Estudo da variabilidade espacial e associação entre precipitação e vazão na relação com a incisão fluvial: bacia hidrográfica do Rio Chapecó - BHRC

Abstract

This dissertation analyzed the relationship between precipitation, long-term mean discharge (Qmlt), specific stream Watershed (CRW), located in western Santa Catarina State, southern Brazil, aiming to understand the hydrological, geomorphological, and morphostructural controls associated with landscape evolution in a passive-margin setting developed over volcanic rocks of the Paraná Basin. The research was based on the stream power model and employed a methodological approach adapted from Ferrier et al. (2013), applied to 56 tributary sub-basins of the Chapecó and Chapecozinho rivers. Rainfall data from 1991 to 2020 obtained from the HidroWeb/ANA database, ALOS PALSAR digital elevation models, geostatistical rainfall spatialization techniques, hydrological regionalization for Qmlt estimation, and calculations of specific stream power and fluvial incision rates were employed. The results demonstrated that precipitation exhibits a relatively homogeneous spatial distribution throughout the watershed, exerting an indirect influence on incision through runoff generation, whereas Qmlt and specific stream power constitute the principal controls on fluvial erosive energy. Specific stream power ranged from approximately 279 to 8,933 W/m², while estimated incision rates varied from 0.08 to 2.80 mm/year, with a regional average ranging between 0.35 and 0.45 mm/year. A positive correlation was observed between stream power and estimated incision rates, as well as a moderate relationship between incision rates and local relief amplitude (R² = 0.41), indicating that more deeply dissected sub-basins tend to present higher fluvial energy. Spatial analysis revealed a marked contrast between the Dissected Plateau of the Uruguay River and the Campos Gerais Plateau, with the former characterized by higher incision rates, more deeply incised relief, and shorter theoretical times for the development of the current landscape dissection. Temporal extrapolation of the estimated rates indicated times ranging from approximately 56 ka to 996 ka, suggesting that contemporary incision rates alone cannot fully explain the current watershed morphology. It is concluded that the geomorphological evolution of the CRW results from the interaction between hydrological controls, morphostructural inheritance, drainage reorganization, and possible past phases of intensified erosion associated with Quaternary paleoclimatic oscillations.