Confluence analysis at basin scale in a tropical bedrock river – The Ivaí River, Southern Brazil

Abstract

River confluences are sites that operate with complex interactions between material and energy, provided by the combination of different flow patterns that present continuous changes in flow structure and sediment transport. In addition, river confluences have intrinsic ecological value, where biophysical processes and ecosystem services may be concentrated. This study aimed to analyze the morphology, flow structure, and hydrosedimentary interaction along tributary-trunk river confluences in a bedrock-alluvial plateau basin. The study included a field investigation into the mixed bedrock-alluvial basin of morphology, bed sediments, and hydrologic condition (including the flow structure) of 29 confluences to identify and analyze the similarities and differences between these confluences at the basin scale. For example, we considered the Ivaí River Basin, a medium-sized dam-free river that exhibits a mixed bedrock-alluvial bed and heterogeneity in both geology and longitudinal profile. Our findings show that the flow structure and morphology are conditioned by geological aspects, and the composition of the flow is extremely affected by the Ivaí River. In general, our results presented distinct differences from field-based data described in the literature for alluvial river confluences.