reserve, a region with one of highest biodiversity in the planet. Past studies related to flow, sediment and morphology at confluences have been performed for single threat channels. Herein a detailed mapping, sediment sampling and hydrodynamics are carried for a confluence between anabranching and meandering channels. Furthermore, remote sensing analysis have been performed to understand that the confluence point has been changing at the geologcal time scale increasing the morphological structures around the Ucamara depression, where the Pacaya-Samiria reserve is located.

Results of the field studies indicate complex mixing processes downstream of the confluence, where secondary flows are observed driven the sediment mixing. The dynamic of the confluence point is governed by the evolution of the Ucayali River and the local geology. These findings will help us to relate mixing processes in one of the largest wetlands in the world.