Modelagem hidrológica para previsão de vazões afluentes às usinas hidrelétricas da bacia do Alto Rio Tocantins

Abstract

Brazil is heavily dependent on hydroelectric power, making efficient plant management essential for the security of the electrical system. Operating these facilities requires planning that considers periods of high flow, which can compromise the integrity of the structures and the continuity of power generation. In this context, the Tocantins River basin plays a strategic role, as it is home to important power plants such as Serra da Mesa, Cana Brava, and São Salvador. Monitoring and forecasting flow, including incremental flow between plants, is essential to reduce hydrological risks and optimize hydroelectric plant operations. This study aimed to calibrate the Large Basin Model (MGB-IPH), developed by the Institute of Hydraulic Research (IPH), to simulate the hydrological behavior of the section of the Tocantins River basin corresponding to the Cana Brava and São Salvador hydroelectric plants. The methodology adopted included basin preprocessing using the IPH Hydro Tools plugin in QGIS to discretize mini-basins, map the drainage network, and define hydrological response units (HRUs). These units were established based on land cover, topography, and soil characteristics, considering classes such as forest, agriculture, field, floodplain, and water bodies. This approach allowed the model to adequately reproduce the different hydrological behaviors throughout the basin, ensuring that each unit responded coherently to rainfall and streamflow. The initial calibration of the model was performed using the Serra da Mesa HPP, located upstream, and demonstrated good performance in reproducing the natural water movement of this unit. However, the results for the Cana Brava and São Salvador HPP sub-basins presented limitations due to the influence of upstream reservoirs. To address this issue, the model's calculated flows were replaced by observed outflows from the reservoirs, allowing for a realistic representation of plant operation and current propagation throughout the basin, including the contribution of incremental flow between developments. The results demonstrate that the MGB-IPH, properly calibrated and adjusted, is a reliable tool for flow forecasting and operational planning in large basins. The model's application supports strategic decisions for the safe and efficient operation of hydroelectric plants, contributing to the mitigation of hydrological risks, strengthening the security of the national electricity system, and considering the impact of incremental flows on hydroelectric power plant operations. Furthermore, comparison with previous studies conducted in other large Brazilian basins showed that the performance achieved in the Alto Tocantins region is consistent with the literature, reinforcing the model's consistency and the importance of careful calibration to ensure reliable forecasts.