Hydromorphodynamics of a large river confluent meander bend through seasonal flood wave: Pantanal wetlands, Brazil

LEANDRO LUZ; STEVAUX, JOSÉ ; SZUPIANY, RICARDO NICOLÁS; PAROLIN, MAURO; AGUINALDO SILVA

Washington

Congreso; AGU FALL MEETING; 2018

American Geophysical Union

Rivers confluences have gained more attention in the past decades with studies related to bed morphology, hydrodynamics, flow structure and sediment transport. Most of them in asymmetrical and symmetrical angle junction. In contrast, meander bend function has not yet well understood and few works have been addressed to the theme. The Paraguay and Cuiabá river confluence located in the Pantanal, the world?s largest wetlands, is an example of a confluent meander bend in large rivers (>100 m wide). The purpose of this study is to enhance the knowledge about the hydrodynamics and bed morphology changes throughout the seasonal flood wave. Flow velocity data were collected using an acoustic Doppler current profiler (ADCP) in cross-sections before and after the confluence, while bathymetric data were collected using an single beam echo-sounder. During the low-water level, the confluence presents a tributary-dominance (Cuiabá River) in momentum and discharge ratios. As result, a prominent recirculation cell has been produced toward the downstream corner, which is nonexistent in the high-water level survey. Besides, secondary velocities have changed their direction from clockwise to anticlockwise during the seasonal flood. Bed morphology has also presented changes during the seasonal flood, regarding the previous hydraulic conditions. The centrifugal force applied by the Cuiabá River flow in the confluent meander bend interferes in the helical motion and as well as the position of the zone of maximum flow velocity. This study provides an important framework of the hydrodynamics and morphology functioning in confluent meander bend in large rivers in different stages of the seasonal flood wave.