Hydrosedimentary dynamics and morphological features of a rocky channel bend: Piquiri River, PR, Brazil

Abstract

The size and geometry of alluvial river bends are a result of the stream power and the sediment load. However, the efficiency of these variables is not the same in rivers over rocky substrates. Considering the hypothesis that a channel bend influences the flow dynamics and characterizes specific flow zone conditions, bed morphology, and sediment load distribution, the objective of this study is to characterize these variables in a rocky-bottom controlled bend of the Piquiri River, PR, Southern Brazil. The methods used for this were: a) Field data collection (bottom and suspended sediments, bathymetric Esurveys, and flow discharge and velocity); b) echosounder and ADCP data were processed by the ArcGis 10.4 and VMT (Velocity Mapping Toolbox) software; and c) Laboratory procedure (quantification of suspended and bottom sediment). The results demonstrate that the bottom morphology and channel curvature influence the depth variation, highlighting the increase in depth in the downstream section of the bend, as well as in the flow distribution and velocity with the generation of helical cells in the channel bend zone. The concentration of suspended sediment varies, both from upstream to downstream, as well as at different depths, being, however, significantly higher downstream of the bend. These results denote great importance in understanding the dynamics and flow processes in channel bends with rocky beds, with emphasis on the behavior of the flow with different pressure gradients.