Dinâmica hidrogeomorfológica da microbacia do Rio Urutago, Francisco Beltrão-PR

Abstract

In a context of intensified land use and land cover changes and increasing vulnerability of water systems, it becomes essential to understand the physical processes that regulate the dynamics of small watersheds in order to support effective environmental management and conservation actions. In this context, the present research seeks to analyze the hydrogeomorphological dynamics of the Urutago River microbasin, located in Francisco Beltrão, through the integration of morphometric, hydraulic, and sedimentological data. These parameters are correlated with the implications of current environmental legislation, the issues related to its modifications and interpretations, as well as the different land uses and land cover patterns within the study area. Furthermore, the study investigates the behavior of suspended sediment load in the microbasin under different climatic conditions—drought periods, inter-harvest intervals, and flood events—seeking to understand variations in hydrosedimentological processes and their relationship with both anthropogenic and natural system dynamics. The research is structured into two methodological stages. The first consists of a theoretical review and the survey of morphometric data for the study area using QGIS software version 3.34.6. The second stage involves the collection of primary data through field campaigns and laboratory analyses. The Digital Elevation Model (DEM), with a 5 m altimetric resolution, enabled precise watershed delimitation, whose altitudinal range varies between 534.67 and 761.33 m, highlighting well-defined water divides. The microbasin covers an area of 7.27 km², has an elongated shape and low circularity, attributes that indicate a longer surface runoff concentration time and a lower natural predisposition to flash floods. The drainage network, classified as fourth order, exhibits a dendritic pattern, low sinuosity, and a reduced degree of relief dissection, suggesting relative geomorphological stability and moderate runoff efficiency. However, the spatial analysis of channels along the upper, middle, and lower reaches revealed significant morphological and hydraulic variations related both to longitudinal position, channel bed differentiation within the basin, and anthropogenic interventions. The most preserved stretches, especially in the upper reach, maintain greater vegetation cover and less alteration of the cross-section, whereas the middle and lower sectors show evidence of channel straightening, canalization, and absence of riparian vegetation. Field campaigns demonstrate temporal variability in width, depth, wetted area, velocity, and discharge, reflecting the fluvial system’s sensitivity to seasonal hydrological conditions. The highest discharges occur during periods of greater antecedent precipitation, resulting from the combined increase in cross-sectional area and mean flow velocity. In contrast, during drought conditions, reduced discharge and slower flow predominate.Suspended sediment load shows strong temporal variability, with increases following rainfall events and ubsequent decreases, highlighting the control exerted by rainfall regime, land use, and availability of erodible material. From a legal perspective, the results indicate that although the Brazilian regulatory framework—particularly the Lei nº 12.651 (Brazilian Forest Code)—establishes the protection of Permanent Preservation Areas (APPs) along watercourses, the flexibilization of these buffer zones, especially in urban areas, has contributed to the maintenance of consolidated occupations and reduced the effectiveness of riparian protection. This condition directly reflects the intensification of erosive processes, increased sediment transport, and greater hydrodynamic instability in the most altered river sections. Overall, the findings demonstrate that the current dynamics of the Urutago River are less controlled by its natural geomorphological characteristics and more influenced by anthropogenic transformations associated with land use and the limited enforcement of environmental legislation. Thus, the research reinforces the need for effective implementation of legal standards and restoration of Permanent Preservation Areas as fundamental strategies to maintain hydrosedimentological balance and fluvial stability within the microbasin.