Impactos da operação intermitente de UHES na mortandade de peixes devido à supersaturação gasosa

Abstract

The intermittent operation of hydroelectric power plants (HPPs), characterized by constant fluctuations in water levels and discharge, alters the hydrodynamic conditions within reservoirs and downstream river reaches. This operational regime enhances water aeration, particularly during spillway passage, increasing the dissolution of gases such as oxygen and nitrogen. This effect is exacerbated when the HPP operates as a runof- river facility and employs a submerged-crest spillway. Such operational patterns may generate significant impacts on aquatic fauna, particularly fish mortality induced by gas supersaturation. This phenomenon occurs when the concentration of dissolved gases exceeds the natural saturation capacity of water under specific temperature and pressure conditions. The resulting supersaturation leads to the formation of gas bubbles within fish tissues, triggering severe physiological disorders, including gas embolism—commonly referred to as gas bubble disease (GBD). Gas embolism obstructs blood circulation and causes extensive damage to vital organs such as gills, swim bladder, and the nervous system. The physiological stress associated with these conditions also compromises the immune system of fish, increasing their susceptibility to secondary diseases. Mitigating these impacts requires the adoption of strategic measures. Continuous monitoring of gas saturation in the water enables the identification of hazardous conditions and supports preventive action. In addition, operational adjustments in HPPs can minimize abrupt variations in flow and pressure, while controlled aeration devices and depressurization systems can reduce excess dissolved gases. Furthermore, the creation of fish refuge areas provides protective habitats during critical periods. Therefore, this thesis aimed to investigate the formation of gas supersaturation, reproduce this event under controlled laboratory conditions, and propose mitigation strategies for fish mortality. This study represents a multifaceted challenge that demands collaboration among engineers, biologists, environmental managers, and local communities. A comprehensive understanding of the underlying mechanisms and the implementation of technical and environmental solutions are essential to balance hydroelectric power generation with the preservation of aquatic biodiversity.